http://invisible-island.net/xterm/
Copyright © 1997-2018,2019 by Thomas E. Dickey

Here is the latest version of this file.

# XTerm – Frequently Asked Questions (FAQ)

## What is XTerm?

From the manual page:

> The xterm program is a terminal emulator for the X Window System. It provides DEC VT102/VT220 and selected features from higher-level terminals such as VT320/VT420/VT520 (VTxxx). It also provides Tektronix 4014 emulation for programs that cannot use the window system directly. If the underlying operating system supports terminal resizing capabilities (for example, the SIGWINCH signal in systems derived from 4.3bsd), xterm will use the facilities to notify programs running in the window whenever it is resized.

That is, xterm (pronounced "eks-term") is a specific program, not a generic item. It is the standard X terminal emulator program.

This FAQ presents various useful bits of information for both the specific program as well as other programs that imitate it.

As a stylistic convention, the capitalized form is "XTerm", which corresponds to the X resource class name. Similarly, uxterm becomes "UXTerm".

## Who wrote XTerm?

I've been working on xterm since early 1996 (see my changelog for details).

But the program is much older than that.

### A Prehistory Perspective

A lot of people, cited at the bottom of the manual page wrote the original xterm program, maintained by the X Consortium (later part of The Open Group – I'm well aware of the distinction, but am citing when the work was done, not who the current owner may be). There is no changelog, and it is not clear who did what. Email from Jim Gettys (September 1998) provides some background:

> Cast of thousands...

> To give a bit of history, xterm predates X!

> It was originally written as a stand-alone terminal emulator for the VS100 by Mark Vandevoorde, as my coop student the summer that X started.

> Part way through the summer, it became clear that X was more useful than trying to do a stand alone program, so I had him retarget it to X. Part of why xterm's internals are so horrifying is that it was originally intended that a single process be able to drive multiple VS100 displays. Don't hold this against Mark; it isn't his fault.

> I then did a lot of hacking on it, and merged several improved versions from others back in.

> Notable improvements include the proper ANSI parser, that Bob McNamara did.

> The Tek 4010 support came from a guy at Smithsonian Astrophysical Observatory whose name slips my mind at the moment.

> Ported to X11 by Loretta Guarino.

> Then hacked on at the X Consortium by uncounted people.

There is a git repository here which gives some more of xterm's prehistory.

Email from Doug Mink (October 1999) provides more background:

> I was checking out the newly revised AltaVista search engine to see what was on the net about xterm, and I found your pages. I can add to the FAQ in that I was the "guy at the Smithsonian Astrophysical Observatory" Jim Gettys refers to. I am listed at the end of the man page under authors. What happened was that I was hired by SAO (after leaving the research staff at MIT) in October 1985 to write analysis software for the Spacelab 2 Infrared Telescope which was to fly on the Space Shuttle in 1985 less than six months after I was hired. I came with a tar tape full of software I had written for Unix and Tektronix terminals, but I was presented with a VS100 terminal which had an early version (X6 or so) of xterm, with no graphics capabilities. SAO is at Harvard, across Cambridge from MIT, where Jim Gettys was detailed from DEC to the X project, and Jim had connections with SAO, having worked here after college (MIT, where we had both worked at the observatory at various times); he was still sharing an apartment with an SAO colleague of mine, too. Anyway, everyone decided that since I knew Tektronix commands pretty well, and our group desparately needed the graphics capabilities, it would be a good use of my time to implement a Tektronix terminal emulator under X. So I set to work learning more C--I had only written a couple of wrappers to C I/O routines so I could use them with my Fortran software--and wrote a Tektronix emulator. The only X documentation at the time was the code itself. While I was at it, I wrote an improved Tektronix emulator for our Imagen laser printer which used the full resolution of that 300 dpi printer instead of the effective 100 dpi (i.e. jaggy) emultator distributed with the printer. The original xterm Tek emulator shared a window with the VT100 emulator, much like on the VT240 terminals which I had been using at MIT before I came to Harvard. With a VAX 750 running several VS100's, window creation was sloowww, so sharing a window was the quickest way to do things, and all of my software was written for that mode of operation, anyway. While I wrote the emulator so that my software would work on it, it was tested by the X group against a BBN graphics package, the name of which slips my mind right now.

> Anyway, 15 years later, I am still using xterm and some of the same mapping software I wrote the emulator for. And I am still at the Smithsonian Astrophysical Observatory.

### My Involvement

My involvement with xterm through XFree86 began at the end of 1995. This website has been "here" since 2001/6/5, replacing my ClarkNet page. I started the ClarkNet page 1996/12/31, as a followup to the release of ncurses 4.0) which featured xterm as one of the 16 programs I was involved with. From the outset, the page provided a link to a snapshot of the current source. Copies of patches which I sent to XFree86 were available on the ftp area.

XFree86 had its sources in CVS, but (like others in that era), were not directly visible to random developers. That came later. I started by downloading the sources (30Mb of compressed tar-files on a 56Kb phone connection took about 6 hours) and updating them with patches from the XFree86 mailing list.

Like the other programs that I worked on with others (vile, tin, lynx), I set up an RCS archive to track my changes locally before sending patches to the development list. As the XFree86 developers issued new patches, I would re-synchronize my archive. Later, XFree86 provided CVS (initially readonly). I was granted commit privileges on this in November 2000.

Throughout this period, my work on xterm was released as part of XFree86. It was rare for a separate package to be provided. That was due to the potential conflict between the install procedures. Users of the downloads from my web/ftp site were predominantly individual developers.

There were exceptions. Christian Weisgerber proposed a package for FreeBSD ports later in 1999 (ports/15545: new port: x11/xterm, followup in March 2000). However, that was an exception. None of the Linux distributions provided a separate package before 2003 (when Mike Harris created a package of patch #177 for Red Hat). Again that is more of an exception than a rule:

- SuSE's package began October 23, 2004 with patch #196.
- Mandriva's package began October 22, 2005 with patch #205.
- The Debian package for xterm began in January 6, 2006 with patch #204.

Given that context (sources distributed via XFree86 CVS, releases via XFree86), the statement made by an Xorg hacker early in 2005 asserting that "It has not been maintained by anyone within the XFree86 or X.org trees for many years" was at best misleading.

After the "fork" (sic) of Xorg in 2004, I continued to commit changes for xterm in XFree86 CVS until patch #216 in mid-2006. I stopped at that point because it was not possible to incorporate changes into xterm which were not sent to me first. I still send patch announcements to both the XFree86 and Xorg mailing lists, of course.

### Focus of this FAQ

This FAQ is oriented toward the version of xterm originally distributed with XFree86 (more commonly known as modern, or "new xterm", with a corresponding terminal description "xterm-new"), which was based on the X11R6.3 xterm, with the addition of ANSI color and VT220 controls.

## What is a VT220?

- Why a VT220?
- What is a State Table?
- Why not emulate VT320?
- Why emulate VT420?
- Why not emulate VT520?

### Why a VT220?

The manual page mentions a VT220. Most terminal emulators documentation talk about VT100. But a VT100 is a rather limited subset of what people expect:

- VT100s have no function keys. Arguably, PF1-PF4 are function keys. My keyboard has 12 function keys.
- VT100s do not do color.

Initially, I was only interested in making colors workable for curses programs.

Later, I noticed that xterm had some support for what would now be termed as ISO-2022. That was a VT220 feature which preceded ISO-2022 called National Replacement Character sets. In any case, it was not a VT100 feature. There were some missing pieces. So I decided to fill in those pieces and make xterm a VT220 emulator. (VT220s do not do ANSI color either—the missing pieces were in other areas).

XTerm also provides features that are in neither VT100 nor VT220, which are used by other programs as "xterm emulation".

- set (and retrieve) window- and icon-labels using escape sequences.
- interpret mouse clicks as escape sequences that can be read by a program.

By the way, the control string used for setting the titles was not in a standard format:

- In X10 (1988), the string was simply terminated by any nonprinting character.
- X11R4 (1989) modified that to ensure that the nonprinting character is an ASCII BEL (control/G).
- There is no explanation in the (sketchy) notes distributed with the X11R4 xterm; in retrospect it seems that the most likely explanation for the choice is that it was simpler to implement in shell scripts than `ESC \`.

ECMA-48 (the standard) does not describe this particular control, but prescribes its format (an operating system command). It does not use a `BEL`.

I revised that area starting in 1996,

- first to use xterm's state table for handling the input, and then
- to accept the standard string terminator as well.

In addition to implementing the VT220's National Replacement Character sets (see vttest screenshots), I added other features to emulate the successive models of DEC terminals. The `decTerminalID` resource (in 1999) lets users select the emulation to use. Because many of my changes were extensions (features not in any of DEC's terminals) and because well-behaved VT100 applications would not use features from higher-level terminals it was not initially important to prevent use of those by applications which assumed they were using just a VT100. Knowledgable users could easily configure xterm to emulate a VT220. In 2012, I changed the default from VT100 to VT420.

### What is a State Table?

That was mentioned regarding the title strings. XTerm uses a state machine to handle incoming characters. That is essentially what a real terminal does. Other "xterm" terminal emulators typically do not do this, which makes them not do well with vttest.

### Why not emulate VT320?

You could do that (by changing `decTerminalID`, but the results were not that interesting). In retrospect, the VT320 was a stopgap implementation designed to bridge between the VT200 series and the VT420. It provided a standard codepage (for ISO Latin-1).

While it had other features not found in the VT200-series, most of those are less useful in a terminal emulator. I did adapt the ECMA-48 scrolling operations which the VT320 interpreted as panning the visible display in the terminal's memory. Expect some difference there (if you can find an application on VMS which used the feature).

The VT320 was popular with developers of commercial terminal emulators, whose literature referred to it as supporting ANSI color. It did not do this.

### Why emulate VT420?

The VT420 was interesting because it provided two features that could be useful:

- rectangles
- left/right margins (like the top/bottom scrolling margins)

A VT420, of course, supports all of the features in VT320, in turn all of the features in VT220, and in turn VT100. Users would not lose features by changing the default emulation to VT420. By changing the default emulation, most users would automatically be able to use applications (such as `tmux`) that could perform better if the left/right margin feature is available. I changed the emulation to VT420 in 2012 for this reason.

XTerm does not emulate some esoteric features (such as dual sessions) because those require hosts using special software, and no publicly-available documentation was available.

### Why not emulate VT520?

Again, the VT500-series is less interesting because most of the features which are not hardware-specific (such as reporting transmission rate) are less useful.

However:

- the VT500-series provides additional codepages (like the VT320). XTerm does that.
- the VT500-series supports some of the ECMA-48 cursor-movement operations which had been overlooked in the previous terminals. XTerm does that (based on ECMA-48 itself, and later on DEC's documentation).

As for the other features, most are not useful in emulation (since they are hardware-specific). Additionally, these less-used features are not documented precisely and since the only point of providing them would be for successful interoperability with legacy applications, some reverse-engineering would be needed to provide a faithful emulation. To date there are no known terminal emulators which do that.

## What platforms does it run on?

XTerm runs in all of the implementations of X11. As of 2000, I had built and run these since I started working on xterm in 1996:

- AIX 3.2.5, 4.1, 4.3 (cc)
- Digital Unix 3.2, 4.0, 5.0 (cc)
- FreeBSD 2.2.6 to 6.0 (gcc 2.8)
- HP-UX 9.05 to 11.23 (gcc 2.7.2 to 3.4)
- IRIX 5.2, 6.2 (cc, gcc 2.7.2, gcc 2.8)
- Linux 2.0.0 to 2.6.26 (gcc 2.7.2 to 4.3)
- SCO OpenServer 5 (cc, gcc).
- Solaris 2.4, 2.5, 2.5.1, 2.6, 7, 8 (cc, gcc 2.7.2)
- SunOS 4.1.1, 4.1.3 (gcc 2.7.2)

The older configurations have X11R5 libraries. Only minor changes are needed to make xterm work on those systems. However, X11R6 provided better locale support, as well as new features such as the active icon. X11R7... not much to say there.

Since 2000, there have been many changes (including new platforms such as MacOS, NetBSD, OpenBSD, etc., as well as QNX, Cygwin, and Minix).

## What is the latest version?

The most recent (and well supported) version of xterm is the one that I maintain:

- current source (ftp)
- current source (http)

## What versions are available?

There are several other versions of xterm, based on xterm's source. These include

- ansi_xterm
- color_xterm
- cxterm (Chinese)
- hanterm (Korean)
- mxterm
- nxterm
- kterm (Japanese)
- xterm (from X Consortium)

There are similar programs not based on xterm's source, which are compatible to different degrees. These include

- dtterm
- emu (from X Consortium)
- Eterm
- GNOME Terminal
- Multi GNOME Terminal (MGT)
- mterm
- konsole
- mlterm (Multi Lingual)
- osso-xterm
- roxterm
- rxvt
- st
- xfce-term
- xgterm
- xiterm

Some of these use the VTE widget. Since that supplies most of the terminal emulation, the remaining differences between programs using VTE tend to be at the level of the window manager (menus, borders, etc.). Other (older) programs which are based on reusable widgets include dtterm and emu.

(I am aware of a few others, such as xcterm, but have not seen a working version of these).

Finally of course, there are a multitude of programs which set TERM to "xterm", in the hope that applications will treat them the same as xterm. For example,

- PuTTY does this (see its FAQ A.5.1 What terminal type does PuTTY use?). But its wrapping behavior is incompatible with xterm (and any vt100 emulator). You can see this in the first menu entry for vttest.
- VTE does this. But consider the list of problems with VTE and with GNOME Terminal. The attitude of the developers is that by copying from xterm, they are entitled to do this whether or not the program actually matches xterm's terminal description. This is unchanged since the mid-2000s (see Debian #368916 for example).
- Konsole does this as well—intentionally as shown in KDE #145977 – Konsole has a terminfo entry of its own; please change default $TERM. The reasoning expressed there is that Konsole "should" match xterm. Incidentally, one of the comments (about xterm's support for mouse) cited as proof a page about Gpm from Linux Journal which was more than 12 years old.

Each of the programs noted here which are well-established and which are known to differ markedly from xterm have their own terminal descriptions in ncurses, to which TERM should be set. Otherwise, bug-reports are misdirected to ncurses which should have been addressed by the respective developers of these programs. These include

- Eterm
- gnome (obsolete)
- konsole
- mlterm
- mrxvt
- putty
- rxvt
- st
- vte (preferred)

## Comparing versions, by counting controls

Several of these programs are claimed (either by their developers, or their users) to emulate "most" of xterm. To me, "most" would be something quantifiable, e.g., 80 percent. To satisfy my curiousity, I wrote a script to extract the control sequence information from ctlseqs.txt. This counts each control sequence, as well as the variations such as setting bold, color, inverse video. Then I (laboriously) inspected these terminal implementations:

- xterm patch #266 ("xterm-new")
- X11R6.3 xterm (xterm-r6)
- DEC vt220
- DEC vt102
- rxvt 2.7.10
- rxvt-unicode 9.09 (urxvt)
- konsole 2.5.3
- VTE 0.25.91 (vte), used in GNOME-Terminal and kindred.

As of mid-November 2010, these were the latest implementations. I included data for the vt220 and vt102 to be able to contrast the various terminal emulators against those as well as xterm. There were:

- 498 control sequences listed in the corresponding file for xterm patch #266.
- 192 of those are "primary", e.g., disregarding parameters such as those distinguishing bold from color.
- 37 of the primary control sequences have secondary sequences.

For each control, there are three possibilities:

1. "yes" — the terminal implements it, matching xterm. If xterm implements it, and it is a feature of vt220 or vt102, then in turn xterm's behavior must match vt220 or vt102.
2. "partial" — the terminal implements it, but its behavior does not match the reference noted above.
3. "no" — the terminal does not implement the control.

The control sequences document lists a few controls which xterm does not (completely) implement, e.g.,

- key-repeat
- enabling LEDs other than scroll-lock

None of the other terminal emulators implements those either.

Comparing against the control sequences document
yes | partial | no | program
--- | --- | --- | ---
488 | 4 | 6 | xterm-new
154 | 6 | 338 | xterm-r6
188 | 5 | 305 | vt220
104 | 0 | 394 | vt102
204 | 3 | 291 | rxvt
219 | 3 | 276 | urxvt
191 | 2 | 305 | putty
170 | 3 | 325 | konsole
184 | 6 | 308 | vte

Modern xterm implements 188 primary controls. In this table, vte ranks lower than PuTTY because it does not support vt52 emulation. This is not unusual, since the rxvt-based emulators do not, either. However, all vt100's provide this feature; programs lacking this are not really a vt100 emulator. On the other hand, PuTTY (which is not a vt100 emulator due to its incompatible wrapping behavior) supports this feature.

Aside from that, the various emulators implement much the same features from xterm. None implements as many as half of xterm's controls.

Comparing against xterm
yes | partial | no | program
--- | --- | --- | ---
488 | 0 | 0 | xterm-new
154 | 6 | 328 | xterm-r6
182 | 2 | 304 | vt220
98 | 0 | 390 | vt102
204 | 3 | 281 | rxvt
219 | 3 | 266 | urxvt
189 | 2 | 297 | putty
170 | 3 | 315 | konsole
184 | 6 | 298 | vte

DEC VT220 implements 96 primary controls. Modern xterm (as documented), implements most of the VT220. VTE implements fewer than half. The others are a little better. None of the others could be used as a real VT220.

Comparing against vt220
yes | partial | no | program
--- | --- | --- | ---
182 | 0 | 6 | xterm-new
78 | 6 | 104 | xterm-r6
188 | 0 | 0 | vt220
104 | 0 | 84 | vt102
101 | 3 | 84 | rxvt
106 | 3 | 79 | urxvt
107 | 2 | 79 | putty
100 | 3 | 85 | konsole
88 | 6 | 94 | vte

DEC VT102 (the actual flavor used for "vt100" in most cases), implements 68 primary controls. Again, VTE fares worst, and the others a little better.

Comparing against vt102
yes | partial | no | program
--- | --- | --- | ---
98 | 0 | 6 | xterm-new
70 | 6 | 28 | xterm-r6
104 | 0 | 0 | vt220
104 | 0 | 0 | vt102
79 | 2 | 23 | rxvt
81 | 2 | 21 | urxvt
86 | 2 | 16 | putty
85 | 3 | 16 | konsole
60 | 1 | 43 | vte

I have continued to add features to xterm:

- as of September 2013, it implemented 546 of 556 documented controls
- as of October 2019, xterm implemented 713 of 723 documented controls.

The other programs change far more slowly. As a result they implement a smaller fraction of xterm's repertoire in 2019 than in 2010. Even for cases where they implement a function, it may not work properly (see for example the screenshot of VTE in the vttest NRCS examples).

In summary, none of the other terminal emulators emulates "most" of xterm. Instead, they implement the most commonly-used control sequences, and there are differences between them.

## How do I ...

Not really problems, but frequently asked questions (the point of this, after all):

- How do I change the font size?
- How do I print the screen?
- How do I set up function keys?
- How do I set the title?
- How do I make the cursor blink?

### How do I change the font size?

XTerm uses fonts given as resource settings. You can switch between these fonts at runtime, using a menu. This is documented in the manpage, in the MENUS section.

X Consortium xterm provides popup menus, by pressing the control key together with the mouse button. Control right mouse button pops up the VT FONTS menu, from which you can select fonts that are specified in xterm's resources. Usually these are in increasing order of size.

Modern xterm provides the menu, plus a feature adapted from rxvt: pressing the shifted keypad plus or minus keys steps through the font menu selections, in order of their size.

XTerm's manpage does not document the syntax for X resources; it is done in the X documentation. If you are instead asking about a problem displaying a given font, it may be due to a problem with your resource settings.

### How do I print the screen?

That depends on why you want to print it.

If you want a trace of an interactive session, you should use the script program. It records every character sent to the screen, recording them in a file `typescript`. There are two drawbacks to this approach:

- Every character is recorded. Even cursor movement, if you run an editor.
- You must start a new shell to capture the `typescript` file.

Well, what about logging? Some versions of xterm support logging to a file. In fact modern xterm does. Logging was dropped from X Consortium xterm during X11R5 due to security concerns. Those were addressed, but logging was not reinstated (in fact there is a related bug in xterm). Some people prefer this, because it is convenient: you can start and stop logging a popup menu entry. However

- Every character is recorded. Even cursor movement, if you run an editor.
- Line drawing characters are translated to control characters, i.e., codes 0-31 (this may be fixed sometime, it is a problem inherited from X Consortium xterm).

Both script and logging are useful for recording, but they require interpretation to make sense of the trace. You probably would not send that trace to a printer (not twice, anyway).

If you want to print the contents of the screen, modern xterm implements, as part of the VT100 emulation, an "attached" printer.

- The printer is really a pipe command, to which xterm writes.
- You can print the current line, page, or continuously with the corresponding control sequences. That takes an application program which knows how to print the screen.
- If you do not have an application, xterm has a popup menu entry to print the window.

There are limitations and tradeoffs using the "attached" printer, because it is an emulation:

- The emulation is based on detailed documentation for a VT320. This states that control sequences are sent in each line to reset bold, underlining and other printable attributes, and to set them as needed. Your printer probably does not understand this sort of input. Use the xterm resource `printAttributes` to get more easily printed output.
- The printer may hang. Not really, but it seems that way. If you use the "attached" printer from an application designed for the VT100 terminal, it is written with the assumption that the printer is a dedicated piece of hardware, printing onto a continuous form. Use the `printerAutoClose` resource to change xterm's behavior to close the printer pipe whenever the terminal is told to switch the printer offline.

If you use the popup menu to print the screen, this will close the printer pipe unless it was already opened by the application running in xterm.

### How do I set up function keys?

With modern xterm, this is relatively simple. So I'll answer that first.

With X Consortium xterm, you had partial support for DEC VTxxx function keys. Function keys F1 to F12 correspond to DEC's F1 to F12 (sort of). Actually, DEC's VT220 terminals do not have codes for F1 through F5. They are reserved for local functions. And the VT220 (and up) terminals have 20 function keys. So you cannot do anything with the F13 through F20 (i.e., DO, HELP and SELECT). Finally, though xterm is reputed to be VT100-compatible, it has no support for the VT100 keypad (PF1 to PF4, and the "," key).

Modern (XFree86) xterm changed the X Consortium codes for F1 to F4 to match the VT100 PF1 to PF4, except when the emulation level is VT220 and up. In this case, it generates the same F1 to F4 codes as X Consortium xterm. Moreover, it adds a new resource `sunKeyboard`, which tells the program whether it has only 12 function keys (i.e., a Sun or PC keyboard). If so (this is selectable from the popup menu), you can use the control key with F1 to F12 to get F13 to F24, and use the "+" key on the keypad as an alias for "," (comma).

