WAIT(2)                   NetBSD System Calls Manual                   WAIT(2)

NAME
     wait, waitid, waitpid, wait6, wait4, wait3 -- wait for process termina-
     tion

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/wait.h>

     pid_t
     wait(int *status);

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

     int
     waitid(idtype_t idtype, id_t id, siginfo_t *info, int options);

     #include <sys/resource.h>

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

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

     pid_t
     wait6(idtype_t idtype, id_t id, int *status, int options,
         struct __wrusage *wrusage, siginfo_t *infop);

DESCRIPTION
     The wait() function suspends execution of its calling process until
     status information is available for a terminated child process, or a sig-
     nal 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() and wait6() call provides a more general interface for pro-
     grams 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().  or
     wait6().

     The wpid parameter 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 parameter is defined below.

     The options parameter contains the bitwise OR of any of the following
     options:

     WNOHANG    This option is used to indicate that the call should not block
                if there are no processes that wish to report status.

     WUNTRACED  If this 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.

     WALTSIG    If this option is specified, the call will wait only for pro-
                cesses that are configured to post a signal other than SIGCHLD
                when they exit.  If WALTSIG is not specified, the call will
                wait only for processes that are configured to post SIGCHLD.

     __WCLONE   This is an alias for WALTSIG.  It is provided for compatibil-
                ity with the Linux clone(2) API.

     WALLSIG    If this option is specified, the call will wait for all chil-
                dren regardless of what exit signal they post.

     __WALL     This is an alias for WALLSIG.  It is provided for compatibil-
                ity with the Linux clone(2) API .

     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 processes).

     The wait6() function is the most general function in this family and its
     distinct features are:

     All of the desired process statuses to be waited on must be explicitly
     specified in options.  The wait(), waitpid(), wait3(), and wait4() func-
     tions all implicitly wait for exited and trapped processes, but the
     waitid() and wait6() functions require the corresponding WEXITED and
     WTRAPPED flags to be explicitly specified.  This allows waiting for pro-
     cesses which have experienced other status changes without having to also
     handle the exit status from terminated processes.

     The wait6() function accepts a wrusage argument which points to a struc-
     ture defined as:

     struct wrusage {
             struct rusage   wru_self;
             struct rusage   wru_children;
     };

     This allows the calling process to collect resource usage statistics from
     both its own child process as well as from its grand children.  When no
     resource usage statistics are needed this pointer can be NULL.

     The last argument infop must be either NULL or a pointer to a siginfo_t
     structure.  If non-NULL, the structure is filled with the same data as
     for a SIGCHLD signal delivered when the process changed state.

     The set of child processes to be queried is specified by the arguments
     idtype and id.  The separate idtype and id arguments support many other
     types of identifiers in addition to process IDs and process group IDs.

              If idtype is P_PID, waitid() and wait6() wait for the child
               process with a process ID equal to (pid_t)id.

              If idtype is P_PGID, waitid() and wait6() wait for the child
               process with a process group ID equal to (pid_t)id.

              If idtype is P_ALL, waitid() and wait6() wait for any child
               process and the id is ignored.

              If idtype is P_PID or P_PGID and the id is zero, waitid() and
               wait6() wait for any child process in the same process group as
               the caller.

     Non-standard identifier types supported by this implementation of
     waitid() and wait6() are:

     P_UID     Wait for processes whose effective user ID is equal to (uid_t)
               id.

     P_GID     Wait for processes whose effective group ID is equal to (gid_t)
               id.

     P_SID     Wait for processes whose session ID is equal to id.  If the
               child process started its own session, its session ID will be
               the same as its process ID.  Otherwise the session ID of a
               child process will match the caller's session ID.

     For the waitpid() and wait4() functions, the single wpid argument speci-
     fies 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.

     WCONTINUED  Report the status of selected processes that have continued
                 from a job control stop by receiving a SIGCONT signal.

     WNOHANG     Do not block when there are no processes wishing to report
                 status.

