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

NAME
       kill - send signal to a process

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

       int kill(pid_t pid, int sig);

   Feature Test	Macro Requirements for glibc (see feature_test_macros(7)):

       kill(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE ||	_POSIX_SOURCE

DESCRIPTION
       The  kill()  system  call can be	used to	send any signal	to any process
       group or	process.

       If pid is positive, then	signal sig is sent to the process with the  ID
       specified by pid.

       If pid equals 0,	then sig is sent to every process in the process group
       of the calling process.

       If pid equals -1, then sig is sent to every process for which the call-
       ing  process  has  permission  to  send	signals,  except for process 1
       (init), but see below.

       If pid is less than -1, then sig	 is  sent  to  every  process  in  the
       process group whose ID is -pid.

       If  sig	is 0, then no signal is	sent, but error	checking is still per-
       formed; this can	be used	to check for the existence of a	process	ID  or
       process group ID.

       For  a  process	to  have permission to send a signal it	must either be
       privileged (under Linux:	have the CAP_KILL capability), or the real  or
       effective  user	ID of the sending process must equal the real or saved
       set-user-ID of the target process.  In the case of SIGCONT it  suffices
       when  the  sending  and receiving processes belong to the same session.
       (Historically, the rules	were different;	see NOTES.)

RETURN VALUE
       On success (at least one	signal was sent), zero is returned.  On	error,
       -1 is returned, and errno is set	appropriately.

ERRORS
       EINVAL An invalid signal	was specified.

       EPERM  The  process  does not have permission to	send the signal	to any
	      of the target processes.

       ESRCH  The pid or process group does not	exist.	Note that an  existing
	      process  might  be  a  zombie, a process which already committed
	      termination, but has not yet been	wait(2)ed for.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

NOTES
       The only	signals	that can be sent to process ID 1,  the	init  process,
       are  those  for	which  init  has explicitly installed signal handlers.
       This is done to assure the system is not	brought	down accidentally.

       POSIX.1-2001 requires that kill(-1,sig) send sig	to all processes  that
       the  calling  process may send signals to, except possibly for some im-
       plementation-defined system processes.  Linux allows a process to  sig-
       nal  itself,  but  on  Linux  the call kill(-1,sig) does	not signal the
       calling process.

       POSIX.1-2001 requires that if a process sends a signal to  itself,  and
       the  sending  thread  does  not	have  the signal blocked, and no other
       thread has it unblocked or is waiting for it in	sigwait(3),  at	 least
       one unblocked signal must be delivered to the sending thread before the
       kill() returns.

   Linux notes
       Across different	kernel versions, Linux has  enforced  different	 rules
       for the permissions required for	an unprivileged	process	to send	a sig-
       nal to another process.	In kernels 1.0 to 1.2.2,  a  signal  could  be
       sent  if	 the effective user ID of the sender matched effective user ID
       of the target, or the real user ID of the sender	matched	the real  user
       ID  of  the  target.  From kernel 1.2.3 until 1.3.77, a signal could be
       sent if the effective user ID of	the sender matched either the real  or
       effective  user	ID of the target.  The current rules, which conform to
       POSIX.1-2001, were adopted in kernel 1.3.78.

BUGS
       In 2.6 kernels up to and	including 2.6.7, there was a  bug  that	 meant
       that  when  sending  signals to a process group,	kill() failed with the
       error EPERM if the caller did not have permission to send the signal to
       any  (rather  than  all)	of the members of the process group.  Notwith-
       standing	this error return, the signal was still	delivered  to  all  of
       the processes for which the caller had permission to signal.

SEE ALSO
       _exit(2),  killpg(2),  signal(2), tkill(2), exit(3), sigqueue(3), capa-
       bilities(7), credentials(7), signal(7)

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2013-09-17			       KILL(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

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