wait3, wait4 - wait for process termination, BSD style
pid_t wait3(int *status, int options,
struct rusage *rusage))
pid_t wait4(pid_t pid, int *status, int options
struct rusage *rusage))
The wait3 function suspends execution of the current process
until a child has exited, or until a signal is delivered
whose action is to terminate the current process or to call
a signal handling function. If a child has already exited
by the time of the call (a so-called "zombie" process), the
function returns immediately. Any system resources used by
the child are freed.
The wait4 function suspends execution of the current process
until a child as specified by the pid argument has exited,
or until a signal is delivered whose action is to terminate
the current process or to call a signal handling function.
If a child as requested by pid has already exited by the
time of the call (a so-called "zombie" process), the func-
tion returns immediately. Any system resources used by the
child are freed.
The value of pid can be one of:
< -1 which means to wait for any child process whose process
group ID is equal to the absolute value of pid.
-1 which means to wait for any child process; this is
equivalent to calling wait3.
0 which means to wait for any child process whose process
group ID is equal to that of the calling process.
> 0 which means to wait for the child whose process ID is
equal to the value of pid.
The value of options is a bitwise OR of zero or more of the
WNOHANG which means to return immediately if no child is
there to be waited for.
which means to also return for children which are
stopped, and whose status has not been reported.
If status is not NULL, wait3 or wait4 store status informa-
tion in the location pointed to by status.
This status can be evaluated with the following macros
(these macros take the stat buffer (an int) as an argument -
not a pointer to the buffer!):
is non-zero if the child exited normally.
evaluates to the least significant eight bits of the
return code of the child which terminated, which may
have been set as the argument to a call to exit() or
as the argument for a return statement in the main
program. This macro can only be evaluated if WIFEX-
ITED returned non-zero.
returns true if the child process exited because of
a signal which was not caught.
returns the number of the signal that caused the
child process to terminate. This macro can only be
evaluated if WIFSIGNALED returned non-zero.
returns true if the child process which caused the
return is currently stopped; this is only possible
if the call was done using WUNTRACED.
returns the number of the signal which caused the
child to stop. This macro can only be evaluated if
WIFSTOPPED returned non-zero.
If rusage is not NULL, the struct rusage as defined
in <sys/resource.h> it points to will be filled with
accounting information. See getrusage(2) for
The process ID of the child which exited, -1 on error (in
particular, when no unwaited-for child processes of the
specified kind exist) or zero if WNOHANG was used and no
child was available yet. In the latter two cases errno will
be set appropriately.
No unwaited-for child process as specified does exist.
if WNOHANG was not set and an unblocked signal or a
SIGCHLD was caught. This error is returned by the sys-
tem call. The library interface is not allowed to
return ERESTARTSYS, but will return EINTR.
signal(2), getrusage(2), wait(2),