wait(2)                                                         wait(2)

  wait()

  NAME

    wait(), waitpid() - wait for process termination

  SYNOPSIS

    #include 

    pid_t wait (int *status)
    pid_t waitpid (pid_t wpid, int *status, int options)

  DESCRIPTION

    The wait(2) function suspends execution of its calling process until
    status information is available for any terminated child process, or a
    signal is received. On return from a successful wait(2) call, the
    notification area contains termination information about the process that
    exited as defined below. waitpid(2) is a more general interface that
    allows you more control over the behavior.

    The status parameter is a pointer to an integer description of the status
    of the child process, which can be interpreted using macros:

    The following macros may be used to test the manner of exit of the
    process. One of the first three macros will evaluate to a non-zero (true)
    value:
    WIFEXITED(status)
        True if the process terminated normally by a call to _exit(2) or
        exit(3).
    WIFSIGNALED(status)
        True if the process terminated due to receipt of a signal.
    WIFSTOPPED(status)
        True if the process has not terminated, but has stopped and can be
        restarted. This macro can be true only if the wait call specified the
        WUNTRACED option.

    Depending on the values of those macros, the following macros produce the
    remaining status information about the child process:
    WEXITSTATUS(status)
        If WIFEXITED() is true, evaluates to the low-order 8 bits of the
        argument passed to _exit(2) or exit(3) by the child.
    WTERMSIG(status)
        If WIFSIGNALED() is true, evaluates to the number of the signal that
        caused the termination of the process.
    WCOREDUMP(status)
        If WIFSIGNALED() is true, evaluates as true if the termination of the
        process was accompanied by the creation of a core file containing an
        image of the process when the signal was received.
    WSTOPSIG(status)
        If WIFSTOPPED() is true, evaluates to the number of the signal that
        caused the process to stop.

    The waitpid(2) call also takes the pid argument, specifying which child
    processes will be waited for, and the options argument, a bitwise OR of
    flags controlling waitpid(2)'s behavior.

    Values for pid can be:
    pid=-1:
        Status is requested for any child process (this is identical to
        wait(2)).
    pid>0:
        Status is requested for the child process with process ID pid.
    pid=0:
        Status is requested for any child process whose process group ID is
        equal to that of the calling process.
    pid<-1:
        Status is requested for any child process whose process group ID is
        equal to the absolute value of pid.

    The options parameter contains the bitwise OR of any of the following
    options, defined in :

    WNOHANG
        the call should not block if there are no processes that want to
        report status.

    WUNTRACED
        children of the current process that are stopped due to a SIGTTIN,
        SIGTTOU, SIGTSTP, or SIGSTOP signal also have their status reported.

  RETURN VALUES

    If wait(2) 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.

    If waitpid(2) returns due to a stopped or terminated child process, the
    process ID of the child is returned to the calling process. If there are
    no children not previously awaited, -1 is returned with errno set to
    [ECHILD]. Otherwise, if WNOHANG is specified and there are no stopped or
    exited children, 0 is returned. If an error is detected or a caught signal
    aborts the call, a value of -1 is returned and errno is set to indicate
    the error.

  ERRORS

    The wait(2) call will fail and return immediately if:

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

    [EINTR]
        The call was interrupted by a caught signal.

    [EINVAL]
        The options argument was invalid.

  USAGE NOTES

    All of these functions are thread safe.

    All of these functions are async-signal safe.