The kill builtin command¶
Synopsis¶
kill [-s SIGNAL | -n SIGNALNUMBER | -SIGNAL] PID|JOB
kill -l|-L [SIGNAL...]
Description¶
The kill command is used to send signals to processes specified by their PID or their JOB-specification.
The signal(s) to be specified can have the following formats:
- Numerical: The signal is specified using its constant numeric value. Be aware that not all systems have identical numbers for the signals.
- Symbolic (long): The signal is specified using the same name that is used for the constant/macro in the C API (
SIG<name>) - Symbolic (short): The signal is specified using the name from the C API without the
SIG-prefix (<name>)
Without any specified signal, the command sends the SIGTERM-signal.
The kill command is a Bash builtin command instead of relying on the external kill command of the operating system to
- be able to use shell job specifications instead of Unix process IDs
- be able to send signals ("kill something") also, when your process limit is reached
Options¶
| Option | Description |
|---|---|
-s SIGNAL | specifies the signal to send |
-n SIGNALNUMBER | specifies the signal to send |
-SIGNAL | specifies the signal to send |
-l [SIGNAL...] | Lists supported/known signal numbers and their symbolic name. If SIGNAL is given, only list this signal, translated (if a number is given the symbolic name is printed, and vice versa) |
-L [SIGNAL...] | Same as -l [SIGNAL] (compatiblity option) |
Return status¶
| Status | Reason |
|---|---|
| 0 | no error/success |
| !=0 | invalid option |
| !=0 | invalid signal specification |
| !=0 | error returned by the system function (e.g. insufficient permissions to send to a specific process) |
Examples¶
List supported signals¶
kill -l
Send KILL to a process ID¶
kill -9 12345
kill -KILL 12345
kill -SIGKILL 12345
Portability considerations¶
- POSIX(R) and ISO C only standardize symbolic signal names (no numbers) and a default action