mosh + tmux helper to kill disconnected leftover sessions from the same machine

moshshell.sh

#!/bin/sh
host="$1"
[ -z "$host" ] && host=homeshell
port="$2"
[ -z "$port" ] && port=60001
slave="$3"
[ -z "$slave" ] && slave=`hostname -s` # use a fixed string if needed
main=$4
[ -z "$main" ] && main=0

session="${main}_${slave}"
server="env MOSH_SERVER_SIGNAL_TMOUT=20 mosh-server"

attempted_detach=0
while true; do
    if mosh --server="$server" -P "$port" "$host" -- bin/tmx prefix '^b' "$main" "$slave"; then
        exit 0
    elif [ $attempted_detach = 1 ]; then
        exit 1
    fi
    # Try to detach the existing client from holding up our port
    # (it will not detach if it is still live due to -P and
    # MOSH_SERVER_SIGNAL_TMOUT)

    echo "Attempting to detach session $session..." >&2
    ssh "$host" -- tmux lsc -F '\#{client_pid}' -t "$session" \| \
                   xargs ps -o ppid= \| xargs kill -SIGUSR1 >&2
    attempted_detach=1
done

(And yes, of course you could just unconditionally send SIGUSR1 to every mosh-server to kill all the idle ones, but that's not wanted here, since they may be legitimate sessions from other devices that are sleeping at the moment. And at the same time, I want to keep the idle threshold very short, i.e., shorter than the time it takes to reboot.)