Shell signal values

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  • You must know signal and their values while writing the shell scripts.
  • You cannot use (trap) all available signals.
  • Some signals can never be caught. For example, the signals SIGKILL (9) and SIGSTOP (19) cannot be caught, blocked, or ignored.
  • The following table is a list of the commonly used signal numbers, description and whether they can be trapped or not:
Number Constant Description Default action Trappable (Yes/No)
0 0 Success Terminate the process. Yes
1 SIGHUP Hangup detected on controlling terminal or death of controlling process. Also, used to reload configuration files for many UNIX / Linux daemons. Terminate the process. Yes
2 SIGINT Interrupt from keyboard (Ctrl+C) Terminate the process. Yes
3 SIGQUIT Quit from keyboard (Ctrl-\. or, Ctrl-4 or, on the virtual console, the SysRq key) Terminate the process and dump core. Yes
4 SIGILL Terminate the process and dump core. Illegal instruction. Yes
6 SIGABRT Abort signal from abort(3) - software generated. Terminate the process and dump core. Yes
8 SIGFPE Floating point exception. Terminate the process and dump core. Yes
9 SIGKILL Kill signal Terminate the process. No
15 SIGTERM Termination signal Terminate the process. Yes
20 SIGSTP Stop typed at tty (CTRL+z) Stop the process. Yes

To view list of all signals, enter:

kill -l

To view numeric number for given signal called SIGTSTP, enter:

kill -l SIGTSTP

You can also view list of signal by visiting /usr/include/linux/signal.h file:

more /usr/include/linux/signal.h
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