I cannot figure out what the difference is between
kill -9 <pid>
kill -INT <pid>
can anyone explain it to me like I am 3 years old?
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kill -INT $pid sends the "interrupt" signal to the process with process ID
pid. However, the process may decide to ignore the signal, or catch the signal and do something before exiting and/or ignore it.
kill -9 $pid sends the "kill" signal which cannot be caught or ignored. The process will be forcibly shut down with no notification to the process, and no chance to do any cleanup what so ever.
kill -9 $pid should almost never be recommended or used, though sometimes it's necessary.
kill -INT $pid is the same as
kill -2 $pid.
kill -9 $pid is the same as
kill -KILL $pid
There are many versions of the
kill command. Most shells (ksh, bash, dash, etc) have built-in
kill commands, and there's also one in
/bin/kill. They are all slightly different but most of them support the above examples.
Most kill commands have a
-L option to list the signals:
$ /bin/kill -L 1 HUP 2 INT 3 QUIT 4 ILL 5 TRAP 6 ABRT 7 BUS 8 FPE 9 KILL 10 USR1 11 SEGV 12 USR2 13 PIPE 14 ALRM 15 TERM 16 STKFLT 17 CHLD 18 CONT 19 STOP 20 TSTP 21 TTIN 22 TTOU 23 URG 24 XCPU 25 XFSZ 26 VTALRM 27 PROF 28 WINCH 29 POLL 30 PWR 31 SYS $
A good place to read about signals is the "signal" man page in section 7 of the manual:
man 7 signal.