The emulation level for modern xterm is set via the resource `decTerminalID`, e.g., to 220 for a VT220. Once set, applications can set the emulation level up or down within that limit. DEC's terminals are configured in much the same way by a setup option.

That is the simple way, using a couple of new resources. The traditional way to get function keys involves translations. I have seen a few postings on the newsgroups that do this. Here is one from Bruce Momjian <root@candle.pha.pa.us> for a VT220:

> xterm $XTERMFLAGS +rw +sb +ls $@ -tm 'erase ^? intr ^c' \
> -name vt220 -title vt220 -tn xterm-220 "$@" &

with the corresponding resources:

> XTerm*VT100.translations: #override \n\
> <Key>Home: string(0x1b) string("[3~") \n \
> <Key>End: string(0x1b) string("[4~") \n
> vt220*VT100.translations: #override \n\
> ~Shift <Key>F1: string(0x1b) string("OP") \n \
> ~Shift <Key>F2: string(0x1b) string("OQ") \n \
> ~Shift <Key>F3: string(0x1b) string("OR") \n \
> ~Shift <Key>F4: string(0x1b) string("OS") \n \
> ~Shift <Key>F5: string(0x1b) string("[16~") \n \
> ~Shift <Key>F6: string(0x1b) string("[17~") \n \
> ~Shift <Key>F7: string(0x1b) string("[18~") \n \
> ~Shift <Key>F8: string(0x1b) string("[19~") \n \
> ~Shift <Key>F9: string(0x1b) string("[20~") \n \
> ~Shift <Key>F10: string(0x1b) string("[21~") \n \
> ~Shift <Key>F11: string(0x1b) string("[28~") \n \
> ~Shift <Key>F12: string(0x1b) string("[29~") \n \
> Shift <Key>F1: string(0x1b) string("[23~") \n \
> Shift <Key>F2: string(0x1b) string("[24~") \n \
> Shift <Key>F3: string(0x1b) string("[25~") \n \
> Shift <Key>F4: string(0x1b) string("[26~") \n \
> Shift <Key>F5: string(0x1b) string("[K~") \n \
> Shift <Key>F6: string(0x1b) string("[31~") \n \
> Shift <Key>F7: string(0x1b) string("[31~") \n \
> Shift <Key>F8: string(0x1b) string("[32~") \n \
> Shift <Key>F9: string(0x1b) string("[33~") \n \
> Shift <Key>F10: string(0x1b) string("[34~") \n \
> Shift <Key>F11: string(0x1b) string("[28~") \n \
> Shift <Key>F12: string(0x1b) string("[29~") \n \
> <Key>Print: string(0x1b) string("[32~") \n\
> <Key>Cancel: string(0x1b) string("[33~") \n\
> <Key>Pause: string(0x1b) string("[34~") \n\
> <Key>Insert: string(0x1b) string("[2~") \n\
> <Key>Delete: string(0x1b) string("[3~") \n\
> <Key>Home: string(0x1b) string("[1~") \n\
> <Key>End: string(0x1b) string("[4~") \n\
> <Key>Prior: string(0x1b) string("[5~") \n\
> <Key>Next: string(0x1b) string("[6~") \n\
> <Key>BackSpace: string(0x7f) \n\
> <Key>Num_Lock: string(0x1b) string("OP") \n\
> <Key>KP_Divide: string(0x1b) string("Ol") \n\
> <Key>KP_Multiply: string(0x1b) string("Om") \n\
> <Key>KP_Subtract: string(0x1b) string("OS") \n\
> <Key>KP_Add: string(0x1b) string("OM") \n\
> <Key>KP_Enter: string(0x1b) string("OM") \n\
> <Key>KP_Decimal: string(0x1b) string("On") \n\
> <Key>KP_0: string(0x1b) string("Op") \n\
> <Key>KP_1: string(0x1b) string("Oq") \n\
> <Key>KP_2: string(0x1b) string("Or") \n\
> <Key>KP_3: string(0x1b) string("Os") \n\
> <Key>KP_4: string(0x1b) string("Ot") \n\
> <Key>KP_5: string(0x1b) string("Ou") \n\
> <Key>KP_6: string(0x1b) string("Ov") \n\
> <Key>KP_7: string(0x1b) string("Ow") \n\
> <Key>KP_8: string(0x1b) string("Ox") \n\
> <Key>KP_9: string(0x1b) string("Oy") \n
> ! <Key>Up: string(0x1b) string("[A") \n\
> ! <Key>Down: string(0x1b) string("[B") \n\
> ! <Key>Right: string(0x1b) string("[C") \n\
> ! <Key>Left: string(0x1b) string("[D") \n\
> *visualBell: true
> *saveLines: 1000
> *cursesemul: true
> *scrollKey: true
> *scrollBar: true

Note that real VT220 terminals use shifted function keys to mean something different: the user-programmable keys (i.e., DECUDK). Modern xterm supports this, but the translations do not (they're using shift to select F13 to F20).

Here's another one, from Robert Ess <ress@spd.dsccc.com>:

> #!/bin/sh
> # vax
> # 09-17-96 Bob Ess - initial creation
> # 09-26-96 Shig Katada - Additional keybindings
> #
> # Script file to incorporate keybindings and command line
> # options for connecting to a VAX node
> # Usage statement
> Usage(){
> echo
> echo " Usage : vax -options"
> echo
> echo " Options: -80 for 80 column terminal"
> echo " -132 for 132 column terminal"
> echo " -fg colorname"
> echo " -bg colorname"
> echo " -fn fontname"
> echo " -fb bold fontname"
> echo " -host [altair] [devel] [leonis] [castor]"
> echo ""
> echo " Example: \"vax -80 -fg white -bg black -fn 9x15 -fb 9x15b -host castor\""
> echo " Starts a VAX session with an 80 column terminal"
> echo " with a black background, white foreground, a normal"
> echo " font of 9x15 and a bold font of 9x15b, and connects"
> echo " to the node 'castor'"
> echo
> echo " If you need additional help, please call Workstation"
> echo " Services at x92396."
> echo
> exit 1
> }
> # Default to a black foreground with a white background.
> # Use the 9x15 and 9x15bold fonts. Connect to castor by default.
> #
> FG=black
> BG=white
> HOST=castor
> FONT=9x15
> BFONT=9x15bold
> COLS=80
> # Parse the command line arguments
> #
> while [ $# != 0 ];
> do
> case $1 in
> -80) COLS=80
> FONT=spc12x24c
> BFONT=spc12x24b
> shift
> ;;
> -132) COLS=132
> FONT=9x15
> BFONT=9x15b
> shift
> ;;
> -fg) shift
> FG=$1
> shift;;
> -bg) shift
> BG=$1
> shift;;
> -fn) shift
> FONT=$1
> shift;;
> -fb) shift
> BFONT=$1
> shift;;
> -host) shift
> HOST=$1
> shift;;
> -help) Usage;;
> *) Usage;;
> esac
> done
> xterm -title "VAX" -sb -sl 1200 -geo ${COLS}x24 -fg ${FG} -bg ${BG} \
> -cr red -fn ${FONT} -fb ${BFONT} -xrm \
> 'XTerm*VT100.translations: #override \n\
> <Key>Insert: string(\001) \n\
> Shift <Key>Up: scroll-back(1,lines) \n\
> Shift <Key>Down: scroll-forw(1,lines) \n\
> Shift <Key>Right: string(0x1b) string("f") \n\
> Shift <Key>Left: string(0x1b) string("b") \n\
> Shift <Key>Delete: string(0x1b) string(0x08) \n\
> Shift <Key>Tab: string(0x1b) string("*") \n\
> <Key>0x1000FF0D: scroll-back(1,page) \n\
> <Key>0x1000FF0E: scroll-forw(1,page) \n\
> <Key>0x1000FF09: string(\010) \n\
> <Key>0x1000FF0A: string(\005) \n\
> <Key>BackSpace: string(0xff) \n\
> <Key>Select: select-start() \n\
> <Key>0x1000FF02: select-end(PRIMARY,CUT_BUFFER0) \n\
> Meta <Key>0x1000FF02: select-end(CLIPBOARD) \n\
> <Key>0x1000FF04: insert-selection(PRIMARY,CUT_BUFFER0) \n\
> Meta <Key>0x1000FF04: insert-selection(CLIPBOARD) \n\
> <Key>F1: string(0x1b) string("OP") \n\
> <Key>F2: string(0x1b) string("OQ") \n\
> <Key>F3: string(0x1b) string("OR") \n\
> <Key>F4: string(0x1b) string("OS") \n\
> <Key>F5: string(0x1b) string("OA") \n\
> <Key>F11: string(0x1b) string("[23~") \n\
> <Key>F12: string(0x1b) string("[24~") \n\
> <Key>KP_0: string(0x1b) string("Op") \n\
> <Key>KP_1: string(0x1b) string("Oq") \n\
> <Key>KP_2: string(0x1b) string("Or") \n\
> <Key>KP_3: string(0x1b) string("Os") \n\
> <Key>KP_4: string(0x1b) string("Ot") \n\
> <Key>KP_5: string(0x1b) string("Ou") \n\
> <Key>KP_Divide: string(0x1b) string("OP") \n\
> <Key>KP_Multiply: string(0x1b) string("[29~") \n\
> <Key>KP_Enter: string(0x1b) string("OM") \n\
> <Key>KP_Subtract: string(0x1b) string("Om") \n\
> <Key>KP_Add: string(0x1b) string("Ol") \n\
> <Key>KP_Decimal: string(0x1b) string("On") \n\
> <Btn1Down>: select-start() \n\
> <Btn1Motion>: select-extend() \n\
> <Btn1Up>: select-end(PRIMARY,CUT_BUFFER0) \n\
> Button1<Btn2Down>: select-end(CLIPBOARD) \n\
> Button1<Btn2Up>: ignore()' \
> -e telnet $HOST &

Finally (for the moment) is a further modification of Robert Ess's script by Erik Ahlefeldt, <oahlefel@metz.une.edu.au>. From his readme file, for vmsterm:

> This script is for people who wish to connect from a Linux or Unix computer to a VMS computer using telnet and get a good VT100 or VT220 emulation. The key mappings have been specifically designed to emulate the VT terminal auxiliary numeric keypad, so that you can use VMS EDT and TPU editors, as well as the many VMS applications use keys PF1 to PF4. The script should work with any recent version of Xterm using a standard extended IBM PC keyboard or a Sun keyboard.

> About the keymappings. First the auxiliary numeric keypad. My prime objective with these mappings was to produce a setup that I could use with the EDT and TPU editors which make extensive use of the numeric keypad. The top row of keys PC numeric keypad (Num Lock, Divide, Multiply, Subtract) are where you find PF1, PF2, PF3, PF4 on a VT keyboard, so I have mapped them to PF1 thru PF4. The PC numeric keypad Add key (+) takes up the space of two keys which are Minus and Comma on the VT keyboard – I have mapped it to Comma (Delete Character in the EDT editor). I have then used the PC Pause key to map to VT key Minus (Delete Word in the EDT editor). The remaining keys on the auxiliary numeric keypad are the same for PC and VT.

> The six keys between the main and numeric keypads on the PC (Insert, Home, Page Up, Delete End, Page Down) are usually mapped to the VT keys by either position or by (approximate) function. As I rarely use these keys I have mapped them by function as follows: PC key Insert to VT Insert Here, PC Home to VT Find, PC Page Up to VT Prev, PC Delete to VT Remove, PC End to VT Select, PC Page Down to VT Next.

> Function keys.
>   There are 12 function keys on the PC keyboard and 20 on the VT keyboard, so I map PC F1 thru F12 to VT F1 thru F12 (except for F1 thru F5 as noted below) and PC Shift F1 thru Shift F10 to VT F11 thru F20.

>   The VT keys F1 thru F5 are local hardware function keys so there is nothing to emulate, however some PC to VT emulations in the past have mapped PF1 thru PF4 here, so I have done that too, even though they are already mapped on the auxiliary numeric keypad.

> Xterm functionality.
>   You lose some xterm functions when you remap the keyboard, however this script implements a scroll back buffer of 1000 lines which you scroll through using Shift and Up (a.k.a. Up Arrow or Cursor Up key) or Shift and Down.

a summary of the keyboard mapping:

>     PC Key     maps to   VT Key.
>     ------               ------
>     F1                   PF1
>     F2                   PF2
>     F3                   PF3
>     F4                   PF4
>     F5                   unused
>     F6                   F6
>     F7                   F7
>     F8                   F8
>     F9                   F9
>     F10                  F10
>     F11                  F11
>     F12                  F12
>     Shift F1             F11
>     Shift F2             F12
>     Shift F3             F13
>     Shift F4             F14
>     Shift F5             F15 (Help)
>     Shift F6             F16 (Do)
>     Shift F7             F17
>     Shift F8             F18
>     Shift F9             F19
>     Shift F10            F20
>     Shift F11            F11
>     Shift F12            F12
>     Print                Help (F15)
>     Cancel               Do   (F16)
>     Pause                Keypad Minus

>     Insert               Insert Here
>     Delete               Remove
>     Home                 Find
>     End                  Select
>     Prior                Prev
>     Next                 Next
>     BackSpace            BackSpace (sends DEL - ascii 127)

>     Num_Lock             PF1
>     KP_Divide            PF2
>     KP_Multiply          PF3
>     KP_Subtract          PF4
>     KP_Add               Keypad Comma
>     KP_Enter             Enter
>     KP_Decimal           Period
>     KP_0                 Keypad 0
>     KP_1                 Keypad 1
>     KP_2                 Keypad 2
>     KP_3                 Keypad 3
>     KP_4                 Keypad 4
>     KP_5                 Keypad 5
>     KP_6                 Keypad 6
>     KP_7                 Keypad 7
>     KP_8                 Keypad 8
>     KP_9                 Keypad 9
>     Up                   Up
>     Shift Up             Scroll Back
>     Down                 Down
>     Shift Down           Scroll Forward
>     Right                Right
>     Left                 Left

and the script:

> #!/bin/sh
> # vmsterm
> # from an original script by Bob Ess
> # key translations by Erik Ahlefeldt
> #
> # Script file using Xterm and telnet to connect to a VMS host
> # and give a decent vt220 emulation.
> #
> # Usage statement
> Usage(){
> echo
> echo " Usage : vmsterm -options"
> echo
> echo " Options: -80 for 80 column terminal"
> echo " -132 for 132 column terminal"
> echo " -bg colorname"
> echo " -fg colorname"
> echo " -fn fontname"
> echo " -fb bold fontname"
> echo " -host [crusher.saltmine.com] [earth] [192.168.7.7]"
> echo ""
> echo " Example: \"vmsterm -80 -fg white -bg black -fn 9x15 -fb 9x15b -host earth\""
> echo " Starts a VMS session with an 80 column terminal"
> echo " with a black background, white foreground, a normal"
> echo " font of 9x15 and a bold font of 9x15b, and connects"
> echo " to the node 'earth'"
> echo ""
> echo " Example: \"vmsterm -host earth\""
> echo " Starts a VMS session with default terminal settings "
> echo ""
> echo " Example: \"vmsterm -help\""
> echo " Displays vmsterm options "
> echo
> exit 1
> }
> # Default to a black foreground with a white background.
> # Use the 9x15 and 9x15bold fonts. Connect to 192.168.3.3 by default.
> #
> FG=black
> BG=white
> HOST=192.168.3.3
> FONT=9x15
> BFONT=9x15bold
> COLS=80
> # Parse the command line arguments
> #
> while [ $# != 0 ];
> do
> case $1 in
> -80) COLS=80
> FONT=spc12x24c
> BFONT=spc12x24b
> shift
> ;;
> -132) COLS=132
> FONT=9x15
> BFONT=9x15b
> shift
> ;;
> -fg) shift
> FG=$1
> shift;;
> -bg) shift
> BG=$1
> shift;;
> -fn) shift
> FONT=$1
> shift;;
> -fb) shift
> BFONT=$1
> shift;;
> -host) shift
> HOST=$1
> shift;;
> -help) Usage;;
> *) Usage;;
> esac
> done
> xterm -title "VMSTERM" -sb -sl 1000 -geo ${COLS}x24 -fg ${FG} -bg ${BG} \
> -cr blue -fn ${FONT} -fb ${BFONT} -xrm \
> "XTerm*vt100.translations: #override \n \
> ~Shift <Key>F1: string(0x1b) string("OP") \n \
> ~Shift <Key>F2: string(0x1b) string("OQ") \n \
> ~Shift <Key>F3: string(0x1b) string("OR") \n \
> ~Shift <Key>F4: string(0x1b) string("OS") \n \
> ~Shift <Key>F5: string("Break") \n \
> ~Shift <Key>F6: string(0x1b) string("[17~") \n \
> ~Shift <Key>F7: string(0x1b) string("[18~") \n \
> ~Shift <Key>F8: string(0x1b) string("[19~") \n \
> ~Shift <Key>F9: string(0x1b) string("[20~") \n \
> ~Shift <Key>F10: string(0x1b) string("[21~") \n \
> ~Shift <Key>F11: string(0x1b) string("[23~") \n \
> ~Shift <Key>F12: string(0x1b) string("[24~") \n \
> Shift <Key>F1: string(0x1b) string("[23~") \n \
> Shift <Key>F2: string(0x1b) string("[24~") \n \
> Shift <Key>F3: string(0x1b) string("[25~") \n \
> Shift <Key>F4: string(0x1b) string("[26~") \n \
> Shift <Key>F5: string(0x1b) string("[28~") \n \
> Shift <Key>F6: string(0x1b) string("[29~") \n \
> Shift <Key>F7: string(0x1b) string("[31~") \n \
> Shift <Key>F8: string(0x1b) string("[32~") \n \
> Shift <Key>F9: string(0x1b) string("[33~") \n \
> Shift <Key>F10: string(0x1b) string("[34~") \n \
> Shift <Key>F11: string(0x1b) string("[28~") \n \
> Shift <Key>F12: string(0x1b) string("[29~") \n \
> <Key>Print: string(0x1b) string("[28~") \n \
> <Key>Cancel: string(0x1b) string("[29~") \n \
> <Key>Pause: string(0x1b) string("Om") \n \
> <Key>Insert: string(0x1b) string("[2~") \n \
> <Key>Delete: string(0x1b) string("[3~") \n \
> <Key>Home: string(0x1b) string("[1~") \n \
> <Key>End: string(0x1b) string("[4~") \n \
> <Key>Prior: string(0x1b) string("[5~") \n \
> <Key>Next: string(0x1b) string("[6~") \n \
> <Key>BackSpace: string(0x7f) \n \
> <Key>Num_Lock: string(0x1b) string("OP") \n \
> <Key>KP_Divide: string(0x1b) string("OQ") \n \
> <Key>KP_Multiply: string(0x1b) string("OR") \n \
> <Key>KP_Subtract: string(0x1b) string("OS") \n \
> <Key>KP_Add: string(0x1b) string("Ol") \n \
> <Key>KP_Enter: string(0x1b) string("OM") \n \
> <Key>KP_Decimal: string(0x1b) string("On") \n \
> <Key>KP_0: string(0x1b) string("Op") \n \
> <Key>KP_1: string(0x1b) string("Oq") \n \
> <Key>KP_2: string(0x1b) string("Or") \n \
> <Key>KP_3: string(0x1b) string("Os") \n \
> <Key>KP_4: string(0x1b) string("Ot") \n \
> <Key>KP_5: string(0x1b) string("Ou") \n \
> <Key>KP_6: string(0x1b) string("Ov") \n \
> <Key>KP_7: string(0x1b) string("Ow") \n \
> <Key>KP_8: string(0x1b) string("Ox") \n \
> <Key>KP_9: string(0x1b) string("Oy") \n \
> ~Shift <Key>Up: string(0x1b) string("[A") \n \
> Shift <Key>Up: scroll-back(1,lines) \n \
> ~Shift <Key>Down: string(0x1b) string("[B") \n \
> Shift <Key>Down: scroll-forw(1,lines) \n \
> <Key>Right: string(0x1b) string("[C") \n \
> <Key>Left: string(0x1b) string("[D")" \
> -e telnet $HOST

### How do I set the title?

The control sequences for doing this are documented in ctlseqs.ms.

The usual context for this question is setting the title according to the current working directory. People post answers to this periodically on the newsgroups. Here is one that I have seen, from Roy Wright <nobody@roystoy.dseg.ti.com>. In your /etc/profile after:

> if [ "$SHELL" = "/bin/pdksh" -o "$SHELL" = "/bin/ksh" ]; then
> PS1="! $ "
> elif [ "$SHELL" = "/bin/zsh" ]; then
> PS1="%m:%~%# "
> elif [ "$SHELL" = "/bin/ash" ]; then
> PS1="$ "
> else
> PS1='\u@\h:\w\$ '
> fi

add:

> if [ "$TERM" = "xterm" ]; then
> PS1="\033]2;\u@\h:\w\007bash$ "
> fi

The terminator "\007" is a problem area. XTerm historically uses this character, though it is non-ANSI. The "correct" character should be a "\233" string terminator, or "\033\\", which is the 7-bit equivalent. Modern xterm recognizes either (the "\007" or string terminator); waiting for the first of these.

You may have resource or environment problems that prevent you from setting the title at all. Newer xterms (starting somewhere in X11R5) use the $LANG variable. If your locale is incorrectly installed, you will be unable to set the xterm's title. As noted by Mikhail Teterin <mi@rtfm.ziplink.net>: Make sure that the locale (LANG and/or LOCALE environment variable) is known to X Window System. Check ${X11ROOT}/lib/X11/locale.* for it. If it is not listed in either one of the files, find the nearest match and add an alias to it. Restart X if you have made changes.

On a related note, some people want to know how to read the title from an xterm. This works for modern xterm and dtterm, but not for other variations:

> #!/bin/ksh
> # Echo the current X term title bar to standard output.
> # Written by Icarus Sparry <icarus@bath.ac.uk> 11 Apr 1997
> #
> exec </dev/tty
> old=$(stty -g)
> stty raw -echo min 0 time ${1-10}
> print "\033[21t\c" > /dev/tty
> IFS='' read -r a
> stty $old
> b=${a#???}
> print -R "${b%??}"

But it is possible to avoid escape sequences altogether (from Hemant Shah <shah@typhoon.xnet.com>):

>     $ xprop -id $WINDOWID | grep WM_NAME
>     WM_NAME(STRING) = "this is my title"
>     current_title=$(xprop -id $WINDOWID | grep WM_NAME | cut -d= -f2)

Here's another source of information: Xterm-Title HowTo

### How do I make the cursor blink?

Standard xterm does not implement a blinking cursor. Some of the variations do: dtterm, GNOME Terminal, and modern xterm (from mid 1999, patch 107).

