How to start tmux with attach if a session exists

Question

If I use

tmux attach

I can attach to a running session but if there is no session running, I only get the error

no sessions

How can I automatically start a new session if there is none running? something like

tmux attach-or-create-new-session

related: https://stackoverflow.com/questions/3432536/how-to-create-new-tmux-session-if-none-exists — Ciro Santilli OurBigBook.com, Apr 03 '19 at 14:24

score 302 · Answer 1 · edited Feb 26 '21 at 08:34

302

If naming your session is okay, then it's easy to do with the new-session command:

tmux new-session -A -s main

where main is the session name that will be attached to or created if needed.

From man tmux:

The -A flag makes new-session behave like attach-session if session-name already exists; in this case, -D behaves like -d to attach-session.

This can be shortened to rely on the default session name (which is 0):

tmux new -As0

Please also note that the -A option was introduced in tmux version 1.8 on 26 March 2013. For earlier versions, use:

tmux attach || tmux

edited Feb 26 '21 at 08:34

Walf

1,321

answered Dec 31 '14 at 22:43

Wesley Baugh

3,138

2

In my alias list: alias "tmux-attach-or-create-main-session=tmux new-session -A -s main". Thanks for the tip! Manual page: http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man1/tmux.1 – Jeroen Wiert Pluimers Oct 14 '15 at 10:40
tmux: unknown option -- A This only seems to be available in recent versions. – xApple Mar 26 '16 at 18:15
This is the method I used, but you can no longer use "tmux detach". You need to use the shortcut b - d to save and exit an existing session. – Jess Sep 20 '17 at 17:14
3

[ -z "$TMUX" ] && exec tmux new -As . this is what I use in my .bashrc. – ryenus Nov 24 '17 at 03:26
1

+1 for pointing to an intrinsic feature which eliminates the need for shell-specific scripting. – Wil Moore III Jun 16 '18 at 21:47
2

As screen-transitioner, this command is way too long compared to screen -xR main. It can be shortened to tmux new -As main, which is acceptable with only 2 extra characters. – BlackShift Jan 07 '19 at 11:35
4

If you usually only work with one session, it's default name is 0, so you can do: tmux new-session -A -s 0. – Ciro Santilli OurBigBook.com Mar 31 '19 at 12:19
Nice! I came up with tmux a || tmux which works for me. – Markus Zeller Feb 28 '23 at 08:56

score 80 · Accepted Answer · answered Dec 06 '13 at 01:19

80

The answer is much simpler. Just put this in your ~/.tmux.conf file:

# if run as "tmux attach", create a session if one does not already exist
new-session -n $HOST

If you run tmux attach and there is a session, then it will attach to that session (whether it's already attached or not). If there is not a session already then it will create one for you.

answered Dec 06 '13 at 01:19

Joe Casadonte

1,094

19

this is a neat trick, but there is a caveat: if tmux is invoked without arguments, it will create a new session and then create a second session as soon it reaches this line in your ~/.tmux.conf. You can see this issue by executing tmux ls after creating the first session. In practice, after you put this in your file, you cannot call tmux with no arguments anymore – Bruno Polaco Nov 23 '14 at 23:35
6

So you would have to add an alias alias tmux="tmux attach" to prevent this problem – rubo77 Mar 21 '15 at 15:07
@BrunoPolaco: what is the big caveat with an extra empty tmux session running all the time (apart from that it doesn't look tidy in the task-list)? – rubo77 Sep 26 '16 at 03:14
1

@rubo77 Resources. Some people have a few default tools, windows, panes, etc created when they launch tmux. – rovr138 Mar 24 '17 at 17:05

rubo77 · Answer 3 · 2015-05-07T08:35:35.097

52

This will start a new session if attach gives an error:

tmux attach || tmux new

So an alias will do the job:

tm="tmux attach || tmux new"

edited May 07 '15 at 08:35

answered Dec 05 '13 at 22:11

rubo77

28,966

You can even make it shorter by changing tmux attach for tmux a – Bruno Polaco Nov 24 '14 at 10:46
While this is functional, Wesley Baugh's solution uses tmux's built-in functionality to do the same thing – Ari Patrick Mar 21 '15 at 14:08
fwiw this does seem like the best answer for older versions, before -A was introduced (e.g. v1.6) – Christopher Peterson Jan 16 '19 at 14:35
Do you need the "new"? – rubo77 May 16 '21 at 17:15
1

