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@thomasfr
Last active January 5, 2024 08:11
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Systemd service for autossh
[Unit]
Description=Keeps a tunnel to 'remote.example.com' open
After=network.target
[Service]
User=autossh
# -p [PORT]
# -l [user]
# -M 0 --> no monitoring
# -N Just open the connection and do nothing (not interactive)
# LOCALPORT:IP_ON_EXAMPLE_COM:PORT_ON_EXAMPLE_COM
ExecStart=/usr/bin/autossh -M 0 -N -q -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -p 22 -l autossh remote.example.com -L 7474:127.0.0.1:7474 -i /home/autossh/.ssh/id_rsa
[Install]
WantedBy=multi-user.target
@Iiridayn
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@jotakar I've been using:

[Unit]
Description=Keep open a reverse tunnel to my computer via the DMZ server
After=network.target

[Service]
ExecStart=/usr/bin/ssh -NT tunnel
RestartSec=5
Restart=always

[Install]
WantedBy=multi-user.target

With tunnel defined in /root/.ssh/config as

Host                    tunnel
HostName                <redacted>
User                    <redacted>
IdentityFile    ~/.ssh/id_tunnel
ProxyCommand    ssh bastion -W %h:%p
RemoteForward   <redacted port> localhost:22
ExitOnForwardFailure yes
ServerAliveCountMax 5

And the bastion host also defined in the same file as

Host           bastion
HostName       <redacted>
User           <redacted>
IdentityFile   ~/.ssh/id_tunnel
ForwardAgent yes

I also have

Host *
ServerAliveInterval 60
IdentitiesOnly yes

at the top of my /root/.ssh/config, on the off-chance that's relevant.

I've found this to be very consistent and stable, and easy to test (ssh bastion, ssh -NT tunnel) when setting it up. Perhaps removing autossh and setting it up this way might help?

@mikkorantalainen
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mikkorantalainen commented Mar 22, 2023

For completeness, you should also add:

ExecStop=kill -9 autossh

Without it systemctl stop autossh won't do anything.

I think it would be better idea to add

KillMode=control-group

to the .service file because that will kill everything that was started (recursively) and nothing more. In addition, it will first send SIGTERM and use SIGKILL only if the process will not stop nicely.

If you randomly kill one or all autossh processes in the system, you might kill more than expected if autossh is used for other stuff, too.

See https://www.freedesktop.org/software/systemd/man/systemd.kill.html#KillMode= for details

@MestreLion
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MestreLion commented Jun 16, 2023

@jotakar :

What I see is that service stop autossh every few minutes, why? where is the error?

Don't use -f when using autossh as a systemd simple service. It will fork autossh (put in the background) and confuse systemd into thinking it ended.

@ScumCoder

Of course you do, without it autossh will give up if the very first connection attempt fails.

Systemd's Restart=always and RestartSec=60 can take care of that. You usually want autossh to fail fast if it can't do the first connection, as it usually means misconfiguration or authentication issues, and giving up after first attempt helps highlighting that on the journalctl logs.

@stokito
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stokito commented Jul 4, 2023

JFYI: I created an SSH tunnel SystemD service that works without the autossh github.com/yurt-page/sshtunnel

@zhangw
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zhangw commented Dec 31, 2023

@jotakar :

What I see is that service stop autossh every few minutes, why? where is the error?

Don't use -f when using autossh as a systemd simple service. It will fork autossh (put in the background) and confuse systemd into thinking it ended.

@ScumCoder

Of course you do, without it autossh will give up if the very first connection attempt fails.

Systemd's Restart=always and RestartSec=60 can take care of that. You usually want autossh to fail fast if it can't do the first connection, as it usually means misconfiguration or authentication issues, and giving up after first attempt helps highlighting that on the journalctl logs.

Yes, I just remove the '-f' option, it seems fine.

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