Reverse SSH systemd service

rssh.service

# /etc/systemd/system/rssh.service
[Unit]
Description=Reverse SSH Service
ConditionPathExists=|/usr/bin
After=network.target

[Service]
User=<USERNAME HERE>
ExecStart=/usr/bin/ssh -NTC -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -o StrictHostKeyChecking=no -i /home/<USERNAME>/.ssh/h -R <PORT YOU WANT OPEN ON REMOTE MACHINE>:localhost:<LOCAL SSH PORT> -l <REMOTE USERNAME> -N <REMOTE HOST> -p <REMOTE LISTENING PORT>

# Restart every >2 seconds to avoid StartLimitInterval failure
RestartSec=3
Restart=always

[Install]
WantedBy=multi-user.target