Code
[Unit]
Description=ngroc service
After=network-online.target nss-lookup.target time-sync.target
Wants=network-online.target nss-lookup.target time-sync.target
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/path/to/ngrok tcp 22
[Install]
WantedBy=multi-user.target
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^ something like that in /storage/.config/system.d/ngrok.service
Then "systemctl enable /storage/.config/system.d/ngrok.service" and "systemctl start ngrok.service" .. it should then be persistent over restarts and even upgrades (as long as ngrok itself continues to run).