## Frequent problems

- Starting xterm, or not
  - Xterm does not run (no available pty's)
  - I need /etc/termcap
  - Why does $LD_LIBRARY_PATH get reset?
  - Why do the -e and -ls options not work together?
  - Why is my screen size not set?
  - Why are the menus tiny?
- Font problems
  - My terminal doesn't show box characters
  - The bold font is ugly
  - I see little dots on the screen
  - My terminal doesn't display Cyrillic characters
  - I see boxes instead of characters in uxterm
  - The first popup menu is very slow
- Keyboard problems
  - Why can't I input 8-bit characters?
  - Why doesn't my delete key work?
  - Why did my delete key stop working?
  - Well, how can I set my delete key?
  - Why doesn't my keypad work?
  - How can my program distinguish control-I from tab?
  - Why can't I use the pageup/pagedown keys?
  - Why can't I use the home/end keys?
  - Why can't I use the cursor keys in (whatever) shell?
  - Alt-keys do not work in bash
- Colors and other graphic rendition
  - My terminal doesn't recognize color
  - What $TERM should I use?
  - Reverse video is not reset
  - My colors changed in vim
  - Aren't bright colors the same as bold?
  - Can I set a color by its number?
  - I don't like that shade of blue
  - Why doesn't xterm support italics?
  - "grep --color" does not show the right output
  - That description of wrapping is odd, say more?
  - That color scheme is odd, say more?
- Odd behavior
  - Why can't I select/paste in xterm?
  - Why can't I select/paste to/from other programs?
  - Why can't I select tab-characters in xterm?
  - FVWM does weird things when I try to resize xterm
  - Why doesn't the screen clear when running vi?
  - Why doesn't the screen clear when I type control/L?
  - Why is the cursor misplaced after running vi?
  - Why doesn't the scrollbar work?
  - Can I improve the scrollbars?
  - Can I improve the scrolling speed?
  - Why can't my program read the window title?
  - Why can't my program set the window size?
  - Why is the text in the wrong place?
- Sample .Xdefaults Color-Settings for XTerm
- What is this warning message?

### Starting xterm, or not

#### XTerm does not run (no available pty's)

Your copy of xterm may not have enough permissions to use existing pty's:

- you may have to make xterm run setuid to root (though newer systems have wrappers that make this unnecessary).
- the pty's permissions may be restrictive (that is ok, but you have to make xterm agree with it). Usually this is done by making the group ownership of the pty's "tty", and requiring that xterm run setgid to "tty". This is done rather than make xterm run setuid to root, since that presents problems with security.
- newer systems (with Unix98 pty's) have a single entry under /dev which has to have the right permissions. For example:

  >     # ls -l /dev/ptmx
  >     crw-rw----    1 root     tty        5,   2 Aug 21 20:19 /dev/ptmx

Perhaps your system does not have enough pty's, or (problems reported with newer Linux kernels supporting Unix98 pty's, beginning with RedHat 6.0) the major device numbers of the pty's may have changed during a kernel upgrade. (This is described in `/usr/src/linux/Documentation`).

See also the MAKEDEV script, which usually exists under /dev.

#### I need /etc/termcap

If you have a termcap version of xterm on a system with no termcap libraries, you may also be missing /etc/termcap.

A workaround is to copy /usr/X11R6/lib/X11/etc/xterm.termcap to /etc/termcap.

This is fixed another way starting with XFree86 3.3.1. If xterm cannot find the terminal description, it will accept that, though it will print a warning. If xterm does not find the termcap entry, it will not set the $TERMCAP variable.

#### Why does $LD_LIBRARY_PATH get reset?

If xterm is running setuid (which is needed on some systems which have no wrappers for opening pty's and updating utmp), newer systems automatically set or reset environment variables which are considered security problems. These include `$PATH` and `$LD_LIBRARY_PATH`, since they affect the choice of which programs are run if not specified via a full pathname.

This means, for example, that if you attempt to run

>     xterm -e foo

where `foo` is a program that uses shared libraries in `/usr/local/lib`, then the command will fail, because `/usr/local/lib` is not considered part of `root`'s environment.

Modern Unix systems (such as recent Solaris and HPUX versions) do not require you to run xterm setuid. Some will result in odd malfunctions if you do this.

#### Why do the -e and -ls options not work together?

XTerm has two useful options for controlling the shell that is run:

-e
  tells xterm to execute a command using the remaining parameters after this option.
-ls
  tells xterm to invoke a login shell, making it read your `.login` file, for instance.

The two are not compatible. If you specify both, xterm uses `-e`, and if that fails for whatever reason will fall through to the `-ls` option. It cannot (in general) combine the two, since some shells permit this (e.g., bash), and others do not (e.g., tcsh).

#### Why is my screen size not set?

Well, it may be set, but not correctly. You may notice these symptoms:

- When editing with vi, you cannot see the beginning of the file, or
- Running

  >     stty -a

  shows the rows and/or columns values as 0, or some other value (such as 65) which has nothing to do with the actual window size.

XTerm knows how big the screen is (of course), and tries to tell your applications (e.g., by invoking ioctl's and sending SIGWINCH). But sometimes it cannot:

- XTerm itself may have been built incorrectly (the #ifdef's that make the logic work are inactive).
- You may be running xterm via a remote connection which refuses to pass that information. This can happen even on "modern" networks where the connection crosses domain boundaries.
- You may be running su'd to another account. SIGWINCH is just another signal; signals do not propagate for security reasons.

Most full-screen applications such as vi are designed to use the ioctl calls that return the screen size. When they fail, the applications use the size defined in the terminal's terminfo or termcap description.

You may be able to use the resize program to issue the ioctl's that will notify your application of the actual screen size. This does not always work for the reasons just mentioned. Newer versions of stty let you specify the screen size, though it will not be updated if you resize the xterm window:

>     stty rows 24 columns 80

Most full-screen applications also check if the $LINES and $COLUMNS variables are set, using those values to override the terminal description:

>     setenv LINES 24
>     setenv COLUMNS 80

Why 65 lines? The standard xterm terminfo description specifies 65 lines, perhaps because someone liked it that way. Real VT100's are 24 lines. I once used (and wrote applications for) a Bitgraph terminal, which emulated VT100, but displayed 65 lines.

#### Why are the menus tiny?

Everything seems to work, except that the xterm menus (VT options, fonts, etc.) do not display properly; the menus pop up, but only with a tiny display area in which none of the options are visible (and only part of the menu title is visible).

You have specified the geometry for xterm too high in the hierarchy, and that 24x80 (or whatever the -geometry parameter happens to be) is applying to the menus in pixels. This resource makes the geometry apply to the menus as well as the VT100 widget:

> XTerm*geometry: 80x24

while this applies only to the VT100 widget (which is probably what you intended):

> XTerm.VT100.geometry: 80x24

or better yet (to allow for the toolbar option, which uses a level of widget hierarchy):

> XTerm*VT100.geometry: 80x24

### Font problems

#### My terminal doesn't show box characters

XTerm displays the 7-bit ASCII and VT100 graphic characters (including box corners) using specially arranged fixed-pitch fonts. The first 32 glyph positions (which would correspond to nonprinting control characters) are used to hold the VT100 graphic characters. Some fonts that otherwise look fine (such as courier) do not have glyphs defined for these positions. So they display as blanks. Use xfd to display the font.

Modern xterm can form its own line-drawing characters (see patch 90, for example). It does not draw all of the graphic characters, only those that may be done with straight lines. But those are the most used, making most of the fixed-pitch fonts useful for xterm.

You may also have a problem with the terminfo description. As distributed, the X11R6 terminfo for xterm does not have the acsc string defined, so most implementations of curses do not try to use the alternate character set.

Finally, some people confuse the VT100 graphic characters with the VT220 support for DEC technical character set. These are distinct (7-bit) character sets. Xterm currently does not support this.

#### The bold font is ugly

XTerm lets you directly specify one bold font, which is assumed to correspond to the default font. Older versions of xterm make a fake bold font for the other choices via the fonts menu by drawing the characters offset by one pixel. I modified xterm to ask the font server for a bold font that corresponds to each font (other than the default one). Usually that works well. However, sometimes the font server gives a poor match. Xterm checks for differences in the alignment and size, but the font server may give incorrect information about the font size. The scaled bitmap font feature gives poor results for the smaller fonts. In your X server configuration file, that can be fixed by disabling the feature, e.g., by appending ":unscaled" to the path:

> FontPath "/usr/lib/X11/fonts/100dpi/:unscaled"
> FontPath "/usr/lib/X11/fonts/75dpi/:unscaled"
> FontPath "/usr/lib/X11/fonts/misc/:unscaled"

You can suppress xterm's overstriking for bold fonts using the `alwaysBoldMode` and related resources. However, rendering ugly bold fonts is a "feature" of the font server. In particular, the TrueType interface provides less ability to the client for determining if a particular font supports a bold form.

#### I see little dots on the screen

Well, I do. Perhaps you do not. It depends on the fonts you choose, and how you use them.

Standard xterm has a "normal" font for which a bold font can be chosen, and several alternative fonts, useful for changing the font size. The alternative fonts do not have corresponding bold fonts. Xterm simulates bold fonts in this case by overstriking the character one pixel offset. That can make an bold character extend into the area that another character occupies. When erasing a bold character from the screen, xterm does not erase the extra pixel. This is corrected in modern xterm, subject to the available fonts (from late 1998, patch 85). For each font, it asks the font server for a corresponding bold font. Your font server may not have the bold font (or it may incorrectly report that it does). But it usually works.

#### My terminal doesn't display Cyrillic characters

Cyrillic encodings typically use characters in the range 128-159. For a VT220 (or any terminal that follows ISO 6429), those are treated as control characters. Still, some people want to use KOI8-R, etc. I modified xterm in patch 175 to add an option (`-k8`) and corresponding resource settings to allow them to customize their environment. Here is a sample script and resource file which I use for testing this configuration.

#### I see boxes instead of characters in uxterm

XTerm may show boxes instead of characters if the font that you have selected does not contain those characters. Normally you can fix most of that using the UTF-8 feature, with `uxterm`. However, your X resource settings may be the source of the problem.

One pitfall to setting X resources is that they allow you to specify wildcards, e.g., the "*" character. When you give a wildcard, the X resource matches any number of levels in the widget hierarchy.

XTerm has more than one widget matching "font" at different levels of the hierarchy. There are the popup menus, and there are the fonts used for `uxterm`. The latter is where an overbroad pattern can cause xterm to use a different font than you expect.

Suppose your resource setting includes this pattern

> *VT100*font: fixed

It could be interpreted as this:

> *VT100.font: fixed
> *VT100.utf8Fonts.font: fixed

XTerm uses the `utf8Fonts` subresources to provide runtime-switchable fonts between IS0-8859-1 (Latin-1) and ISO-10646 (Unicode). Modifying the Unicode font to "fixed" will make most of the characters unavailable (i.e., shown as boxes). If instead your resource looks like

> *VT100.font: fixed

it would be unambiguous, and not modify the `utf8Fonts` value.

#### The first popup menu is very slow

Some users report that when starting xterm, it is very slow, that their computer's CPU time increases, etc.

This is a longstanding bug in the X libraries. There is a workaround using a resource setting for xterm.

##### Details

XTerm uses the Athena (Xaw) widgets to display popup menus. In the normal case, those are initialized one-by-one as they are first used. If you have configured xterm to use its toolbar configuration, they are all initialized on startup. In the latter, performance problems are more noticeable.

The Athena widgets `XawInitializeWidgetSet` function goes through several levels down to the X library `_XlcAddUtf8LocaleConverters` function to call `create_tocs_conv` and related functions to make a list of character sets from the locale, which is used in menus to get all possible fonts needed for a fontset.

If your current locale uses UTF-8 encoding, this will read a long list of bitmap fonts—everything whose encoding might be useful for displaying the menus. For example, this list (from `lcUTF8.c`) which dates from around 2000 is the core of the problem:

> ISO10646-1, ISO8859-1, ISO8859-2, ISO8859-3, ISO8859-4, ISO8859-5, ISO8859-6, ISO8859-7, ISO8859-8, ISO8859-9, ISO8859-10, ISO8859-11, ISO8859-13, ISO8859-14, ISO8859-15, ISO8859-16, JISX0201.1976-0, TIS620-0, GB2312.1980-0, JISX0208.1983-0, JISX0208.1990-0, JISX0212.1990-0, KSC5601.1987-0, KOI8-R, KOI8-U, KOI8-C, TATAR-CYR, ARMSCII-8, IBM-CP1133, MULELAO-1, VISCII1.1-1, TCVN-5712, GEORGIAN-ACADEMY, GEORGIAN-PS, ISO8859-9E, MICROSOFT-CP1251, MICROSOFT-CP1255, MICROSOFT-CP1256, BIG5-0, BIG5-E0, BIG5-E1, ISO10646-1, ISO10646-1

However, xterm is going to use only the characters shown in the popup menus. It is unlikely that you need Chinese fonts for that.

##### Solution

XTerm's `menuLocale` resource can be set to an explicit value, e.g., "C" to override the current locale as seen by this initialization debacle.

##### Limitations

The workaround does not prevent some hacker from "improving" the X libraries still further.

### Keyboard problems

#### Why can't I input 8-bit characters?

You must have the `eightBitInput` resource set to do this.

#### Why doesn't my delete key work?

This seems to have begun as a problem with the older XFree86 release (3.1.2). I have picked up pieces of the story (xterm and the keyboard work as designed under XFree86 3.2 and up).

The underlying problem is that we've accumulated three things that are being equated as "Delete":

>     ASCII BS (backspace, code 8)
>     ASCII DEL (delete. code 127)
>     VT220 "remove" aka "delete" (ESC [ 3 ~)

You are probably talking about the backarrow key (on my keyboard, at the upper right of the QWERTY block), or the key labeled delete which is on the 6-key "editing keypad". Since xterm is emulating a VT100/VT220, the backarrow key should generate a 127 (often displayed as `^?`). You would use a control/H to obtain a backspace on a real VT220.

The reason why `BS` and `DEL` are of special interest is that on Unix, the `stty` command and the underlying termios/termio system calls allow only single-byte codes to be assigned to special functions such as `erase`. For instance, you could see something like this on your terminal:

>     $ stty -a
>     speed 38400 baud; rows 40; columns 80; line = 0;
>     intr = ^C; quit = ^\; erase = ^H; kill = ^U; eof = ^D; eol = <undef>;
>     eol2 = <undef>; swtch = <undef>; start = <undef>; stop = <undef>; susp = <undef>;
>     rprnt = ^R; werase = ^W; lnext = ^V; flush = ^O; min = 1; time = 0;
>     -parenb -parodd cs8 -hupcl -cstopb cread -clocal -crtscts
>     -ignbrk brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl ixon -ixoff
>     -iuclc -ixany -imaxbel -iutf8
>     -opost -olcuc -ocrnl -onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0
>     isig -icanon -iexten -echo -echoe -echok -echonl -noflsh -xcase -tostop -echoprt
>     -echoctl -echoke

Tastes differ. On Unix, people expect the backarrow key to generate a backspace (or not). As I understand it, at one point, XFree86 picked up the sense of the erase character during initialization, so that xterm would in effect use the same erase character as the console. The current scheme (X11R6) uses keyboard mapping tables that are independent of the environment.

Modern xterm (since patch #83 in 1998) provides a resource toggle backarrowKey (and an escape sequence from VT320) that changes this key between the two styles (backspace or delete).

With modern xterm patch 95 (also in the stable version as "88c"), you may have an xterm which can automatically initialize the backarrow key to backspace or delete depending on the pseudo terminal's sense, or based on the termcap setting of kbs (backspace key). This feature is controlled by the resource setting ptyInitialErase.

#### Why did my delete key stop working?

Well, something changed. You have to determine what did.

This may be because an upgrade introduced different X resource settings, or because you are using the newer xterm with the ptyInitialErase resource (or perhaps both). Use

>     appres XTerm

to see the X resources that you are using, in particular the `translation` (or `Translation`) resource for the vt100 widget.

One unexpected scenario came out of hiding when I was implementing the ptyInitialErase resource. When xterm is (by default) built to support this, it sets the pty's erase character to match the termcap entry. Xterm also sets the $TERMCAP environment variable to match. So everything is consistent, and everything defined. The `stty erase` character is either backspace (^H) or delete (^?).

The problem arises because there are two things called "delete", which were not well-defined: ASCII delete (127) and the PC-style adaptation of VT220 `remove` assigned to the key Delete.

However, the screen program prefers to make the termcap delete (`kD`) an <escape>[3~, which corresponds to the VT220 `remove` key. If $TERMCAP is set when starting screen, it will translate stty's erase character into the <escape>[3~, making most curses and termcap applications work. But stty still has the original erase character. So low-level applications which check stty will not work. I found that unsetting $TERMCAP before running would work, but this was not a good solution. Someone pointed out (see patch 129), that the problem really was because termcap `kD` should delete the character at the current position. So it cannot be the same as `stty erase`.

As a matter of fact, `stty erase` has to be a single character, so <escape>[3~ would not work anyway.

#### Well, how can I set my delete key?

When people first started asking this question in 1995-1996, it appeared in the context of making Netscape work. Netscape's use of the delete key running in X did not match user's expectations when compared to that other platform. They were commonly advised to use xmodmap, e.g.,

>     keysym BackSpace = Delete

or

>     keycode 22 = 0xff08

Either way is a bad technical solution – it works for some people but not others (on my keyboard at work, keycode 22 is the numeric keypad '9').

Alternatively, you can set resources. This works reasonably well for environments where you have different versions of xterm, e.g.,

> XTerm*VT100.translations: #override \n\
> <Key>Delete: string(0x7f)

I do not do that either, because it is not flexible. Not all programs use the same sense of `stty erase`; some use termcap or terminfo, and some are hardcoded. So I prefer to be able to switch the xterm's keyboard at runtime. You cannot do that with resources. (Or not really – xterm has a `keymap()` action which could support this if you provided a rather complex resource settings, but the X library support for that is broken in X11R6). Instead, I have added to xterm a set of resources (and popup menu entries) to allow simple switching between the different styles of keyboard, in particular for the backspace/delete issues. See the manual page for `backarrowKey` `backarrowKeyIsErase` and `deleteIsDEL` as well as `sunKeyboard`.

#### Why doesn't my keypad work?

A few people have commented that the keypad does not work properly. Aside from bugs (I have fixed a few), the most common problem seems to be misconception.

Here's a picture of the VT100 numeric keypad:

>     +-----+-----+-----+-----+
>     | PF1 | PF2 | PF3 | PF4 |
>     +-----+-----+-----+-----+
>     |  7  |  8  |  9  |  -  |
>     +-----+-----+-----+-----+
>     |  4  |  5  |  6  |  ,  |
>     +-----+-----+-----+-----+
>     |  1  |  2  |  3  |     |
>     +-----+-----+-----+ ENT +
>     |     0     |  .  |     |
>     +-----+-----+-----+-----+

and the similar Sun and PC keypads:

>     +-----+-----+-----+-----+
>     | NUM |  /  |  *  |  -  |
>     +-----+-----+-----+-----+
>     |  7  |  8  |  9  |     |
>     +-----+-----+-----+  +  +
>     |  4  |  5  |  6  |     |
>     +-----+-----+-----+-----+
>     |  1  |  2  |  3  |     |
>     +-----+-----+-----+ ENT +
>     |     0     |  .  |     |
>     +-----+-----+-----+-----+

Working in X11, the NUM (NumLock) key has better uses than an alias for PF1 (and is sometimes reserved). I use the F1 through F4 on the keyboard to implement PF1 through PF4, alias the keypad "+" to "," and use the existing "-" key.

VT220 emulation uses the VT100 numeric keypad as well as a 6-key editing keypad. Here's a picture of the VT220 editing keypad:

>     +--------+--------+--------+
>     | Find   | Insert | Remove |
>     +--------+--------+--------+
>     | Select | Prev   | Next   |
>     +--------+--------+--------+

and the similar Sun and PC keypads:

>     +--------+--------+--------+
>     | Insert | Home   | PageUp |
>     +--------+--------+--------+
>     | Delete | End    | PageDn |
>     +--------+--------+--------+

I chose to use keys that are mnemonic rather than in the "same" positions, though some emulators (e.g., Tera Term) use the same positions:

>     +--------+--------+--------+
>     | Insert | Find   | Prev   |
>     +--------+--------+--------+
>     | Remove | Select | Next   |
>     +--------+--------+--------+

I test the keyboard (for VT52/VT100/VT220) using vttest. If you find (or think that you have found) a problem with the keyboard handling of xterm, please test it with vttest first.

Other arrangements of the keyboard are possible of course. If you prefer to use the top row of the numeric keypad as PF1 through PF4, you should do this using xterm's X resources.

In 2014, I noticed a comment, which relates to the PF1-PF4 assignment, but also to the use of function-key modifiers.
Because that is a digression, I have expanded it in a separate page.

#### How can my program distinguish control-I from tab?

Your program can use xterm's modifyOtherKeys feature, e.g., using a control sequence such as

>     \033 [ > 4 ; 2 m

to temporarily switch into a mode where shift, alt, control and meta modifiers applied to a key tell xterm to send an escape sequence which encodes all of that information. The `tab` key would send a tab, but control-i would send

>     \033 [ 2 7 ; 5 ; 1 0 5 ~

while control-shift-i would send

>     \033 [ 2 7 ; 6 ; 7 3 ~

Your program should turn that off when it is not needed; it is a real nuisance when you cannot type control-characters as they were meant to be used:

>     \033 [ > 4 m

In 2019, Bram Moolenaar asked for more details about modifying other keys; I have expanded that in a separate page.

#### Why can't I use the pageup/pagedown keys?

Some vendors, e.g,. Sun, added key translations which make the pageup and pagedown keys talk to the xterm's scrollbar instead of your application. They did the same thing for the home and end keys, thereby obscuring a bug in xterm.

You can override this by specifying your own translations in your resource file. The issue was first noted with Solaris 2.5, with the file given in two locations:

>     /usr/lib/X11/app-defaults/XTerm
>     /usr/openwin/lib/app-defaults

using a symbolic link to relate the two. Later releases of Solaris, e.g., 8-10 omitted the former location.
Solaris 11 provides modern xterm (patch #271), and does not have this problem.

