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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 calling process has per-
       mission 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 performed;  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.

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 pro-
	      cesses.

       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 implementation-defined system processes.
       Linux allows a process to signal itself, but on Linux the call kill(-1,sig) does not  sig-
       nal 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 signal 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  that  of
       the receiver, or the real user ID of the sender matched that of the receiver.  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 receiver.  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.	Notwithstanding  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),	capabilities(7),  creden-
       tials(7), signal(7)

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at
       http://www.kernel.org/doc/man-pages/.

Linux					    2013-02-05					  KILL(2)
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