How to create new tmux session if none exists

Question

I am trying to figure out how to attach to a tmux session if a named tmux session exists, if not I want to create a new one with the given name.

Currently, I know of a few tmux commands which can partly achieve what I am looking for, but its not clear how to combine them together to get what I am looking for:

tmux attach attaches to an automatically existing session - but errors out if no session exists
tmux new creates a new session - but it does so every time, so I can't leave it in my .tmux.conf
tmux has-session tests whether a session exists - but I don't know how to stitch it together with the other commands

Thus, I would like to create a tmux script, so that this happens automatically, instead of having to manually create it everytime I need to log into a sessions.

How can I write a automatic script so as to create a new tmux session (if a given session name doesnt exist) or attach to a session name (if it exists)?

I have written another possible answer for this question as a gist, in case anyone's interested: https://gist.github.com/chakrit/5004006 — chakrit, Feb 21 '13 at 11:22
Meanwhile, my `man tmux` says: "The -A flag makes new-session behave like attach-session if session-name already exists" — Petr Viktorin, Nov 18 '13 at 13:13
For those flagging to move this, I should note that even moderators cannot migrate questions more than 60 days old to another site. The reasons for this system limit are explained [here](http://meta.stackexchange.com/questions/151890/disable-migration-for-questions-older-than-60-days). — Brad Larson, Feb 21 '17 at 03:22
https://gist.github.com/MohamedAlaa/2961058 find list of all commands — ULLAS K, Mar 16 '17 at 18:31
@BradLarson, currently, the best/simplest option to do this is answered in a comment, way down: https://stackoverflow.com/questions/3432536/create-session-if-none-exists#comment74258862_7799360. Most users who come here wont be able to find this. This is obviously a very important question as you can see by the number of votes. Is it possible to open this question, so I can add that as an answer, so new people can find this? — alpha_989, Mar 06 '18 at 13:33
@alpha_989 - I've reopened it. Feel free to leave a new answer. — Brad Larson, Mar 06 '18 at 15:11
related: https://unix.stackexchange.com/questions/103898/how-to-start-tmux-with-attach-if-a-session-exists — Ciro Santilli Путлер Капут 六四事, Apr 03 '19 at 14:25

rampion · Answer 1 · 2018-03-06T16:02:12.053

168

I figured it out (and had it pointed out to me).

tmux attach || tmux new

edited Mar 06 '18 at 16:02

answered Aug 08 '10 at 01:31

rampion

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This answer works better for me because I can name the session: `tmux attach-session -t my-session || tmux new-session -s my-session`. The only problem is this is not atomic. tmux really ought to have a create-or-attach command. – Andrew May 11 '12 at 20:19
5

I have next alias in bash - `alias tm='tmux attach || tmux new'` – azat Apr 17 '13 at 19:51
10

Upvoting because with a small tweak this works with named sessions: `tmux attach -t some_name || tmux new -s some_name`. Change some_name to $1 add a shebang, and save. – Cheezmeister Jan 09 '14 at 04:48
@RandalSchwartz, yes - why `new-session` is better? – anatoly techtonik Feb 05 '14 at 13:00
I think both answers are good for different use cases. I modified this to not output any error messages with attach: `(tmux has &>/dev/null) && tmux attach || tmux new`. I currently use both answers in different environments. – daboross May 11 '14 at 18:41
11

Note to those unfamiliar with tmux and wondering about `new` vs `new-session`: they are synonyms, and so are `attach` and `attach-session`. – Esteis Jul 24 '15 at 08:38
1

`tmux new-session -ds default \; split-window -dv 2>/dev/null; tmux attach -t default` works far better and does not open a second tmux in case you `/bin/kill` the first one. The only downside is that you need to name the sessions for this. – Tino May 25 '16 at 16:05
@rampion, the link doesnt seem to be working.. also a better solution maybe available here: https://stackoverflow.com/questions/3432536/how-to-create-new-tmux-session-if-none-exists?noredirect=1#comment74258862_7799360 – alpha_989 Mar 06 '18 at 15:55
Someone who met a unexpected error to run this command with tmux 3.2 can try `tmux a || true && tmtux n`, which is more robust. – Chang Ye Jul 18 '20 at 15:55

Leonid Shevtsov · Accepted Answer · 2011-01-18T12:34:17.833

90

Alternately, you can add

new-session

to your .tmux.conf - that will create a default session on server start.

Then tmux attach will either attach to the current session (running server, that is), or create a new session (start the server, read the config file, issue the new-session command) and attach to that.

edited Jan 18 '11 at 12:34

answered Jan 17 '11 at 20:49

Leonid Shevtsov

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3

When this creates a new session, the default path is my home directory, not the path from which tmux was invoked. – Richard Hansen Sep 14 '11 at 22:31
2

@A.B: which answer do you mean? – Jürgen A. Erhard Jun 15 '12 at 13:58
Is there a way to make this solve @RichardHansen's issue? Invoking from the current path seems to make the most sense, and if `new-session` destroys that then it seems to be a real issue. – Lee Olayvar Sep 29 '13 at 16:50
There is one problem with that solution. It doesn't allow to create named sessions that way. – Hauleth Dec 19 '13 at 09:51
2

