Section: User Commands (1)
Updated: July 2014
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kill - terminate a process
sends the specified signal
to the specified processes or process groups.
If no signal is specified, the TERM signal is sent.
The default action for this signal is to terminate the process.
This signal should be used in preference to the
KILL signal (number 9), since a process may install a handler for the
TERM signal in order to perform clean-up steps before terminating in
an orderly fashion.
If a process does not terminate after a TERM signal has been sent,
then the KILL signal may be used; be aware that the latter signal
cannot be caught, and so does not give the target process the opportunity
to perform any clean-up before terminating.
Most modern shells have a builtin kill command, with a usage rather similar to
that of the command described here. The
options, and the possibility to specify processes by command name, are local extensions.
If signal is 0, then no actual signal is sent, but error checking is still performed.
The list of processes to be signaled can be a mixture of names and PIDs.
can be one of four things:
is larger than 0. The process with PID
All processes in the current process group are signaled.
All processes with a PID larger than 1 are signaled.
is larger than 1. All processes in process group
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.
All processes invoked using this name will be signaled.
- -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
- -L, --table
Similar to -l, but it will print signal names and their corresponding
- -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
Print PID(s) that will be signaled with kill along with the signal.
- -q, --queue value
argument is an integer that is sent along with the signal. If the
receiving process has installed a handler for this signal using the
then it can obtain this data via the
field of the
Although it is possible to specify the TID (thread ID, see
of one of the threads in a multithreaded process as the argument of
the signal is nevertheless directed to the process
(i.e., the entire thread group).
In other words, it is not possible to send a signal to an
explicitly selected thread in a multithreaded process.
The signal will be delivered to an arbitrarily selected thread
in the target process that is not blocking the signal.
For more details, see
and the description of
has the following return codes:
partial success (when more than one process specified)
The original version was taken from BSD 4.4.
The kill command is part of the util-linux package and is available from
Linux Kernel Archive