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Linux 2.6 - man page for kill (linux section 2)

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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.
       (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  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 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.  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 3.55 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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