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Asked: 2021-03-28 06:30:02 +0800 CST

systemd service produces Exec format error

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I have created the following systemd service to automatically keep an autossh tunnel open between two servers:

#Systemd unit file for autossh
[Unit]
Description=Autossh Tunnel

[Service]
Type=forking

ExecStart=/usr/bin/autossh -M 20009 -f -N -L 3307:127.0.0.1:3306 remoteServer
ExecStop=pkill autossh

User=ubuntu
Group=ubuntu
UMask=0007
RestartSec=1
Restart=always

[Install]
WantedBy=multi-user.target

The file is loacted in /etc/systemd/system/autossh-tunnel.service

When I run it I get the following error message:

ubuntu@verifier:~/.ssh$ sudo systemctl daemon-reload
ubuntu@verifier:~/.ssh$ sudo service autossh-tunnel start
Failed to start autossh-tunnel.service: Unit autossh-tunnel.service is not loaded properly: Exec format error.
See system logs and 'systemctl status autossh-tunnel.service' for details.
ubuntu@verifier:~/.ssh$ systemctl status autossh-tunnel.service
● autossh-tunnel.service - Autossh Tunnel
   Loaded: error (Reason: Exec format error)
   Active: inactive (dead)

which autossh yields:

ubuntu@verifier:~/.ssh$ which autossh
/usr/bin/autossh

I have also tried to run the exact same command /usr/bin/autossh -M 20009 -f -N -L 3307:127.0.0.1:3306 remoteServer in the console and I did not have any problems. However, as a systemd service it fails.

What is wrong here? I have another server with the same setup and there this script runs without any issues. So I do not understand what is going on here...

ssh ssh-tunnel systemd-service

1 Answers

  1. Quick answer: Make sure to check the output of /var/log/syslog for detailed error messages.

    Long answer: Okay, I found out what the problem is.

    Shortly after calling sudo service autossh-tunnel start I check the output in sudo tail -n 200 /var/log/syslog and I got the output:

    Mar 27 20:29:01 verifier systemd[1]: /etc/systemd/system/autossh-tunnel.service:9: Executable path is not absolute: pkill autossh
Mar 27 20:29:17 verifier systemd[1]: /etc/systemd/system/autossh-tunnel.service:9: Executable path is not absolute: pkill autossh

    So I changed the service file to call /usr/bin/pkill instead of just pkill.

    That did solve the prolem. Now sudo tail -n 200 /var/log/syslog yields:

    Mar 27 20:29:59 verifier systemd[1]: Starting Autossh Tunnel...
Mar 27 20:29:59 verifier systemd[1]: Started Autossh Tunnel.

    And a ps aux | grep autossh also shows me that it is running.

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