Introduction
Your original question pertains to how you can get more output from systemd.
Have a look at How to debug systemd unit ExecStart
But let's see if we can not get your service working first.
About systemd
Some issues
- ssh is forking after it has started.
- An ssh tunnel should run in the background
- A systemd process is by default run as type "simple" - which expects that the command in StartExec is the main service (see "1")
- For systemd to know if your service is alive or not a PIDFile is required a lot of the time. GuessMainPID defaults to yes, but might be, and is with regards to ssh, mistaken.
- You kill the tunnel locally - no need to go abroad with a sword
This introduce a lot of complexity which is better handled by a wrapper script.
/etc/systemd/system/ssh-tunnel-foo-de.service
[Unit]
Description=Tunnel For ssh-tunnel-foo-de
After=network-online.target
[Unit]
Description=Tunnel For ssh-tunnel-foo-de
After=network-online.target
[Service]
User=autossh
ExecStart=/home/autossh/bin/ssh-tunnel.sh start
ExecStop=/home/autossh/bin/ssh-tunnel.sh stop
PIDFile=/home/autossh/bin/ssh-tunnel.pid
Restart=always
RestartSec=5s
StartLimitInterval=0
SuccessExitStatus=255
Type=forking
[Install]
WantedBy=multi-user.target
Explanations to systemd
The wrapper script saves the pid to PIDFile. If you change the location you must keep your service file and your wrapper script in sync.
You must set the "Type" to forking so that systemd knows that a fork is happening.
SuccessExitStatus - seems the process dies with 255 - so we handle that so that a stopped service is not listed as "failed" after it is stopped.
Wait until after the network-online.target is started. This means you actually have a network connection, not just a network management stack.
https://www.freedesktop.org/wiki/Software/systemd/NetworkTarget/
https://www.freedesktop.org/software/systemd/man/systemd.unit.html#
A wrapper script:
/home/autossh/bin/ssh-tunnel.sh
Of course you need to decide where you actually want to put this and fix paths accordingly.
#!/bin/bash
MYHOST=tunnel@foo.de
usage () {
echo "usage: $0 {start|stop}"
exit
}
cd $HOME/bin
case $1 in
"start")
/usr/bin/ssh -M -S socket-${MYHOST} -fnNT -o BatchMode=yes -o ExitOnForwardFailure=yes -o ServerAliveInterval=60 -R 1080:localhost:1080 ${MYHOST}
EC=$? ; [ $EC -ne 0 ] && exit $EC
PID=$(/usr/bin/ssh -S socket-${MYHOST} -O check socket-${MYHOST} 2>&1 | awk '/Master running \(pid=/ { sub(/^.+pid=/,"") ; sub(")","") ; print }')
echo $PID > $HOME/bin/ssh-tunnel.pid
;;
"stop")
/usr/bin/ssh -S socket-${MYHOST} -O exit ${MYHOST}
/bin/rm -f $HOME/bin/ssh-tunnel.pid
exit 0
;;
*) usage ;;
esac
Some explanations:
Look up some of the parameters for ssh.
- -M and -S sets up a Master connection and a named Socket to control the master.
- f - go to the background
- n - Prevent reading from stdin (implied by -f)
- N - No remote command
- T - Disable pseudo-tty allocation
The "start" part sets up the tunnel and the "master".
Then it queries the master for the pid of the tunnel and saves this to a pid-file to the benefit of systemd. If run as root you could save to /var/run/*pid.
The "stop" part connects to the master and issues an "exit". Then removes the pid file.
Credits to https://stackoverflow.com/a/15198031/2045924
