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.

With:

> 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.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/unix
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	FreeBSD
Architecture