FAQ

tmux frequently asked questions

* How is tmux different from GNU screen? What else does it offer?

tmux offers several advantages over screen:

- a clearly-defined client-server model: windows are independent entities which
  may be attached simultaneously to multiple sessions and viewed from multiple
  clients (terminals), as well as moved freely between sessions within the same
  tmux server; 
- a consistent, well-documented command interface, with the same syntax
  whether used interactively, as a key binding, or from the shell;
- easily scriptable from the shell;
- multiple paste buffers;
- choice of vim or emacs key layouts;
- an option to limit the window size;
- a more usable status line syntax, with the ability to display the first line
  of output of a specific command;
- a cleaner, modern, easily extended, BSD-licensed codebase.

There are still a few features screen includes that tmux omits:

- builtin serial and telnet support; this is bloat and is unlikely to be added
  to tmux;
- wider platform support, for example IRIX and AIX, and for odd terminals.
- better UTF-8 support.

* I found a bug! What do I do?

Please send bug reports by email to nicm@users.sourceforge.net. Please
include as much of the following information as possible:

- the version of tmux you are running;
- the operating system you are using and its version;
- the terminal emulator you are using and the TERM setting when tmux was 
  started;
- a description of the problem;
- if the problem is repeatable, the steps to repeat the problem;
- for screen corruption issues, a screenshot and the output of "infocmp $TERM"
  from outside tmux are often very useful.

* Why doesn't tmux do $x?

Please send feature requests by email to nicm@users.sourceforge.net.

* Why do you use the screen termcap inside tmux? It sucks.

It is already widely available. It is planned to change to something else
such as xterm-color at some point, if possible.

* I don't see any colour in my terminal! Help!

On some platforms, common termcaps such as xterm do not include colour. screen
ignores this, tmux does not. If the terminal emulator in use supports colour,
use a termcap which correctly lists this, such as xterm-color.

* tmux freezes my terminal when I attach to a session. I even have to kill -9
  the shell it was started from to recover!

Some consoles really really don't like attempts to set the window title. Tell
tmux not to do this by turning off the "set-titles" option (you can do this
in .tmux.conf):

     set -g set-titles off

If this doesn't fix it, send a bug report.

* Why is C-b the prefix key? How do I change it?

The default key is C-b because the prototype of tmux was originally developed
inside screen and C-b was chosen not to clash with the screen meta key. It
also has the advantage of not interfering with the use of C-a for start-of-line
in emacs and the shell (although it does interfere with previous-character).

Changing is simple: change the "prefix-key" option, and - if required - move
the binding of the "send-prefix" command from C-b (C-b C-b sends C-b by
default) to the new key. For example:

	set -g prefix C-a
	unbind C-b
	bind C-a send-prefix

* How do I use UTF-8?

When running tmux in a UTF-8 capable terminal, two things must be done to
enable support. UTF-8 must be turned on in tmux; this may be done separately
for each tmux window or globally by setting the "utf8" flag:

	setw -g utf8 on

And, as it is not possible to automatically detect that a terminal is UTF-8
capable, tmux must be told by passing the -u flag when creating or
attaching a client to a tmux session:

	  $ tmux -u new

* How do I use a 256 colour terminal?

tmux will attempt to detect a 256 colour terminal both by looking at the Co
termcap entry and, as this is broken for some terminals such as xterm-256color,
by looking for the string "256col" in the termcap name.

If both these methods fail, the -2 flag may be passed to tmux when attaching
to a session to indicate the terminal supports 256 colours.

* vim or $otherprogram doesn't display 256 colours. What's up?

Some programs attempt to detect the number of colours a terminal is capable of
by checking the Co termcap entry. However, this is not reliable, and in any
case is missing from the "screen" termcap used inside tmux.

There are three options to allow programs to recognise they are running on
a 256-colour terminal inside tmux:

- Manually force the application to use 256 colours always or if TERM is set to
  screen. For vim, you can do this by overriding the t_Co option, see
  http://vim.wikia.com/wiki/256_colors_in_vim.
- If the platform includes it, using the "screen-256color" termcap (set
  TERM=screen-256color). "infocmp screen-256color" can be used to check if this
  is supported. It is not currently possible to set this globally inside tmux
  but it may be done in a shell startup script by checking if TERM is screen
  and exporting TERM=screen-256color instead.
- Creating a custom terminfo file that includes Co#256 in ~/.terminfo and using
  it instead. These may be compiled with tic(1).

* How do I make Ctrl-PgUp and Ctrl-PgDn work in vim?

tmux supports passing through ctrl (and where supported by the client terminal,
alt and shift) modifiers to function keys using xterm(1)-style key sequences.
This may be enabled per window, or globally with the tmux command:

	setw -g xterm-keys on

Because the TERM variable inside tmux must be set to "screen", vim will not
automatically detect these keys are available; however, the appropriate key
sequences can be overridden in .vimrc using the following:

	if &term == "screen"
	set t_kN=^[[6;*~
	set t_kP=^[[5;*~
	endif

And similarly for any other keys for which modifiers are desired.

Please note that the "xterm-keys" setting may affect other programs, in the
same way as running them in a standard xterm; for example most shells do not
expect to receive xterm(1)-style key sequences so this setting may prevent keys
such as ctrl-left and ctrl-right working correctly. tmux also passes through
the ctrl (bit 5 set, for example ^[[5~ to ^[[5^) modifier in non-xterm(1) mode;
it may be possible to configure vim to accept these, an example of how to do so
would be welcome.

* Why doesn't elinks set the window title inside tmux?

There isn't a way to detect if a terminal supports setting the window title, so
elinks attempts to guess by looking at the environment. Rather than looking for
TERM=screen, it uses the STY variable to detect if it is running in screen;
tmux does not use this so the check fails. A workaround is to set STY before
running elinks.

The following shell function does this, and also clears the window title on
exit (elinks, for some strange reason, sets it to the value of TERM):

	elinks() {
        	STY= `which elinks` $*
	        echo -ne \\033]0\;\\007;
	}

* What is the proper way to escape characters with #(command)?

When using the #(command) construction to include the output from a command in
the status line, the command will be parsed twice. First, when it's read by the
configuration file or the command-prompt parser, and second when the status
line is being drawn and the command is passed to the shell. For example, to
echo the string "(test)" to the status line, either single or double quotes
could be used:

	set -g status-right "#(echo \\\\(test\\\\))"
	set -g status-right '#(echo \\\(test\\\))'

In both cases, the status-right option will be set to the string "#(echo
\\(test\\))" and the command executed will be "echo \(test\)".

* tmux uses too much CPU. What do I do?

Automatic window renaming may use a lot of CPU, particularly on slow computers:
if this is a problem, turn it off with "setw -g automatic-rename off". If this
doesn't fix it, please report the problem.