KILL(2)                   FreeBSD System Calls Manual                  KILL(2)

NAME
     kill - send signal to a process

LIBRARY
     Standard C Library (libc, -lc)

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

     int
     kill(pid_t pid, int sig);

DESCRIPTION
     The kill() system call sends the signal given by sig to pid, a process or
     a group of processes.  The sig argument 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 user must be the super-user, or the real or saved user ID of
     the receiving process must match the real or effective user ID of the
     sending process.  A single exception is the signal SIGCONT, which may
     always be sent to any process with the same session ID as the sender.  In
     addition, if the security.bsd.conservative_signals sysctl(9) is set to 1,
     the user is not a super-user, and the receiver is set-uid, then only job
     control and terminal control signals may be sent (in particular, only
     SIGKILL, SIGINT, SIGTERM, SIGALRM, SIGSTOP, SIGTTIN, SIGTTOU, SIGTSTP,
     SIGHUP, SIGUSR1, SIGUSR2).

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

     If pid is zero:
             The sig signal 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(2).

     If pid is -1:
             If the user has super-user privileges, the signal is sent to all
             processes excluding system processes (with P_SYSTEM flag set),
             process with ID 1 (usually init(8)), and the process sending the
             signal.  If the user is not the super user, the signal is sent to
             all processes which the caller has permissions to, excluding the
             process sending the signal.  No error is returned if any process
             could be signaled.

     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).

RETURN VALUES
     The kill() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The kill() system call will fail and no signal will be sent if:

     [EINVAL]           The sig argument is not a valid signal number.

     [ESRCH]            No process or process group can be found corresponding
                        to that specified by pid.

     [EPERM]            The sending process does not have permission to send
                        sig to any receiving process.

SEE ALSO
     getpgrp(2), getpid(2), killpg(2), sigaction(2), sigqueue(2), raise(3),
     init(8)

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

HISTORY
     A version of the kill() function appeared in Version 3 AT&T UNIX.  The
     signal number was added to the kill() function in Version 4 AT&T UNIX.

FreeBSD 13.1-RELEASE-p6        December 1, 2019        FreeBSD 13.1-RELEASE-p6