Why does starting `tmux` on sway launch over `swaymsg` does make tmux inaccesible?

Question

I want to start tmux server on sway startup. Therefore I created in sway.conf the following:

exec ~/.config/sway/scripts/start-up.sh

in which script I start tmux as such:

#!/usr/bin/env bash
# shellcheck disable=SC1091,SC2034
# set -e
# set -u

LOG=~/.sway-startup.log

# Save stdout and stderr to file
exec 3>&1 4>&2 >"$LOG" 2>&1

# Start tmux and make terminal on workspace 1.
echo "Start tmux, let it recreate the workspaces with resurrect"
tmux start-server
echo "Server started."
sleep 3

tmux list-sessions || {
    echo "ERROR: The exit-empty is not set to off, so the server directly exits!" >&2
}

# Create one session if not yet existing, detach from it.
tmux new-session -D -s Main-1

echo "Sessions are:"
tmux list-sessions || {
    echo "ERROR: Sessions should now be available restored from tmux-ressurect???!" >&2
}
echo "-----------"

echo "Finished"

In the tmux.conf I have set exit-empty false such that tmux does not quit if no session on `tmux start-server (weird behavior...).

I am really unsure if I need to block the script start-up.sh from exiting or not, because the log ~/.sway-startup.log from launching the script with swaymsg exec .../start-up.sh reports the following:

Start tmux, let it recreate the workspaces with resurrect
Server started.
Astrovim: 1 windows (created Sat Nov 25 21:40:20 2023)
Main-1: 1 windows (created Sat Nov 25 21:40:20 2023)
Main-2: 1 windows (created Sat Nov 25 21:40:20 2023)
NixOS: 1 windows (created Sat Nov 25 21:40:20 2023)
duplicate session: Main-1 ### <<<<<<<<<<<<<<<- thats because resurrect created the above sessions automatically. 
Sessions are:
Astrovim: 1 windows (created Sat Nov 25 21:40:20 2023)
Main-1: 1 windows (created Sat Nov 25 21:40:20 2023)
Main-2: 1 windows (created Sat Nov 25 21:40:20 2023)
NixOS: 1 windows (created Sat Nov 25 21:40:20 2023)
-----------
Finished

After that when I tmux a it reports there are no sessions. This is so weird, the server runs as I can see in btop (running under my user name) but also using tmux -S /run/user/1000/tmux-1000 a pointing to the socket does report no sessions?

I am really puzzled and dont know whats going on? How can I resolve this strange issue? Somehow this is permission problem when starting over swaymsg.

Answer 1

In NixOS using homemanager, some env variables are not yet sourced when this start-up.sh script runs. The one missing is TMUX_TMPDIR which is set afterwards.

I needed to write out this variable to be able to source it in the startup script by doing with home-manager:

  # We need this file to source in `~/.config/sway/scripts/start-up.sh`
  # to be able to properly start tmux because these variables are not
  # yet sourced.
  xdg.configFile."tmux/.tmux-env".text = ''
    TMUX_TMPDIR="${config.home.sessionVariables.TMUX_TMPDIR}"
  '';

So when sway started it wrote the default socket to /tmp/$USER-1000/default etc. which was not the directory which tmux was looking for after the sessionVariables were set.