tmux frequently asked questions

******************************************************************************
* PLEASE NOTE: most display problems are due to incorrect TERM! Before       *
* reporting problems make SURE that TERM settings are correct inside and     *
* outside tmux.                                                              *
*                                                                            *
* Inside tmux TERM must be "screen" or similar (such as "screen-256color").  *
* Don't bother reporting problems where it isn't!                            *
*                                                                            *
* Outside, it must match your terminal: particularly, use "rxvt" for rxvt    *
* and derivatives.                                                           *
******************************************************************************

* How is tmux different from GNU screen?

tmux and GNU screen have many similarities. Some of the main differences I am
aware of are (bearing in mind I haven't used screen for a few years now):

- tmux uses a client-server model. Each server has single Unix domain socket in
  /tmp and within one server there are multiple sessions which may be attached
  to multiple clients (terminals).

  This has advantages, notably: windows may be linked simultaneously to
  multiple sessions; windows may be moved freely between sessions; and a client
  may be switched between sessions easily (C-b D). There is one major
  disadvantage: if the server crashes, game over, all sessions die. In
  practice, however, tmux is quite stable and gets more so as people report any
  bugs they hit :-).

  This model is different from screen, where typically each new screen instance
  is independent. tmux supports the same behaviour by using multiple servers
  with the -L option but it is not typically recommended.

- Different command interfaces. One of the goals of tmux is that the shell
  should be easily usable as a scripting language - almost all tmux commands
  can be used from the shell and behave identically whether used from the
  shell, from a key binding or from the command prompt. Personally I also find
  tmux's command interface much more consistent and clearer, but this is
  subjective.

- tmux calls window names (what you see in the status line) "names", screen
  calls them "titles".

- tmux has a multiple paste buffers. Not a major one but comes in handy quite a
  lot.

- tmux supports automatically renaming windows to the running application
  without gross hacks using escape sequences. Its even on by default.

- tmux has a choice of vi or emacs key layouts. Again, not major, but I use
  emacs so if tmux did support only one key set it would be emacs and then all
  the vi users would get humpy. Key bindings may be completely reconfigured in
  any case.

- tmux has an option to limit the window size.

- tmux has search in windows (C-b f).

- The window split (pane) model is different. tmux has two objects, windows and
  panes; screen has just windows. This difference has several implications:

  * In screen you can have a window appear in several layouts, in tmux a pane
  can only be in one window (fixing this is a big todo item but quite
  invasive).

  * tmux layouts are immutable and do not get changed unless you modify them.

  * In tmux, all panes are closed when you kill a window.

  * tmux panes do not have individual names, titles and so on.

  I think tmux's model is much easier to manage and navigate within a window,
  but breaking panes off from and joining them to windows is more clumsy.

  tmux also has support for preset pane layouts.

- tmux's status line syntax is more readable and easier to use. I think it'd be
  hard for anyone to argue with this. tmux doesn't support running a command
  constantly and always using the last line of its output, commands must be run
  again each time.

- tmux has modern, easily extended code. Again hard to argue screen is better
  if you have looked at the code.

- tmux depends on libevent. I don't see this as a disadvantage: libevent is
  small and portable, and on modern systems with current package management
  systems dependencies are not an issue. libevent brings advantages in code
  simplicity and performance.

- screen allows the window to be bigger than the terminal and can pan around
  it. tmux limits the size to the largest attached client. This is a big todo
  item for tmux but it is not trivial.

- screen has builtin serial and telnet support; this is bloat and is unlikely
  to be added to tmux.

- Environment handling is different.

- tmux tends to be more demanding on the terminal so tends to show up terminal
  and application bugs which screen does not.

- screen has wider platform support, for example IRIX, and for odd terminals.

* I found a bug! What do I do?

Check the latest version of tmux from Git to see if the problem is still
reproducible.  Sometimes the length of time between releases means a lot of
fixes can be sitting in Git and the problem might already be fixed.

Please send bug reports by email to nicholas.marriott@gmail.com or
tmux-users@googlegroups.com. 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 tmux-users@googlegroups.com.

