I just installed tmux on Ubuntu 10.04 and tried to remap the prefix key to C-a by creating the file ~/.tmux.conf with these lines:

set-option -g prefix C-a
unbind-key C-b

When starting tmux, both regularly and with -f ~/.tmux.conf, the prefix is effectively the same default C-b

There are no errors or warnings whatsoever.

Any idea what's wrong with the loading of the conf?

  • 3
    It Works For Me™. Try running strace -s9999 -f -o tmux.strace tmux -c true and post the output of grep -C5 'tmux\.conf' tmux.strace. Sep 14, 2010 at 20:24
  • I had this same problem, no existing sessions, ('tmux ls' reported connection refused, i.e. not running), but it still wasn't reading the conf file. I was launching it with a CWD somewhere in /usr, but when I switched to ~/ and launched tmux, it processed the conf file. It's weird behaviour, but that's something to check. Jan 26, 2013 at 21:30

9 Answers 9


The file ~/.tmux.conf is loaded when the tmux server is first started. So if there are existing tmux sessions, starting a new session with tmux does not result in reloading the .tmux.conf file. Try restarting tmux server: Use the command tmux list-sessions to see if there are existing sessions. Exit them (e.g. tmux attach then kill all windows and exit). Once all sessions are gone, try tmux again. This time the rebinding should work.

  • 36
    killall tmux or tmux kill-server will get the job done too
    – Matt
    Jun 25, 2011 at 2:01
  • 6
    I used killall tmux and tmux kill-server and still my conf is not loaded. I can confirm it is valid, since using :source-file ~/.tmux.conf in tmux does actually make the config changes! Can't figure out what is causing this behavior.
    – Ambidex
    Apr 24, 2015 at 8:17
  • I wonder why reloading the config wasn't mentioned in this answer. It sometimes works and sometimes doesn't. Any ideas on that?
    – Paghillect
    Apr 13, 2018 at 0:25
  • tmux ls short version of tmux list-sessions. tmux a short version to attach to last used session. :kill-server to kill all sessions at once.
    – Dzintars
    Jun 7, 2022 at 16:55

To reload your ~/.tmux.conf without killing your session, you can simply do:

<prefix> :source-file /absolute/path/to/your/.tmux.conf

where <prefix> is <C-b> by default.

  • 7
    You can add the following to .tmux.conf to use Ctrl-A r to reload: bind r source-file ~/.tmux.conf \; display-message "Config reloaded..."
    – RedPixel
    Aug 19, 2015 at 8:08
  • 1
    +1 for pointing out the necessity of absolute path Jan 28, 2019 at 22:43
  • 1
    Note that this was not enough for my use case. I had added some styles to my .tmux.conf, then removed them and reloaded, but some of them were not overwritten just by sourcing the file without them. I had to actively kill the session, and then the next session I created had the correct styling.
    – Neil Traft
    Oct 20, 2021 at 2:42

run inside your tmux session:

tmux source-file /absolute/path/to/your/.tmux.conf
  • 1
    Note: this will not affect the current tmux window (obviously), but all new tmux windows.
    – Klaws
    Mar 12, 2019 at 7:21
  • If your admins start tmux automatically, add this line to your ~/.bashrc
    – Greg
    Sep 6, 2022 at 22:52

There's also a default keyboard shortcut binding to reload your ~/.tmux.conf, at least in my installation: C-b r. If you hit C-b ? it brings up a list of all bound keyboard shortcuts, so you can see if you have one already defined.

  • That is specific to your installation/configuration. By default, <prefix> r is bound to refresh-client (what you describe would be something like source ~/.tmux.conf). Jan 1, 2012 at 3:09

12 years ago

A hero left a comment.

It Works For Me™. Try running strace -s9999 -f -o tmux.strace tmux -c true and post the output of grep -C5 'tmux\.conf' tmux.strace. – Gilles 'SO- stop being evil' Sep 14, 2010 at 20:24

A master class in understatement

With no fanfaronade they dropped a single sentence in a comment that should have been, not only an answer but, the answer. Not only the answer to this question, but the reference answer to an entire class of questions.

