wait4

NAME

       wait3, wait4 - wait for process termination, BSD style

SYNOPSIS

       #define _USE_BSD
       #include <sys/types.h>
       #include <sys/resource.h>
       #include <sys/wait.h>


       pid_t wait3(int *status, int options,
             struct rusage *rusage)

       pid_t wait4(pid_t pid, int *status, int options,
             struct rusage *rusage)

DESCRIPTION

       The  wait3 function suspends execution of the current pro-
       cess until a child has exited, or until a signal is deliv-
       ered  whose  action is to terminate the current process or
       to call a  signal  handling  function.   If  a  child  has
       already  exited by the time of the call (a so-called "zom-
       bie" process), the function returns immediately.  Any sys-
       tem resources used by the child are freed.

       The  wait4 function suspends execution of the current pro-
       cess until a child as specified by the  pid  argument  has
       exited,  or until a signal is delivered whose action is to
       terminate the current process or to call a signal handling
       function.   If  a  child  as  requested by pid has already
       exited by the time of the call (a so-called "zombie"  pro-
       cess),  the  function  returns  immediately.   Any  system
       resources used by the child are freed.

       The value of pid can be one of:

       < -1   which means to wait for  any  child  process  whose
              process  group ID is equal to the absolute value of
              pid.

       -1     which means to wait for any child process; this  is
              equivalent to calling wait3.

       0      which  means  to  wait  for any child process whose
              process group ID is equal to that  of  the  calling
              process.

       > 0    which  means to wait for the child whose process ID
              is equal to the value of pid.

       The value of options is an exclusive OR of zero or more of
       the following constants:


       WNOHANG
              which  means  to  return immediately if no child is
              there to be waited for.

       WUNTRACED
              which means to also return for children  which  are
              stopped, and whose status has not been reported.

       If  status is not NULL, wait3 or wait4 store status infor-
       mation in the location pointed to by statloc.

       This status can be evaluated with the following macros:

       WIFEXITED(*status)
              is non -zero if the child exited normally.

       WEXITSTATUS(*status)
              evaluates to the least significant  eight  bits  of
              the  return  code  of  the  child which terminated,
              which may have been set as the argument to  a  call
              to  exit  or as the argument for a return statement
              in the main program.  This macro can only be evalu-
              ated if WIFEXITED returned non-zero.

       WIFSIGNALED(*status)
              returns true if the child process exited because of
              a signal which was not caught.

       WTERMSIG(*status)
              returns the number of the signal  that  caused  the
              child  process to terminate. This macro can only be
              evaluated if WIFSIGNALED returned non-zero.

       WIFSTOPPED(*status)
              returns true if the child process which caused  the
              return  is currently stopped; this is only possible
              if the call was done using WUNTRACED.

       WSTOPSIG(*status)
              returns the number of the signal which  caused  the
              child to stop.  This macro can only be evaluated if
              WIFSTOPPED returned non-zero.

              If rusage is not NULL, the struct rusage as defined
              in  <sys/resource.h>  it  points  to will be filled
              with accounting information.  See getrusage(2)  for
              details.

RETURN VALUE

       The  process  ID of the child which exited, -1 on error or
       zero if WNOHANG was used and no child  was  available  (in
       which case, errno will be set appropriately).

ERRORS

       ECHILD  if  the  child  process  specified in pid does not
               exist.

       EPERM   if the effective userid  of  the  calling  process
               does  not  match  that of the process being waited
               for, and the effective userid of the calling  pro-
               cess it not that of the superuser.

       ERESTARTSYS
               if  WNOHANG was not set and an unblocked signal or
               a SIGCHLD was caught; this is an extension to  the
               POSIX.1 standard.

CONFORMS TO

       POSIX.1

SEE ALSO

       signal(2), getrusage(2), wait(2), signal(7)