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

It is already widely available. It is planned to change to something else such
as xterm-xfree86 at some point, if possible.

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

On some platforms, common terminal descriptions such as xterm do not include
colour. screen ignores this, tmux does not. If the terminal emulator in use
supports colour, use a value for TERM 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, UTF-8 must be turned on in tmux;
as of release 0.9, tmux attempts to autodetect a UTF-8-capable terminal by
checking the LC_ALL, LC_CTYPE and LANG environment variables. list-clients may
be used to check if this is detected correctly; if not, the -u command-line
flag may be specified when creating or attaching a client to a tmux session:

	$ tmux -u new

Since the 1.0 release, tmux will turn on UTF-8 related options automatically
(ie status-utf8, and utf8) if the above conditions are met.

* How do I use a 256 colour terminal?

Provided the underlying terminal supports 256 colours, it is usually sufficient
to add the following to ~/.tmux.conf:

	set -g default-terminal "screen-256color"

Note that some platforms do not support "screen-256color" ("infocmp
screen-256color" will return an error) - in this case see the next entry in
this FAQ.

tmux attempts to detect a 256 colour terminal both by looking at the colors
terminfo entry and by looking for the string "256col" in the TERM environment
variable.

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 colors terminfo or Co termcap entry. However, this is not
reliable, and in any case is missing from the "screen" terminal description
used inside tmux.

There are two options (aside from using "screen-256color") 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.
- Creating a custom terminfo file that includes colors#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.

vim users may also want to set the "ttyfast" option inside tmux.

* How do I make ctrl and shift arrow keys work in emacs?

The terminal-init-screen function in term/screen.el is called for new frames,
but it doesn't configure any function keys.

If the tmux xterm-keys option is on, it is enough to define the same keys as
xterm. Add the following to init.el or .emacs to do this:

(defadvice terminal-init-screen
  ;; The advice is named `tmux', and is run before `terminal-init-screen' runs.
  (before tmux activate)
  ;; Docstring.  This describes the advice and is made available inside emacs;
  ;; for example when doing C-h f terminal-init-screen RET
  "Apply xterm keymap, allowing use of keys passed through tmux."
  ;; This is the elisp code that is run before `terminal-init-screen'.
  (if (getenv "TMUX")
    (let ((map (copy-keymap xterm-function-map)))
    (set-keymap-parent map (keymap-parent input-decode-map))
    (set-keymap-parent input-decode-map map))))

And ensure .tmux.conf contains "set -g xterm-keys on".

Alternatively, the screen.el file can be copied to the load path and
customized.

* 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.

* I use PuTTY and my tmux window pane separators are all qqqqqqqqq's! 

PuTTY is using a character set translation that doesn't support ACS line
drawing. With a Unicode font, try setting PuTTY to use a different translation
on the Window -> Translation configuration page. For example, change UTF-8 to
ISO-8859-1 or CP437. It may also be necessary to adjust the way PuTTY treats
line drawing characters in the lower part of the same configuration page.

* What is the best way to display the load average? Why no #L?

It isn't possible to get the load average portably in code and it is preferable
not to add portability goop. The following works on at least Linux, *BSD and OS
X:

uptime|awk '{split(substr($0, index($0, "load")), a, ":"); print a[2]}'

* How do I attach the same session to multiple clients but with a different
  current window, like screen -x?

One or more of the windows can be linked into multiple sessions manually with
link-window, or a grouped session with all the windows can be created with
new-session -t.

* Ctrl and arrow keys doesn't work in putty! What do I do?

putty inverts the sense of the cursor key mode on ctrl, which is a bit hard for
tmux to detect properly. To get ctrl keys right, change the terminfo settings
so kUP5 (Ctrl-Up etc) are the adjusted versions, and disable smkx/rmkx so tmux
doesn't change the mode. For example with this line in .tmux.conf (assuming you
have TERM set to xterm):

set -g terminal-overrides "xterm*:kLFT5=\eOD:kRIT5=\eOC:kUP5=\eOA:kDN5=\eOB:smkx@:rmkx@"

Note that this will only work in tmux 1.2 and above.

