What is 'kill -15' ?

thomas2004ch · 07-03-2013, 01:27 AM

Till now I konw kill -9. But how is 'kill -15'?

chrism01 · 07-03-2013, 01:34 AM

Code:

kill -l
 1) SIGHUP	 2) SIGINT	 3) SIGQUIT	 4) SIGILL	 5) SIGTRAP
 6) SIGABRT	 7) SIGBUS	 8) SIGFPE	 9) SIGKILL	10) SIGUSR1
11) SIGSEGV	12) SIGUSR2	13) SIGPIPE	14) SIGALRM	15) SIGTERM
16) SIGSTKFLT	17) SIGCHLD	18) SIGCONT	19) SIGSTOP	20) SIGTSTP
21) SIGTTIN	22) SIGTTOU	23) SIGURG	24) SIGXCPU	25) SIGXFSZ
26) SIGVTALRM	27) SIGPROF	28) SIGWINCH	29) SIGIO	30) SIGPWR
31) SIGSYS	34) SIGRTMIN	35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
63) SIGRTMAX-1	64) SIGRTMAX

http://linux.die.net/man/1/kill

David the H. · 07-03-2013, 04:06 PM

The problem is though that that just lists the names. It doesn't actually explain anything about what they do. And frankly I don't quite know the answer either. I've never found anything that definitively explains what all those listed signals are supposed to do.

I do know that SIGKILL is considered the sledgehammer of process destruction, immediately terminating it without any cleanup whatsoever. It can trash filesystems, corrupt files, and do other damage, so most net advice says to never* use it.

SIGTERM, OTOH, is a much more gentle signal that gives the process a chance to clean up and terminate properly. It's the one you generally should be using first when trying to stop a misbehaving process.

*In my experience though, I can't see how that's really possible. When you have a process that isn't responding to anything, and you have to stop it somehow, what else is there to use?

chrism01 · 07-03-2013, 09:06 PM

Yeah, you have to google around a bit to find them.
This explains the most commonly used ones http://linuxandfriends.com/linux-signals/ and the signal man page goes into a few.
Some programming sites provide a bit of detail eg http://www.comptechdoc.org/os/linux/...pgsignals.html

Ser Olmy · 07-03-2013, 09:24 PM

Quote:

Originally Posted by David the H.

I do know that SIGKILL is considered the sledgehammer of process destruction, immediately terminating it without any cleanup whatsoever. It can trash filesystems, corrupt files, and do other damage, so most net advice says to never* use it.

In short, there are two types of signals. One type is the non-catchable signal like SIGKILL and SIGSTOP; the other type, catchable, covers the rest.

When a process receives a signal, the signal handler (if one exists within the process) is invoked. The process can choose to do something in response to the signal, or it can just ignore it. The various signal types indicate what a process is supposed to do when it receives a certain signal, but whether a given process actually follows these guidelines is quite another matter.

SIGKILL and SIGSTOP are handled by the OS (I believe they are the only ones, but I could be wrong) and cannot be "caught" by a signal handler. SIGKILL terminates the process and frees any memory it was using, while SIGSTOP stops/pauses the process until a SIGCONT is sent.