Reverse SSH tunnel as a systemd service

autossh.sh

#!/bin/bash
echo 'Starting reverse SSH tunnel'
/usr/bin/autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -o "ExitOnForwardFailure=yes" -tt -R \*:2222:localhost:22 user@your.server

phone-home.service

[Unit]
Description=Phone home using SSH
ConditionPathExists=|/usr/bin
After=network.target

[Service]
User=user
ExecStart=/home/user/bin/autossh.sh
RestartSec=3
Restart=always

[Install]
WantedBy=multi-user.target

Also requires you to:

• Add "GatewayPorts yes" to /etc/ssh/sshd_config in your server
• Add your local SSH public key to ~/.ssh/authorized_keys in your server
• Install autossh
• Install your systemd unit

chmod +x /home/user/bin/autossh.sh
cp phone-home.service /etc/systemd/system/phone-home.service
systemctl daemon-reload
systemctl enable phone-home.service
systemctl start phone-home.service