wait, waitpid, wait4, wait3 - wait for process terminatation
#include <sys/types.h>
#include <sys/wait.h>
pid = wait(status)
int pid;
union wait *status;
#include <sys/time.h>
#include <sys/resource.h>
pid = waitpid(wpid, status, options);
int pid;
int wpid;
union wait *status;
int options;
pid = wait3(status, options, rusage);
int pid;
union wait *status;
int options;
struct rusage *rusage;
pid = wait4(wpid, status, options, rusage);
int pid;
int wpid;
union wait *status;
int options;
struct rusage *rusage;
The
function suspends execution of its calling process until
information is available for a terminated child process,
or a signal is received.
On return from a successful
call,
the
area contains termination information about the process that exited
as defined below.
The
call provides a more general interface for programs
that need to wait for certain child processes,
that need resource utilization statistics accummulated by child processes,
or that require options.
The other wait functions are implemented using
The
parameter specifies the set of child processes for which to wait.
If
is -1, the call waits for any child process.
If
is 0,
the call waits for any child process in the process group of the caller.
If
is greater than zero, the call waits for the process with process id
If
is less than -1, the call waits for any process whose process group id
equals the absolute value of
The
parameter is defined below.  The
parameter contains the bitwise OR of any of the following options.
The
option
is used to indicate that the call should not block if
there are no processes that wish to report status.
If the
option is set,
children of the current process that are stopped
due to a
or
signal also have
their status reported.
If
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).
When the
option is specified and no processes
wish to report status,
returns a
process id
of 0.
The
call is identical to
with an
value of zero.
The older
call is the same as
with a
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:

- True if the process terminated normally by a call to
or

- True if the process terminated due to receipt of a signal.

- 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
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:

- If WIFEXITED(status)
is true, evaluates to the low-order 8 bits
of the argument passed to _exit(2)
or exit(2)
by the child.

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

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.

If WIFSTOPPED(status)
is true, evaluates to the number of the signal
that caused the process to stop.
See
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
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.
If
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
is set to indicate the error.
If
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
set to
Otherwise, if
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
is set to indicate the error.
will fail and return immediately if:
[ECHILD]
The calling process has no existing unwaited-for
child processes.
[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 had the
flag set.
The
and
functions are defined by POSIX;
and
are not specified by POSIX.
The
macro
and the ability to restart a pending
call are extensions to the POSIX interface.

HISTORY
A function call appeared in Version 6 AT&T UNIX.