#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

       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.

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

       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.

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

       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.

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

       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux                             2009-09-15                           KILL(2)
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