Explanation: Signalling Processes
Now that we know how to monitor processes with ps, pstree, and top; it may become necessary to stop a rogue process from running. To do so, we send signals to the process.
This post is an overview of the available signals, and subsequent posts will contain more detail about each one. There’s a numeric value next to each signal. I’ll talk about those values in the detailed posts coming up.
HUP 1
“Hang Up”. Left over from the modem days, today this signal will cause most daemons to reload their configuration file. Useful when you’ve made a change to your Apache config and want to load the new config without bringing the server down, for example.
INT 2
“Interrupt”. Just plain old stop running. This is the signal that is sent when you hit Control-C
KILL 9
“Die, you bastard, die!”. Yup – this kills the process dead. Not graceful, but very effective.
TERM 15
“Terminate”. But nicely if at all possible. Much more graceful than the kill signal
TSTP 18
“Stop, but be ready to continue”. This is the same signal that is sent when you press Control-Z
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