As of February 2014, I am able to verify that AIX and HPUX have updated to modern xterm, e.g.,

- patch #180 on HPUX 11.31,
- patch #222 on AIX 6.1 and 7.1,

Older AIX and HPUX releases distributed the X Consortium (1994) app-defaults file.

> In updating this question in February 2014, I noticed that IBM added their copyright notice in AIX's copy of the app-defaults file in

> >     /usr/lpp/X11/lib/X11/app-defaults

> There were no other changes to the file. Someone at IBM blundered.
> In patch #252, I ensured that my copyright notice is on those files (I am the sole author, and can do that).

Use the translations in the system's app-defaults file as a guide. The relevant section of the app-default file looks like

> *VT100.translations: #override \
> @Num_Lock<Key>KP_0: string(0)\n\
> @Num_Lock<Key>KP_1: string(1)\n\
> @Num_Lock<Key>KP_2: string(2)\n\
> @Num_Lock<Key>KP_3: string(3)\n\
> @Num_Lock<Key>KP_4: string(4)\n\
> @Num_Lock<Key>KP_5: string(5)\n\
> @Num_Lock<Key>KP_6: string(6)\n\
> @Num_Lock<Key>KP_7: string(7)\n\
> @Num_Lock<Key>KP_8: string(8)\n\
> @Num_Lock<Key>KP_9: string(9)\n\
> @Num_Lock<Key>KP_Add: string(+)\n\
> @Num_Lock<Key>KP_Decimal: string(.)\n\
> @Num_Lock<Key>KP_Divide: string(/)\n\
> @Num_Lock<Key>KP_Enter: string(\015)\n\
> @Num_Lock<Key>KP_Equal: string(=)\n\
> @Num_Lock<Key>KP_Multiply: string(*)\n\
> @Num_Lock<Key>KP_Subtract: string(-)\n\
> <Key>Prior:scroll-back(1,page)\n\
> <Key>Next:scroll-forw(1,page)\n\
> <Key>F16: start-extend() select-end(PRIMARY, CUT_BUFFER0, CLIPBOARD) \n\
> <Key>F18: insert-selection(PRIMARY, CLIPBOARD) \n\
> <Key>F27: scroll-back(100,page) \n\
> <Key>R13: scroll-forw(100,page) \n\
> <Key>Home: scroll-back(100,page) \n\
> <Key>End: scroll-forw(100,page) \n

For example, a more-specific pattern for the resource name lets you override:

> XTerm*VT100.translations: #override \n\
> ~Shift<Key>Home: string(\033[1~)\n\
> ~Shift<Key>End: string(\033[4~)\n\
> ~Shift<Key>Prior: string(\033[5~)\n\
> ~Shift<Key>Next: string(\033[6~)\n\
> Shift<Key>Prior: scroll-back(1,page) \n\
> Shift<Key>Next: scroll-forw(1,page) \n\
> Shift<Key>Home: scroll-back(100,page) \n\
> Shift<Key>End: scroll-forw(100,page) \n

makes the home/end and pageup/pagedown keys usable by your editor, while leaving their shifted equivalents available for the scrollbar.

#### Why can't I use the home/end keys?

This is a long story, unless you are referring to X Consortium xterm. That program is simply broken in this respect.

At the beginning, when the home/end keys were fixed for modern xterm (in early 1996), there was some discussion regarding what the escape sequences should be for those keys (for the 6-key editing keypad). Those were chosen as "PC-style" codes (like SCO "ansi"), i.e.,

>     ESC [ H
>     ESC [ F

for normal mode, and

>     ESC O H
>     ESC O F

for cursor application mode.

That style of coding fit easily into the existing logic of xterm. It was not my change, and (because xterm should be based upon standards), I did question this, and asked the opinion of the person who was at that time developing rxvt. He had chosen a layout based on DEC's VT220 terminals, though the key labels on the typical PC keyboard did not match. At that point, neither of us knew enough to make a good case for this.

Somewhat later I could see that xterm had a number of undocumented extensions to support the VT220-style (pre-ISO 2022) character sets. I decided to complete the functionality by making xterm a VT220 emulator. This would require that it provide the same escape sequences for the editing and numeric keypads. I could not simply change the escape sequences from "PC-style" to "VT220-style", since a number of users "knew" that the keypad "ought to" send home, end, cursor keys, etc., because they had labels indicating that use. To retain compatibility (but allow easy reconfiguration to make a VT220 emulator), I added popup-menu items to switch between the modes. With minor refinements, this was the approach for about two years, culminating with the "stable" patch #88, which is essentially the version distributed with XFree86 3.3.x.

NOTE:
  the terminfo distributed with xterm patch #88 is incorrect: the escape sequences given for home/end keys are the VT220-style, rather than the default PC-style. Too accustomed to switching modes on the fly, I overlooked a line in my .Xdefaults file:

  > *sunKeyboard: true

  Downstream packagers (when they noticed this) accommodated the bug by modifying the VT100 translations resource which is not a good technical solution since it interferes with the users' ability to modify that resource. For example, Red Hat bug #100695 quoted a suggested patch which shows that the package had overridden the xterm behavior for shifted function keys. See this for more discussion.

But xterm continues to evolve past the stable patch #88. The keyboard support was still unsatisfactory for two reasons:

- some users wanted to be able to use applications that detected whether the control key was pressed (e.g., control/F1).
- the compromises made for `xkb` with X11R6 interfered with xterm's use of the NumLock key for the numeric keypad.

The former could be addressed by expanding the escape sequences sent by the PC-style function keys, while the latter was a VT100/VT220 design issue. I decided to redesign function-key support to separate the two styles of function keys better, but leaving the choice still controlled by the `sunKeyboard` resource. Partway through that, I was asked to do similar cleanup and redesign of the backspace and delete key handling, e.g., the ptyInitialErase resource. Because it is a redesign, I chose to not make the keyboard differences between the old and new xterms completely compatible. If you were to run both on the same system, one or the other would have some problems with the editing keypad or the backspace/delete keys which would be addressed by the popup-menu selections.

For example, at this time (2001/9/4):

- Debian stable is xterm-88c, which should be identical to the XFree86 3.3.6 version, but is not (there are some label differences in the resource-file, but nothing interesting relative to home/end keys). And of course, Debian changes the terminfo `kbs` from `^H` to `^?`. As noted, the terminfo I wrote for XFree86 3.3.x has an error. Setting

  > *sunKeyboard: true

  in the app-defaults file fixes the problem with xterm-88, which was that I documented in the terminfo the behavior with that resource set. Similarly, setting

  > *backarrowKey: false

  is one way to address Debian's change to `kbs`.

- Debian unstable is xterm-149. Other than omitting the color resources from the app-defaults file, I see that it sets

  > *backarrowKeyIsErase: true

  which would not affect the home/end keys. (The color resources are redundant, so that is not a problem either).

Here is a resource file which I tested with xterm-88c, xterm-149 and xterm-158, using $TERM set to xterm-debian:

> ! $Id: xterm.faq.html,v 1.169 2012/02/05 11:58:56 tom Exp $
> ! Settings to make xterm-88c work as expected for Debian.
> !
> ! Patch #88 was the basis for XFree86 3.3.1 xterm. There were a few additions
> ! through patch 88c, to incorporate the ptyInitialErase resource. Debian uses
> ! the VT220-style keyboard, which at #88 was the xterm-xfree86 terminfo entry,
> ! with one change: kbs changed from ^H to ^?.
> !
> ! After patch 88, I started work on keyboard changes. The result was that the
> ! xterm-xfree86 terminfo entry was set to the PC-style keyboard, and I added
> ! xterm-vt220, which corresponded mostly to the older (patch-88) version of the
> ! xterm-xfree86 terminfo entry.
> ! The terminfo with patch #88 assumed sunKeyboard was set (actually a bug, but
> ! also assumed in Debian).
> !
> ! A different problem (addressed after patch #88) is that if you wanted to use
> ! a VT100/VT220-style numeric keypad's escape sequences, you had to have
> ! NumLock set. Otherwise, in keypad application mode, the keys would transmit
> ! only the PC-style escape sequences corresponding to the key labels, e.g., the
> ! page-up string rather than the escape sequence for keypad-9.
> XTerm*sunKeyboard: true
> ! These settings overlap to some extent (backarrowKeys says to send a 127 for
> ! the "backspace" key, and ptyInitialErase says to use the pty's initial sense
> ! of the erase character, which is reported to be the same on Linux).
> XTerm*backarrowKey: false
> XTerm*ptyInitialErase: true

#### Why can't I use the cursor keys in (whatever) shell?

VTxxx (VT100 and up) terminals may send different escape sequences for the cursor (arrow) keys depending on how they are set up. The choices are referred to as the normal and application modes. Initially, the terminal is in normal mode.

VTxxx terminals are usually set up so that full-screen applications will use the cursor application mode strings. This is good for full-screen applications, including legacy applications which may have hard-coded behavior, but bad for interactive shells (e.g., ksh, tcsh, bash) which use arrow keys to scroll through a history of command strings.

To see the difference between normal/application modes, consider this example:

- In normal (non-application) mode, the terminal transmits a down-arrow as \E[C, which happens to echo as a down-arrow.
- In application mode the terminal transmits \EOC, which echoes as C. That is because the \EO is the SS3 control, which says to use the character from the G3 character set for the next cell.

Since termcaps and terminfo descriptions are written for full-screen applications, shells and similar programs often rely on built-in tables of escape sequences which they use instead. Defining keys in terms of the termcap/terminfo entry (e.g., by capturing the string sent by tputs) is apt to confuse the shell.

Depending on the terminal type, the keypad(s) on the keyboard may switch modes along with the cursor keys, or have their own independent modes. The control sequences for these are independent of the ones used for cursor-addressing, but are grouped together, e.g., as the terminfo `smkx` and `rmkx` capabilities. Terminfo entries are written assuming that the application has initialized the terminal using the `smkx` string before it is able to match the codes given for the cursor or keypad keys.

#### Alt-keys do not work in bash

See Alt-keys do not work in bash.

### Colors and other graphic rendition

#### My terminal doesn't recognize color

First, ensure that you have set up xterm to render color. Modern xterm renders color only if you have set resources to do this; the default behavior is monochrome to maintain compatibility with older applications. The manual page describes these resources. I set them in my .Xdefaults file.

Even if you set the resources properly, there may be another application running which prevents xterm from allocating the colors you have specified. But you should see a warning message for this.

Check the terminal description, to see if it is installed properly, e.g., for ncurses, which uses terminfo.

Finally, some applications (that do not interface properly with terminfo or termcap) may need the environment variable $COLORTERM to be set.

#### What $TERM should I use?

XTerm provides in its sources both terminfo and termcap files. They are designed to allow scripting to override the most common choices, e.g., the backspace key.

The `xterm-color` value for $TERM is a bad choice for modern xterm because it is commonly used for a terminfo entry which happens to not support `bce`. Complicating matters, FreeBSD (after dithering for a few years on the matter) introduced a bastardized version which implies the opposite sense of `bce`, (because it uses SGR 39 and 49), but does not set it. After lengthy discussion, FreeBSD began using the terminal descriptions which I've written.

The most recent XFree86 version's terminal description corresponds to `xterm-xfree86` (also distributed with ncurses). I have continued to make changes; the most recent version is simply named `xterm-new` (also distributed with ncurses).

The term "`bce`" stands for "back color erase". Terminals such as modern xterm and rxvt implement back color erase, others such as dtterm do not. (Roughly half of the emulators that I know about implement bce). When an application clears the screen, a terminal that implements back color erase will retain the last-set background color. A terminal that does not implement back color erase will reset the background color to the default or initial colors. Applications that paint most of the screen in a single color are more efficient on terminals that support back color erase. Inevitably, there are tradeoffs and issues with standardization of the feature as noted in the ncurses FAQ. Unsurprisingly, ncurses supports xterm's behavior.

Curses libraries that support color know about `bce` and do the right thing – provided that you tell them what the terminal does. That is the whole point of setting $TERM. The "xterm-color" description distributed with ncurses does not list `bce`, because it was applied originally to a terminal type which does not implement back color erase. It will "work" for modern xterm, though less efficient. Some other applications such as the slang library have hardcoded support for terminals that implement back color erase. Given the "xterm-color" description, those will be efficient – and fortuitously work. However, slang (through version 1.4.0) did not work properly for the terminals that xterm-color was designed for. See this page for an example of (n)curses and slang running on dtterm. That bug in slang is reported to be fixed for succeeding versions, though your application may require changes to use this fix. (The demo which comes with slang to illustrate the use of `bce` does not work properly, for instance).

The `xterm-color` value for $TERM is also (for the same reason) a bad choice for rxvt, but "works" due to the large number of hard-coded applications that override this.

Some people recommend using `xtermc`. That is installed on Solaris. However, it does not match any xterm in current use. (Apparently it was written for an obsolete version on Unixware). The colors work, true, but the mouse will not, nor will the function keys.

#### Reverse video is not reset

When running less or other programs that do highlighting, you see the highlighting not turned off properly.

This may be due to incompatible terminal descriptions for xterm. With XFree86 3.2, I modified the terminal description for XFree86 xterm to use the VT220 (aka ISO 6429) controls that allow an application to turn off highlighting (or bold, underline) without modifying the other attributes. The X Consortium xterm does not recognize these controls.

If, for example, you are running an older xterm and rlogin to a system where the newer xterm has been installed, you will have this problem, because both programs default to $TERM set to xterm. The solution for mixed systems is to install the newer terminal description as as a different name (e.g., `xterm-color`) and set the `termName` resource accordingly in the app-defaults file for the system which has the newer xterm.

However – see above.

#### My colors changed in vim

Some `vim` users may notice their colors change after updating to patch 238. Before, some text would display in a dark color using a bold font. Now, it displays in a bright color and normal font.

This is not a bug, but the result of a feature tcap-query which was added for vim in 2000. Several vim users requested that it be enabled by default in the configure script. It allows vim to ask what characters the different function keys actually send, eliminating the chance that the termcap does not match.

Vim also asks how many colors the terminal supports. Since patch 148, xterm has responded with the number of distinct colors that it can display. By default, that is 16 (8 ANSI colors with bright counterparts for displaying PC-style "bold" text).

The interpretation of this depends on the application: termcaps do not tell how to display more than 8 colors. But vim understands how to tell xterm to display using 16 colors. It makes a difference when displaying bright colors. Vim has a table of 16 color names ("dos-colors"), which one can use to define parts of the color scheme. If the terminal supports only 8 colors (colors 0-7), vim uses the bold attribute to simulate colors 8-15.

Changing the color scheme to use bold where it is wanted will make the colors work as before – and work consistently with other terminals.

#### Aren't bright colors the same as bold?

No.

Actually, "bold" happens to be whatever the terminal shows when it is sent the control-string that says "show bold".

The standard (ANSI aka ISO-6429 or ECMA-48) says no more than that. ANSI specified eight (8) colors. In fact, ANSI did not specify the appearance. That is an implementation detail.

XTerm can be configured to use colors 8-15 for displaying bold text. Or it can be configured to use those colors as part of a 16-color scheme (a feature of aixterm). They use different control strings. When xterm is configured to use the 16-color scheme, it displays bold text by relying on the font to show "bold" (usually thicker characters).

By default, colors 8-15 are brighter versions of colors 0-7 (with some special handling for blue). But again, xterm is configurable and you can use anything that you like for the numbered colors.

#### Can I set a color by its number?

Well, yes: you can set a color in several ways:

- using the color name
- using an RGB value
- selecting an index from the color palette

That last (an index) is what some people think of as the color number. The short answer is that you can find on the web tables of colors and match them up to the “color number”. But the number itself has no meaning.

In my reply to tput setaf color table? How to determine color codes?, I noted

> You may find this question/answer helpful as well: RGB values of the colors in the Ansi extended colors index (17-255)

although both question and answer raise additional questions. This FAQ is the logical place to answer those questions.

Presumably you are reading this to better understand how xterm works. But you may be interested in the way in which other terminals emulate xterm. If so, this explanation may help as well.

The long answer is that the correct mapping depends on the terminal — other terminals do not necessarily match xterm.

From a shell script, you might use tput with a parameter to an escape sequence referred to as `setaf` in the terminal description. `tput` attaches no particular meaning to the number. That actually depends upon the particular terminal emulator.

A while back, ANSI defined codes for 8 colors, and there were two schemes for numbering those. The two are seen in some terminal descriptions as the pairs `setf/setb` or `setaf/setab`. Since the latter has the connotation of "ANSI colors", you will see that used more often. The former (`setf/setb`) switched the order for red/blue as noted in Why are red/blue interchanged?, but in either case, the scheme was established for just numbering the colors. There is no predefined relationship between those numbers and RGB content.

For specific terminal emulators, there are predefined color palettes which can be enumerated easily enough — and can be programmed using these escape sequences. There are no relevant standards, and you will see differences between terminal emulators, as noted in I don't like that shade of blue.

However, convention is often confused with standards. Because xterm has been around a while, it is regarded as a standard by some.

XTerm had color support before I began working on it at the end of 1995. Some of this was mentioned in XFree86's changelog:

>     XFree86 3.1.2Be (10 January 1996)
>     203. Major xterm cleanup (including prototyping), and fixes to the colour
>          code (Thomas E. Dickey).
>     XFree86 3.1.2a (23 September 1995)
>      14. Colour support for xterm (David Wexelblat).
>      13. Fix usage of $LINES and $COLUMNS by xterm on SVR4 (David Wexelblat).

and some was not:

- The “dynamic colors” feature came from a patch written by Erik Fortune (at SGI). Someone applied this to the XFree86 sources (probably early 1995).

  Since X11R4, xterm had colors for foreground and background in the VT100 and Tek4014 widgets, as well as cursor- and mouse-colors which could be set via resources. But those were static. The dynamic colors feature allowed those colors to be set via escape sequences.

- “Colour support” was a set of changes for ANSI color. It might have been based on a patch (said to be of unknown authorship) for X11R5 xterm incorporated into a program called color_xterm. Raymond's comment in terminfo.src implies that this program was distributed earlier; however the copy of `color_xterm-alpha4` which I have at hand has file modification dates starting in December 1995. Wexelblat's commit is an earlier non-patch use of the feature for xterm.

  Both were probably due to Tom Weinstein (also at SGI) in 1992, which you can find in the historic Linux archive. The `README.color` file in this earlier color_xterm says

  >     2) Added ISO 6429 support for color text.  You can set the foreground
  >        and background color for text using SGR.  For example, to make the
  >        foreground red, you do:  "^[[31m".  The values from 30 to 37 set
  >        foreground, those from 40 to 47 set background.  The default colors
  >        are:
  >             0) black   1) red   2) green  3) yellow  4) blue  5) magenta
  >             6) cyan    7) white

  >        These are settable with the resources "color0" to "color1"

  Aside from `README.color`, there was no documentation. The terminal description was unmodified.

Thus, from the start there were two types of color support in xterm. ANSI colors treats the available colors as an array (its palette) which can be programmed, while dynamic colors applies a single color to a feature.

There have been some changes since the color_xterm in 1992:

> Resource | 1992 | 1995 | 2016
> --- | --- | --- | ---
> `color0` | `Black` | `black` | `black`
> `color1` | `Red` | `red3` | `red3`
> `color2` | `Green` | `green3` | `green3`
> `color3` | `Yellow` | `yellow3` | `yellow3`
> `color4` | `Blue` | `blue3` | `blue2`
> `color5` | `Magenta` | `magenta3` | `magenta3`
> `color6` | `Cyan` | `cyan3` | `cyan3`
> `color7` | `White` | `gray90` | `gray90`
> `color8` |  | `gray30` | `gray50`
> `color9` |  | `red` | `red`
> `color10` |  | `green` | `green`
> `color11` |  | `yellow` | `yellow`
> `color12` |  | `blue` | `rgb:5c/5c/ff`
> `color13` |  | `magenta` | `magenta`
> `color14` |  | `cyan` | `cyan`
> `color15` |  | `white` | `white`
> `colorUL` |  | `yellow` | `foreground`
> `colorBD` |  | `white` | `foreground`
> `colorRV` |  |  | `foreground`
> `colorIT` |  |  | `foreground`

In development of xterm over the past 20 years, we

- incorporated ANSI (8) colors,
- adapted the aixterm feature (16) colors,
- added extensions for 88- and 256-colors.

Much of that has been adopted by other developers for different terminal emulators. That is summarized in Why not make "xterm" equated to "xterm-256color"?.

As hinted by the table, the 16-color extension was partly implemented in xterm by late 1995, using the scheme of Linux console: bold fonts are shown as brighter equivalents of the ANSI 8 colors. Unlike the Linux console, xterm can use bold fonts and (aside from providing similar appearance to the Linux console for programs such as dialog) there was no reason to pretend that bold and bright were synonymous.

The `colorUL` and `colorBD` features are part of this discussion because I incorporated those into the indexing scheme for colors. More on that later.

First, deal with the 256- and 88-color extensions.

The reason for 256 colors is that the index would fit in a byte. Larason's scheme was simple enough:

- the existing 16 colors
- a color cube (6x6x6 is 216, which is the largest cube no larger than 256).
- a grayscale "ramp", using the remaining 24 entries.

The xterm source-code includes scripts for demonstrating the colors, e.g., using the same escape sequences that `tput` would use:

- patch #94 (1999/03/27) added `8colors.sh, 16colors.sh`
- patch #111 (1999/07/10) added `256colors.pl and 256colors2.pl`
- patch #115 (1999/07/18) added `88colors.pl and 88colors2.pl`

I added the scripts in patch #94 because of some user comments that there were scripts of that sort available, that there were some deficiencies in those, and and it would be nice to have some good examples in xterm's source. Coincidentally, that gave Todd Larason and Stephen P Wall a starting point for the changes to support 256- and 88-colors.

The 256-color extension came first. 88-colors (using the same control sequence) came next, to reduce the amount of memory needed. XTerm stores both foreground and background color indexes for each cell on the screen. That is two bytes, which doubled the amount of memory used by xterm for the scrollback. Reducing that to a single byte allowed a similar scheme using a 4x4x4 cube and a proportionately shorter grayscale ramp.

Like the aixterm 16-color extension, these colors are stored in an array. Unlike aixterm (whose developers invented a new set of escape sequences not found in ANSI or ECMA-48), we used sequences found in ECMA-48: SGR codes 38 and 48. However, the feature evolved:

- The default color palette for xterm uses header-files generated using scripts similar to the ones provided for demonstrations (patch #112).

  The first 16 colors (except for blue) use names in the X `rgb.txt`.

- The X libraries cannot handle enough resources to specify all of the 256 colors as well as other features in xterm.

