Supervise critical services

If any of the core services (e.g. Tor) crashes, a clueless user will have to reboot after realising that "Internet won’t come back". That can be quite frustrating.

Supervising these services would be nice.

Given we’ll move to an init system (#5821 (closed)) that knows how to baby-sit services once Tails is based on Jessie, we can use it and find / adapt / write systemd unit files for the services we want to supervise.

Most of the work should be done in Debian and upstream first.

Related issues

• Related to #10528 (closed)
• Blocked by #5821 (closed)

Original created by @tails on 5750 (Redmine)