This breaks the tmux config reloading in case you use it (`source-file ~/.tmux.conf`) – Sebastian Blask Dec 15 '15 at 15:52
11

@SebastianBlask you can use the `-A` option to `new-session` if you name your session. `new-session -A -s mysession` will play nicely with config reloading. – jkoelker Mar 22 '16 at 06:22

score 88 · Answer 3 · edited Mar 06 '18 at 16:22

88

As pointed out in comments from Petr Viktorin, jkoelker and pjincz, you can use the following command to attach to mySession if it exists, and to create it if it doesn't:

 tmux new -A -s mySession

From man tmux:

new-session[-AdDEP] [-cstart-directory] [-Fformat] [-nwindow-name] [-ssession-name] [-tgroup-name] [-xwidth] [-yheight] [shell-command]

(alias: new)

Create a new session with name session-name.

[...]

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.

new-session has supported -A since tmux-1.8.

edited Mar 06 '18 at 16:22

rampion

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answered Mar 06 '18 at 15:52

alpha_989

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If you are going to use this in something like `gnome-terminal` as the command I'd suggest leaving off the `-s` and the specific session name so you don't end up with EVERY new `gnome-terminal` session attached to the same session. You can always select an existing session with `prefix + s` after opening a new terminal. – dragon788 Jul 04 '18 at 03:58

score 15 · Answer 4 · answered Aug 16 '12 at 19:12

Adapting Alex's suggestion to include project based configuration upon startup, I started using the following:

# ~/bin/tmux-myproject shell script
# The Project name is also used as a session name (usually shorter)
PROJECT_NAME="myproject"
PROJECT_DIR="~/myproject"

tmux has-session -t $PROJECT_NAME 2>/dev/null
if [ "$?" -eq 1 ] ; then
    echo "No Session found.  Creating and configuring."
    pushd $PROJECT_DIR
    tmux new-session -d -s $PROJECT_NAME
    tmux source-file ~/bin/tmux-${PROJECT_NAME}.conf
    popd
else
    echo "Session found.  Connecting."
fi
tmux attach-session -t $PROJECT_NAME

where tmux-myproject.conf is my startup series of tmux commands to create my windows and panes, as well as start my editors.

score 14 · Answer 5 · answered Aug 29 '11 at 14:46

Although I find rampion's answer is sufficient for using 1 session, this script lets you setup multiple sessions:

SESSIONS="work play"

function has-session {
    tmux has-session -t $1 2>/dev/null
}

function except 
{
    if [ "$?" -eq 1 ] ; then
        $1
    fi
}

# Configure your sessions here
function session-work
{
    tmux new-session -d -s work
    tmux neww -k -t work:1
}

function session-play
{
    tmux new-session -d -s play
    tmux neww -k -t play:1
}

#
#MAIN 
for x in $SESSIONS
do
    echo $x
    has-session $x
    except session-$x
done

NOTE:

-k  --> new-window will not be created if already exists
-d  --> start session or window, but don't attach to it yet
-s  --> name the session
-t  --> specify a target location in the form session:window.pane

score 9 · Answer 6 · edited Feb 12 '18 at 18:30

9

I use an alias to create a new session if needed, and attach to my default session if it already exists:

alias tmuxre='tmux new-session -t default || tmux new-session -s default'

I added this to my .login on my server.

The reason I do it this way is because I don't want to attach to the same actual session, I want a new session which uses the same group of windows.

This is also similar to running screen -xRR.

edited Feb 12 '18 at 18:30

Dakusan

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answered Oct 17 '11 at 20:45

Michael

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If you are in and out of your session often, this leaves lots of unused sessions, as seen by `tmux list-sessions`. – Anm Aug 16 '12 at 19:09
Yeah, it does, I just clean them up every now and then. It's a minor drawback to get the functionality I want. – Michael Aug 23 '12 at 21:49
Hey @mateusz-piotrowski - I agree with the edit to wrap my code in a code block but why would you edit the other text to be different than what I said? Sorry to comment here but I didn't see anywhere else to. – Michael Jan 25 '16 at 23:02
I didn't mean to offend you. I just thought you couldn't _run_ an alias _in_ a config file and so it must have been a typo. – Mateusz Piotrowski Jan 25 '16 at 23:08
Proper grammar/phrasing or not, I would hope that if user content is going to be edited on this site, there is some discussion with the user involved, as it seems very heavy-handed and easy to abuse otherwise. I didn't see any way to participate in this process myself, you just arbitrarily decided what I must have meant and changed what I said without bothering to ask for clarification. – Michael Jan 26 '16 at 21:39
3

By now, you can just type: `tmux new -A -s default` to launch a new session if it is not exist or attach automatically. I think it's much better than editing config file. – pjincz Apr 25 '17 at 07:56
@pjincz - that doesn't do what I wanted. That just makes a single session, whereas I wanted multiple sessions connected to the same window set. – Michael Apr 25 '17 at 21:12

score 2 · Answer 7 · answered May 07 '18 at 00:21

2

For those who want to do the same thing in fish:

tmux attach -t mysesh; or tmux new -s mysesh

answered May 07 '18 at 00:21

tinyspark

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How to create new tmux session if none exists

7 Answers7

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