Linux updater

A single POSIX shell script (needs only curl) run every 2 minutes by a systemd timer, or by cron on systems without systemd. It is not a management agent: it does DDNS and nothing else.

Install

curl -fsSL https://docs.justasrv.com/downloads/install-linux.sh -o install-linux.sh
sudo sh install-linux.sh acme-main.ddns.justasrv.com

The installer asks for the token without echoing it. For unattended installs set JUSTASRV_TOKEN in the environment instead.

What it installs

How it behaves

• Each run asks https://ddns.justasrv.com/ip for the public address (one small request).
• It sends an update only when the address changed, or every 10 minutes as a heartbeat. Heartbeats are answered nochg and cause no DNS write.
• After a failure it backs off exponentially (1, 2, 4… minutes up to an hour, plus jitter); rejected tokens back off 30 minutes. It recovers by itself when the network returns.
• The token is passed to curl on stdin, never on a command line, so it does not appear in ps.
• The config is re-read every run: after rotating a token, edit TOKEN= in the config file and the next run uses it.

Operate

journalctl -t justasrv -n 20            # log
sudo /usr/local/bin/justasrv-update     # run now
systemctl list-timers justasrv-update.timer
sudo sh install-linux.sh --uninstall

Download