kill command in Linux with Examples

Name

kill - send a signal to a process

Synopsis

kill [options] <pid> [...]
kill [-l | --list | -t | --table] [SIGNAL]...

Description

kill command sends a signal to processes, causing them to terminate. It is normally a shell builtin meaning the command is called from a users shell rather than an external executable program. The first form of the kill command sends a signal to all PID arguments. The default signal for kill command is TERM signal (terminate an active process). On specifying a particular SIGNAL (name or number), the process acts upon receiving the signal in a specified way.

Alternatively, kill command can list information about types of available signals. Use -l or -L to list all available signals. Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0. Signals may be specified in three ways: -9, -SIGKILL or -KILL.

Negative PID values may be used to choose whole process groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process itself and init.

Options

<pid> [...]
   Send signal to every <pid> listed.

-<signal>
-s <signal> --signal <signal>
   Specify the signal to be sent. The signal can be specified by using name or number. The behavior of signals is explained in signal(7) manual page.
-l, --list [signal]
   List signal names. This option has optional argument, which will convert signal number to signal name, or other way round.
-L, --table
   List signal names in a nice table.

NOTES: Your shell (command line interpreter) may have a built-in kill command. You may need to run the command described here as /bin/kill to solve the conflict.

Examples

1. Send the default signal, SIGTERM, to all those processes.

$ kill 20539 20549 20559 20720

2. Kill all the processes you can kill.

$ kill -9 -1

3. Translate signal number 11 into a signal name.

$ kill -l 11
SEGV

$ kill -l 6
ABRT

4. To view signal names and numbers pass the -l option to the kill command.

$ kill -l
1) SIGHUP        2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP
6) SIGABRT       7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1
11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
16) SIGSTKFLT	17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
26) SIGVTALRM	27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
63) SIGRTMAX-1	64) SIGRTMAX

5. There is a special signal number ‘0’. It does not denote a valid signal, but it can be used to test whether the PID arguments specify valid processes to which a signal could be sent.

$ ps
PID TTY          TIME CMD
11571 pts/20   00:00:00 bash
22166 pts/20   00:00:00 ps

6. Here 11571 is a valid PID. When a signal 0 is sent to this process, kill command exits with an exit status 0. While when the same 0 signal is sent to a non-existent PID like 11579, it reports that there is no such process currently in the system.

$ kill -s 0 11571

$ kill -s 0 11579
bash: kill: (11579) - No such process

If PID is positive, the signal is sent to the process with the process ID PID. If PID is zero, the signal is sent to all processes in the process group of the current process. If PID is −1, the signal is sent to all processes for which the user has permission to send a signal. If PID is less than −1, the signal is sent to all processes in the process group that equals the absolute value of PID.

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