I would like to know if there is a way to get tmux to behave like screen -D -R so I could say, have the command as a default command in Putty.

These screen switches would force detach of an existing screen session for my user (even if it was still active and logged-in somewhere else) and reattach it to the current session. Also, in the case that no screen session existed, it would create a new one.

I like tmux and can see clear benefits over screen, but the existence of this feature would really seal the deal.

tmux attach doesn't seem to create a new session if there isn't one.

The man page for tmux says:

If no server is started, attach-session (attach) will attempt to start it; this will fail unless sessions are created in the configuration file.

What does the section in bold mean? (I can't find an example of creating a session in the conf file).

  • From the man page: "The configuration file is a set of tmux commands which are executed in sequence when the server is first started." -- you could actually have attach or new-session as a line in your .tmux.conf.
    – sr_
    Mar 5, 2012 at 13:35
  • @sr_ Well, the when the server is first started new-session would have just happened anyway...
    – Chris Down
    Mar 5, 2012 at 13:36
  • Just found this (closed) question on SO. Same question with similar answers. stackoverflow.com/q/3432536/168034
    – phunehehe
    May 29, 2013 at 12:34

7 Answers 7


Yes: tmux attach -d || tmux new.

-d is necessary to behave like screen -D, ie, detach everybody else.

Connect by ssh, then attach or create could be something like:

$ cat bin/stmux
exec ssh -t "$@" 'tmux attach -d || tmux new'

$ stmux my.remote.box
  • 1
    Yes - this seems to be the most effective way to achieve the what I requested. Likewise, I disapprove of new-session in the config file in case you want to edit it and reload during a tmux session.
    – Geeb
    Jan 16, 2014 at 10:07

To make tmux attach create a new session when there isn't one, use the option new-session in the tmux config file. Create the file ~/.tmux.conf if it doesn't exist, and add


to it. Also, I alias tmux to tmux attach :)

  • 1
    I prefer not to have new-session in ~/.tmux.conf because if I reload the configuration using command source-file ~/.tmux.conf (see this) a new session will be launched. Yes, I can kill it and then attach to the previous one but that is a little annoying.
    – mmoya
    May 14, 2012 at 11:04

You can emulate this with a shell function, this should work for any POSIX-compliant shell:

tmux() {
    if [ "$#" -ge 1 ] && [ "$1" = -z ]; then
        command tmux detach 2>/dev/null
        command tmux attach "$@" || command tmux new-session "$@"
        command tmux "$@"

Now if you launch it as tmux -z, it should perform the actions you're looking for.


this one works a bit better for me:

tmux new-session -AD -s <session-name>

I find this works best for me on .bashrc

if [[ -z $TMUX ]]; then
  tmux attach-session || tmux new-session
  • How does that explain the bold section in the OP?
    – Anthon
    Oct 14, 2013 at 5:53

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

if tmux ls
  exec tmux attach
  exec tmux

To compliment the answer from @mmoya, add this line to the end of your ~/.bashrc

alias tmux-dr="tmux attach -d || tmux new"

Open a new terminal and run tmux-dr

  • You may suggest edits to existing answers.
    – Kusalananda
    Aug 1, 2021 at 8:13

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