KILL(2)                          System Calls                          KILL(2)

NAME

       kill - send signal to a process

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.  Signals are software  interrupts;  they  act  just
       like  hardware  interrupts  and  can also be used for basic IPC (inter-
       process communication).

       Sig may be one of the signals specified in signal(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  desig‐
       nated  by  pid,  the real or effective user ID of the receiving process
       must match that of the sending process or the user must have  appropri‐
       ate  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  process group ID of the sender, and for which the process has per‐
       mission; this is a variant of killpg(2).  If pid is -1, and if the user
       has  super-user privileges, the signal is sent to all processes exclud‐
       ing 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  er‐
       ror 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)

              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 effec‐
                     tive 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.

BUGS

       Do  not  attempt to send signals from inside a CDA (Classic Desk Acces‐
       sory) or interrupt handler.

SEE ALSO

       getpid(2), getpgrp(2), killpg(2), signal(2)

STANDARDS

       The kill function is  expected  to  conform  to  IEEE  Std  1003.1-1988
       (POSIX).



GNO                             16 January 1997                        KILL(2)