tmux a || tmux – Arnie97 Dec 10 '22 at 11:20

score 9 · Answer 4 · answered Feb 01 '18 at 18:01

To expand on Wesley Baugh's answer (which was double-nesting sessions for me when used in .bashrc on logins) and add a bit of flexibility since I often use sudo -s on servers (which would dutifully load my .bashrc again and double nest), here's what I have in my .bashrc:

if [ -z "$TMUX" ] && [ ${UID} != 0 ]
then
    tmux new-session -A -s main
fi

This checks for a tmux session and makes sure you aren't superuser before creating a new session or attaching to that existing one named main.

score 5 · Answer 5 · edited Jan 30 '22 at 18:58

5

If you're using this inside a .shrc file or similar with exec I'd recommend

if tmux ls &> /dev/null; then
  exec tmux attach
else
  exec tmux
fi

edited Jan 30 '22 at 18:58

Farid Cheraghi

107

answered Feb 05 '16 at 22:55

Aaron J Lang

385

For a more in depth example see https://github.com/aaronjameslang/dotfiles/blob/master/.zshrc – Aaron J Lang Nov 22 '16 at 11:38
1

Isn't the equivalent of just tmux && exec tmux attach || exec tmux? – Pablo A May 28 '20 at 06:06
It's worth to mention that it may block from creating new windows in the result (i.e. Prefix + c). – Artfaith Mar 20 '23 at 20:43

score 4 · Answer 6 · answered Dec 05 '13 at 19:18

Consider adding the following to your .bashrc

if [ -z "$TMUX" ]; then
    base_session='my_session'
    # Create a new session if it doesn't exist
    tmux has-session -t $base_session || tmux new-session -d -s $base_session
    # Are there any clients connected already?
    client_cnt=$(tmux list-clients | wc -l)
    if [ $client_cnt -ge 1 ]; then
        session_name=$base_session"-"$client_cnt
        tmux new-session -d -t $base_session -s $session_name
        tmux -2 attach-session -t $session_name \; set-option destroy-unattached
    else
        tmux -2 attach-session -t $base_session
    fi
fi

You can see my use of this in my ZSH resource file at my github repo

score 3 · Answer 7 · edited Jun 11 '20 at 14:16

Here is an alternative solution from this blog. Works like a charm.

session="main"
Check if the session exists, discarding output
We can check $? for the exit status (zero for success, non-zero for failure)
tmux has-session -t $session 2>/dev/null
if [ $? != 0 ]; then
Set up your session
fi
Attach to created session
tmux attach-session -t $session

From man page

has-session [-t target-session] (alias: has)
Report an error and exit with 1 if the specified session does not exist.
If it does exist, exit with 0.

score 3 · Answer 8 · answered May 16 '21 at 15:37

3

Use this:

$ tmux a || tmux

The || operator is the opposite of the && operator, meaning the second command is performed if the first one fails.

Make an aliast of it if it's too long.

answered May 16 '21 at 15:37

Michał Leon

282

1

this is what I needed for connecting to Centos 7. [omitting the alternate gave me an exit] – Chris F Carroll Jun 04 '21 at 16:33

score 2 · Answer 9 · edited Mar 20 '17 at 10:18

Drew Frank answered this here: https://superuser.com/questions/487363/tmux-equivalent-of-screen-r

Here's the script I now use for this (though, I've switched back to screen due to another issue with tmux) /somewhere/on/your/path/ttmux or as a shell function:

#!/bin/sh
# many thanks to Drew Frank: https://superuser.com/questions/487363/tmux-equivalent-of-screen-r
(tmux ls | grep -vq attached && tmux -2 at) || tmux -2

The -2 options make tmux assume 256 color terminal support, so those may not be appropriate for your situation.

score 2 · Answer 10 · answered Feb 25 '16 at 00:47

2

I improved on @SuperMagic answer a little. I put this block at the top of my .zshrc

if [[ $TMUX = "" ]]; then
  # try to reattach sessions
  tmux ls | grep -vq attached && TMUXARG="attach-session -d"
  exec eval "tmux -2 $TMUXARG"
fi

answered Feb 25 '16 at 00:47

cmcginty

2,683
4
21
12

Edgardo Arriagada · Answer 11 · 2023-06-18T18:32:04.690

I did create this function, hope it helps!

