KILL(2)                   OpenBSD Programmer's Manual                  KILL(2)

NAME
     kill - send signal to a process



SYNOPSIS
     #include <signal.h>

     int
     kill(pid_t pid, int sig);

DESCRIPTION
     The kill() function sends the signal given by sig to pid, a process or a
     group of processes.  sig may be one of the signals specified in sigac-
     tion(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 receiving process must match
     that of the sending process or the user must have appropriate privileges
     (such as given by a set-user-ID program or the user is the super-user).
     A single exception is the signal SIGCONT, which may always be sent to any
     descendant of the current process.

     If pid is greater than zero:
             sig is sent to the process whose ID is equal to pid.

     If pid is zero:
             sig is sent to all processes whose group ID is equal to the pro-
             cess group ID of the sender, and for which the process has per-
             mission; this is a variant of killpg(3).

     If pid is -1:
             If the user has super-user privileges, the signal is sent to all
             processes excluding system processes and the process sending the
             signal.  If the user is not the super user, the signal is sent to
             all processes with the same uid as the user excluding the process
             sending the signal.  No error is returned if any process could be
             signaled.

     Setuid and setgid processes are dealt with slightly differently.  For the
     non-root user, to prevent attacks against such processes, some signal de-
     liveries are not permitted and return the error EPERM. The following sig-
     nals are allowed through to this class of processes: SIGKILL, SIGINT,
     SIGTERM, SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP, SIGHUP, SIGUSR1, SIGUSR2.

     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(3).

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:

     [EINVAL]      sig is not a valid signal number.

     [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.

     [EPERM]       The sending process is not the super-user and its effective
                   user ID does not match the effective user ID of the receiv-
                   ing process.  When signaling a process group, this error is
                   returned if any members of the group could not be signaled.

SEE ALSO
     getpgrp(2),  getpid(2),  sigaction(2),  killpg(3)

STANDARDS
     The kill() function is expected to conform to IEEE Std1003.1-1988
     (``POSIX'').

OpenBSD 2.6                     April 19, 1994                               2