Bash interactive shell hangs when Tmux is suspended if it was automatically started by Bash startup file

bashjob-controltmux

When I manually start Tmux by issuing tmux from my Bash interactive shell I can later suspend Tmux with CTRL-BZ without problems. Pressing this key combination brings me back to the parent process, i.e. the Bash interactive shell from which I started Tmux.

But I've got the following code snippet at the very end of my configuration file for Bash interactive shells (~/.bashrc) defined:

# Test if neither _Tmux_ nor _Screen_ is running.
if ! [[ -n "$TMUX" || "$TERM" =~ screen ]]; then
  # Test if _Tmux_ is on the `$PATH`.
  if type -p tmux &> /dev/null; then
    # Try to attach to latest unattached session or start a new one.
    { tmux attach-session || tmux new-session; } &> /dev/null
  fi
fi

This code snippet automatically starts Tmux whenever I start a Bash interactive shell given that there no terminal multiplexer program running yet.

But pressing CTRL-BZ this time around suspends Tmux leaving me in an unresponsive parent process, i.e. the Bash interactive shell that automatically started Tmux from its startup file (~/.bashrc).

Apart from detaching Tmux from and reattaching it to a session, is there a way to make Tmux suspend in such a way that I can continue to work in its parent Bash interactive shell and come back later foregrounding it with fg?

Please note that for various reasons I intend to let Bash fork Tmux and and not replace itself by it (exec).

Best Answer

You should turn job control on with set -m in your .bashrc before starting tmux.

Bash runs startup files like .bashrc with job control disabled. From shell.c:

#if defined (JOB_CONTROL)
  /* Startup files should be run without job control enabled. */
  old_job_control = interactive_shell ? set_job_control (0) : 0;
#endif

Please notice that C-b C-z does not set tmux in the background by itself; absent job control in the upper shell, the SIGTSTP signal tmux sends itself will just cause it to stop; the tmux process will still be in the foreground process group of the terminal (despite the deceptive switching from the alternate screen with the the exit_ca_mode/rmcup/te escape on some terminal emulators like xterm)

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How to Suspend and Resume Processes Like Bash

Shell jobs live in "process groups"; look at the PGRP column in extended ps output. These are used both for job control and to determine who "owns" a terminal (real or pty).

POSIX (taken from System V) uses a negative process ID to indicate a process group, since the process group is identified by the first process in the group ("process group leader"). So you would use ps to determine the process group, then kill -s TSTP "-$pgrp". (Try ps -u"$USER" -opid,ppid,pgrp,cmd.)

In your process tree, the process group starts with the firefox script launched by bash, so the process group would be 27980 and the command would be kill -s TSTP -27980.

Naturally, to resume the process group, issue kill -s CONT -- -27980.

Bash – Why might tmux only be capable of attaching once per shell session

In my Shell's config file (I use zsh, so its in my .zshrc, should work in a .bashrc) I have the following:

# Default to TMUX
if [ -z "$TMUX" ]; then
  base_session=$USER"_session"
  # Create the base session if it doesn't exist
  tmux has-session -t $base_session || tmux new-session -d -s $base_session
  # Get a count of clients connected
  client_cnt=$(tmux list-clients | wc -l)
  if [ $client_cnt -ge 1 ]; then
    # Make a unique session name
    session_name=$base_session"-"$client_cnt
    # Create the new session based on the base_session
    tmux new-session -d -t $base_session -s $session_name
    # Launch the connection with a few caveats (kill the session when the client goes away)
    tmux -2 attach-session -t $session_name \; set-option destroy-unattached
  else
    tmux -2 attach-session -t $base_session
  fi
fi

Now I can connect many times using PuTTY to a single server and see the same session in all windows (and change one connection to display a different window). I would also like to

Edit

I thought this was working once before, then I just learned that I must have still been in screen, so I have fixed this to do separate sessions. I commented, so let me know if you have any questions. Now there is one downside to this, it will choose the smallest size for both windows. That isn't helpful...I am working on finding a fix currently.

Edit 2

In order to fix the resizing issue, add the following line to your .tmux.conf file

set-option -g aggressive-resize on

Best Answer

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