kill


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

       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 3.54 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                             2013-09-17                           KILL(2)
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