waitpid

NAME

       wait, waitpid - wait for process termination

SYNOPSIS

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

       pid_t wait(int *status)
       pid_t waitpid(pid_t pid, int *status, int options);

DESCRIPTION

       The  wait  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  waitpid  function  suspends  execution of the current
       process 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

       -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
              the same behaviour which wait exhibits.

       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  has
               exited.


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

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

       This  status  can  be  evaluated with the following macros
       (these macros take the stat buffer as an argument -- not a
       pointer to the buffer!):

       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  state-
               ment  in the main program.  This macro can only be
               evaluated 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.

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 is set to an appropriate value).

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), wait4(2), signal(7)