* How can I blank the tmux window?

GNU screen has a feature whereby it will blank the screen after a period of
inactivity. To do the same thing in tmux, use the lock-command setting, for
example (with GNU bash):

set -g lock-command 'tput civis && read -s -n1'

This will remove the cursor and tell the shell to quit once a key has been
pressed. For zsh, use "read -s -k1".

In addition, it's possible to have both blanking and locking (for instance via
lock(1) or vlock(1)) by using the following:

bind x set lock-command '/usr/bin/vlock' \; lock-client \; set lock-command 'tput civis && read -s -n1'

* I don't see italics! Or less and vim show italics and reverse the wrong way round!

GNU screen does not support italics and the "screen" terminfo description uses
the italics escape sequence incorrectly.

As of tmux 2.1, if default-terminal is set to "screen" or matches "screen-*",
tmux will behave like screen and italics will be disabled.

To enable italics, create a new terminfo entry called "tmux" (some platforms
may already have this, you can check with "infocmp tmux"):

	$ cat <<EOF|tic -x -
	tmux|tmux terminal multiplexer,
		ritm=\E[23m, rmso=\E[27m, sitm=\E[3m, smso=\E[7m, Ms@,
		use=xterm+tmux, use=screen,

	tmux-256color|tmux with 256 colors,
		use=xterm+256setaf, use=tmux,
	EOF
	$

And tell tmux to use it in ~/.tmux.conf:
	
	set -g default-terminal "tmux"

If using urxvt, make sure you have an italics capable font enabled. for
example, add to ~/.Xdefaults:

	urxvt.italicFont: xft:Bitstream Vera Sans Mono:italic:autohint=true

* How can I make tmux use my terminal's scrollback buffer?

Normally, tmux enables the terminal's "alternate screen". Most terminals (such
as xterm) do not save scrollback for the alternate screen. You might prefer
tmux to use the normal screen, so it uses your terminal's scrollback
buffer. This way, you can access the scrollback buffer as usual, for example
using the mouse wheel - although there is no guarantee output inside tmux will
always (or ever) be added to the scrollback.

You can make tmux use the normal screen by telling it that your terminal does
not have an alternate screen. Put the following in ~/.tmux.conf:

        set -ga terminal-overrides ',xterm*:smcup@:rmcup@'

Adjust if your $TERM does not start with xterm.

tmux will still emulate the alternate screen for applications run under tmux,
so you don't really lose anything with this setting. The only disadvantage is
that when you exit tmux, it will not restore whatever was there before you
started.

* How do I see the default configuration?

Show the default session options by starting a new tmux server with no
configuration file:

        $ tmux -Lfoo -f/dev/null start\; show -g

Or the default window options:

        $ tmux -Lfoo -f/dev/null start\; show -gw

* How do I copy a selection from tmux to the system's clipboard?

When running in xterm(1), tmux can automatically send copied text to the
clipboard. This is controlled by the set-clipboard option and also needs this
X resource to be set:

	XTerm*disallowedWindowOps: 20,21,SetXprop

For rxvt-unicode (urxvt), there is an unofficial Perl extension here:

        http://anti.teamidiot.de/static/nei/*/Code/urxvt/

Otherwise a key binding for copy mode using xclip (or xsel) works:

	bind -temacs-copy C-y copy-pipe "xclip -i >/dev/null"

Or for inside and outside copy mode with the prefix key:

        bind C-y run -b "tmux save-buffer - | xclip -i"

On OS X, reattach-to-usernamespace lets pbcopy/pbpaste work:

        https://github.com/ChrisJohnsen/tmux-MacOSX-pasteboard
 
* Why do I see dots around a session when I attach to it?

tmux limits the size of the window to the smallest attached session. If
it didn't do this then it would be impossible to see the entire window.
The dots mark the size of the window tmux can display.

To avoid this, detach all other clients when attaching:

	$ tmux attach -d

Or from inside tmux by detaching individual clients with C-b D or all
using:

	C-b : attach -d
