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WAIT(2)                       System Calls Manual                      WAIT(2)

NAME
       wait, waitpid - wait for process to terminate

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
       Wait  causes  its  caller to delay until a signal is received or one of
       its child processes terminates.  If any child has died since  the  last
       wait,  return is immediate, returning the process id and exit status of
       one of the terminated children.  If there are no  children,  return  is
       immediate with the value -1 returned.

       On  return from a successful wait call, status is nonzero, and the high
       byte of status contains the low byte of the argument to  exit  supplied
       by  the  child process; the low byte of status contains the termination
       status of the process.  A more precise definition of the status word is
       given in <sys/wait.h>.  If wait can called with a null pointer argument
       to indicate that no status need be returned.

       Waitpid provides an alternate interface  for  programs  that  must  not
       block  when  collecting  the status of child processes, or that wish to
       wait for one particular child.  The pid parameter is the process ID  of
       the  child  to  wait  for,  -1  for any child.  The status parameter is
       defined as above.  The options parameter is used to indicate  the  call
       should  not  block if there are no processes that wish to report status
       (WNOHANG), and/or that children of the current process that are stopped
       due  to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal should also have
       their status reported (WUNTRACED).  (Job control is not implemented for
       Minix, but these symbold and signals are.)

       When  the  WNOHANG  option is specified and no processes wish to report
       status, waitpid returns -1 with errno set to EAGAIN.  The  WNOHANG  and
       WUNTRACED options may be combined by or'ing the two values.

NOTES
       The call wait(&status) is equivalent to waitpid(-1, &status, 0).

       See sigaction(2) for a list of termination statuses (signals); 0 status
       indicates normal termination.  A special status (0177) is returned  for
       a  stopped  process  that  has not terminated and can be restarted; see
       ptrace(2).  If the 0200 bit of the termination status is  set,  a  core
       image of the process was produced by the system.

       If  the  parent process terminates without waiting on its children, the
       initialization process (process ID = 1) inherits the children.

       _sys/wait.h_ defines a number of macros that operate on a status word:

       WIFEXITED(status)
            True if normal exit.

       WEXITSTATUS(status)
            Exit status if  the  process  returned  by  a  normal  exit,  zero
            otherwise.

       WTERMSIG(status)
            Signal number if the process died by a signal, zero otherwise.

       WIFSIGNALED(status)
            True if the process died by a signal.

       WIFSTOPPED(status)
            True if the process is stopped.  (Never true under Minix.)

       WSTOPSIG(status)
            Signal number of the signal that stopped the process.

RETURN VALUE
       If  wait  returns  due  to  a  stopped or terminated child process, the
       process ID of the child is returned to the calling process.  Otherwise,
       a value of -1 is returned and errno is set to indicate the error.

       Waitpid  returns -1 if there are no children not previously waited for,
       if the process that it wants to wait for doesn't exist, or  if  WNOHANG
       is specified and there are no stopped or exited children.

ERRORS
       Wait  will  fail and return immediately if one or more of the following
       are true:

       [ECHILD]       The calling process has no existing  unwaited-for  child
                      processes.

       [EFAULT]       The status argument points to an illegal address.

       [EAGAIN]       Waitpid  is  called with the WNOHANG option and no child
                      has exited yet.

SEE ALSO
       execve(2), exit(2), sigaction(2).

4th Berkeley Distribution        June 30, 1985                         WAIT(2)
NAME | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUE | ERRORS | SEE ALSO