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.

- screen has support for updating utmp. Nobody has really come up with a clean,

portable way to do this without making tmux setuid or setgid yet.

- 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 HP-UX, and for odd

terminals.

* I found a bug! What do I do?

Please send bug reports by email to nicm@users.sourceforge.net or

tmux-users@lists.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 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.

* 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'

* How can I open a new window in the same directory as the current window?

One option is to just run "TMUX= tmux" in the window. However, this only works if no

command is running, so that you can input the command.

A workaround is to let tmux know about the current path through an environment

variable. To do so, use the following command:

[ -n "$TMUX" ] && tmux setenv TMUXPWD_$(tmux display -p "#I") $PWD

Which sets TMUXPWD_i (where i is the number of the current window) to the path

of the current directory. This command can be added to PS1, for example:

PS1='$([ -n "$TMUX" ] && tmux setenv TMUXPWD_$(tmux display -p "#I") $PWD)\h$ '

When a new window is created, the shell should be asked to change

directory. You can define a new binding (for example, if using GNU bash):

bind-key C-c run-shell 'tmux neww "cd $(tmux display -p "\$TMUXPWD_#I"); exec bash"'

This solution will work even if a command is currently running in the terminal,

but it will not work from a window that has just been swapped with another

because TMUXPWD_i will not be updated after a swap. However, once a new prompt

is displayed, TMUXPWD_i is updated properly.

* tmux doesn't start with "daemon failed"

tmux shows something similar to this when started:

fatal: server_start: daemon failed: No such file or directory

fatal: main_dispatch: imsg_read failed

A possible reason is that /dev/null is not a character device or is otherwise

inaccessible.

Check with:

file /dev/null

ls -l /dev/null

If it is not a character device or has incorrect permissions, it can typically

be recreated with:

cd /dev && rm null && ./MAKEDEV null

* vim displays reverse video instead of italics, while less displays italics

(or just regular text) instead of reverse. What's wrong?

Screen's terminfo description lacks italics mode and has standout mode in its

place, but using the same escape sequence that urxvt uses for italics. This

means applications (like vim) looking for italics will not find it and might

turn to reverse in its place, while applications (like less) asking for

standout will end up with italics instead of reverse. To make applications

aware that tmux supports italics and to use a proper escape sequence for

standout, you'll need to create a new terminfo file with modified sgr, smso,

rmso, sitm and ritm entries:

$ mkdir $HOME/.terminfo/

$ screen_terminfo="screen"

$ infocmp "$screen_terminfo" | sed \

-e 's/^screen[^|]*|[^,]*,/screen-it|screen with italics support,/' \

-e 's/%?%p1%t;3%/%?%p1%t;7%/' \

-e 's/smso=[^,]*,/smso=\\E[7m,/' \

-e 's/rmso=[^,]*,/rmso=\\E[27m,/' \

-e '$s/$/ sitm=\\E[3m, ritm=\\E[23m,/' > /tmp/screen.terminfo

$ tic /tmp/screen.terminfo

And tell tmux to use it in ~/.tmux.conf:

set -g default-terminal "screen-it"

If your terminal supports 256 colors, use:

$ screen_terminfo="screen-256color"

instead of "screen". See the FAQ entry about 256 colors support for more info.

Also note that tmux will still display reverse video on terminals that do not

support italics.

If your urxvt cannot display italics at all, make sure you have an italics

capable font enabled, for example, add to ~/.Xdefaults:

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

$Id: FAQ,v 1.43 2011-05-18 17:47:33 nicm Exp $