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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);

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  termination,  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 pro-
       cesses.	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)
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