[Main]

Kill System Call

 #include <sys/types.h>
     #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 sigac-
     tion(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 validity 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 group ID is equal to the pro-
	     cess group ID of the sender, and for which the process has per-
	     mission; this is a variant of killpg(2).

     If pid is -1:
	     If the user has super-user privileges, the signal is sent to all
	     processes excluding system processes (with P_SYSTEM flag set),
	     process with ID 1 (usually init(8)),  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(2).

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.

HISTORY

     A kill() function call appeared in Version 7 AT&T UNIX.