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KILL(2)                       System Calls Manual                      KILL(2)

NAME
     kill - send signal to a process

LIBRARY
     Standard C Library (libc, -lc)

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
     sigaction(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 process group ID is equal to
             the process group ID of the sender, and for which the process has
             permission; 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, otherwise ESRCH is returned.

     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).

     If sig is equal to 0, then no signal is sent to the process ID or process
     group ID, but error checking is performed.  This can be used to check if
     the process ID or process group ID exist.

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.

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

     [ESRCH]            No process can be found corresponding to that
                        specified by pid; or the process id was given as 0 but
                        the sending process does not have a process group.

SEE ALSO
     getpgrp(2), getpid(2), sigaction(2), killpg(3), signal(7)

STANDARDS
     The kill() function is expected to conform to IEEE Std 1003.1-1990
     ("POSIX.1").

NetBSD 10.99                   February 8, 2021                   NetBSD 10.99