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KILL(2)                     BSD System Calls Manual                    KILL(2)

     kill -- send signal to a process

     #include <&lt;signal.h>&gt;

     kill(pid_t pid, int sig);

     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 superuser).  A
     single exception is the signal SIGCONT, which may always be sent to any
     process with the same session ID as the caller.

     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
             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 superuser privileges, the signal is sent to all
             processes excluding system processes and the process sending the
             signal.  If the user is not the superuser, 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

     Setuid and setgid processes are dealt with slightly differently.  For the
     non-root user, to prevent attacks against such processes, some signal
     deliveries are not permitted and return the error EPERM.  The following
     signals are allowed through to this class of processes: SIGKILL, SIGINT,

     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

     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the

     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 speci-
                        fied by pid.

     [EPERM]            The sending process is not the superuser 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 none of the members
                        of the group could be signaled.

     getpgrp(2), getpid(2), sigaction(2), killpg(3), raise(3)

     The kill() function is expected to conform to IEEE Std 1003.1-2008

     The kill() system call first appeared in Version 3 AT&T UNIX.  The sig
     argument was introduced in Version 4 AT&T UNIX.

     IEEE Std 1003.1-2008 (``POSIX.1'') specifies that kill(0, sig) should
     send signal sig to the calling process, but OpenBSD doesn't do so for
     historical reasons.

BSD                             March 30, 2017                             BSD