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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 <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 send-
     ing 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, SI-
     GUSR2).

     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  ISO/IEC  9945-1:1990
     ("POSIX.1").

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

FreeBSD ports 15.quarterly	December 1, 2019			 KILL(2)

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