How to deal with tmux "protocol version mismatch"

protocol-fix.txt

$ tmux attach
protocol version mismatch (client 7, server 6)

$ pgrep tmux
3429
$ /proc/3429/exe attach

This saved me from a potential blunder while attempting to update my ubuntu installation! Thank you for this! I know this is 2 years old but thought I would still chime in!

You are my hero! had exactly the same problem while upgrading. I guess this is also useful for many other cases. Thanks a lot!

Wow, this was extremely helpful! Thanks a lot!

This is awesome! Thanks.

This just helped me too. Thanks

This helped me with the error "server version is too old for client" which gives a whopping 3 hits on google. Commenting here so that someone else googleing this will find this.

Is there a solution for macOS ?

By the way, if all else is failing, and you installed your first version from distro, and your second version from source (In my case, i installed tmux 3.0a from apt-get install, then I wanted to upgrade to 3.1b , so installed from source)

apt remove tmux , and then following the source install instructions should work

Here's a oneliner:

$(echo "/proc/`pgrep -o tmux -u $(whoami)`/exe attach")

On multi-user systems (e.g. on HPCs), you might need to filter by your own username. You can also add the function to your .bash_profile, e.g.:

function last_tmux(){
    $(echo "/proc/`pgrep -o tmux -u $(whoami)`/exe attach")
}