Add support for signal "observers" #207
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- Add an optional third parameter to -r/--rewrite (-r s:r[:observer]) that specifies a script/executable that should be called when signal s is received (whether or not it is forwarded). - The observer may be specified as a full path or PATH will be searched. - The observer is called without any arguments, but the signal and replacement are provided by the DUMB_INIT_SIGNUM and DUMB_INIT_REPLACEMENT_SIGNUM environment variables, respectively. - The intention is that the observer has no impact on dumb-init or the child process(es), for example if it exits with failure. It is simply an observer.
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-r/--rewrite(-r s:r[:observer]) that specifies a script/executable that should be called when signal s is received (whether or not it is forwarded).PATHwill be searched.DUMB_INIT_SIGNUMandDUMB_INIT_REPLACEMENT_SIGNUMenvironment variables, respectively.I desperately need this for a Nomad environment. When template files get automatically updated by service discovery or key-value changes, the only notification options are to restart the app/container (not good for this case) or signals; however, the process I am using does not have special signal-handling I need. So, I want to intercept the signal and execute a custom script ("observer").
Note: I am no expert with signal handling or fork+exec, so feel free to fix (and teach me)! The same goes for the tests I added which are very much a cut+paste job. :-)