KILL

Section: System Calls (2)
Updated: August 1, 1992
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NAME

kill - send signal to a process

SYNOPSIS

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

int kill(pid_t pid, int sig);

DESCRIPTION

The kill function sends the signal sig to a process, specified by the process number pid. Its argument sig may be one of the signals specified in sigvec(2), or it may be 0, in which case error checking is performed but no signal is actually sent. This can be used to check the validity of pid.

For a process to have permission to send a signal to a process designated by pid, the real or effective user ID of the sending process must match the real or saved set-user-ID of the receiving process, unless the sending process has superuser privileges. The only exception is the signal SIGCONT, which may always be sent to any descendant of the current process.

If the process number is 0, the signal is sent to all processes in the sender's process group; this is a variant of killpg(2).

If the process number is -1 and the user is the super-user, the signal is broadcast universally except to system processes and the process sending the signal. If the process number is -1 and the user is not the super-user, the signal is broadcast universally to all processes with the same uid as the user except the process sending the signal. No error is returned if any process could be signaled.

For compatibility with System V, if the process number is negative but not -1, the signal is sent to all processes whose process group ID is equal to the absolute value of the process number. This is a variant of killpg(2).

Processes may send signals to themselves.

RETURN VALUE

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

The kill function will fail and no signal will be sent if any of the following occur:

[EINVAL]: sig is not a valid signal number.

[EPERM]: The process does not have permission to send the signal to any receiving process. [ESRCH] No process can be found corresponding to that specified by pid.
[ESRCH]: The process id was given as 0 but the sending process does not have a process group.

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