| WAIT(2) | System Calls Manual | WAIT(2) | 
wait, waitid,
  waitpid, wait6,
  wait4, wait3 —
#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);
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() and
    wait6() 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(). or wait6().
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()
    functions 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 processes 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 structure 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.
P_PID,
      waitid() and wait6() wait
      for the child process with a process ID equal to
      (pid_t)id.P_PGID,
      waitid() and wait6() wait
      for the child process with a process group ID equal to
      (pid_t)id.P_ALL,
      waitid() and wait6() wait
      for any child process and the id is ignored.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(uid_t) id.P_GID(gid_t) id.P_SIDFor the waitpid() and
    wait4() functions, the single
    wpid argument specifies the set of child processes for
    which to wait. The following symbolic constants are defined in
    <sys/wait.h>
#define WAIT_ANY (-1) /* any process */ #define WAIT_MYPGRP 0 /* any process in my process group */
WAIT_ANY, the
      call waits for any child process.WAIT_MYPGRP, the
      call waits for any child process in the process group of the caller.The status argument is defined below.
The options argument contains the bitwise OR of any of the following options.
WALLSIGWALTSIGSIGCHLD
      when they exit. If WALTSIG is not specified, the
      call will wait only for processes that are configured to post
      SIGCHLD.WCONTINUEDSIGCONT signal.WEXITEDwait(),
      waitpid(), wait3(), and
      wait4().
    waitid() and wait6()
      functions, the flag has to be explicitly included in
      options if status reports from terminated processes
      are expected.WNOHANGWNOWAITWNOZOMBIEWSTOPPEDWUNTRACED.WTRAPPEDwait(), waitpid(),
      wait3(), and wait4().
    waitid() and wait6()
      functions, the flag has to be explicitly included in
      options if status reports from trapped processes are
      expected.WUNTRACEDSIGTTIN, SIGTTOU,
      SIGTSTP, or SIGSTOP
      signal.__WALLWALLSIG. It is provided for
      compatibility with the Linux
      clone(2) API .__WCLONEWALTSIG. It is provided for
      compatibility with the Linux
      clone(2) API.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 hanging 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
    children.
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 status, 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 status, 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)WIFSIGNALED(status)WIFSTOPPED(status)WUNTRACED option or if the child process is being
      traced (see ptrace(2)).WIFCONTINUED(status)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)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)WIFSIGNALED(status) is
      true, evaluates to the number of the signal that caused the termination of
      the process.WCOREDUMP(status)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)WIFSTOPPED(status) is
      true, evaluates to the number of the signal that caused the process to
      stop.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 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
    siginterrupt(3).
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.
wait() will fail and return immediately if:
ECHILD]SIGCHLD or setting the flag
      SA_NOCLDWAIT for that signal.EFAULT]EINTR]SA_RESTART flag set.In addition, wait6(),
    wait3(), wait4(),
    waitid(), and waitpid() will
    fail and return immediately if:
EINVAL]wait() and waitpid()
  functions conform to IEEE Std 1003.1-1990
  (“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.
wait() function call appeared in
  Version 1 AT&T UNIX.
| September 2, 2019 | NetBSD 9.4 |