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Linux: How to create an SSH tunnel as a systemd service

Much often you will need a constant SSH tunnel connection, to avoid the administrative load for those tunnels after a reboot is to configure them as systemd services and use SSH keys to avoid passwords.

Also its nice and super helpfull to create the systemd service as a template that can accept tunnel parameters from a file, this allow very easily to manage your tunnels (add,delete,modify,start,stop).

This configuration requires ssh keys in order to communicate with the SSH Gateway

Create the following template file

/etc/systemd/system/secure-tunnel@.service

Content:

[Unit]
Description=Setup a secure tunnel to %I
After=network.target
[Service]
Environment="LOCAL_ADDR=localhost"
EnvironmentFile=/etc/default/secure-tunnel@%i
ExecStart=/usr/bin/ssh -NT -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -L ${LOCAL_ADDR}:${LOCAL_PORT}:${REMOTE_HOST}:${REMOTE_PORT} ${TUSER}@${TARGET}
# Restart every >2 seconds to avoid StartLimitInterval failure
RestartSec=5
Restart=always
[Install]
WantedBy=multi-user.target

Explanation of the file variables

• ${LOCAL_ADDR} ← The local ip to bind the tunnel