Setup a secure (SSH) tunnel as a systemd service. #systemd #ssh #ssh-tunnel #ssh-forward

README

Create a template service file at /etc/systemd/system/[email protected]. The template parameter will correspond to the name of target host: (If you want a reverse tunnel change the -L to -R and name the file .../[email protected])

[Unit]
Description=Setup a secure tunnel to %I
After=network.target

[Service]
Environment="LOCAL_ADDR=localhost"
Environment="TARGET_PORT=22"
EnvironmentFile=/etc/default/secure-tunnel@%i
ExecStart=/usr/bin/ssh -p ${TARGET_PORT} -NT -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -L ${LOCAL_ADDR}:${LOCAL_PORT}:localhost:${REMOTE_PORT} ${TARGET}
User=${LOCAL_USER}
Group=${LOCAL_GROUP}

# Restart every >2 seconds to avoid StartLimitInterval failure
RestartSec=5
Restart=always

[Install]
WantedBy=multi-user.target

We need a configuration file (inside /etc/default) for each target host we will be creating tunnels for. For example, let's assume we want to tunnel to a host named jupiter (probably aliased in /etc/hosts). Create the file at /etc/default/secure-tunnel@jupiter:

TARGET=jupiter
TARGET_PORT=22
LOCAL_USER=exampleUser
LOCAL_GROUP=exampleGroup
LOCAL_ADDR=0.0.0.0
LOCAL_PORT=20022
REMOTE_PORT=22

Note that for the above to work we need to have allready setup a password-less SSH login to target (e.g. by giving access to a non-protected private key).

Now we can start the service instance:

systemctl start [email protected]
systemctl status [email protected]

Or enable it, so it get's started at boot time:

systemctl enable [email protected]

ranomier/README-setup-tunnel-as-systemd-service.md

README