Tmux - Check if server is up

Question

Is there any known tmux-function, like tmux has-session -t <session>, but to check if the tmux server is currently running? It would be handy when writing automation-scripts. When checking if a session exists with

$ tmux has-session -t SomeSession

the user is, unless the tmux server is already running, presented with the error

failed to connect to server

Therefore, I want to check beforehand if the server is currently running. If it is, check for sessions et cetera. Is there any way to silence this without piping to /dev/null?

Answer 1

Run

if tmux info &> /dev/null; then 
  echo running
else
  echo not running
fi

Answer 2

[[ -n $(pgrep tmux) ]] && echo true || echo false

If a process with “tmux” in it name is running, this will print true, otherwise it will print false.

This works because pgrep finds all process with "tmux" in their names and returns their PIDs. The "-n" basically tests whether the output of $(pgrep tmux) exists. If the output does exist (ex. "14204 23137"), then the test evaluates to true. If the output doesn't exist (or is undefined), the test evaluates to false.

If you prefer long-form:

if [[ -n $(pgrep tmux) ]]; then
  echo true
else
  echo false
fi

Note that what bnjmn said applies here. Namely, that this will give a false positive if a process is running other than tmux, but has "tmux" in its name.

Answer 3

You can use ps -e | grep -q program to check if program program is running in a general way.

As an example in a shell :

if $(ps -e | grep -q tmux); then echo "Tmux is running."; fi

Answer 4

There are problems with the other answers, but it seems like whether or not Tmux is running can be reliably tested with:

if tmux run 2>/dev/null; then
    echo "Tmux running"
else
    echo "Tmux not running"
fi

When run when Tmux isn't running tmux run will output the following to standard error (which is why redirecting stderr to /dev/null is necessary):

no server running on /tmp/tmux-1000/default

I originally tried tmux run-shell true (and the equivalent tmux run : if you want to be terse) and both commands work quite well, but leaving out the shell command to be run altogether (as above) also work (and might be more efficient since no shell command need to run.

The problem with tmux info

This returns false when there is a Tmux server running which does not have any sessions in it. (E.g. if you started a server using tmux -D &.)

The problem with pgrep tmux

This will return true if any user has a process called tmux running – though this might be improved using pgrep -u"$USER" tmux there's no real attempt to check anything beyond the name of the process.