cs.app.svcd 20171118

SvcD class and "svcd" command to run persistent service programmes.

This provides the features one wants from a daemon for arbitrary commands providing a service:

• process id (pid) files for both svcd and the service command

• filesystem visible status (command running, service enabled) via cs.app.flag

• command restart if the command exits

• command control (stop, restart, disable) via cs.app.flag

• test function to monitor for service viability; if the test function fails, do not run the service. This typically monitors something like network routing (suspend service while laptop offline) or a ping (suspend ssh tunnel while target does not answer pings).

• signature function to monitor for service restart; if the signature changes, restart the service. This typically monitors something like file contents (restart service on configuration change) or network routing (restart ssh tunnel on network change)

• callbacks for service command start and end, for example to display desktop notifications

I use this to run persistent ssh port forwards and a small collection of other personal services. I have convenient shell commands to look up service status and to start/stop/restart services.

See cs.app.portfwd which I use to manage my ssh tunnels; it is a single Python programme running multiple ssh commands, each via its own SvcD instance.