On Tue, Feb 5, 2019, 2:20 AM Laurent Bercot wrote: > >Be careful, though. If the service is down, kill will use -1 for the PID, > >and will probably signal everything in your system except PID 1. > > That's a good point. Should s6-svstat use 0 as the "service is down" > pid value instead, to avoid this ? > 0 behaves better for this use case, but can still produce unexpected behavior. The construction "echo 0 | xargs kill -STOP" for example leaves behind a paused background task that needs to be cleaned by hand. The construction "kill -STOP $(echo 0)" hangs the terminal until someone resumes the user's shell. Most other "kill -whatever $(echo 0)" results in the shell exiting and the user having to log back in. So, 0 is a lot better than -1, but still not great. Not outputting anything causes kill (on my system at least) to exit non 0 and give some diagnostic ("`' not a pid or valid pid spec", "you need to specify whom to kill", or the usage message). That's nice, but would probably break other scripting that expects a value, especially for s6-svstat showing multiple fields. I can't think of a safe and simple way to do this. For example, we could suggest people do something like this (based on Roger Pate's post): pid=$(s6-svstat -p /my/service) && [ "$pid" -ne -1 ] && kill -SIGNAL $pid but that's a lot of typing and requires that people see and remember the suggestion, so not quite simple :-/ -- John O'Meara >