KILL(2)                                                                KILL(2)


NAME
     kill - send a signal to a process or a group of processes

C SYNOPSIS
     #include <sys/types.h>
     #include <signal.h>

     int kill (pid_t pid, int sig);

DESCRIPTION
     kill sends a signal to a process or a group of processes.  The process or
     group of processes to which the signal is to be sent is specified by pid.
     The signal that is to be sent is specified by sig and is either one from
     the list given in signal(2), or 0.  If sig is 0 (the null signal), error
     checking is performed but no signal is actually sent.  This can be used
     to check the validity of pid.

     The real or effective user ID of the sending process must match the real,
     saved,  or effective user ID of the receiving process, unless the
     effective user ID of the sending process is super-user.  An exception to
     this is the signal SIGCONT, which may be sent to any descendant, or any
     process in the same session (having the same session ID) as the current
     process.

     The processes with a process ID of 0 and a process ID of 1 are special
     processes [see intro(2)] and will be referred to below as proc0 and
     proc1, respectively.

     If pid is greater than zero, sig will be sent to the process whose
     process ID is equal to pid.  Pid may equal 1.

     If pid is 0, sig will be sent to all processes excluding proc0 and proc1
     whose process group ID is equal to the process group ID of the sender.

     If pid is -1 and the effective user ID of the sender is not super-user,
     sig will be sent to all processes excluding proc0 and proc1 whose real
     user ID is equal to the effective user ID of the sender.

     If pid is -1 and the effective user ID of the sender is super-user, sig
     will be sent to all processes excluding proc0 and proc1.

     If pid is negative but not -1, sig will be sent to all processes whose
     process group ID is equal to the absolute value of pid.

     If the value of pid causes sig to be generated for the sending process,
     and if sig is not blocked for the calling thread and if no other thread
     has sig unblocked or is waiting in a sigwait function for sig, either sig
     or at least one pending unblocked signal shall be delivered to the
     calling thread before the kill() function returns.


     kill will fail and no signal will be sent if one or more of the following
     are true:

     [EINVAL]       Sig is not a valid signal number.

     [EPERM]        Sig is SIGKILL and pid is 1 (proc1).

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

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

     [EPERM]        The user ID of the sending process is not super-user, and
                    its real or effective user ID does not match the real,
                    saved,  or effective user ID of the receiving process.

SEE ALSO
     sigaction(2), sigprocmask(2), sigqueue(3), sigwait(3), sigvec(3B),
     sigblock(3B), sigsetmask(3B), killpg(3B), pthread_kill(3P)

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


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