     WUNTRACED   Report the status of selected processes which are stopped due
                 to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal.

     WSTOPPED    An alias for WUNTRACED.

     WTRAPPED    Report the status of selected processes which are being
                 traced via ptrace(2) and have trapped or reached a break-
                 point.  This flag is implicitly set for the functions wait(),
                 waitpid(), wait3(), and wait4().
                 For the waitid() and wait6() functions, the flag has to be
                 explicitly included in options if status reports from trapped
                 processes are expected.

     WEXITED     Report the status of selected processes which have termi-
                 nated.  This flag is implicitly set for the functions wait(),
                 waitpid(), wait3(), and wait4().
                 For the waitid() and wait6() functions, the flag has to be
                 explicitly included in options if status reports from termi-
                 nated processes are expected.

     WNOWAIT     Keep the process whose status is returned in a waitable
                 state.  The process may be waited for again after this call
                 completes.

     For the waitid() and wait6() functions, at least one of the options
     WEXITED, WUNTRACED, WSTOPPED, WTRAPPED, or WCONTINUED must be specified.
     Otherwise there will be no events for the call to report.  To avoid hang-
     ing indefinitely in such a case these functions return -1 with errno set
     to EINVAL.

     If rusage is non-NULL, a summary of the resources used by the terminated
     process and all its children is returned.

     If wrusage is non-NULL, separate summaries are returned for the resources
     used by the terminated process and the resources used by all its chil-
     dren.

     If infop is non-NULL, a siginfo_t structure is returned with the si_signo
     field set to SIGCHLD and the si_pid field set to the process ID of the
     process reporting status.  For the exited process, the si_status field of
     the siginfo_t structure contains the full 32 bit exit status passed to
     _exit(2); the status argument of other calls only returns 8 lowest bits
     of the exit status.

     When the WNOHANG option is specified and no processes wish to report sta-
     tus, waitid() sets the si_signo and si_pid fields in infop to zero.
     Checking these fields is the only way to know if a status change was
     reported.

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

     The waitpid() call 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.  Note that these macros expect the status value itself, not a
     pointer to the status value.  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 spec-
             ified the WUNTRACED option or if the child process is being
             traced (see ptrace(2)).

     WIFCONTINUED(status)
             True if the process has not terminated, but has been continued
             via the delivery of the SIGCONT signal.  This macro can be true
             only if the wait call specified the WCONTINUED option.

     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 termina-
             tion 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 indi-
     cates normal termination.

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

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

RETURN VALUES
     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.

     If wait6(), wait4(), wait3() or waitpid() 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.

     If waitid() returns because one or more processes have a state change to
     report, 0 is returned.  If an error is detected, a value of -1 is
     returned and errno is set to indicate the error.  If WNOHANG is specified
     and there are no stopped, continued or exited children, 0 is returned.
     The si_signo and si_pid fields of infop must be checked against zero to
     determine if a process reported status.

ERRORS
     wait() will fail and return immediately if:

     [ECHILD]           The calling process has no existing unwaited-for child
                        processes; or 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 arguments point 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.

     In addition, wait6(), wait3(), wait4(), waitid(), and waitpid() will fail
     and return immediately if:

     [EINVAL]           An invalid value was specified for options.

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

STANDARDS
     The wait() and waitpid() functions conform to ISO/IEC 9945-1:1990
     (``POSIX.1''); the waitid() function conforms to IEEE Std 1003.1-2004
     (``POSIX.1''); the wait3() function conforms to X/Open Portability Guide
     Issue 4 (``XPG4''); wait4() is an extension.  The WCOREDUMP() macro and
     the ability to restart a pending wait() call are extensions to the POSIX
     interface.

HISTORY
     A wait() function call appeared in Version 2 AT&T UNIX.

NetBSD 7.0                       April 5, 2016                      NetBSD 7.0

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©1996-2016 Modified for NetBSD by Kimmo Suominen