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WAIT(2)                   FreeBSD System Calls Manual                  WAIT(2)

NAME
     wait, waitpid, wait4, wait3 - wait for process termination

LIBRARY
     Standard C Library (libc, -lc)

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

     pid_t
     wait(int *status);

     #include <sys/time.h>
     #include <sys/resource.h>

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

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

     pid_t
     wait4(pid_t wpid, int *status, int options, struct rusage *rusage);

DESCRIPTION
     The wait() function suspends execution of its calling process until
     status information is available for a terminated child process, or a
     signal is received.  On return from a successful wait() call, the status
     area contains termination information about the process that exited as
     defined below.

     The wait4() system call provides a more general interface for programs
     that need to wait for certain child processes, that need resource
     utilization statistics accumulated by child processes, or that require
     options.  The other wait functions are implemented using wait4().

     The wpid argument specifies the set of child processes for which to wait.
     If wpid is -1, the call waits for any child process.  If wpid is 0, the
     call waits for any child process in the process group of the caller.  If
     wpid is greater than zero, the call waits for the process with process id
     wpid.  If wpid is less than -1, the call waits for any process whose
     process group id equals the absolute value of wpid.

     The status argument is defined below.  The options argument contains the
     bitwise OR of any of the following options.  The WCONTINUED option
     indicates that children of the current process that have continued from a
     job control stop, by receiving a SIGCONT signal, should also have their
     status reported.  The WNOHANG option is used to indicate that the call
     should not block if there are no processes that wish to report status.
     If the WUNTRACED option is set, children of the current process that are
     stopped due to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal also have
     their status reported.

     If rusage is non-zero, a summary of the resources used by the terminated
     process and all its children is returned (this information is currently
     not available for stopped or continued processes).

     When the WNOHANG option is specified and no processes wish to report
     status, wait4() returns a process id of 0.

     The waitpid() function is identical to wait4() with an rusage value of
     zero.  The older wait3() call is the same as wait4() with a wpid value of
     -1.

     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:

     WIFCONTINUED(status)
             True if the process has not terminated, and has continued after a
             job control stop.  This macro can be true only if the wait call
             specified the WCONTINUED option).

     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 or if the child process is being
             traced (see ptrace(2)).

     Depending on the values of those macros, the following macros produce the
     remaining status information about the child process:

     WEXITSTATUS(status)
             If WIFEXITED(status) 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(status) is true, evaluates to the number of the
             signal that caused the termination of the process.

     WCOREDUMP(status)
             If WIFSIGNALED(status) 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(status) is true, evaluates to the number of the
             signal that caused the process to stop.

NOTES
     See sigaction(2) for a list of termination signals.  A status of 0
     indicates normal termination.

     If a parent process terminates without waiting for all of its child
     processes to terminate, the remaining child processes are assigned the
     parent process 1 ID (the init process ID).

     If a signal is caught while any of the wait() calls are pending, the call
     may be interrupted or restarted when the signal-catching routine returns,
     depending on the options in effect for the signal; see discussion of
     SA_RESTART in sigaction(2).

     The implementation queues one SIGCHLD signal for each child process whose
     status has changed, if wait() returns because the status of a child
     process is available, the pending SIGCHLD signal associated with the
     process ID of the child process will be discarded.  Any other pending
     SIGCHLD signals remain pending.

     If SIGCHLD is blocked, wait() returns because the status of a child
     process is available, the pending SIGCHLD signal will be cleared unless
     another status of the child process is available.

RETURN VALUES
     If wait() returns due to a stopped, continued, 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 wait4(), wait3(), or waitpid() returns due to a stopped, continued, 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, continued 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() function will fail and return immediately if:

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

     [ECHILD]           No status from the terminated child process is
                        available because the calling process has asked the
                        system to discard such status by ignoring the signal
                        SIGCHLD or setting the flag SA_NOCLDWAIT for that
                        signal.

     [EFAULT]           The status or rusage argument points to an illegal
                        address.  (May not be detected before exit of a child
                        process.)

     [EINTR]            The call was interrupted by a caught signal, or the
                        signal did not have the SA_RESTART flag set.

SEE ALSO
     _exit(2), ptrace(2), sigaction(2), exit(3), siginfo(3)

STANDARDS
     The wait() and waitpid() functions are defined by POSIX; wait4() and
     wait3() are not specified by POSIX.  The WCOREDUMP() macro and the
     ability to restart a pending wait() call are extensions to the POSIX
     interface.

HISTORY
     The wait() function appeared in Version 6 AT&T UNIX.

FreeBSD 11.0-PRERELEASE        November 12, 2005       FreeBSD 11.0-PRERELEASE

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | NOTES | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY

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