kill - terminate a process
kill [-signal|-s signal|-p] [-q value]
[-a] [--timeout milliseconds signal] [--]
kill -l [number] | -L
The command kill 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
Most modern shells have a builtin kill command, with a
usage rather similar to that of the command described here. The
--all, --pid, and --queue 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 expressed in one of the following
where n is larger than 0. The process with PID
n is signaled.
All processes in the current process group are
All processes with a PID larger than 1 are
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.
All processes invoked using this name will be
-s, --signal signal
The signal to send. It may be given as a name or a
-l, --list [number]
Print a list of signal names, or convert the given signal
number to a name. The signals can be found in
Similar to -l, but it will print signal names and
their corresponding numbers.
Do not restrict the command-name-to-PID conversion to
processes with the same UID as the present process.
Only print the process ID (PID) of the named processes,
do not send any signals.
Print PID(s) that will be signaled with kill along
with the signal.
-q, --queue value
Send the signal using sigqueue(3)
. The 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 SA_SIGINFO
flag to sigaction(2)
, then it can
obtain this data via the si_sigval
field of the siginfo_t
--timeout milliseconds signal
kill has the following exit status values:
Send a signal defined in the usual way to a process,
followed by an additional signal after a specified delay. The --timeout
option causes kill
to wait for a period defined in milliseconds
before sending a follow-up signal
to the process. This feature is
implemented using the Linux kernel PID file descriptor feature in order to
guarantee that the follow-up signal is sent to the same process or not sent if
the process no longer exists.
Note that the operating system may re-use PIDs and implementing an
equivalent feature in a shell using kill and sleep would be
subject to races whereby the follow-up signal might be sent to a different
process that used a recycled PID.
The --timeout option can be specified multiple times: the
signals are sent sequentially with the specified timeouts. The
--timeout option can be combined with the --queue option.
As an example, the following command sends the signals QUIT, TERM
and KILL in sequence and waits for 1000 milliseconds between sending the
kill --verbose --timeout 1000 TERM --timeout 1000 KILL \
--signal QUIT 12345
partial success (when more than one process
Although it is possible to specify the TID (thread ID, see gettid(2)) of
one of the threads in a multithreaded process as the argument of kill,
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 signal(7) and the description of
CLONE_THREAD in clone(2).
Various shells provide a builtin kill command that is
preferred in relation to the kill(1) executable described by this
manual. The easiest way to ensure one is executing the command described in
this page is to use the full path when calling the command, for example:
Salvatore Valente <firstname.lastname@example.org>, Karel Zak
The original version was taken from BSD 4.4.