Breaking it down

What does strace -s9999 -f -o tmux.strace tmux -c true mean?

It's sort of like 2 commands in 1. The main command is tmux but it is given a "prefix"/"wrapper" called strace. This is very similar to running time df to measure how much time it takes to run the df command.

strace -s9999 -f -o tmux.strace

$ man strace | grep -A1 ^NAME
       strace - trace system calls and signals

$ man strace | grep -EA10 '^ *DESCRIPTION($| )'
       In the simplest case strace runs the specified command until it  exits.   It
       intercepts  and  records  the system calls which are called by a process and
       the signals which are received by a process.  The name of each system  call,
       its  arguments  and its return value are printed on standard error or to the
       file specified with the -o option.

       strace is a useful diagnostic, instructional, and  debugging  tool.   System
       administrators,  diagnosticians and trouble-shooters will find it invaluable
       for solving problems with programs for  which  the  source  is  not  readily
       available  since  they  do not need to be recompiled in order to trace them.

$ man strace | grep -EA4 '^ *-s($| )'
       -s strsize
                   Specify the maximum string size to print (the  default  is  32).
                   Note  that  filenames  are not considered strings and are always
                   printed in full.

$ man strace | grep -EA6 '^ *-f($| )'
                   Trace child processes as they are created  by  currently  traced
                   processes as a result of the fork(2), vfork(2) and clone(2) sys‐
                   tem calls.  Note that -p PID  -f  will  attach  all  threads  of
                   process  PID  if  it  is  multi-threaded,  not  only thread with
                   thread_id = PID.

$ man strace | grep -EA8 '^ *-o($| )'
       -o filename
                   Write the trace output to  the  file  filename  rather  than  to
                   stderr.   filename.pid  form  is used if -ff option is supplied.
                   If the argument begins with '|' or '!', the rest of the argument
                   is  treated as a command and all output is piped to it.  This is
                   convenient for piping the debugging output to a program  without
                   affecting  the redirections of executed programs.  The latter is
                   not compatible with -ff option currently.

tmux -c true

$ man tmux | grep -EA4 '^ *-c($| [^ ]*$)'
     -c shell-command
                   Execute shell-command using the default shell.  If necessary,
                   the tmux server will be started to retrieve the default-shell
                   option.  This option is for compatibility with sh(1) when tmux
                   is used as a login shell.

$ man true | grep -A1 ^NAME
       true - do nothing, successfully


use -c with tmux?

Since we only really care about the startup process of tmux, we don't need to use it interactively. Therefore, we will instruct it to run a command in place of our normal interactive shell.

use true as the tmux command?

Because it exits very quickly and will keep our log short.

use -o tmux.strace with strace?

It's just file to store the output. Naming things is hard. It was not important to match the basename or the extension to anything else.

use -f with strace?

I'll assume you read the excerpt from the man page and not redundacate. Any reasonably complex application is going to create child processes. Since tmux is magnificently complex, we definitely want to strace those too.

use -s9999 with strace?

Since we are writing the output to a file, we don't need line truncated to fit our terminal width. Set it large. Deal with displaying it later if it's a problem.

Why do any of this?

If by any, you mean write this long-ass answer...

  1. Because I train engineering teams and will point them to this answer.
  2. Because Giles...
    • is freaking hero
    • had 0 upvotes on their comment for 10+ years
    • has gone unnoticed for too long, and I refuse to let it continue

If you don't see why this process is The Way to answer a question like "Any idea what's wrong with the loading of the conf?" then I would refer you to the XY Problem

It is not only questioners who fall into the XY Problem. It extremely common for answers to ~make this mistake~ do this also. In this case, many answers to this question instruct the reader how to load/reload a config file after the process has started. That suggests ignoring the fact the process fails to load the file as it should.

