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Manual page for kill(2)

kill - send a signal to a process or a group of processes

SYNOPSIS

#include <sys/types.h>
#include <signal.h>

int kill(pid_t pid, int sig);

MT-LEVEL

Async-Signal-Safe

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 signal), 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 sending process is super-user, (see intro.2 or sig is SIGCONT and the sending process has the same session ID as the receiving process.

If pid is greater than 0, sig will be sent to the process whose process ID is equal to pid.

If pid is negative but not (pid_t)-1, sig will be sent to all processes whose process group ID is equal to the absolute 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 special processes (see intro.2 whose process group ID is equal to the process group ID of the sender.

If pid is (pid_t)-1 and the effective user ID of the sender is not super-user, sig will be sent to all processes excluding special processes whose real user ID is equal to the effective user ID of the sender.

If pid is (pid_t)-1 and the effective user ID of the sender is super-user, sig will be sent to all processes excluding special processes.

RETURN VALUES

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

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.
EPERM: sig is SIGKILL and pid is (pid_t)1 (that is, the calling process does not have permission to send the signal to any of the processes specified by pid).
EPERM: The effective user of the calling process does not match the real or saved user and is not super-user, and the calling process is not sending SIGCONT to a process that shares the same session ID.
ESRCH: No process or process group can be found corresponding to that specified by pid.

NOTES

sigsend.2 is a more versatile way to send signals to processes.

Last modified 21/April/97