cs.app.svcd 20190729

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

Release 20190729: Get DEVNULL via cs.py3 instead of directly from subprocess.

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

#Release Log#

Release 20190729: Get DEVNULL via cs.py3 instead of directly from subprocess.

Release 20190602.2: Another doc tweak.

Release 20190602.1: Improve module documentation formatting.

Release 20190602: Support alert groups. Catch and report exceptions from the monitor signature function. Python 2 port fix for DEVNULL.

Release 20171118: Bugfix for su invocation in setuid mode. Improved signature command tracing with -x option.

Release 20171026: Improved logic around signature changes.

Release 20171025: New "-F flag,..." option for svcd. Improve stop logic. Other small fixes.

Release 20170906: Initial PyPI release.