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



NAME
       kill - send signal to a process

SYNOPSIS
       #include 
       #include 

       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  pro-
       cess 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.

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
       implementation-defined  system  processes.   Linux  allows a process to
       signal 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().

   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	 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 effec-
       tive 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 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 pro-
       cesses for which the caller had permission to signal.

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

COLOPHON
       This  page  is  part of release 3.22 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				  2008-08-29			       KILL(2)