tmux frequently asked questions

* What is tmux? How is it different from GNU screen?

...

* 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.

* 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 interfere 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.

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 on some platforms for some terminals such
as xterm-256color, by looking for the string "256col" in the termcap name.

If both these methods failed, 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 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; 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;
	}