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NAME

     kill — send signal to a process

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

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

     int
     kill(pid_t pid, int sig);

DESCRIPTION

     The kill() system call sends the signal given by sig to pid, a process or a group of
     processes.  The sig argument 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 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
     process with the same session ID as the caller.

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

     If pid is zero:
             The sig signal is sent to all processes whose 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(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

     The kill() function returns the value 0 if successful; otherwise the value -1 is returned
     and the global variable errno is set to indicate the error.

ERRORS

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

     [EINVAL]           The sig argument 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), killpg(2), sigaction(2), raise(3), init(8)

STANDARDS

     The kill() system call is expected to conform to ISO/IEC 9945-1:1990 (“POSIX.1”).

HISTORY

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