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The kill command

kill command in Linux (located in /bin/kill), is a built-in command which is used to terminate processes manually. The kill command sends a signal to a process which terminates the process. If the user doesn’t specify any signal which is to be sent along with kill command then default TERM signal is sent that terminates the process.

Signals can be specified in three ways: - By number (e.g. -5) - With SIG prefix (e.g. -SIGkill) - Without SIG prefix (e.g. -kill)

Syntax

kill [OPTIONS] [PID]...

Examples:

  1. To display all the available signals you can use below command option:

kill -l

  1. To show how to use a PID with the kill command.

$kill pid

  1. To show how to send signal to processes. kill {-signal | -s signal} pid

  2. Specify Signal:

  • using numbers as signals kill -9 pid
  • using SIG prefix in signals kill -SIGHUP pid
  • without SIG prefix in signals kill -HUP pid

Arguments:

The list of processes to be signaled can be a mixture of names and PIDs.

   pid    Each pid can be expressed in one of the following ways:

          n      where n is larger than 0.  The process with PID n is signaled.

          0      All processes in the current process group are signaled.

          -1     All processes with a PID larger than 1 are signaled.

          -n     where n is larger than 1.  All processes in process group  n  are  signaled.
                 When  an  argument  of  the  form '-n' is given, and it is meant to denote a
                 process group, either a signal must be specified first, or the argument must
                 be  preceded  by  a '--' option, otherwise it will be taken as the signal to
                 send.

   name   All processes invoked using this name will be signaled.

Options:

   -s, --signal signal
          The signal to send.  It may be given as a name or a number.

   -l, --list [number]
          Print a list of signal names, or convert the given signal number to  a  name.   The
          signals can be found in /usr/include/linux/signal.h.

   -L, --table
          Similar to -l, but it will print signal names and their corresponding numbers.

   -a, --all
          Do  not  restrict the command-name-to-PID conversion to processes with the same UID
          as the present process.

   -p, --pid
          Only print the process ID (PID) of the named processes, do not send any signals.

   --verbose
          Print PID(s) that will be signaled with kill along with the signal.
Last update: 2022-05-12
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