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

Project description

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 <https://pypi.org/project/cs.app.flag/>_
  • command restart if the command exits
  • command control (stop, restart, disable) via cs.app.flag <https://pypi.org/project/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 <https://pypi.org/project/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.

Function main(argv=None)

Command line main programme.

Class SvcD

MRO: cs.app.flag.FlaggedMixin
A process based service.

Method SvcD.__init__(self, argv, name=None, environ=None, flags=None, group_name=None, pidfile=None, sig_func=None, test_flags=None, test_func=None, test_rate=None, restart_delay=None, once=False, quiet=False, trace=False, on_spawn=None, on_reap=None)

Initialise the SvcD.

Parameters:

  • argv: command to run as a subprocess.
  • flags: a cs.app.flag.Flags -like object, default None; if None the default flags will be used.
  • group_name: alert group name, default "SVCD " + name.
  • pidfile: path to pid file, default $VARRUN/{name}.pid.
  • sig_func: signature function to compute a string which causes a restart if it changes
  • test_flags: map of {flagname: truthiness} which should be monitored at test time; truthy flags must be true and untruthy flags must be false
  • test_func: test function with must return true if the comannd can run
  • test_rate: frequency of tests, default TEST_RATE
  • restart_delay: delay before start of an exiting command, default RESTART_DELAY
  • once: if true, run the command only once
  • quiet: if true, do not issue alerts
  • trace: trace actions, default False
  • on_spawn: to be called after a new subprocess is spawned
  • on_reap: to be called after a subprocess is reaped

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