If you have made it this far, what I want you to take away is take it's only okay to ignore a failure if you are:

  • moving past a blocker so that you can remove yourself as a blocker for others
  • going to come back a fix the problem correctly later

The Take Away

Many problems can be distilled down to "What's wrong with the loading of the file?". That question should tickle a spidey-sense in the form of "Is it trying to load the file? What is happening when it tries?"

You can/should[?] use strace solve anything that can be be questioned as:

  • What is this process trying to do?
  • What is it experiencing when it tries to do that [thing it's trying to do]?

Often, it is not a failure of the process to do a thing, but a failure of the user expecting the process to do a thing. And, the process experiences a lot of things that the user is not informed of.

Enough with the abstract pontification. Let's consider an example:

$ tmux kill-server; rm tmux.strace; strace -s9999 -f -o tmux.strace tmux -c true
no server running on /tmp/tmux-1000/default

$ ls -lh tmux*
-rw-r--r-- 1 bruno bruno  21K Jun 11 10:58 tmux-client-18358.log
-rw-r--r-- 1 bruno bruno 324M Jun 11 10:58 tmux-server-18360.log
-rw-r--r-- 1 bruno bruno 342K Jun 11 13:48 tmux.strace

$ grep 'tmux\.conf' tmux.strace
521744 readlink("/etc/tmux.conf", 0x7ffe2c0446d0, 1023) = -1 ENOENT (No such file or directory)
521744 readlink("/home/bruno/.tmux.conf", 0x7ffe2c0446d0, 1023) = -1 ENOENT (No such file or directory)
521744 readlink("/home/bruno/.config/tmux/tmux.conf", 0x7ffe2c0446d0, 1023) = -1 ENOENT (No such file or directory)

$ ls -lA /home/bruno/.config/tmux
-rw-r--r-- 1 bruno bruno 307 Jun 10 20:29 tmux.config

Do you see it? Look at the output of the last 2 commands. Maybe it would help if I showed you how I fix it.

$ mv ~/.config/tmux/tmux.config \

$ tmux kill-server; rm tmux.strace; strace -s9999 -f -o tmux.strace tmux -c true
no server running on /tmp/tmux-1000/default

$ grep -A2 '\.config/tmux/tmux\.conf' tmux.strace
527872 openat(AT_FDCWD, "/home/bruno/.config/tmux/tmux.conf", O_RDONLY) = 8
527872 newfstatat(8, "", {st_mode=S_IFREG|0644, st_size=307, ...}, AT_EMPTY_PATH) = 0
527872 read(8, "set -sg escape-time 0\nset -g mode-keys vi\n\n# remap prefix from 'C-b' to 'C-f'\nset-option -g prefix C-f\nunbind-key C-b\nbind-key C-f send-prefix\n\n# split panes using | and -\nbind | split-window -h\nbind - split-window -v\n# bind \"\33OA\" # scroll natural up\n# bind \"\33OB\" # scroll natural down\nunbind '\"'\nunbind %\n\n", 4096) = 307

Note: That last line is the entire contents of my (previously misnamed) ~/.config/tmux/tmux.conf file.


I quit and reopened my terminal and that's the only way I could get it to work again. Not sure why.

using Terminal on Mac OSX


I had this problem because I was using tmux-next.

Initially I solved it just by passing the config file explicitly tmux -f ~/.tmux.conf as the question here points out. (I had already aliased tmux-next to tmux.)

Then I realised tmux-next is using tmux-next.conf, so just symlink it if using this and only need to run the next tmux version.

ln -s ~/.tmux.conf ~/.tmux-next.conf


tmux not load ~/.tmux.conf automatically, you must source manually, for the first time that you install tmux or every time that you change anything in ~/.tmux.conf by:

tmux source-file ~/.tmux.conf
  • it's different with vim (vim source files after every time opened)

My issue is laughable: It is a syntax error 🤣🤣. I missed a closing quote at the end of this statement 👇 . I wish they could at least report some errors to new users like me.

 set -g @plugin 'olimorris/tmux-pomodoro-plus'
  • As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
    – Community Bot
    Apr 4 at 12:44

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