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I know I can kill any process with kill -9 command . But sometimes i see that even if I have terminated a program with CTRL+C , the process doesn't get killed . So I want to know the difference between kill -9 vs CTRL+C

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See also What causes various signals to be sent? – Gilles Jan 23 '13 at 22:11
up vote 6 down vote accepted

^C send the interrupt signal, which can be handled by a program (you can ignore it)

kill -9 send the sigkill signal which kills the program that you can't handle.

That's why you can't kill some programs with ^C

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One critical difference is that "well behaved" programs will catch ctrl-C and clean up after themselves (detach from any shared resources, destroy temporary files, reset the terminal to a sane state), SIGKILL doesn't give them that chance. BTW, it can happen that a program is stuck in an unkillable state inside the kernel. – vonbrand Jan 23 '13 at 12:38
@l0b0: ^C sends SIGINT. kill (without -9) sends SIGTERM. Both those work the same, and can be handled by the program, but they're independent signals. – ams Jan 23 '13 at 13:00
If ^C doesn't work then you should try kill next, and then only kill -9 if you have to. The difference is that kill on it's own gives the program chance to clean up its files and whatnot. kill -9 just removes it without asking nicely. – ams Jan 23 '13 at 13:03
Aka. SIGINT (thanks @ams) and SIGKILL – l0b0 Jan 23 '13 at 13:56

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