SIGTERM ignored when process has been detached from terminal
I've tried to write a simple Unix daemon that reacts to signals. Here is the reduced source code sample:
import Control.Concurrent import Control.Monad import System.Exit import System.IO import System.Posix.Signals loop = forever $ threadDelay 1000000 main = do ppid <- myThreadId mapM (\sig -> installHandler sig (Catch $ trap ppid) Nothing) [ lostConnection, keyboardSignal, softwareTermination, openEndedPipe ] loop trap tid = do hPutStrLn stderr "Signal received.\n" throwTo tid ExitSuccess
Such daemons usually run in background without a terminal attached. I verified that I can kill the process after being started on the terminal:
> ./daemon Signal received.
> killall daemon
in other terminal.
Other test, when I run it in background:
> ./daemon (press Ctrl+Z) > bg > killall daemon Signal received.
This case is also ok. Now the third test which is also OK:
> ./daemon > log 2>&1 (press Ctrl+Z) > bg > exit
In second terminal:
> cat log > killall daemon > cat log Signal received. > killall daemon No matching processes belonging to you were found
Now the fourth test which is simply without a log file and this one fails:
> ./daemon (press Ctrl+Z) > bg > exit
On some other terminal try to kill the process:
> killall xxx > killall xxx > killall xxx > killall -9 xxx > killall xxx No matching processes belonging to you were found
Signal 9 (SIGKILL) kills the process hard without the signal trap. That's why it works, of course, but SIGTERM is being ignored for some reason. Maybe I am forgetting something, but in my opinion this should end the process properly, too.
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