Trouble setting up persistent SSH tunnel via Systemd

Coopdis

5/9/24, 10:29 PM

I'm trying to get a persistent SSH tunnel running on Ubuntu 22.04.

My command works fine from the command line, but fails when run via a systemctl service?

Here is my (redacted) rtunnel.service...

[Unit]
Description=Remote ssh tunnel
Wants=network-online.target
After=network-online.target 

[Service]
User=<username>
Group=<username>
Type=simple
ExecStart=/usr/bin/ssh -gnNT -o ExitOnForwardFailure=yes -o ServerAliveInterval=30 -o PasswordAuthentication=no -o PubkeyAuthentication=yes -i /home/<username>/.ssh/id_rsa -R <remote_port>:localhost:<local_port> username@<remotehost>
RestartSec=5
Restart=always

[Install]
WantedBy = multi-user.target

This fails with the following error from journalctl |grep ssh

 <username>@<remotehost>: Permission denied (publickey,keyboard-interactive).

If I just run the command from my command line as like so...

/usr/bin/ssh -gnNT -o ExitOnForwardFailure=yes -o ServerAliveInterval=30 -o PasswordAuthentication=no -o PubkeyAuthentication=yes -i /home/<username>/.ssh/id_rsa -R <remote_port>:localhost:<local_port> username@<remotehost>

everything works great!?

If I run the command in sudo or as root, like so...

sudo /usr/bin/ssh -gnNT -o ExitOnForwardFailure=yes -o ServerAliveInterval=30 -o PasswordAuthentication=no -o PubkeyAuthentication=yes -i /home/<username>/.ssh/id_rsa -R <remote_port>:localhost:<local_port> username@<remotehost>

I get a prompted for a password (<username@remotehost>) Password: despite the fact that both the username and the private key ought to be set within the command itself.

Thanks you for you help!

Bill

147

1 + 1

ssh

tunnel

systemd

steeldriver

5/10/24, 9:02 AM

Does `/home/<username>/.ssh/id_rsa` have an empty passphrase, or are you not being asked to supply a passphrase because the key is cached by an ssh-agent in your user session?

Score:0

Ubuntu

Coopdis

5/16/24, 4:48 PM

Thanks for your reply steeldriver.

I figured out what was going on.

I was ssh'ing into the computer I was trying to set the tunnel up on. The computer I was ssh'ing from had a valid key. That key was getting forwarded so that I was able to run the command from the command line (via ssh) successfully, but when I tried to run the command via systemd (not through my ssh session) there was no valid key available locally.

Thanks for your help.

+ 0

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