  Starting with patch #129, I made the resource settings for colors past the first 16 a compile-time option. If you prefer to have the colors as X resource values, you lose UTF-8. Since xterm accepted escape sequences for setting the palette, this was not a problem.

- Steve Wall modified the palette in 2002 (patch #166), making it a little brighter.

- We used semicolon (like other SGR parameters) for separating the R/G/B values in the escape sequence, since a copy of ITU T.416 (ISO-8613-6) which presumably clarified the use of colon for this feature was costly.

  Using semicolon was incorrect because some applications could expect their parameters to be order-independent. As used for the R/G/B values, that was order-dependent. The relevant information, by the way, is part of ECMA-48 (not ITU T.416, as mentioned in Why only 16 (or 256) colors?). Quoting from section 5.4.2 of ECMA-48, page 12, and adding emphasis (not in the standard):

  > Each parameter sub-string consists of one or more bit combinations from 03/00 to 03/10; the bit combinations from 03/00 to 03/09 represent the digits ZERO to NINE; bit combination 03/10 may be used as a separator in a parameter sub-string, for example, to separate the fractional part of a decimal number from the integer part of that number.

  and later on page 78, in 8.3.117 SGR – SELECT GRAPHIC RENDITION, the description of SGR 38:

  > (reserved for future standardization; intended for setting character foreground colour as specified in ISO 8613-6 [CCITT Recommendation T.416])

  Of course you will immediately recognize that `03/10` is ASCII colon, and that ISO 8613-6 necessarily refers to the encoding in a parameter sub-string. Or perhaps you will not.

  It took several years for this to become an issue. The developers of other terminal emulators were not the ones who first complained about it. In fact, though the order-dependence was mentioned, no one pointed to a specific program which was affected. Still, it was a known problem.

  Finally, in 2012 (patch #282), I extended the parser to accommodate the "correct" syntax. The original remains, simply because of its widespread use. As before, it took a few years for other terminal developers to notice and start incorporating the improvement. As of March 2016, not all had finished noticing.

As others incorporated the xterm 256-color feature, the ability to set the palette was usually not done before announcing that a program had the 256-color feature. Others acquired the ability to set the palette after a lapse of years. As an exception, Geoff Wing (rxvt developer) implemented the complete feature in August 2002 (release 2.7.9). Any xterm-compatible implementation with support for 256-colors automatically supports 88-colors, since the palette is modifiable, which makes comments such as this at best badly informed.

XTerm stores the colors for `colorUL`, etc., at the end of the color array used for ANSI, 16-, 88- and 256-colors. An application can modify the colors using `OSC 4`, which does not reduce the range available for the `SGR 38/48` index used for selecting colors (underline, bold, reverse — and italics — all have their place in the video attribute fields). Like dynamic colors, this was a feature found in XFree86 but not in X11R5 or X11R6. According to David Dawes, some people liked the feature. Mark J Olesen incorporated the same into rxvt mid-1996, and I added the other two attributes. However, it was mainly popular with Red Hat users who wanted to color their manpages. After Werner Lemberg changed groff behavior in 2001 to color manpages, this feature is not that well known.

Finally, there are the default foreground and background colors set using `SGR 39/49`.

If one wants to enumerate the colors which can be set by index in xterm, there are multiple indices that are needed:

- SGR number (for the 8 ANSI colors, the extra 8 aixterm colors and the default colors)
- SGR 38/48 with (index) parameter (for the 88-colors and the 256-colors, keeping in mind that those include the first 16 ANSI and aixterm colors)
- OSC 4 with (index) parameter (colored video attributes)
- OSC numbers 10-19 (dynamic colors)

The sample scripts in xterm's sources demonstrate these features. Some are written in POSIX shell, the remainder are in Perl.

#### I don't like that shade of blue

Nobody does. But there are no universal solutions.

If your terminal (or the application running in it has a dark background, then darker blues are hard to see. With a light background, yellows are hard to see.

The available standards do not help: there are no standards for terminal colors. Here is an illustration which I made in reply to a bug report, contrasting different choices for blue, against some of the other terminals which (were said to) provide "standard vt100 colors":

Of course, anyone developing a terminal emulator already knew that vt100's never did do colors.

Ultimately it is up to the application running in a terminal to enforce the colors it needs. XTerm merely provides the best compromise on default visibility that I and my users have found.

#### Why doesn't xterm support italics?

Well, actually it does and it doesn't.

You can display "any" font using xterm (though proportional fonts may be disappointing).

But xterm has specific types of graphic rendition that it will do. If you want italics, then xterm has an option (`italicULMode`) to use that rendition instead of underlining. That is the usual typographic alternative, though of course some people want both at the same time.

However, standard curses does not support italics. Few terminals do this reliably, so it was disregarded long ago, never was supported except for low-level applications (in terminfo). No bit was reserved in the curses header for adding italics for high-level applications. (As a special case, ncurses was modified to provide partial support, but programs using this feature will not work with other implementations).

XTerm stores each cell of the display in fixed-size structures. One byte stores the graphic rendition. XTerm is using all of the bits in this byte for its VT220 emulation:

Mnemonic | Bit | Description
--- | --- | ---
INVERSE | 0 | show cell reverse-video
UNDERLINE | 1 | show cell underlined
BOLD | 2 | show cell as bold
BLINK | 3 | show cell as blinking
BG_COLOR | 4 | use background color
FG_COLOR | 5 | use foreground color
PROTECTED | 6 | character cannot be erased
CHARDRAWN | 7 | character has been drawn here on the screen

While additional bytes could be added to each cell, the cost to the typical user has so far not been in line with the usefulness of the feature.

For those who are not constrained by cost, since patch #305 xterm provides an experimental compile-time option to support italics. The main reason for implementing this is to be able to test the italics feature added in ncurses (patch 5.9.20130831):

- this increases the size of the attributes data.
- the feature requires some overhead for font-switching (treating italics as "rare")

The increase in size is not entirely wasted. The SGR attributes for dim, strike-out, and double-underscore also are implemented. However, the last two are not in the portable terminfo definition (from X/Open), and are not supported in the higher-level curses interface (there is no `A_STRIKE` for that reason).

Here are screenshots showing the ncurses test-program displaying video attributes (including italics). The first uses bitmap fonts:

and the second uses a (same size) TrueType font:

#### "grep --color" does not show the right output

GNU grep (version 2.5) introduced a `--color` option.

It does this for each highlighted match:

1. it writes the text up to (not including the match)
2. it writes an ANSI color control control sequence
3. it writes the matched text
4. it writes a control sequence to clear to the end of the line
5. it writes an ANSI control sequence to reset graphic rendition.
6. repeat this process until the entire line is written.

One problem is in the second and fourth steps. If the preceding text brought us up to the last column, then xterm (and any VT100-compatible terminal) is waiting for graphic text to wrap to the next line. Any controls would take effect on the current column position. Newlines are ignored while in this state.

However, if xterm gets a control sequence while waiting to wrap to the next line, it will update the screen according to that control. Then it is ready to accept more data. But at this point, it is no longer waiting to wrap; the special case is for newline versus graphic characters. For instance, backspacing clears the state (vttest illustrates this). So the data starts to write at the current column (the last one on the line), rather than at the beginning of the next line. In that case, grep's output will not look right.

Here are some relevant bug reports:

- Debian #456943 - grep: incorrect display with color and wrapping in some terminals
- Fedora #1006310 - xterm does not print a character if the character is last on a row and a color-change ANSI sequence follows
- Novell #148844 - terminal text wrapping bug

#### That description of wrapping is odd, say more?

This is one of the aspects of the so-called "vt100 glitch", as mentioned in the terminfo manpage:

> Terminals which ignore a line-feed immediately after an am wrap, such as the Concept and vt100, should indicate xenl.

When the terminal reaches the right margin, it is in a special state where it ignores tab characters and other formatting controls (carriage return and newline), and in effect is expecting only printable characters to wrap to the next line.

Without it, it is misleading to refer to a terminal as a vt100 emulator. After all, it is a well-known feature named for the VT100. The applicable standards (ISO-6429, ECMA-48) do not go into enough detail to address this sort of behavior, so the other terminal emulators can be referred to most accurately as ANSI terminals (if they obey the other guidelines).

In 2004, I added a test-screen to vttest to demonstrate this. It was in response to someone who insisted that xterm was wrong and one of those other terminal emulators was "right". I investigated, found that the behavior had not changed in xterm at least since the early 1990s, and that it matched the description of behavior from the DEC manuals. One of my users verified the correctness of the test on a VT520.

Reviewing the results with xterm-alikes or less ambitious "vt100 emulators" in mid-2013:

- xterm, kterm, mlterm, some operating system consoles are consistent with the VT100 behavior.

- rxvt, screen, putty (pterm), konsole, vte (gnome-terminal, xfce4-terminal) are not consistent with VT100 (and behave differently compared to each other).

  I included screen here because it claims to be a vt100 emulator, and putty since it claims to be an xterm emulator. I did not include tmux, because it does not make either claim.

- mrxvt does not get to that screen; it resizes its window to a single line.

In the vttest page, I have provided screenshots to illustrate these points.

Since 2013, Mattias Engdegård created a test program to explore this area, citing DEC's internal standard document for terminals (DEC STD 070 Video Systems Reference Manual). That document refers to this as the last column flag.

Revisiting this in 2019, no improvement has been observed in the problematic programs from 2013. A VTE user gave this example

> #!/bin/bash
> echo -e "\e[2J"
> echo -e "\e[1;79Hx\b\vx\b\vx\n"
> echo -e "\e[5;80Hx\b\vx\b\vx\n"

In this case, DEC's documentation for the last column flag mentions that cursor-positioning resets the flag. Because xterm takes that into account (while the others from 2013 do not), the example will show different results. Markus Schmidt provided a screenshot which demonstrates that DEC's documentation is correct and that some terminal emulators (e.g., xterm, zoc, MacOS Terminal, st) implement this detail in the same way that the hardware terminal did:

#### That color scheme is odd, say more?

Occasionally someone questions the behavior of the bce (background color erase) feature in xterm, and mentions that some DEC terminal did not behave that way with ANSI colors.

First off:

- Aside from the VT525, DEC terminals had no support for ANSI colors.

- Likely, they were thinking of a terminal emulator which supported colors. A while back, there was more than one which said they were a “VT340” and the misconceptions began. Not all of those behaved the same.

  Some developers were aware of this, others were not. The comp.os.vms newsgroup thread How to setting color in code for a VT terminal shows both.

- From the outset, modern xterm was a VT100 or VT220 with ANSI colors. No technical manual was available for a VT525 at the time. Lacking a technical manual, information about a VT525 was no more reliable than the statements about a VT340.

The design used for xterm imitated Linux console, which itself came about from different people (see this page for some background).

The VT525 programmer's reference manual is vague on the details (ANSI color is mentioned in a fraction of one percent of the manual), but the DEC standard for terminals is clear that it would not implement bce: any erase command will reset the video attributes. It documents ANSI color in the section on video attributes without mentioning a special case. Color would be reset as well.

### Odd behavior

#### Why can't I select/paste in xterm?

When an application sets xterm to any of its mouse tracking modes, it reserves the unshifted mouse button clicks for the application's use. Unless you have modified the treatment of the shifted mouse button events (e.g., with your window manager), you can always do select/paste by pressing the shift key while clicking with the mouse.

This is all done using the translations resource (see the Default Key Bindings section in the manual page).

#### Why can't I select/paste to/from other programs?

Whether you select text in xterm and paste into another window, or the reverse, the X client in which you have selected text may provide the data in different formats and different containers:

> formats

>   Originally (and by default) xterm made the selected data available with ISO-8859-1 encoding (Latin-1). Since patch #101 (1999), it has provided it also in UTF-8.

>   Regarding the type of data:

>   - X11R4's ICCM documented "string" selection data with ISO-8859-1, while
>   - X11R6 documented "compound text" (another name for multibyte encoding, without specifying what encoding).
>   - Selection data using UTF-8 was an extension by XFree86.

>   The client holding the selection advertises the formats that it can provide, and other client(s) ask for it using one of those formats.

>   Xterm can ask for UTF-8 even if it is not configured to use UTF-8. In that case, it converts (a small number of) useful characters to their ASCII or VT100 line-graphics equivalents, and uses a "#" character for those which cannot be converted.

> containers

>   By default, xterm follows the Inter-Client Communication Conventions Manual (ICCM). That dates back to X11R4 in 1989, with minor updates in 1996 for X11R6. The copyright for ICCM 1.0 is 1988/1989, making it slightly older than Microsoft Windows.

>   The ICCM specifies "selection atoms" which are maintained by the X server. According to the ICCM:

>   > The selection named by the atom PRIMARY is used for all commands that take only a single argument and is the principal means of communication between clients that use the selection mechanism.

>   and

>   > The selection named by the atom CLIPBOARD is used to hold data that is being transferred between clients, that is, data that usually is being cut or copied, and then pasted.

>   xterm uses PRIMARY by default. The default translations also update something called CUT_BUFFER0 (also part of the ICCM).

>   Unlike the PRIMARY selection, a cut buffer can hold only "type STRING and format 8" (which happens to be ISO-8859-1). That sounds like a drawback, but on the other hand, cut buffers are persistent, while the PRIMARY selection is not. An X client can provide data using the PRIMARY selection only as long as it holds the selection.

If xterm does not own the selection, it cannot supply the data (and you cannot select/paste). Initially, xterm held the PRIMARY selection only as long as the text was highlighted. Another application could assert the selection, but generally losing the PRIMARY selection in xterm was the same as losing highlighting. That has been improved, e.g., using the `keepSelection` resource in patch #230 (2007), as well as refinements to retain highlighting when it updates other parts of the window.

A more likely reason for failing to select/paste is that the other application may not use the same selection atom (container). In the mid-1990s, Netscape set out to compete with Internet Explorer. Part of that involved copying many aspects of the way Internet Explorer worked, including the way it worked with the Microsoft Windows clipboard. Netscape on non-Windows platforms, "of course" assumed the clipboard was the way to do things, and used the X11 clipboard rather following the ICCM. (The way it used the X11 clipboard was also not in line with the ICCM, but it was "close").

Not all applications followed Netscape and its descendents, making it a nuisance if one wanted to select/paste text to/from the web browser.

Since patch #209 (2006), xterm has provided a workaround: a menu entry (and resource `selectToClipboard`) which changes xterm's behavior for a special token SELECT in its default translations. If the resource is true (or the menu item enabled), xterm provides its selection to the CLIPBOARD. A menu item is provided, of course, since many applications follow the ICCM. In the default translations, these lines use SELECT:

>     Shift <KeyPress> Select:select-cursor-start() \
>                                select-cursor-end(SELECT, CUT_BUFFER0) \n\
>     Shift <KeyPress> Insert:insert-selection(SELECT, CUT_BUFFER0) \n\

#### Why can't I select tabs in xterm?

This issue was noted early on, here in 1997.

XTerm is copying from the screen, which stores only printable characters. That includes spaces and line-drawing characters. But tabs are special; they are used for more than one purpose.

If the screen is cleared in some part, that stores nulls. Cursor addressing does not fill in nulls as it jumps around, though xterm does supply blanks for the most useful cases, especially when getting data for a selection.

Full-screen programs such as text-editors tend to write in random fashion, and generally do not print nulls to the screen. Curses on the other hand, may supply tabs where you thought there were none. Also, the terminal driver can expand tabs (and often is set to do this by default).

So the whole thing is unreliable: unless you make special arrangements for each of the programs running inside xterm, you would often get a tab when you expect, and vice versa.

For the special case where your expectations would match the available data, it is solvable. There are basically two ways it could be done:

- set a bit in each cell's data which says it was skipped over via a tab. The complication is that xterm is using all of the flag bits in each cell.
- store literal tabs and nulls to be interpreted later – both by the display and the selection logic.

As of 2010, a few other terminals do implement this feature. But the reason that it's been low-priority is that it's of very limited usefulness when copying between terminal sessions (and for that matter, from other clients).

#### FVWM does weird things when I try to resize xterm

I have an old (3.1.2G) bug report for xterm which may be related to the second (3.9s) problem:

- Steven Lang <tiger@ecis.com> reports a problem with extra resize events for xterm.

  When I change font size often I will get the double-refresh, and when that happens the text program gets 2 resize events.. Running a quick test, I got this: Going to a bigger font, it got a 53x20 resize, then a 80x24 resize. Going to a smaller font, it got a 120x27 resize, then a 80x24 resize.

  Earlier I made a mention of changing font size in rxvt (And xterm does it to) causing 2 resize events. Well I just happened to do it in fvwm (Instead of fvwm 95) and found it seems to be a 'feature' of fvwm95, not XFree86 as I'd initially assumed.

- Stephen Marley <stephen@memex.com> reports a problem with the active icon (from X11R6.3 xterm):

  Using the XFree86 xterm-53 with the active icon feature on, I get some problems resizing where the xterm window shrinks as small as possible and won't stay at whatever size you set it thereafter.

  Comment out the PixmapPath and IconPath from your .fvwmrc file to disable the fvwm icons and restart the WM. Start an xterm. Iconify xterm and maximize it again. Use resize button or corners to resize the xterm.

  The xterm now shrinks to a tiny size and attempts to resize it result in it shrinking again.

  I've tried this with fvwm 1.23 and fvwm 2.0.46 with the same results. Olvm, olvwm and twm all behave correctly so it may be a fvwm problem.

I have not observed the first, but have reproduced the second.

#### Why doesn't the screen clear when running vi?

This refers to the "alternate screen" feature, which has been used in its termcap file since 1988. On various systems, this feature may have been removed, although it has always been in the xterm sources.

The feature is controllable (it can be enabled or disabled). However, as it was originally conceived, that ability to control it applies only to programs using termcap.

Under SunOS 4.x, the termcap description for xterm embeds in the `ti` and `te` capabilities a command to switch to xterm's alternate screen (e.g., while running `vi`), and return to the normal screen on exit. This has the effect of clearing the screen. The corresponding terminfo symbols for `ti` and `te` are `smcup` and `rmcup`, respectively.

Beginning with Solaris 2.x, the terminfo description did not use the alternate screen (it is a matter of preference after all), so that the text from vi remains on the screen after exit. Sun patched the X11R5 terminfo description to omit the `smcup` and `rmcup` capabilities. However, Sun began distributing modern xterm on the freeware companion (a CDROM) beginning with Solaris 8. In Solaris 10 for instance, the ncurses 5.6 package provided a usable terminal description for xterm which uses the alternate screen. Solaris 11 distributes modern xterm (though perhaps oddly) using an old—unpatched—terminal description.

Because it is in the terminal description, the feature is configurable...

For example (from Bjorn Helgaas <helgaas@dhc.net>) this procedure adds these capabilities to the "xterm" terminfo definition on HP-UX 10.20:

> cp /usr/lib/terminfo/x/xterm /usr/lib/terminfo/x/xterm.orig
> untic xterm > /tmp/xterm.src
> echo " smcup=\E7\E[?47h, rmcup=\E[2J\E[?47l\E8," >> /tmp/xterm.src
> tic /tmp/xterm.src

In this example, the terminfo strings are a series of operations:

> `smcup`
>   `\E7` saves the cursor's position
>   `\E[?47h` switches to the alternate screen
> `rmcup`
>   `\E[2J` clears the screen (assumed to be the alternate screen)
>   `\E[?47l` switches back to the normal screen
>   `\E8` restores the cursor's position.

However, xterms that are linked with termcap are more flexible in this area than those linked with terminfo libraries. The xterm program supports a resource `titeInhibit` which manipulates the $TERMCAP variable to accomplish this. It sets the $TERMCAP variable for the client with the `ti` and `te` capabilities suppressed. Systems that use terminfo cannot do this. If you are running terminfo with the alternate screen controls in the terminal description, then you can suppress the switching to the alternate screen by the `titeInhibit`, but not the associated cursor save/restore and clear-screen operations.

XFree86 3.9s xterm implemented a different set of controls (private setmodes 1047, 1048 and 1049) which address this (in addition to the older set of controls, for compatibility). The new set of controls implements the entire `ti` sequence (save cursor, switch to alternate screen, clear screen) and `te` (switch to normal screen, restore cursor) as two control sequences that can be disabled by `titeInhibit`.

The 1049 code is a refinement of 1047 and 1048, clearing the alternate screen before switching to it rather than after switching back to the normal screen. Since patch #90 in 1998 xterm allows you (with a popup menu entry designed to exploit this behavior) to switch the display back to the alternate screen to select text from it, to paste into the normal screen. You can also set or clear the `titeInhibit` resource using another popup menu entry (`Enable Alternate Screen Switching`).

Most other terminal emulators implement only half of the feature. They recognize the control sequence, but do not provide the ability to change it at runtime, e.g., using a menu entry. Like any other half-done implementation, that is a bug which should be reported to the developers of those programs.

#### Why doesn't the screen clear when I type control/L?

Control/L is ASCII form-feed. Printers do something with form-feed. Terminals do not, as a rule (though I agree it would be nice, e.g., this).

Interpreting form-feed is normally done by your shell, not by the terminal emulator. In a quick check:

- bash, tcsh, zsh interpret form-feed by clearing the screen, while
- csh, dash, ksh, mksh, yash do not

VT100s did not respond to form-feed. A few terminal emulators interpret form-feed (PuTTY and SunOS console), but neither matches VT100 behavior.

Because most people do not see the difference between a form-feed which they type (and is presumably echoed as a form-feed) versus a form-feed which is sent from an application to the terminal, this leads to confusion. Several years ago, I pointed this out as one of the errors in the C FAQ (notwithstanding Summit's comment, he did not update the FAQ).

#### Why is the cursor misplaced after running vi?

Vi and other full-screen applications use the termcap `ti/te` (terminfo `smcup/rmcup`) strings to initiate and end cursor addressing mode. As mentioned in the discussion of titeInhibit, full-screen applications can expect the initialization string to save the cursor's position, and the end-string to restore it.

A few applications (reportedly IRIX 5.x and 6.x `vi` incorrectly move the cursor before initializing cursor-addressing. This will cause the end-string to restore the cursor to its position when it was saved by the initialization string (typically at the upper left corner of the screen).

The usual reason is due to the cursor save/restore controls in the `ti/te` strings. If your application runs a subprocess which in turn runs another full-screen application (or when reinitializing the screen after the shell process), it will save the cursor position again, so the position which is restored when finally exiting your program is the last one saved, not the first. Modern xterm (from late 1998, patch 90) changes the behavior of the cursor save/restore operations so they apply only to the current screen. That makes it less likely to misplace your cursor.

