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guettli
Asked: 2016-04-15 03:12:08 +0800 CST

reliable systemd service for autossh

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I try to create a reliable systemd service for autossh.

The service works, but if the host-keys changes, the service is in state ok (running).

I want it to be in state "failed" if the tunnel does not work.

Here is my current systemd service file:

# Source is in srv/salt/tunnel/autossh\@.service
# which is a git repo.
# Don't edit /etc/systemd/system/autossh\@.service  
[Unit]
Description=Tunnel For %i
After=network.target

[Service]
User=autossh
# https://serverfault.com/a/563401/90324
ExecStart=/usr/bin/autossh -M 0 -N -o "ExitOnForwardFailure yes" -o "ConnectTimeout=1" -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -R 40443:installserver:40443 -R 8080:installserver:8080 tunnel@%i
Restart=always

[Install]
WantedBy=multi-user.target

Here is the output of systemctl status autossh@foo-work

salt:/srv # systemctl status autossh@foo-work
[email protected] - Tunnel For foo-work
      Loaded: loaded (/etc/systemd/system/[email protected]; enabled)
      Active: active (running) since Wed, 2016-02-10 14:35:01 CET; 2 months and 3 days ago
    Main PID: 17995 (autossh)
      CGroup: name=systemd:/system/[email protected]/foo-work
          └ 17995 /usr/bin/autossh -M 0 -N -o ExitOnForwardFailure yes -o ConnectTimeout=1 -o ServerAliveInterval 60 -o ServerAliveCountMax 3 -R 40443:installserver:40443 -R ...

Apr 14 12:35:43 salt autossh[17995]: Host key verification failed.
Apr 14 12:35:43 salt autossh[17995]: ssh exited with error status 255; restarting ssh
Apr 14 12:45:42 salt autossh[17995]: starting ssh (count 618)
Apr 14 12:45:42 salt autossh[17995]: ssh child pid is 22524
Apr 14 12:45:43 salt autossh[17995]: Host key verification failed.
Apr 14 12:45:43 salt autossh[17995]: ssh exited with error status 255; restarting ssh

My problem is not the changed host-key. That's ok.

I just want the service to tell me the truth: If the tunnel is not working, then I want it to see it.

How can I change the systemd service file to tell me the correct status?

Update: I wrote a second follow-up question: How does systemd decide if a service is ok or not

ssh ssh-tunnel systemd

1 Answers

  1. The problem is not that it is failed, but that it is considering service active, because it will be restarted in next 10 minutes.

    I didn't try that, but it might work. Try to add Type=forking and PIDFile

    [Service]
...
Type=forking
Environment="AUTOSSH_PIDFILE=/path/to/pid"
PIDFile=/path/to/pid

    With simple services, systemd can have problems to track them.

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