I'm trying to upgrade to a newer version (that has a bug fix) than my current 1.6. I am on Ubuntu and recently upgraded to Ubuntu 13.04.

Ideally I want to use tmux version 1.8 or even 1.9. I've downloaded newer versions but can't get them working.

I downloaded 1.9a but when I try and run it, it just hangs.

I tried this download: http://sourceforge.net/p/tmux/tmux-code/ci/master/tree/README#l26

and did the

$ sh autogen.sh
$ ./configure && make

but I get

$ ./tmux
$ protocol version mismatch (client 8, server 6)

I tried to download and use a 1.8.4 version but the download didn't seem to have files I could use.


This basically tells you, that you already have an (old) tmux-server running and the new tmux can't connect to it because they don't understand each other anymore. Exit all your existing tmux sessions and start a fresh one using the new version and everything should be fine.

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  • Yeah logging out seemed key. For the 1.6 to 1.7 upgrade I feel that logging out/in was the only fix. Subsequent version upgrades only seemed to require me to log out of all the terminal windows. – Michael Durrant Mar 30 '14 at 14:59
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    Please explain how to exit all tmux-sessions properly if you cannot access them, because tmux is not backward compatible! Killing processes is not what I call exiting, this is more like a massacre. ;) – Tino Aug 17 '15 at 9:14
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    I killed my existing tmux session by using pkill tmux (after seeking a tmux session with pgrep tmux) from a normal terminal. Afterwards, tmux launched/behaved correctly... – temuraru Jan 26 '17 at 10:10

Pretty awesome hack, if you need your tmux working and not want to lose all your sessions:

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

$ pgrep tmux
$ /proc/3429/exe attach

original post on Google Plus - https://plus.google.com/110139418387705691470/posts/BebrBSXMkBp

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  • 2
    This looked so cool! But alas, in my debian squeeze -> jessie upgrade (with a temporary stop on wheezy), I got: tmux at == no sessions. /var/run/tmux/tmux-0/default existed, so I tried: tmux -S /var/run/tmux/tmux-0/default at == protocol version mismatch (client 8, server 6). Now /proc/$(pgrep tmux)/exe == /proc/2534/exe: Permission denied and ls -l /proc/$(pgrep tmux)/exe == /proc/2534/exe -> /usr/bin/tmux (deleted). :-( – Peter V. Mørch Apr 23 '15 at 9:33
  • Note, however, that in the Google Plus post which is referenced, tmux developer Thomas Adam writes that he doesn't recommend doing this. – Abbafei May 27 '15 at 14:53
  • I get the problem that the file handle at /proc/4705/exe is a stale file handle. Can I still use this trick? – Ferrybig Jun 6 '15 at 11:01
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    @PeterV.Mørch The /proc/$pid/exe files aren't regular symlinks; you should be able to use them to invoke the relevant programs even if they've been unlinked. – Blacklight Shining Nov 30 '15 at 4:04
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    pgrep -o tmux gives the (single) pid of the oldest running tmux, presumably the one with the session you need, so /proc/$(pgrep -o tmux)/exe attach might work better than just running pgrep tmux (which can return multiple pids) – Matt Curtis May 26 '17 at 0:14

This perhaps isn't ideal for you, but I created a chroot, and ran tmux from inside it:

sudo -i
debootstrap stable /chroot
mount -o bind /dev /chroot/dev
mount -o bind /dev/pts /chroot/dev/pts
mount -o bind /sys /chroot/sys
mount -o bind /proc /chroot/proc
chroot /chroot
apt-get install tmux ssh
ssh user@localhost
apt-get bla bla bla

This ensures that the tmux environment doesn't change during the upgrade

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kill all tmux process should work as I also encountered this problem.

sudo killall -9 tmux
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Alternatively, you can pass the -L argument to tmux and have it create a new server group (if you don't want to exit your existing sessions -- I ran into this situation while testing a containerized Ubuntu 18.04 on top of my existing Amazon Linux dev box.)

$ tmux    
protocol version mismatch (client 8, server 7)
$ tmux -L /tmp

[in tmux session, then exit out]

[detached (from session 1)]

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