#### Why doesn't the scrollbar work?

Originally xterm was built using imake rather than a configure script. One feature of imake that is not possible to guess within the configure script is the wide-prototype compile-time definition NARROWPROTO. When this is not set properly, the Athena widget scrollbars do not work properly. xterm's configure script has a fallback case which allows disabling imake. However, this is moot with the Xorg "modular" build, whose compiler options are unrelated to imake or older versions of any libraries that it may distribute. In this case, the configure script needs some help. Use this option to enable or disable NARROW proto (and disable imake with the --disable-imake option) to match the whims of Xorg hackers.

For instance

>     configure --disable-imake --disable-narrowproto

#### Can I improve the scrollbars?

Is that a problem with the appearance, or the way they work?

The appearance can be modified (though few do this) by linking with one of the variants of the Athena widget set (Xaw).

To illustrate, here are a few screenshots:

> Xaw (default)

> XawPlus

> Xaw3d

> neXtaw

Those variants use the same calling interface, so supporting them is simple. Adapting to other toolkits would be much more difficult. For instance (see the discussion of mxterm), replacing the scrollbars may require replacing other parts from the library to get consistent initialization and operation. In the case of Motif, it had nothing like the Athena widget set's popup menus.

#### Can I improve the scrolling speed?

Several years ago (before 2010) there was a webpage which gave its author's notion of what constituted a “good” terminal emulator: `cat`'ing (sending) a large file to the terminal would complete in minimal time. Apparently that was the sole interest. Interestingly, its author stated that xterm was the slowest although the presented data do not show this. Also, although the page says “Linux” some of the data are for programs running on Windows. The page spawned a few imitators (with no better methodology), none was systematic, none did any analysis.

Of course, developers do not do that in practice. The terminal is useful for interactive tasks. Compiling is best done by redirecting the build messages to a log file or using a batch process. End users have a different outlook.

There is more than one factor involved in scrolling speed. Here are a few:

- When xterm was first written, machines had less memory, and scrolling back a thousand lines seemed good enough for users. Internally, xterm stored the current screen and saved-lines in a large array. It scrolled the array by shifting the entire array by a given number of rows. For a thousand lines saved-lines (the scrollback region), that works well enough.

  But the `saveLines` resource allows a full integer, and during the mid/late-1990s, a few users found that setting the resource to a million lines made xterm very slow.

  Still, the graphics display was fast enough. By the way, xterm uses the XCopyArea function, and normally (attempts to) display all of the updates to the screen.

- Later, rxvt came along. It limited the number of saved-lines to a signed 16-bit integer, i.e., 32767 (and some packagers limited it to only a few thousand lines), and moved just the pointers to the line data when scrolling rather than shifting all of the text. It also uses XCopyArea, noting in its features

  >     /*
  >      * Define to remove support for XCopyArea() support.  XCopyArea() is useful
  >      * for scrolling on non-local X displays
  >      */
  >     /* #define NO_SLOW_LINK_SUPPORT */

  Unlike xterm, rxvt did not attempt to display all updates. If it fell behind, it would discard some of the updates, to catch up. Doing that had a greater effect on the apparent scrolling speed than its internal memory organization, since it was useful for any number of saved-lines. One drawback was that ASCII animations were somewhat erratic.

- A few other terminal emulators, such as konsole copied the rxvt feature. Others copied, in turn, from whatever source. As a result, one cannot compare the speed of different terminal emulators, since they do not follow the same rules.

- The issue with xterm shifting a large array was a problem which was addressed by changing all of the pointers to its line data into a circular array in 2009 (patch #244).

- Even after improving the memory performance of scrolling, rxvt and its imitators still appeared to scroll faster.

  The `fastScroll` resource added in patch #244 provides a simple implementation of the rxvt (mis?)feature for xterm.

  As implemented, it is rather crude (sometimes xterm — like konsole — appears to stop, since it is waiting for a new set of screen updates after having discarded some).

Scrolling speed is only one aspect of terminal speed, but it is easy to measure. Other aspects (such as the speed with which an application can change color, move the cursor around the screen, write text in various places) can also be measured. But comparing terminals based on that speed can be misleading. When the terminal drops updates to keep up with an application's speed, the result may be unnoticeable (if the application is fast enough), or it may not.

For example, running the dots program from the ncurses-examples shows some interesting misbehavior with gnome-terminal and konsole: both “choke” at times for a few seconds. The dots program prints colored cells randomly around the screen, pausing briefly 1% of the time. However when dots is terminated, it prints the program's notion of the output rate. In spite of the pauses, the program saw a fairly good rate of output. Some terminal emulators cannot keep up with dots; one possible explanation for the discrepancy is that the terminal emulator discards output (as in the special case of scrolling).

Seeing that raised the question of what variation to expect from different terminal emulators, to point out which might discard output to achieve fast scrolling speeds. A simple script showing the elapsed time to send ncurses's `terminfo.src` (1.1Mb) a given number of times to the terminal was used. Here is a table illustrating the differences, using the available terminal emulators for Fedora 26 and Ubuntu 17 in November 2017:

Mode | Terminal | Fedora | Ubuntu
--- | --- | --- | ---
1 | 10 | 99 | 1 | 10 | 99
Remote | gnome-terminal | (1) | (1) | (1) | (1) | (1) | (1)
konsole | 0.12 | 2.10 | 23.2 | 0.26 | 2.65 | 25.7
mlterm | (2) | (2) | (2) | 0.30 | 3.07 | 30.4
pterm / putty | 0.15 | 1.42 | 14.6 | 0.55 | 5.66 | 56.2
rxvt (3) | 0.25 | 2.97 | 29.5 | 0.23 | 3.03 | 29.5
st / stterm (4) | 0.07 | 0.50 | 4.40 | 0.15 | 1.42 | 14.4
terminology | 0.10 | 1.00 | 10.1 | 0.19 | 2.01 | 19.0
urxvt | 0.05 | 0.38 | 3.24 | 0.17 | 1.60 | 15.7
xterm | 0.31 | 3.50 | 34.8 | 0.47 | 4.41 | 44.1
xterm + fastScroll | 0.09 | 0.82 | 8.36 | 0.39 | 2.43 | 22.9
Local | gnome-terminal | 0.12 | 1.16 | 11.4 | 0.29 | 3.14 | 30.6
konsole | 0.11 | 0.82 | 7.97 | 0.22 | 2.17 | 20.1
mlterm | (2) | (2) | (2) | 1.01 | 7.59 | 105.
pterm / putty | 0.17 | 1.52 | 14.6 | (5) | (5) | (5)
rxvt | 1.23 | 11.9 | 118. | 1.75 | 16.9 | 166.
st / stterm (4) | 0.08 | 0.61 | 5.10 | 0.21 | 1.63 | 15.9
terminology | 0.09 | 1.03 | 10.1 | 0.43 | 1.64 | 16.0
urxvt | 0.07 | 0.53 | 4.52 | 0.26 | 2.41 | 23.7
xterm | 1.77 | 18.5 | 178. | 2.70 | 26.5 | 259.
xterm + fastScroll | 0.12 | 0.96 | 9.92 | 0.25 | 2.36 | 22.9

Notes:

1. On both systems, gnome-terminal failed to connect remotely.

2. Fedora does not have mlterm.

3. On Ubuntu, the urxvt package hijacks the name “rxvt”, so the “rxvt” actually tested was rxvt-xpm from the rxvt 2.7.10 package.

4. Fedora has st 0.70, while Ubuntu has version 0.60, which is a couple of years older.

5. Running locally on Ubuntu, pterm 0.70-1 dumped core.

Regarding the selection of terminal emulators:

- Keeping mind that this is an xterm FAQ, the Linux console (and Windows console, and PuTTY running on Windows) are off-topic.

- The table mentions programs which at one time or another have set `TERM=xterm`.

  The actual test does not rely upon the terminal description, nor in fact on any terminal description. The distinction was made for their relevance to this FAQ.

- Given that, rxvt 2.7.10 is listed, as well as its descendent urxvt (rxvt-unicode).

  Other variations of rxvt (such as aterm and mrxvt) were considered, but since much of the related code is identical, not very interesting.

- Both systems have several variants of the skins for the VTE library, but for both systems, the developers have a heavy bias in favor of the GNOME desktop. Comparing the performance of the various skins would be pointless, since not all are equally supported (due to the GNOME developers' practice of making incompatible changes), and would make an unbalanced comparison in any case.

- The Unix port of PuTTY, pterm is listed. It uses GDK.

Interestingly, performance is better running remotely. In the test, the machines are not identical:

- The remote system uses a Mac mini-server.
- The Fedora system is a virtual machine using Parallels.
- The Ubuntu system is a virtual machine using Vmware Fusion.

Possibly displaying on the virtual machines does not perform as well as via XQuartz. But that is a lot of difference to explain. More likely, the local X server is performing badly on some calls.

- For a while, XCopyArea was a problem, where the Xorg hackers had degraded its performance radically. While that might still be the underlying issue, st and urxvt do use that function.

- Another possibility is mentioned in Why is the text in the wrong place? where the apparent root cause was a server feature which only implemented parts of the X protocol.

Using the fastScroll feature made xterm performance comparable to the “desktop” applications. But as usual, with performance data, your mileage may vary.

#### Why can't my program read the window title?

The longstanding control sequence for reading the window title is something that can be abused in special conditions. For novice (unknowledgable) users, this can be a problem.

XTerm provides resource-settings and menu entries to allow this and related features to be enabled or disabled. See for example `allowWindowOps` The default resource settings in xterm can be overridden by a packager. However, a knowledgable user can override those default settings.

It is also possible that an overzealous packager may have crippled xterm by removing the functionality altogether. (That should be reported as a bug, to me).

For instance, one of those sent me a "security fix" some years ago, which deleted most of the control sequences which return data to the host. It broke the `resize` program, and selection, among other uses considered to be benign. In contrast, the same features used in other terminal emulators are tolerated by the same people, so rather than being a misguided attempt at fixing security issues, patches such as that appear to be an attempt at harassment.

#### Why can't my program set the window size?

Some overzealous packagers, perhaps influenced by the demonstration I provided, are protecting you against the possibility of your xterm becoming inaccessible. (That's unlikely...).

You should be able to override it, as noted above via resource settings or menu entry ("Allow Window Ops").

#### Why is the text in the wrong place?

Are you using Ubuntu? This is a frequently-reported problem for Ubuntu users. With other systems, it can occur (as of September 2012), but is less frequent. But it has been an issue with Ubuntu since 2008.

There are several related symptoms, e.g.,

- text may be the wrong size
- repainting the screen puts text in the wrong place

Here are some of the corresponding bug reports:

- Ubuntu #199285 - xterm crashes when compiz is on
- Debian #467399 - compiz fails to take control of windows
- Ubuntu #378668 - Cursor in terminal behaves badly with special characters present
- Novell #622936 - xterm: font drawing glitch
- Redhat #583904 - gnome-terminal and xterm show garbled fonts with compiz enabled (intel graphics)
- Redhat #614542 - xterm graphical corruption when compiz is active
- Ubuntu #635258 - Garbled chars in xterm
- Ubuntu #644943 - xterm fonts get corrupted while typing
- Ubuntu #701160 - /usr/bin/xterm is not functional in natty
- Ubuntu #700477 - Font corruption in xterm under Lucid
- Novell #681359 - xterm: no data shown under the screen program
- Ubuntu #711894 - iconic option does not work with compiz
- Ubuntu #778439 - Typing "exit" in xterm kills X session
- Ubuntu #831336 - running 'xterm' crashes X server
- Ubuntu #841103 - Text has artifacts when typing something else
- Ubuntu #844454 - Garbled chars in xterm (Onieric)
- Ubuntu #1002972 - xterm moves to upper left when clicking titel bar
- Ubuntu #1007722 - xterm doesn't display all the information

Since the problem is not in xterm, all I can do is to help forward those bug-reports to whatever package owns `compiz`. What these have in common is that someone has written code which is tested against only a small subset of the X protocol.

Looking for solutions (since compiz is not being fixed), it is possible to disable compiz. The means for doing this vary with time. Aside from pointing to the root cause of the problem, there is little advice that is useful.

- For instance, this comment by Eric Williams suggests that the problem can be worked around by setting xterm's `borderWidth` resource to zero.
- other comments suggest turning off the "desktop effects" or "animation".
- On my machines using the default Ubuntu desktop, I can see misbehavior easily in Ubuntu 12.04 using vttest. However, Ubuntu 12.04 provides Ubuntu 2D, which does not show those problems (and is noticeably faster).

### Sample .Xdefaults Color-Settings for XTerm

This example dates from March 1997:

> XTerm*internalBorder: 10
> XTerm*highlightSelection: true
> XTerm*VT100.colorBDMode: on
> XTerm*VT100.colorBD: blue
> XTerm*VT100.colorULMode: on
> XTerm*VT100.colorUL: magenta
> XTerm*VT100.eightBitInput: true
> XTerm*VT100.eightBitOutput: true
> XTerm*scrollBar: true
> XTerm*VT100.titeInhibit: true
> XTerm*VT100.colorMode: on
> XTerm*VT100.dynamicColors: on
> ! Uncomment this to use color for underline attribute
> XTerm*VT100.colorULMode: on
> XTerm*VT100.underLine: off
> ! Uncomment this to use color for the bold attribute
> XTerm*VT100.colorBDMode: on
> XTerm*VT100.color0: black
> XTerm*VT100.color1: red3
> XTerm*VT100.color2: green3
> XTerm*VT100.color3: yellow3
> XTerm*VT100.color4: blue3
> XTerm*VT100.color5: magenta3
> XTerm*VT100.color6: cyan3
> XTerm*VT100.color7: gray90
> XTerm*VT100.color8: gray30
> XTerm*VT100.color9: red
> XTerm*VT100.color10: green
> XTerm*VT100.color11: yellow
> XTerm*VT100.color12: blue
> XTerm*VT100.color13: magenta
> XTerm*VT100.color14: cyan
> XTerm*VT100.color15: white
> XTerm*VT100.colorUL: yellow
> XTerm*VT100.colorBD: white
> XTerm*VT100.cursorColor: lime green

XTerm comes with two copies of each resource file, one with color only (`XTerm-col.ad`, which is installed as `XTerm-color`), and the regular one (`XTerm.ad`, installed as `XTerm`). To use the `XTerm-color` file in conjunction with a separate `XTerm` app-defaults file which does not contain color, add the following line to your `.Xdefaults` file:

> *customization: -color

Since 1997, the resource files grew in size and number. Besides `XTerm` and `XTerm-color`, there are also resource files for xterm using different class values, together with the `-color` flavors of these. Because the `-color` flavors differ only by an `#include` statement, the makefile generates these from XTerm-col.ad. Here are the others:

> Program | Resource
> --- | ---
> xterm | XTerm
> uxterm | UXTerm
> koi8rxterm | KOI8RXTerm

Besides just adding files, I continued testing more resource combinations. Originally (in the 1990s for instance), developers could reasonably expect their users to configure resources for themselves, rather than use a single prepackaged flavor. That was a while ago. After 2000, I developed nicer resource files. Rather than modify the installed `app-defaults` file, I use this feature from X:

> Directories named by the environment variable `XUSERFILESEARCHPATH` or the environment variable `XAPPLRESDIR` (which names a single directory and should end with a ‘/’ on POSIX systems), plus directories in a standard place (usually under `/usr/share/X11/`, but this can be overridden with the `XFILESEARCHPATH` environment variable) are searched for for application-specific resources. For example, application default resources are usually kept in `/usr/share/X11/app-defaults/`. See the X Toolkit Intrinsics – C Language Interface manual for details.

That is, if you set the `XAPPLRESDIR` environment variable to point to a directory, you can put application resource files there, and X will find those before the system app-defaults files. That allows more flexibility and better control over the various applications than putting everything into a single `.Xdefaults` file.

On the opposite extreme, some people advise using `xrdb`. Not everyone. Back around 1990 I had an informative conversation with one of the developers at the Software Productivity Consortium. He was a member of a team developing a set of X widgets. The gist of our conversation was that

- using `xrdb` prevented you from changing things dynamically.
- it was like using a hammer (nailing things down to prevent them from being different).
- when the only tool you know how to use is a hammer, all of the problems look like nails.
- a good developer knows how to use more than one tool.

### What is this warning message?

xterm: Error 11, errno 22: permission denied
  Actually, any message like this denotes a failure which requires studying the xterm source to determine the exact problem.

  You have either found a bug in xterm, or there is something wrong with your computer's configuration, e.g., not enough pty's, incorrect permissions, etc.

  The first number is an internal code (defined in error.h in xterm's source), and the second is the system error number (defined in /usr/include/sys/errno.h). The system error number is easier to lookup, but the internal error code tells you where to look in the source.

input method doesn't support my preedit type
  Ignore this if you do not know what input method is. Input methods are used to enter composite characters (e.g., umlauts, other types of punctuated characters, East Asian characters, etc). Your computer's libraries support this, but are missing configuration tables, and xterm is warning you.

  If the message bothers you (e.g., if you aren't starting xterm from a window manager menu), you can suppress it by setting a resource:

  > XTerm*openIm:false

Warning: Actions not found: ignore, "xxx"
  The action "xxx" (for example "scroll-back") is specified in a resource file whose translations match widgets that do not support them. For example, this

  > XTerm*translations: #override\n\
  > <Leave>, ~Ctrl ~Meta <Btn2Up>: ignore()\n\
  > ~Shift <Key>KP_8: scroll-back(1,line)\n\
  > ~Shift <Key>KP_2: scroll-forw(1,line)\n\
  > Shift <Key>KP_8: scroll-back(1,halfpage)\n\
  > Shift <Key>KP_2: scroll-forw(1,halfpage)

  will produce warnings such as

  >     Warning: Actions not found: ignore, scroll-back, scroll-forw
  >     Warning: Actions not found: ignore, scroll-back, scroll-forw
  >     Warning: Actions not found: ignore, scroll-back, scroll-forw

  This is a correct form, assigning the actions to the "VT100" widget.

  > XTerm*VT100.translations: #override\n\
  > <Leave>, ~Ctrl ~Meta <Btn2Up>: ignore()\n\
  > ~Shift <Key>KP_8: scroll-back(1,line)\n\
  > ~Shift <Key>KP_2: scroll-forw(1,line)\n\
  > Shift <Key>KP_8: scroll-back(1,halfpage)\n\
  > Shift <Key>KP_2: scroll-forw(1,halfpage)

Warning: Cannot allocate colormap entry for "xxx"
  This comes from the X library. Modern xterm uses the default color map. What this means is that if your X server has insufficient space to store color information for more than one color map, other applications which could use other color maps may conflict with xterm. In practice, that is 256 unique colors on the screen at a time—not enough for a fancy background or an application such as Netscape.

  During resource initialization, xterm attempts to allocate an entry from the color map for each color which it might use. If there are not enough free slots in the color map, you will see a "Cannot allocate" message for each color that xterm failed to allocate. Those colors will be rendered in the foreground color, making full-screen color applications such as dialog unreadable.

  This problem is alleviated with patch 129, which modified xterm to delay the most color allocation until the colors are first needed. If a color is never needed (xterm allocates 20 colors in this manner), that reduces the number of slots in the color map that are needed. Even with this improvement, xterm must still allocate 4 colors during initialization to determine how to display the cursor. If none of those colors can be allocated, xterm reverts to monochrome.

## Known Bugs in XTerm and Look–alikes

These are the known bugs (or limitations) in modern xterm. They are also present in the other versions based on the X Consortium sources (color_xterm, ansi_xterm, kterm).

Note that of the emulators that support color, some do not support `bce` (back color erase). The bce capability is also called the "new color model", though it has been implemented in the IBM PC for quite a while. Technically, not implementing `bce` (or allowing the choice between it and its complement) is not a bug, since few hardware terminals (with good reason) implemented this feature.

- cut/paste does not select tabs; instead spaces are selected. This is because the selection works from the array of displayed characters, on which tab/space conversion has already been performed.
- does not implement the autorepeat feature of VTxxx terminals.

### X11R6.3 XTerm

The X Consortium version of xterm (and versions based on it) has additional bugs not in modern xterm:

- the program must be run with fixed (nonproportional) fonts.
- the home and end keys do not generate usable escape sequences, due to an indexing error. (Note that it is possible to work around this using the VT100 translations resource, but usually this is not done).
- the Main Options menu is improperly constructed, due to incorrect indices after removing the logging toggle. This makes the list of signals off by one.
- very large screens (e.g., by using nil2 for a font) cause core dumps because the program uses a fixed array (200 lines) for adjusting pointers.
- certain types of key translations cause a core dump because the program does not check the event class before attempting to use events.

(These bugs are also present in the X11R5 version).

Update 2004/04/08:
Complicating this discussion is the "X.Org" xterm (from 2004). That is the XFree86 xterm from XFree86 CVS with all visible "xfree86" strings changed to "X.Org" or "xorg", depending on the use. For example the "xterm-xfree86" terminfo entry becomes "xterm-xorg". The change history for the related CVS for X.Org shows this. Similarly, the release notes for X11R6.7 included my notes for XFree86 4.4.

As of 2009, it was apparent that "X.Org" xterm had died a natural death, since none of the people who created it had any likelihood of maintaining it. Instead, X.Org defers to my version of xterm.

Reviewing in 2014, the major vendors have been using modern xterm (different patch levels) for some time. However, there are documentation problems with AIX, beyond what is noted here:

- AIX provides a copy of luit, and a corresponding manpage—which omits the sections on security, bugs and attribution.
- The xterm manpage provided with AIX says this is X11R6 xterm “with no functional enhancements.” Comparing releases X11R5, X11R6.1, X11R6.3 against the AIX page, it matches X11R6.1 (December 1995). That is, it includes the text of the X11R6.1 xterm manpage plus the control sequences document—again omitting the security, bugs and attribution sections from each.

The other vendors provide documentation which is more up-to-date.

### COLOR_XTERM download

This is based on the X Consortium X11R5 source, with the same bugs.

- implements non-bce color model
- moving the cursor is reported to leave trails of incorrect color
- clearing the screen resets colors (arguably this is a limitation).

Not exactly a bug, but it does not build on Linux with X11R6.3

### ANSI_XTERM download

This is based on the X Consortium source, with the same bugs.

- implements non-bce color model
- fails vttest by not rendering reverse-video screen

### CXTERM download

CXterm stands for "Chinese Xterm". This is based on the X Consortium source.

### DTTERM

This is distributed with CDE. It implements more of the DEC VT220 than the X Consortium xterm, and also adds controls to manipulate the window and icon.

