kill(2) [redhat man page]

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);

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 pid.

       If pid equals 0, then sig is sent to every process in the process group of the current process.

       If pid equals -1, then sig is sent to every process 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 -pid.

       If sig is 0, then no signal is sent, but error checking is still performed.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       EINVAL An invalid signal was specified.

       ESRCH  The  pid or process group does not exist.  Note that an existing process might be a zombie, a process which already committed termi-
	      nation, but has not yet been wait()ed for.

       EPERM  The process does not have permission to send the signal to any of the receiving processes.  For a process to have permission to send
	      a  signal to process pid it must either have root privileges, or the real or effective user ID of the sending process must equal the
	      real or saved set-user-ID of the receiving process.  In the case of SIGCONT it suffices when the	sending  and  receiving  processes
	      belong to the same session.

NOTES

       It  is  impossible to send a signal to task number one, the init process, for which it has not installed a signal handler.  This is done to
       assure the system is not brought down accidentally.

       POSIX 1003.1-2001 requires that kill(-1,sig) send sig to all processes that the current 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 current process.

LINUX HISTORY

       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
       1003.1-2001, were adopted in kernel 1.3.78.

CONFORMING TO

       SVr4, SVID, POSIX.1, X/OPEN, BSD 4.3, POSIX 1003.1-2001

SEE ALSO

       _exit(2), exit(3), signal(2), signal(7)

Linux 2.5.0							    2001-12-18								   KILL(2)

Check Out this Related Man Page

KILL(2) 						      BSD System Calls Manual							   KILL(2)

NAME

     kill -- send signal to a process

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <signal.h>

     int
     kill(pid_t pid, int sig);

DESCRIPTION

     The kill() function sends the signal given by sig to pid, a process or a group of processes.  sig may be one of the signals specified in
     sigaction(2) or it may be 0, in which case error checking is performed but no signal is actually sent.  This can be used to check the valid-
     ity of pid.

     For a process to have permission to send a signal to a process designated by pid, the real or effective user ID of the receiving process must
     match that of the sending process or the user must have appropriate privileges (such as given by a set-user-ID program or the user is the
     super-user).  A single exception is the signal SIGCONT, which may always be sent to any descendant of the current process.

     If pid is greater than zero:
	     sig is sent to the process whose ID is equal to pid.

     If pid is zero:
	     sig is sent to all processes whose process group ID is equal to the process group ID of the sender, and for which the process has
	     permission; this is a variant of killpg(3).

     If pid is -1:
	     If the user has super-user privileges, the signal is sent to all processes excluding system processes and the process sending the
	     signal.  If the user is not the super user, the signal is sent to all processes with the same uid as the user excluding the process
	     sending the signal.  No error is returned if any process could be signaled.

     For compatibility with System V, if the process number is negative but not -1, the signal is sent to all processes whose process group ID is
     equal to the absolute value of the process number.  This is a variant of killpg(3).

RETURN VALUES

     Upon successful completion, a value of 0 is returned.  Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

     kill() will fail and no signal will be sent if:

     [EINVAL]		sig is not a valid signal number.

     [ESRCH]		No process can be found corresponding to that specified by pid.

     [ESRCH]		The process id was given as 0 but the sending process does not have a process group.

     [EPERM]		The sending process is not the super-user and its effective user id does not match the effective user-id of the receiving
			process.  When signaling a process group, this error is returned if any members of the group could not be signaled.

SEE ALSO

     getpgrp(2), getpid(2), sigaction(2), killpg(3), signal(7)

STANDARDS

     The kill() function is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1'').

BSD
								  April 19, 1994							       BSD

Linux and UNIX Man Pages

kill(2) [redhat man page]

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