kill - terminate a process
] | -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
options, and the possibility to specify processes by command
name, are local extensions.
is 0, then no actual signal is sent, but error checking is
The list of processes to be signaled can be a mixture of names and PIDs.
- Each pid can be one of four things:
- where n is larger than 0. The process with PID n is
- All processes in the current process group are signaled.
- All processes with a PID larger than 1 are signaled.
- 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 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 /usr/include/linux/signal.h
- -L, --table
- Similar to -l, but it will print signal names and their
- -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
- Use 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.
Although it is possible to specify the TID (thread ID, see gettid(2)
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
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