V10/man/man2/exit.2

.TH EXIT 2
.CT 2 time_man proc_man
.SH NAME
_exit, wait wait3 \(mi terminate process, wait for child to terminate
.SH SYNOPSIS
.nf
.B void _exit(status)
.B int status;
.PP
.B int wait(status)
.B int *status;
.PP
.B int wait((int *)0)
.PP
.B #include <sys/vtimes.h>
.PP
.B wait3(status, options, ch_vt)
.B int *status;
.B struct vtimes *ch_vt;
.fi
.SH DESCRIPTION
.I _exit
closes all the process's files and notifies the parent process
when the parent executes
.IR wait .
The low-order 8 bits of
.I status
are available to the parent process.
The call never returns.
.PP
The function
.IR exit (3),
which is the normal means of terminating a process,
may cause cleanup actions before finally calling
.IR _exit .
Therefore,
.I _exit
should be called to terminate a child
process after a
.IR fork (2)
to avoid flushing buffered output twice.
.PP
.I Wait
delays until a signal is received or until
a child processes terminates or receives signal
.BR SIGSTOP  .
There is no delay if any child has died since the last
.I wait,
or if there are no extant children.
The normal return yields the process id 
and status of one terminated child.
The status of other children 
may be learned from further
.I wait
calls.
.PP
If
.I status
is nonzero,
.I wait
sets
.IR \f5*\fPstatus " = (" s <<8)+ t
where
.I s
is the low 8 bits
of
.I status
from the child's
.IR exit ,
if any,
and
.I t
is the termination status of the child.
See
.IR signal (2)
for a list of termination statuses (signals);
status 0 indicates normal termination, 0177
a (restartable) process stopped on
.BR SIGSTOP .
If the 0200
bit of the termination status
is set,
a core image of the process was produced
by the system.
.PP
.I Wait3
is similar to
.I wait.
An
.I option
value of 1 prevents waiting for extant, non-stopped children
and causes 0 to be returned if children exist but none have
reportable status.
If
.I ch_vt
is nonzero, resource usage data for the child are reported
as by
.IR vtimes (2).
.PP
If the parent process terminates without
waiting on its children,
they are inherited by
process 1
(the initialization process, 
.IR init (8)).
.SH "SEE ALSO"
.IR fork (2), 
.IR exit (3),
.IR signal (2), 
.IR sh (1)
.SH DIAGNOSTICS
.IR wait ,
.IR wait3 :
.B ECHILD
.SH BUGS
If the argument to
.I wait
is bogus, the user program gets a memory fault rather than an
.BR EFAULT .
.br
The 0 third argument to
.I wait3
is a required historical dreg.