- implements non-bce color model
- fails vttest by clearing its background to solid white rather than preserving its sense in response to ED.
- under some circumstances, scrolling margins are not recognized. For instance, running vile which uses scrolling margins, we see text overwriting the status line.

### EMU 1.3 download

This is not based on the X Consortium source. The authors state that it implements VT220 emulation. It is in need of maintenance, since it builds with some problems to produce an executable that (on Linux and SunOS) does not handle the carriage return and newline translations properly. So I am unable to run vttest on this emulator.

### ETERM link

Eterm was based on rxvt, though the appearance differs. The terminal emulation capabilities appear similar, though I am not able to run the full suite of tests in vttest with this emulator (the core dump noted for rxvt, as well as hanging while awaiting response from one or more control sequences). Oddly, it appears that neither Eterm nor rxvt implement CPR (cursor position report). Finally, it reserves F1 (function-key) for a popup menu. This applies to versions of Eterm through 0.9.

### GNOME TERMINAL link

Unless specifically mentioned, GNOME Terminal and VTE's issues generally accumulate, with occasional veering off with skin-deep "rewrites". Each sighting provides a new episode.

Starting in 1999 —

GNOME Terminal is developed separately from both xterm and rxvt, and was originally based on the zvt (zterm) widget. Like kvt), it appears to have been developed imitating other terminal emulators (Linux console and xterm) rather than strictly emulating a VT102. The documentation is fragmentary (with a comment suggesting that the author does not know where to find relevant information), and the program fares badly with vttest. Beginning with late 1999, reports indicate that it does not properly parse ANSI control sequences: the vim editor is using xterm's vt220-style "Send Device Attributes" (Secondary DA) control sequence to obtain the terminal emulator's version. That is, it sends

>     \E[>c

expecting a response such as

>     \E[>0;138;0c

for vt100. The bug report indicates that the "c" sent by vim is echoed rather than interpreted by the emulator.

But it suffices for vi.

Moving on to 2001 —

A more recent GNOME Terminal uses the VTE widget. I observed version 1.4.0.4 in late 2001, which mentioned it in the credits (although VTE 0.1's ChangeLog mentions no date before February 2002). It does not implement a complete vt102: it was missing several features which can be demonstrated in vttest). Most of the bugs in the Device Attributes responses remain, but it works a little better with vim. However, there are problems with the alternate screen that show up with vim. Again, these can be demonstrated with vttest (menu 11.6.3 in the 20011130 snapshot).

Moving on to 2002 —

Rather than evolving from zvt, VTE is largely a new work. It does credit zvt in one place. However, its source code uses xterm's source code as a resource, accounting for odd (often incomplete) chunks. Reviewing 0.9.0 (September 2002):

- the termcap file. The last comment in the file is copied from xterm's source. The content of course is generated from ncurses with a small number of changes.
- the parser `src/vte.c` —a 14,125 line file. For example, the chunks related to DEC VT220 keyboard queries and DEC private modes contain comments copied from xterm's source code.

Jumping to 2010 —

Later versions of VTE incorporate more features (and comments, symbol names, etc), from xterm's source. In some instances, the copied features were disabled by Red Hat's package for xterm. Here is a related bug report, for key bindings.

The documentation for GNOME Terminal asserts:

> GNOME Terminal emulates the xterm application developed by the X Consortium. In turn, the xterm application emulates the DEC VT102 terminal and also supports the DEC VT220 escape sequences. An escape sequence is a series of characters that starts with the Esc character. GNOME Terminal accepts all of the escape sequences that the VT102 and VT220 terminals use for functions such as to position the cursor and to clear the screen.

That sounds fine, except that it is both inaccurate and misleading:

> inaccurate
>   combining the "X Consortium" and "DEC VT220", for example, since that was done after the demise of said organization.

>   It emulates a subset of VT100, lacks support for most of the VT220 control sequences (including some used for positioning the cursor) that are not recognized by a VT100.

>   Even in the subset which it emulates, GNOME Terminal has bugs. Many of these are easy to demonstrate with vttest.

> misleading
>   as noted in Xterm Control Sequences, xterm (mostly after "X Consortium") supports control sequences which are not VT100/VT220. GNOME Terminal implements many of these, but not all.

Perhaps that was unintentional – GNOME developers did not appear to document what their program does outside of that remark. However, an inspection of the changelog for libvte (VTE) does show that most of the borrowing from xterm is cited in an oblique manner – not once mentioning XFree86 for example, leaving the impression (as indicated by "X Consortium") that all of the work on xterm was done before development of GNOME Terminal commenced.

Most of this observation was documented between 2000 and 2007. Other than maintenance, development of GNOME Terminal appeared to have paused in 2005. As of 2009, its maintainer was (of the development team), the least knowledgeable about terminal emulation. So there was no progress on the large number of bug reports related to xterm-compatibility.

Revisiting in 2018 —

Regarding documentation, the situation is not as good as reported earlier. The problematic documentation was not even part of the "official" GNOME Terminal, but was an add-on by a Debian developer, adapted from GNOME Terminal's online help. The developer's relationship was mentioned in a Debian bug report:

#127622: ncurses-term: terminfo entry for gnome-terminal swaps Backspace/Delete:

>     >> "TD" == Thomas Dickey <dickey@herndon4.his.com> writes:

>     > On Sun, Jan 06, 2002 at 06:13:30PM +0100, Christian Marillat wrote:

>     [...]

>     >> The upstream author should consider ours Debian changes has official
>     >> changes ?

>     > sure - get gnome-terminal's author to make the changes.  (I generally
>     > don't add customizations to ncurses' terminfo unless I see them incorporated
>     > intact by more than one other source).

>     Sorry to say that, but upstream don't care about my patches. I've
>     forwarded patches since one year, and these patches has never been
>     included by upstream. Upstream sayd "commited", but I never seen any
>     changes.

>     Christian

The manual page provided as an attachment to GNOME #311565 identifies the author. However, four years later there is still no manpage for GNOME Terminal. GNOME #701691 mentions this in conjunction with GNOME Terminal's incompatible behavior versus other terminals for the “`-e`” option:

>      Christian Persch 2013-06-06 11:10:43 UTC

>     This works as designed. Note that both -x and -e are deprecated; the only supported way to pass the arguments is after -- like this:

>     $ gnome-terminal -- emacs file

and

>      Christian Persch 2013-06-06 16:02:54 UTC

>     There are no docs for the gnome-terminal command line options.

Admittedly, GNOME Terminal has some documentation, in its online help pages. As mentioned, the misleading comments about X Consortium came from that material, which remained for more than ten years before being revised early in 2013. Here are a few links for that process:

- help: update introduction.page (2013-01-10)
- help: review (2013-01-09)
- help: modified help in accordance with last review (2013-01-09)
- help: write instroduction.page (2013-01-08)
- help: start rewrite in Mallard (2013-01-08)

The document editors removed this statement

> Run any application that is designed to run on VT102, VT220, and `xterm` terminals

as well as the extended comment about the X Consortium, and replaced it with a less specific statement.

> `Terminal` is a terminal emulator application for accessing a UNIX shell environment which can be used to run programs available on your system.

> `Terminal` supports escape sequences that control cursor position and colors.

The assertion about GNOME-Terminal's support for “any” persists in its package description in Debian as of 2018:

> - Access a UNIX shell in the GNOME environment.
> - Run any application that is designed to run on VT102, VT220, and xterm terminals.

Whether the revised manual is improved or even helpful is debatable. For instance, it tells the reader how to turn the scrollbar on and off (using a dialog, of course). But for command-line options, it can print only about 45 lines of option names and short (less than 10 words) descriptions for each if one types

>     gnome-terminal --help-all

Other programs do the equivalent. In a quick check using Debian 8:

- 85 lines for konsole
- 120 lines for xterm patch #331
- 122 lines for mlterm
- 140 lines for urxvt

Bug #311565 was (writing in 2018) more than four years ago, but still there is no manual page, for either the command-line options or the control sequences which it supports.

### Notes on VTE

VTE is used by developers who provide a facade (also referred to as a “skin”) for simple desktop-oriented terminal emulation. This page gives a number of examples with sizes for the skins. The actual program size is far larger in each case, making the size of the skin irrelevant.

For more than ten years, VTE's README file asserted

> VTE supports Unicode and character set conversion, as well as emulating any terminal known to the system's terminfo database.

The latter part of that ("emulating any terminal") was incorrect. It did have the ability to work with the standard function-key definitions which can be defined in a terminfo description. That feature was discarded in 2014.

Notes from 2010 —

Some of the function-key logic was adapted from xterm; generally refactoring the xterm source-code to make it appear different. In places however (naming conventions and comments), there was some verbatim copying. The same observation can be made of "character set conversion". None of that is reflected in VTE's git-log.

As an aside, the credits in GNOME Terminal's "About" box also are inaccurate. For several years (according to its change-log), most of the work on VTE (the principal part of the program) was done by Nalin Dahyabhai.

xterm on the other hand, can be told with the `tcapFunctionKeys` resource setting to use a more complete subset, based on the ncurses extended terminal descriptions. However, terminal descriptions describe only one particular configuration of a terminal. Even xterm's terminfo/termcap descriptions do not cover the (literally) thousands of keyboard combinations which are available via its resource settings.

Outside of function-keys, VTE provided no ability to emulate “any terminal”. A casual glance at its source code revealed the following:

- no support for VT220-style protected areas.
- inconsistent support for modifier keys (the subject of several bug reports misdirected toward ncurses).
- only a subset of the standard terminfo/termcap properties is used (5/36 booleans, 3/33 numbers, 125/242 strings other than function-keys).
- a pervasive assumption that the terminal is something like xterm, e.g., to provide hardcoded behavior where termcap might describe something different.
- it uses termcap to retrieve data, rather than providing a choice between terminfo/termcap, opening up the problem of using an obsolete database.
- using termcap also means that it has no guidance for following features which are absent or have limited-functionality compared to terminfo, such as setting video attributes, colors, etc.

For instance, VTE cannot emulate dtterm, because of differences in color behavior. In fact, VTE does not use any of the termcap data to support its interpretation of color control sequences.

After 2014 —

Until 2014, VTE used a termcap file, with its own reader, presumably under the impression that could be used to describe “any terminal” (although it was fairly well known that terminals could support escape sequences not found in any terminal description). As a separate file, the termcap was a nuisance, whether it was bundled with VTE (and inaccessible to users) or not. The developers tried it both ways.

One recurring problem was that VTE's termcap did not match xterm's function-keys. Even when VTE's developers modified the termcap to match as well as the termcap could, the match was still incomplete. None of the modified keys were correct, since none of those are described by termcap. That meant that a control modifier with a cursor-key or function key was likely to be misread by programs running in VTE.

Finally in 2014, the VTE developers decided to change it. First, one decided to adapt a chunk of source-code from ncurses, perhaps thinking that was the way to get a better reader. That did not work well, and finally they discarded the whole feature, hardcoding the behavior to match xterm's default configuration.

Here are bug reports which give the story:

- #600659 – Home/End generate wrong control sequences.

      Escape sequences of the "default" kbd mode should be okay now.

      Removal of non-default kbd modes is continued in bug 730137.

- #169295 – builtin termcap parser not needed.

      all: Use terminfo instead of termcap

- #730137 – Drop (or fix) nondefault fkey modes.

  Since addressing bug 600659, VTE's default mode pretty accurately matches XTerm. VT220 is okay-ish, Legacy is so-so, HP and Sun are quite broken.

- #728900 – use terminfo instead of termcap.

  Do we want to rely in term{cap,info} *at all*? So far vte has used hardwired sequences most of the time. Even if we clean up everything and drop all fkey modes except the default (request: bug 600659 comment 73) we'd need to keep hardwired sequences for numerous reasons. E.g. Home/End should generate ^[[H/^[[F which are not present in terminfo. Application cursor keys and application keypad mode alter some sequences, with AFAICT no terminfo support whatsoever. F1..F4 completely change their sequences when a modifier is pressed, again probably no support for it in terminfo. Terminfo is just able to encode the complexity (app keypad mode, app cursor mode, modifiers, numlock) we need. Wouldn't life be much simpler with just hardwired xterm-compatible sequences? (With probably a way to override them from config file or dconf for experts.)

As a minor improvement, those changes removed some of the code whose origin was cut/paste from xterm. But that does not mean that the VTE developers stopped that practice. For instance, a change in late 2017 here reminded me to check what VTE does when saving/restoring the cursor position. It turns out that it does something similar, because (see #731205 and #741193) the developer studied xterm's source-code and imitated it (see source changes and followup fixes). There's a quirk in the resulting program (it pays attention to send/receive and insert modes, which are unrelated, while also missing the handling of wrap state), but if the developer had read the documentation (DEC's manuals), that detail would be missing. In reviewing the documentation, I noticed a different aspect which might be used to improve xterm, and ultimately appear in VTE (or perhaps not, since it is in an area poorly supported by VTE, i.e., the bug which was reported).

VTE developers do more than copy from xterm, of course. There are other programs (such as Konsole and Terminal.app) which get similar treatment. Because they tend to copy from others rather than doing their own solutions, they have not acquired the experience to see why features were added or modified (or removed), just that it is there. For instance:

- In a recent rewrite (early 2018), they introduced a skeleton of code from Paul Williams' sample parser. However, that is only a skeleton. For the flesh – the usual approach (see above).

  Two thirds of the functions listed in the skeleton are no-ops (not implemented). Some of those listed as implemented do not work (see vttest screenshot).

  Oddly enough, the developers decided to make the program claim that it is a VT525, though the skeleton demonstrates that it lacks almost all of features provided by the corresponding hardware terminal. In October 2018, the listing shows mostly a subset of VT100, with some (longstanding) features adapted from xterm, and a few inspired by ECMA-48.

- The latter requires some comment: xterm's control-sequences document has mentioned ISO-6429 and ECMA-48 since its earliest version. VTE's developers used that as a reference (see bug reports) along with xterm's source-code rather than ECMA-48 or DEC's manuals until around the end of 2016.

- They did (eventually) read documentation referred to by xterm's documentation. But that took a while, and they began copying from those sources before understanding the tradeoffs in those. Late in 2016, they started copying features mentioned in ECMA-48. The motivation for that appears to be (unsurprisingly) copying from yet another source, e.g., kitty (yet another copyist: see alacritty, but also see this).

- Introducing those ECMA-48 features caused additional failures for VTE versus vttest, which the VTE developers solved by making a copy of vttest, to “fix” the bug. The problematic feature dealt with clearing tab-stops (selection 2).

  ECMA-48 specifies the active line in selection 2. For an explanation of the term, see ECMA-48 section 6.1.5 Relationship between active data position and active presentation position. This is distinct from the feature which DEC's terminals supported.

  The VT520 manual is explicit in this case (only selections 0 and 3 are supported). Per Lindberg's 1985 test demonstrated that the unsupported selection 2 was ignored in a VT100.

- The VT520 did not support the other selection (2) because that would have been used to support bi-directional text. There is no point in having two differently-worded descriptions of the same identical feature.

  At the time the VTE developers copied the feature, they had not begun to develop support bi-directional text (see for example #321490 (vtebidi) and #767529 (vteemoji).

  At this writing (two years later), the developers are talking about working on that. The tab-clear operation is still identical in VTE for both selections 2 and 3, and does not implement any of the features from ECMA-48 not in a DEC terminal.

Other problems with VTE —

These are a few of the interesting bugs found in VTE (or GNOME Terminal) during 2017:

- system crash due to running out of memory
  while running ncurses sample programs dots and picsmap.

- failure to open a remote connection, noticed
  while gathering data for a discussion of scrolling performance.

Other uses of VTE —

Because of GNOME Terminal's reputation for excessive code bloat, developers of every other program based on VTE advertise their version as reduced memory usage, faster startup, etc. Here are a few of the available ones:

- osso-xterm link

  Its home page refers to "at least two versions". I recall seeing an older version which was apparently not based on VTE. There did not appear to be any relevant page (as of 2009) for that version.

- roxterm link

- XFCE Terminal link

### MULTI GNOME TERMINAL (MGT) link

Of particular note, MGT 1.4.0 announcement claims that it works properly for all of vttest)'s tests. On the positive side, it does do VT52 emulation, but (reading the source code did not help) it apparently does not really do VT220 from vttest's perspective.

### HANTERM download

HanTerm stands for "Hangul term" (Korean). This is based on the XFree86 source.

### KONSOLE link

More than just a rewrite of kvt into C++. But there are several incompatibilities between konsole (noted with version 1.0.2 in late 2001) and xterm:

- none of the selections of keyboard mappings match the actual behavior of xterm (a few come close, but do so by matching the terminfo descriptions rather than the programs). In particular, the application keypad does not send vt100-style escapes.
- vttest) demonstrates that konsole does not properly ignore escape sequences to switch character sets that it does not support. Also, the developers of konsole did use an old version of vttest, but that was to add a bogus Device Attributes response (claimed to be for "vt220", but not corresponding to any that DEC produced). They do not use the newer version of vttest (which was available more than a year before development of konsole began).
- konsole implements several features from XFree86 xterm, but some are done incorrectly. In particular, the private setmode 1049 does not save and restore the cursor, causing the cursor to be in unexpected locations after exiting a fullscreen application such as vi.

The problems with setmode 1049 were fixed after some time; other issues linger on.

Like GNOME Terminal, konsole's documentation is incomplete and inaccurate. This gem from its handbook illustrates the problem:

> After a decade, Konsole is the first rewrite from the ground up. While xterm has definitely been hacked to death (its README begins with the words Abandon All Hope, Ye Who Enter Here), Konsole offers a fresh start using contemporary technologies and understanding of X.

The problem:

- the remark was apparently written in 1997. It was inaccurate at that time, since it disregards the earlier xvt/rxvt applications. Limiting it only to a plain statement that konsole was a rewrite of kvt would have been more accurate. Lacking that context, we find nonfactual articles such as this on the net.
- for those lacking a proper education, the README was apparently intended to be a humorous reference to Dante's Inferno.
- reading konsole's source code and considering "hacked to death" can provide some occasion for humor. Enjoy.

### KTERM download

KTerm stands for "Kanji term" (Japanese). This is based on the X Consortium source, with the same bugs (though the list of original authors has been removed; the modifications that comprise kterm is relatively small).

- implements non-bce color model
- implements status line, but uses non-DEC escape sequences for this.

There is a variation of xvt (ancestor of rxvt) originally known as kvt bundled with KDE which may be referred to as "kterm", but I do not find it interesting, other than to comment that it was a poor choice of name.

### MLTERM

Mlterm is not based on xterm or rxvt source, though it implements many of their features. It does fairly well with vttest, except for some odd misbehavior in operations that save/restore the cursor position.

### MTERM

There are a few variants of this: the xterm bundled with some Motif clients is more common. More interesting, however is one (not Motif), attributed to "Der Mouse".

>     (mouse@Lightning.McRCIM.McGill.EDU) Available:
>     larry.mcrcim.mcgill.edu (132.206.1.1) in
>     /X/mterm.src/mterm.ball-o-wax.

I saw only an incomplete version of this while it was advertised in the mid-90's. It is available by email from <mouse@Rodents.Montreal.QC.CA>. or via ftp. This is not a patched version of xterm, though it was apparently written, like rxvt, to emulate vt100's. While it does have some interesting features (such as blinking characters), overall it does not do as well with vttest as the more widely known emulators.

### MXTERM

There are several variants on this: xterm adapted for Motif libraries. I have seen none that work properly:

- MXTERM: a motif Xterm with character attributes color rendered I've noticed this one only recently. It is a reworking of the earlier patches for color_xterm (credited to Erik Fortune at SGI) and the Motif widgets (apparently first done by Ivan M. Hajadi at SGI in 1991, but credited in this release to Mahesh Neelakanta, for Motif 1.2.4).
- ANSI Xterm with Motif Scrollbar Usually seen as the ansi-xterm-R6-motif-sb patch, I used this as the starting point for changes to my #82 patch of xterm in August 1998.

  The original patch changes only the scrollbars to Motif, leaving the popup menus in Athena widgets. That was not what I wanted. My motivation for using Motif is not for performance or esthetics, of course, but to make it simpler to build on hosts that have no Athena widgets installed.

  I set those changes aside, having found (the hard way) that the Motif library has hardcoded behavior regarding the control right-mouse button. According to the O'Reilly book on Motif programming (volume 6), it does a server grab when processing menus. Making the menus behave just as in the Athena widgets can cause the X server to hang. (I was able to do this with both Lesstif and Motif libraries). Given that, I decided to restructure the menus entirely, making a toolbar which could support at compile-time either widget set.

- mxterm This is a different reworking of the Motif widget patch, using a 1993 version (ignoring the more recent 1994 patches noted above). However, it appears to have the same technical defect that I noted above.

### NXTERM

Distributed with Redhat Linux 5.2, it is a repackaging of xterm-sb_right-ansi, to use the Xaw3d widget set. This is based on the X Consortium X11R6 source, with the same bugs.

- implements non-bce color model
- does not implement SGR 39 and SGR 49, all attributes are reset when changing colors.
- popup menus do not appear to work.

Starting with Redhat 6.0, nxterm is the XFree86 3.3.6 xterm. Unfortunately Redhat neglected to update their termcap for nxterm to match the program.

### RXVT link

Rxvt's manual page states the following unqualified comment:

> rxvt, version 2.6.2, is a colour vt102 terminal emulator intended as an xterm(1) replacement for users who do not require features such as Tektronix 4014 emulation and toolkit-style configurability. As a result, rxvt uses much less swap space -- a significant advantage on a machine serving many X sessions.

How much is much less? Perhaps not as much as one would think from reading that. The Tektronix emulation in xterm (which has been optional since late 1997) accounts for about 25kb of the code.

The toolkit-style configurability glibly referenced is the ability to redefine keys on the keyboard without recompiling the program, i.e., the translations resource. It also is the way mouse events and other actions are passed to xterm.

The toolkit-style configurability accounts for about 300kb, which does add up if you happen to be running 50 xterm processes (i.e., about 10Mb).

This comment was topical in December 2001:

> Compared with something like GNOME Terminal, which takes 2-3 times, or KDE konsole, which takes 15-20 times as much memory to run, xterm and rxvt memory requirements are indistinguishable to the normal user.

