kill — terminate a process
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 terminating.
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.
Each pid can be expressed in one of the following ways:
nwhere
nis larger than 0. The process with PIDnis signaled.0All processes in the current process group are signaled.
- −1
All processes with a PID larger than 1 are signaled.
−nwhere
nis larger than 1. All processes in process groupnare 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 signalThe 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, −−tableSimilar to −l, but
it will print signal names and their corresponding
numbers.
−a, −−allDo not restrict the command-name-to-PID conversion to processes with the same UID as the present process.
−p, −−pidOnly print the process ID (PID) of the named processes, do not send any signals.
−−verbosePrint PID(s) that will be signaled with kill along with the signal.
−q, −−queue valueSend the signal using sigqueue(3) rather
than kill(2). 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
structure.
−−timeout milliseconds
signalSend 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 signals:
kill −−verbose −−timeout 1000 TERM −−timeout 1000 KILL \ −−signal QUIT 12345
kill has the following exit status values:
0success
1failure
64partial success (when more than one process specified)
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: /bin/kill −−version
The kill command is part of the util-linux package and is available from Linux Kernel Archive
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Copyright 1994 Salvatore Valente (svalentemit.edu) Copyright 1992 Rickard E. Faith (faithcs.unc.edu) May be distributed under the GNU General Public License |