kill -9 and production application

Question

Which problem can cause kill -9 in production application (in linux to be exact)?

I have application which do some periodical work, stopping these takes long time, and I don't care if some jobs will be aborted - work can be finished by new processes. So can I use kill -9 just to stop it immediately or this can cause serious OS problems?

For example, Unicorn, uses it as normal working procedure:

When your application goes awry, a BOFH can just "kill -9" the runaway worker process without worrying about tearing all clients down, just one.

But this article claims:

The -9 (or KILL) argument to kill(1) should never be used on Unix systems

PS: I understand that kill -9 cannot be handled by application, but I know that for may application it doesnt cause any problems, I just intrested can it cause some problems on OS level? shared memory segments active, lingering sockets sounds dangerous to me.

Answer 1

kill -9 doesn't give an application a chance to shut down cleanly.

Normally an application can catch a SIGINT/SIGTERM and shut down cleanly (close files, save data etc.). An application can't catch a SIGKILL (which occurs with a kill -9) and so it can't do any of this (optional) cleanup.

A better approach is to use a standard kill, and if the application remains unresponsive, then use kill -9.

Answer 2

kill -9 won't cause any "serious OS problems". But the process will stop immediately, which means it might leave data in an odd state.