In June 2010, the numbers had changed somewhat. Here is a table showing the total application and library sizes needed for each of the terminal emulators on my development machine. All sizes are in kb (1024 bytes).

program | base size | total size | libraries
--- | --- | --- | ---
aterm | 127 | 10763 | 45
color_xterm | 142 | 3647 | 13
Eterm | 1 | 5126 | 19
fbiterm | 6 | 2424 | 8
gnome-terminal | 292 | 14587 | 51
hpterm | 146 | 14386 | 31
konsole | 2 | 39815 | 71
kterm | 226 | 4194 | 17
mlterm | 316 | 6606 | 27
mrxvt | 298 | 4515 | 19
multi-aterm | 144 | 2821 | 7
pterm | 405 | 12817 | 42
rxvt 2.6.4 | 108 | 2725 | 6
rxvt 2.7.10 | 152 | 2829 | 7
rxvt-unicode | 1259 | 13641 | 49
terminal.app | 211 | 15274 | 29
wterm | 110 | 2922 | 11
xfce4-terminal | 148 | 14059 | 48
xgterm | 953 | 4602 | 14
xhpterm | 130 | 2748 | 6
xiterm | 12 | 3762 | 16
xterm (everything) | 346 | 5484 | 24
xterm (minimal) | 186 | 4123 | 15
xterm-r5 | 135 | 4164 | 11
xterm-r6 | 140 | 4169 | 11

Counting the libraries is appropriate, since some programs such as xiterm and the VTE-based programs are implemented in libraries.

These comments apply to versions of rxvt through 2.21:

- clearing the screen resets colors
- does not have a delete key
- the implementation of `ech` (erase characters) does not follow DEC VT220 (also ISO 6429), causing applications using this function to misbehave.

A newer version (upgraded to an beta as of 2.6.PRE3, however, since it no longer dumps core in vttest) is reported to fix the `ech` bug. However, it is less VT100-compatible than the earlier versions such as 2.21b because it does not render reverse video (`DECSCNM`) properly. All versions do not update the screen frequently enough, making animation ineffective. See vttest, tests 1 and 2.

One longstanding issue with rxvt impacts use of xterm. While rxvt does not use the X Toolkit (and corresponding X resource matching), it does read your `.Xdefaults` and app-defaults files to extract resource settings. That in itself would not be a problem. However, since rxvt also looks for resources in the `XTerm` class (a parasitic relationship like setting $TERM to "xterm" based on the presumption that it is a nuisance to install its configuration files), there have been several occasions on which xterm's app-defaults files have been modified to accommodate rxvt's variant usage.

That comment applies mainly to the resource patterns. However, even when the pattern is reasonably unambiguous, but overbroad, the results can be conflicting. For example, some versions of rxvt may accept a `font` resource which does not match the XLFD pattern. It accepts a prefix of "xft:". This feature (apparently introduced by konsole) tells rxvt to interpret the remainder of the string as a TrueType (Xft) font rather than a bitmap font. xterm uses the `faceName` resource for these values.

### st link

Rxvt revisited, this program originally depended only on the X11 library. Since then, it has grown a lot, though the project page does not mention it. As of January 2013, it was in heavy development, and (according to comments on its developer's list) growing steadily as the developers implemented useful features adapted from xterm.

For instance, in 2013, the size counting libraries for st 0.3 on my Debian testing machine was on a par with rxvt (and half that of xterm, which uses the X Toolkit library). Revisiting it late in 2015, it had left rxvt behind and was nearly as large as xterm. Here are the sizes which I found in Fedora 22:

LDD-Size | Program
--- | ---
3452986 | rxvt
6060960 | st
6771039 | mrxvt
7785780 | xterm
15060195 | urxvt
20934874 | lxterminal
21089908 | lilyterm
21358156 | xfce4-terminal
25738679 | roxterm
31195794 | gnome-terminal
32780414 | terminology
87813125 | konsole

By the way, the project page quotes the README file from xterm's sources, omitting my editorial comment at the top noting that the paraphrase of the opening from Dante's Inferno dated from 1991, and pointing to this FAQ to provide better context.

### XGTERM link

It has some features which are also in color_xterm:(non-bce ANSI color, colorBD and colorUL resources, cursor warping, etc. The main feature is its Tektronix graphics emulation, which is the main reason for this particular program. Neither program has a change-log, so it is not easy to say which influenced the other.

That is from reading the source code. However testing under Debian Linux, something is wrong with the resource processing (neither popup menus nor colors work).

### XITERM link

This appears to be rxvt 2.20, lightly reformatted, with a few ifdef's changed.

That is, it was. The name was later appropriated by a different program, which also uses the name `iterm`. Like gnome-terminal, iterm aims to be an xterm-emulator rather than a VT102- or VT220-emulator.

An earlier attempt by the same author (the "CSI-xterm") incorporated in 2002 some of the changes I made for XFree86 xterm via cut and paste (but does not mention this in its README). The "borrowed" changes comprised about 10% of the patch provided for X11R6.5.1, summarized here:

>     xterm-6.5.1-i18n-0.7.patch.gz
>      Imakefile     |   25 +
>      RELNOTES-I18N |  104 ++++++
>      XTerm.ad      |    1
>      button.c      |  155 ++++++++-
>      charproc.c    |  979 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
>      data.c        |    6
>      data.h        |    4
>      error.h       |    8
>      fontutils.c   |   78 ++++
>      fontutils.h   |    8
>      input.c       |   11
>      main.c        |   40 +-
>      main.h        |    1
>      misc.c        |   46 ++
>      ptyx.h        |  156 ++++++++-
>      screen.c      |  513 +++++++++++++++++++++++++++---
>      scrollbar.c   |   36 +-
>      util.c        |  218 +++++++++++-
>      18 files changed, 2183 insertions(+), 206 deletions(-)

This patch was said to be the basis for Solaris 10 xterm, and was briefly referred to as the Solaris "color xterm". It did not use the `bce` color model however, and Sun provided no terminal description for it.

Back to iterm: the author's README in the patch used the same terminology as in the later work, demonstrating their relationship:

>      This is a patch for the xterm of X11 release 6.5.1 to fix its
>     internationalization defects. This patch enables xterm to handle
>     whatever the character set encodings and scripts support underlining
>     operating system supports via the technology called CSI(Code Set
>     Independence) and XOM(X Output Method). Traditionally, several
>     X terminal emulators which are hard-wired to specific languages and
>     encodings were introduced to support local language requirements, such
>     as kterm, hanterm, cxterm, UTF-8 xterm and so on. This  truly
>     internationalized terminal emulator supersedes the needs of those
>     multiple locale specific terminalemulators.

The key to understanding the "code set independence" is that the author intended to treat existing character encodings on an equal basis with Unicode and UTF-8. Some of that is reflected in the Solaris International Language Environments Guide, but in explaining how this is done, the documentation is weak, lacking detail.

Either version of iterm has similar problems running vttest.

## How do I build XTerm?

Building a copy of xterm is simple, provided that you have a development configuration for X11:

- Header files and libraries. If you do not have the header files (usually under /usr/include/X11) for your system, you are better off building the libraries yourself. Xterm can be built with either X11R5 or X11R6 libraries; however X11R6 requires much more data to be installed before xterm will run. Xterm uses the `Xaw` library for popup menus.
- imake and `xmkmf`. These utilities produce a Makefile from the Imakefile. They are not essential, but useful, particularly on systems with unusual configurations.

If you have a working `xmkmf` script (or correctly configured imake utility), all you need to do is type

>     xmkmf
>     make

I have written a configure script for xterm which can use `imake` (or `xmkmf`) to generate a Makefile from the Makefile.in. Or it can do without `imake` entirely. I have restructured xterm to eliminate most hardcoded `#ifdef`'s, replacing them with definitions that can be derived with the configuration script. The configure script is more flexible than xmkmf, since it allows you to enable or disable a variety of features. Type

>     configure --help

to get a list of options.

Though I have replaced most hardcoded ifdef's with autoconfigured values, it will still continue to build properly with the imake environment.

However, I usually build xterm using the configure script. By default, it looks for imake and will use it to help with a few places where a reliable configure check cannot be created. One of these (see Why doesn't the scrollbar work?) can be a problem.

As with all of my projects, I routinely check for strict compiler warnings. For gcc, that is done with the "gcc-stricter" script which you can find here. The X libraries have a longstanding issue which has been ignored so far (as of mid-2012). To work around this (and get useful warnings), I apply this patch:

>     --- Intrinsic.h.orig    2009-08-25 13:22:15.000000000 -0400
>     +++ Intrinsic.h 2009-12-06 09:48:39.000000000 -0500
>     @@ -66,7 +66,11 @@

>      #define XtSpecificationRelease 6

>     +#ifdef _CONST_X_STRING
>     +typedef const char *String;
>     +#else
>      typedef char *String;
>     +#endif

>      /* We do this in order to get "const" declarations to work right.  We
>       * use _XtString instead of String so that C++ applications can
>     --- Xresource.h.orig    2009-07-19 14:43:21.000000000 -0400
>     +++ Xresource.h 2009-12-06 10:11:19.000000000 -0500
>     @@ -338,8 +338,8 @@
>      } XrmOptionKind;

>      typedef struct {
>     -    char           *option;        /* Option abbreviation in argv          */
>     -    char           *specifier;     /* Resource specifier                   */
>     +    _Xconst char    *option;       /* Option abbreviation in argv          */
>     +    _Xconst char    *specifier;            /* Resource specifier                   */
>          XrmOptionKind   argKind;       /* Which style of option it is          */
>          XPointer       value;          /* Value to provide if XrmoptionNoArg   */
>      } XrmOptionDescRec, *XrmOptionDescList;

I made note of it on the Xorg mailing list, but as you can see, there was no response.

## How do I report bugs?

You should report bugs to me. I also respond to bug reports in a number of bug-tracking systems, though some are less open to searches than others. See also:

- reporting/patching procedures.
- analyzing problems with configure scripts

## Additional Information

There appears to be no comprehensive source of information on xterm better than the documentation which comes with the source code

- XTerm change log
  - The XTerm Manual
  - XTerm Control Sequences
  - resize – set TERMCAP and terminal settings to current xterm window size
  - uxterm – a UTF-8 wrapper for XTerm
  - koi8rxterm – a KOI8-R wrapper for XTerm
  - luit – Locale and ISO 2022 support for Unicode terminals
- Other Sites
- Interesting but misleading

#### The XTerm Manual

The command-line options, X resources and similar configurable options of xterm are documented in the manual page.

Here are copies of the file in various forms: html, pdf, ps and text.

#### Xterm Control Sequences

Control sequences, i.e., programming information are in the `ctlseqs.ms` file which I bundle with the program source. (It used to be in the same directory in the X distribution, but was moved to a different part of the tree long ago). Note that you must format this file with different options than a manpage, e.g.,

>     tbl ctlseqs.ms | nroff -ms >ctlseqs.txt
>     tbl ctlseqs.ms | groff -ms >ctlseqs.ps

As a PostScript or PDF file, the individual letters of the control sequences are all boxed, for emphasis, but I find the text file equally readable.

Here are copies of the file in various forms: html, pdf, ps and text.

#### resize – set TERMCAP and terminal settings to current xterm window size

resize is useful by itself, but is maintained for historical reasons as part of xterm. html, pdf, ps and text.

#### uxterm – a UTF-8 wrapper for xterm

XTerm does not automatically set your locale. It can be told to use your locale settings. This is a shell script which sets xterm's resources to use UTF-8 encoding, and use UTF-8 fonts. There is a similar lxterm script, but it relies upon non-portable applications, unlike uxterm.

Here are copies of uxterm's documentation: html, pdf, ps and text.

Incidentally, there was a different program named "uxterm" before the shell script was added to xterm in mid-2000. Roman Czyborra commented in 1998 that it was based on the original X11 xterm source (very likely, since "strings" run on the executable shows the xterm actions, resources and even the Tek4014 support). There are few references to it to provide details: the first appearance was in 1994, and the last was Czyborra's page in 1998. For the curious, there is a copy on ibiblio.org (no Linux executables, no source, however).

#### koi8rxterm – a KOI8-R wrapper for xterm

As a special case, this wrapper is packaged with xterm to provide KOI8-R encoding.

Here are copies of koi8rxterm's documentation: html, pdf, ps and text.

#### luit – Locale and ISO 2022 support for Unicode terminals

luit also is maintained as part of xterm, since its upstream maintainer is inactive, and the ostensible maintainers have more than once delivered unusable versions, causing many bug reports to be issued against xterm.

### Other Sites

- I have found Richard Shuford's archive to be invaluable for notes on the DEC VT220 and related terminals. This was a webpage but was last seen via ftp. I have a snapshot of the ftp site, here:

  - ftp://invisible-island.net/shuford/
  - http://invisible-mirror.net/archives/shuford/

- Though not available at the time that I was collecting most of my notes, VT100.net is also a good source of primary information.

- As part of my Git exports work in 2016, I made a repository of the major X release copies of xterm source. Alan Coopersmith has a more extensive repository of the X source, which is also useful although it does not cover the full timespan. In my repository, I combined the controls-sequences document which was in specs with the program:

  - xterm was first released in X10R3, with a manual page in the `man` directory, and program in the `xterm` directory.
  - The developers (re)organized the directory tree in X11, moving some manual pages under the `doc` tree, others went along with the source-code, and moving the programs such as xterm under a `clients` directory.
  - The control-sequences document was first released in X11R4.
  - When making the repository, I overlooked the X10 manual page. Git isn't flexible enough to add that later, without re-creating the repository.

  I use RCS as a starting point for creating Git repositories because it is the simplest way to capture each file's timestamp. Since the X developers switched source repositories between X10 and X11, and the RCS identifiers were no longer in sequence, I used a script to change those identifiers to a form that would not interfere with checking the sources into RCS.

  The dates shown are, of course, for the xterm source-code:

  Date | Release | Mine | Alan's
  --- | --- | --- | ---
  old-xterm | Program | Specs
  2005-12-14 | X11R6.9.0 | link | n/a | n/a
  2005-01-12 | X11R6.8.2 | link | n/a | n/a
  2004-08-20 | X11R6.8.0 | link | n/a | n/a
  2004-04-02 | X11R6.7 | link | n/a | n/a
  2001-02-09 | X11R6.6 | link | n/a | n/a
  2000-08-21 | X11R6.5.1 | link | n/a | n/a
  1998-02-09 | X11R6.4 | link | n/a | n/a
  1996-12-09 | X11R6.3 | link | n/a | n/a
  1996-02-02 | X11R6.1 | link | n/a | n/a
  1995-01-30 | X11R6 | link | link | link
  1993-11-11 | X11R5 | link | link | link
  1989-12-23 | X11R4 | link | link | link
  1988-10-27 | X11R3 | link | link | n/a
  1988-03-01 | X11R2 | link | link | n/a
  1987-09-15 | X11R1 | link | n/a | n/a
  1986-12-25 | X10R4 | link | n/a | n/a
  1986-05-17 | X10R3 | link | n/a | n/a

### Interesting but misleading:

- The ncurses FAQ How do I get color with VT100? discusses a widely cited bit of misinformation.
  For instance, this web search gives 3,000 hits in March 2015.

- Also widely cited, Consistent BackSpace and Delete Configuration gives advice regarding backspace and delete keys which is heavily biased toward Linux. For instance:

  - the console referred to is the Linux console, which initially had as a goal VT220 emulation. Linux never came close to meeting that goal, which was abandoned in the late 1990s when UTF-8 became more important.

    As part of that, Linux's keyboard was (actually modelled on xterm) said to be VT220, and its coding for the backspace key sent `DEL`. In contrast, ncurses' terminal database says `kbs` for the vt220 sends `^H` (`BS`).

  - the guideline uses "newer", "right" and "correct" in the part which describes `DEL`, versus "dirty" and "break", "broken" in that addressing `BS`.

  In addition to bias, the technical remedies are unsuitable for generic advice. In particular, the comments about terminfo, `xmodmap` and xterm's translations resource are suitable only for special cases because the proposed solutions create problems of their own.

  The page itself was written in 1997, with only minor fixes since then. Thus, it does not reflect any of the improvements made to xterm. Its lack of relevance does not prevent people from citing it. For instance, this page's accepted answer recommends that (although neither gives a useful answer to the question). Here are a few clues:

  - Debian's current package for ncurses uses the `--with-xterm-kbs` configure option which I added in 2012. Debian also applies patches to many of the terminal descriptions, including adding a patched copy of xterm's terminfo file to ncurses's terminfo file.

    The patched copy is redundant and a source of problems (since the two overlap, with slightly different goals regarding PC- and VT220-style keyboards). My intent in adding the configure option to ncurses was to wean them away from the patch. That has not happened yet.

  - tmux is (mostly) a terminfo application. However, it does not use the terminal database's `kbs` value. Rather (referring to the source for 1.9a), it uses the termios setting:

    > /*
    > * Check for backspace key using termios VERASE - the terminfo
    > * kbs entry is extremely unreliable, so cannot be safely
    > * used. termios should have a better idea.
    > */
    > bspace = tty->tio.c_cc[VERASE];
    > if (bspace != _POSIX_VDISABLE && key == bspace)
    > key = KEYC_BSPACE;

    At the same time, `tmux` sets `$TERM` to "screen", by default. Debian patches that terminal description, too. Applications running inside `tmux` use that terminal description. If instead `tmux` translated the backspace key to match the value from erasechar (for the given `$TERM`), its clients would receive consistent information.

    Thus, rather than blaming the user (for a "badly configured" xterm), the actual problem is a design flaw in `tmux` which should have been sent to its developers in a bug report.

- Noted here, someone pointed out an NCDware document describing its terminal control sequences.

  Disregarding the title Using VT320 Terminal Emulator Escape Sequences, it described some variant of xterm rather than a DEC VT320. VT320s for example had no "alternate screen". Nor did it have a feature for the "curses (1) fix".

  The NCD documentation (dated December 12, 1997) does not mention xterm. A related manual does mention xterm, but only in other sections. There are other issues with the manual. For example, aixterm (16-color) control sequences are documented as "NCD-specific values". NCD did add escape sequences for status line (kterm did this as well, according to the 6.2.0 sources dated July 1996), as well as VT220 national replacement characters (which I added early in 1998).

- Terminal Function Key Escape Codes has good intentions, but falls astray in several respects.
  For a different treatment of the same material, see my notes:

  > Table of function-keys for XTerm and other Terminal Emulators

  First off, it (like the the documentation for GNOME Terminal) misattributes work which I did, crediting the X Consortium:

  > This brings me to xterm. xterm has a long history, and the function key definitions have changed over time. The original xterm from the X Consortium (even before they were absorbed by The Open Group) used escape codes based on the VT220, but extended to cover the range from F1 to F48. F1 through F12 generated, respectively, codes `^[[11~` to `^[[15~`, `^[[17~` to `^[[21~`, `^[[23~`, and `^[[24~`. `Shift-F1` through `Shift-F12` were used for F13 through F24, and generated codes from `^[[11;2~` to `^[[24;2~`. Similarly `Ctrl-F1` through `Ctrl-F12` were used for F25 through F36 and generated codes `^[[11;5~` to `^[[24;5~`, and `Ctrl-Shift-F1` through `Ctrl-Shift-F12` were used for F37 through F48 and generated codes `^[[11;6~` to `^[[24;6~`. None of the base xterm `$TERM` types on my system correspond to this series of escape codes, though you can still get xterm to exhibit the old behavior by setting the `OldXtermFKeys` resource to 'true'.

  Not only that, but the comment (and much of the page) is inaccurate. For instance:

  - The X Consortium went out of business late in 1996 (see press release from July 1996).
    - The first release of X11R6 was done early in 1996 by X Consortium.
    - I've been working on xterm since before that (see history).
  - The X Consortium xterm only knew about function keys up to F20.
    - X11R5 defined only 20 function keys, and xterm used only those since May 1991.
      X11R6 changes to xterm did not take advantage of additional keys aside from the `Insert` and `Delete` on the keypad.
    - Further changes by The Open Group through X11R6.6 made no changes to xterm's handling of special keys.
    - That came in xterm patch #130 (2000/3/1), starting with the SCO function-keys feature.
  - The X Consortium xterm didn't know about using `Shift` to get F13 through F24.
    - I introduced a similar feature (using `Control`) in patch #51 (1997/9/15) as the `sunKeyboard` resource.
      I did this to leave `Shift` for the VT220 UDK (user-defined keys).
    - rxvt used `Shift`; the key combination was popular.
    - Alexander V Lukyanov's changes in patch #121 to update the terminal descriptions for these keys took that into account.
  - The X Consortium xterm didn't know about using `Control` to get F25 through F36.
    - Even with X11R6, the last function key was `XK_F35`.
    - However, since xterm patch #94 (1999/3/27), it accepts modifiers (shift, control, alt) to extend the actual set of keys to generate different escape sequences.
  - The escape sequences described all date from 2002 (xterm patch #167).
    - Besides function-keys, there are two other groups of special keys on the keyboard: cursor and editing-keypad.
    - Before then, the "2" and "5" in cursor- and home/end sequences would be first (before the semicolon).
    - By that point, GNOME Terminal and KDE Konsole had copied the earlier behavior, and failed to follow this change.
    - At the time, I preferred the VT220 keyboard (that does not support modified special keys).
    - However, the app-defaults file which I provided with xterm did not set the `sunKeyboard` resource to do this.
      Packagers routinely altered the recommended configuration, so this difference was not noticed for a while.
    - In response to a bug report, I switched to the Sun/PC keyboard, using the xterm-pc-fkeys building blocks in ncurses' terminfo description for xterm.
  - The X Consortium xterm had incomplete support for VT100 keypad.
    - I added a resource `sunKeyboard` to tell xterm to look at other keyboards to simulate the keypad.
    - To do this, I made F1 through F4 act like the VT100 PF1 through PF4.
    - That came in xterm patch #79 (1998/6/28).
    - Not everyone liked that, so I added another resource to allow turning off the change to F1 through F4.
    - Actually `OldXtermFKeys` is the resource class; the actual resource is `oldXtermFKeys`.

  By the way, although The Open Group made changes, none of those have been incorporated in this version of xterm. That was intentional (see discussion). Consequently, the xterm copyright makes no mention of The Open Group.

## Ongoing/future work

- soft (downloadable) fonts
- printer interface

  Done, except for the corresponding support in the VT52 emulation. It would be nice to have a dialog to control this.

- allow alternate libraries for popup-menus and dialogs

  My configure script currently provides tests for the variations of Athena widgets (Xaw3D, neXtaw). I intend to make additional changes to support Motif scrollbars and menus. Motif requires a different style of interface for the menus: binding a popup menu to control right mouse may cause the server to hang. As an intermediate step, I implemented a toolbar for the Athena widgets. In turn, that works well enough except with XFree86 4.x: the Xaw library geometry management is broken. (Other implementations of the Athena widgets work well enough).

- popup window that shows hex code for content of a character cell and hexadecimal keyboard entry for all Unicode characters (ISO 14755)
- correct cut&paste of TAB character