When you forcibly killed your Byobu session (which uses Tmux underneath), the Unix domain socket file wasn't properly cleaned up. Tmux uses this socket for inter-process communication, and only one instance can use a specific socket path at a time.

$ ls -la /tmp/tmux-*
srwx------ 1 user user 0 Jan 1 12:34 /tmp/tmux-1000/default

First, identify and remove the stale socket file:

$ tmux ls
can't connect to server: Connection refused
$ lsof /tmp/tmux-*/default
$ rm -f /tmp/tmux-$(id -u)/default

If you need to preserve existing sessions, use a different socket path:

$ tmux -L temp new-session

When basic cleanup fails, completely reset the environment:

$ pkill -9 tmux
$ pkill -9 byobu
$ rm -f /tmp/tmux-*/default

To avoid this in future sessions:

$ byobu-disable
$ byobu-enable

Also consider adding this to your .bash_logout:

# Cleanup tmux sockets on logout
[ -n "$TMUX" ] && tmux detach

In some containerized environments, you might need additional steps:

$ ip netns identify
$ sudo ip netns delete troubled_namespace

---

When you forcefully terminate a Byobu (which uses Tmux as backend) session using kill -9, it doesn't get the chance to properly clean up its Unix domain socket. This socket typically resides in /tmp and follows the pattern tmux-{userid}/default.

The error occurs because:

$ tmux new-session
can't create socket: Permission denied
failed to connect to server

First, verify the status of existing Tmux sessions:

$ ps aux | grep tmux
$ lsof -U | grep tmux

Then check the socket directory permissions:

$ ls -la /tmp/tmux-*
drwx------  2 user user  4096 Jan 31 10:00 tmux-1000

Follow these steps to completely resolve the issue:

1. Remove stale socket files:

$ rm -rf /tmp/tmux-*

2. Kill any remaining tmux processes:

$ pkill -9 tmux
$ pkill -9 byobu

3. Verify no tmux-related processes remain:

$ pgrep -l tmux

4. For system-wide installations, you might need to clean up systemd or upstart sessions:

$ sudo systemctl restart tmux
$ sudo service tmux restart

To avoid this issue in the future:

• Always detach from sessions properly using Ctrl+b d
• When you must kill a session, first try tmux kill-session -t session_name
• Consider adding this alias to your .bashrc:

alias fix-tmux='rm -rf /tmp/tmux-* && pkill -9 tmux'

For power users who frequently encounter this issue, you can configure a custom socket path in ~/.tmux.conf:

set -g base-index 1
set -g default-command "${SHELL}"
set -g default-terminal "screen-256color"
set -g socket-path "~/.tmux_socket"

Then always specify the socket when starting tmux:

tmux -S ~/.tmux_socket new -s mysession