tm() {
  local targetSession="$1"
  local DEFAULT_SESSION="main"
[ -z "$targetSession" ] && targetSession="$DEFAULT_SESSION"
tmux attach-session -t "$targetSession">/dev/null 2>&1 || 

    tmux new -s "$targetSession">/dev/null 2>&1
}
If any, complete with a list of current tmux sessions
complete -C "tmux ls 2>&1 | cut -d':' -s -f1" tm

EDIT:

_tm.getCurrenSession() tmux display-message -p '#S'
tm() {
  local targetSession=${1:='main'}
if outside tmux
[[ -z "$TMUX" ]] && tmux new -A -s ${targetSession} && return $?
if [[ "_tm.getCurrenSession" = "$targetSession" ]]
    then print "You did not move."; return 1
  fi
Create session if it doesn't exists
tmux new -d -s ${targetSession} 2>/dev/null
tmux switch-client -t ${targetSession}
}
_tm() {
  (( $CURRENT > 2 )) && return 0
local tmuxList=( tmux ls -F &quot;#{session_name}&quot; )
if outside tmux
[[ -z "$TMUX" ]] &&  _describe 'command' tmuxList && return 0
local currentSession=( _tm.getCurrenSession )
  local actualList=(${tmuxList:|currentSession})
  _describe 'command' actualList
}
compdef _tm tm

score 0 · Answer 12 · answered Jul 24 '21 at 10:54

Here's a zsh script Eden Berger and I wrote to do this.

If any unused (no clients attached) tmux sessions exist, then tmux will attach to one of them (the first, sorted by their session id). Otherwise, a new tmux session will start.

It also supports skipping tmux altogether if already in a tmux session or if SKIP_TMUX is set. I find the latter useful because this snippet is at the top of my .zshrc. So, to run my terminal without starting or attaching a tmux session, I can run an occasional SKIP_TMUX=1 alacritty.

#!/usr/bin/env zsh
if [ -z $TMUX ] && [ -z $SKIP_TMUX ]; then
  delimiter=","
  sessions=$(tmux list-sessions -F "#{session_attached}${delimiter}#{session_id}")
  unused_sessions=$(echo $sessions | grep ^0)
  unused_sessions_ids=$(echo $unused_sessions | cut --delimiter=$delimiter --fields=2)
  sorted_unused_sessions_ids=$(echo $unused_sessions_ids | sort --numeric)
  first_unused_session_id=$(echo $sorted_unused_sessions_ids | head --lines 1)
  if [ -z $first_unused_session_id ]; then
    exec tmux new-session
  else
    exec tmux attach-session -t $first_unused_session_id
  fi
fi

score 0 · Answer 13 · answered Aug 13 '21 at 03:06

this help me to open `tmux` when `terminal` opened and attach `S1` if exist, if not exist: will be created

i have already a session called S1
for attach tmux to this session from .zshrc or .bashrc i'm add this in .zshrc|.bashrc

if [[ ! $TERM =~ screen ]]; then
    tmux attach -t tmux-ay || tmux new-session -s tmux-ay -n win1-ay
fi

How to start tmux with attach if a session exists

13 Answers13

Check if the session exists, discarding output

We can check $? for the exit status (zero for success, non-zero for failure)

Set up your session

Attach to created session

If any, complete with a list of current tmux sessions

EDIT:

if outside tmux

Create session if it doesn't exists

if outside tmux

this help me to open `tmux` when `terminal` opened and attach `S1` if exist, if not exist: will be created

Linked

How to start tmux with attach if a session exists

13 Answers13

Check if the session exists, discarding output

We can check $? for the exit status (zero for success, non-zero for failure)

Set up your session

Attach to created session

If any, complete with a list of current tmux sessions

EDIT:

if outside tmux

Create session if it doesn't exists

if outside tmux

this help me to open tmux when terminal opened and attach S1 if exist, if not exist: will be created

Linked

this help me to open `tmux` when `terminal` opened and attach `S1` if exist, if not exist: will be created