tmux process exists but no server running

Question

Sometimes after I lost connection to the server, I found I cannot connect to exists tmux session again because of no server running on /tmp/tmux-1000/default, but the process exists.

However, I cannot reproduce this problem, I found it may happen after ssh connection idle timeout or close terminator without exit ssh.

See below as detail:

~ $ ps -ef | grep tmux
huchi    1852249       1  0 10:50 ?        00:00:01 tmux new-session -t cpp
huchi    1862727 1852167  0 19:10 pts/0    00:00:00 grep --color=auto tmux
~ $ 
~ $ tmux ls
no server running on /tmp/tmux-1000/default
~ $ 
~ $ tmux start
~ $ 
~ $ tmux ls
no server running on /tmp/tmux-1000/default

My OS is Linux c-001 4.18.0-193.6.3.el8_2.x86_64 #1 SMP Wed Jun 10 11:09:32 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux and here is the tmux conf:

set -g default-terminal "screen-256color"
unbind C-b
set-option -g prefix C-o
bind C-o send-prefix

This really make me madness!

Answer 1

Perhaps something is removing the tmux socket? If you send it the USR1 signal (pkill -USR1 tmux), tmux will try to recreate it. See if you can attach after that.