kill(2) SYSTEM CALLS kill(2)
NAME
kill - send a signal to a process or a group of processes
SYNOPSIS
#include <sys/types.h>
#include <signal.h>
int kill (pidt pid, int sig);
DESCRIPTION
kill sends a signal to a process or a group of processes.
The process or group of processes to which the signal is to
be sent is specified by pid. The signal that is to be sent
is specified by sig and is either one from the list given in
signal [see signal(5)], or 0. If sig is 0 (the null sig-
nal), error checking is performed but no signal is actually
sent. This can be used to check the validity of pid.
The real or effective user ID of the sending process must
match the real or saved [from exec(2)] user ID of the
receiving process unless the effective user ID of the send-
ing process is superuser, [see intro(2)], or sig is SIGCONT
and the sending process has the same session ID as the
receiving process.
The process with ID 0 and the process with ID 1 are special
processes [see intro(2)] and will be referred to below as
proc0 and proc1, respectively.
If pid is greater than 0, sig will be sent to the process
whose process ID is equal to pid. pid may equal 1.
If pid is negative but not (pidt)-1, sig will be sent to
all processes whose process group ID is equal to the abso-
lute value of pid and for which the process has permission
to send a signal.
If pid is 0, sig will be sent to all processes excluding
proc0 and proc1 whose process group ID is equal to the pro-
cess group ID of the sender. Permission is needed to send a
signal to process groups.
If pid is (pidt)-1 and the effective user ID of the sender
is not superuser, sig will be sent to all processes exclud-
ing proc0 and proc1 whose real user ID is equal to the
effective user ID of the sender.
If pid is (pidt)-1 and the effective user ID of the sender
is superuser, sig will be sent to all processes excluding
proc0 and proc1.
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kill(2) SYSTEM CALLS kill(2)
kill will fail and no signal will be sent if one or more of
the following are true:
EINVAL sig is not a valid signal number.
EINVAL sig is SIGKILL and pid is (pidt)1 (i.e., pid
specifies proc1).
ESRCH No process or process group can be found
corresponding to that specified by pid.
EPERM The user ID of the sending process is not
privileged, and its real or effective user ID
does not match the real or saved user ID of
the receiving process, and the calling pro-
cess is not sending SIGCONT to a process that
shares the same session ID.
SEE ALSO
getpid(2), intro(2), setpgrp(2), signal(2), getsid(2), sig-
send(2), sigaction(2).
kill(1) in the User's Reference Manual.
NOTES
sigsend is a more versatile way to send signals to
processes. The user is encouraged to use sigsend instead of
kill.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Oth-
erwise, a value of -1 is returned and errno is set to indi-
cate the error.
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