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<title>rfork(3) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>RFORK(3)</b><td align=right><b>RFORK(3)</b>
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<br>
<p><font size=+1><b>NAME </b></font><br>
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rfork – manipulate process state<br>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>#include <u.h><br>
#include <libc.h>
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<tt><font size=+1>int rfork(int flags)<br>
</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<i>Rfork</i> is a partial implementation of the Plan 9 system call. It
can be used to manipulate some process state and to create new
processes a la <a href="../man2/fork.html"><i>fork</i>(2)</a>. It cannot be used to create shared-memory
processes (Plan 9’s <tt><font size=+1>RFMEM</font></tt> flag); for that functionality use <i>proccreate</i>
(see <a href="../man3/thread.html"><i>thread</i>(3)</a>).
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The <i>flags</i> argument to <i>rfork</i> selects which resources of the invoking
process (parent) are shared by the new process (child) or initialized
to their default values. <i>Flags</i> is the logical OR of some subset
of<br>
<tt><font size=+1>RFPROC</font></tt> If set a new process is created; otherwise changes affect
the current process.<br>
<tt><font size=+1>RFNOWAIT</font></tt> If set, the child process will be dissociated from the
parent. Upon exit the child will leave no <tt><font size=+1>Waitmsg</font></tt> (see <a href="../man3/wait.html"><i>wait</i>(3)</a>)
for the parent to collect.<br>
<tt><font size=+1>RFNOTEG</font></tt> Each process is a member of a group of processes that all
receive notes when a note is sent to the group (see <a href="../man3/postnote.html"><i>postnote</i>(3)</a>
and <a href="../man2/signal.html"><i>signal</i>(2)</a>). The group of a new process is by default the same
as its parent, but if <tt><font size=+1>RFNOTEG</font></tt> is set (regardless of <tt><font size=+1>RFPROC</font></tt>), the
process becomes the first in a new group, isolated
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from previous processes. In Plan 9, a process can call <tt><font size=+1>rfork(RFNOTEG)</font></tt>
and then be sure that it will no longer receive console interrupts
or other notes. Unix job-control shells put each command in its
own process group and then relay notes to the current foreground
command, making the idiom
less useful.<br>
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<tt><font size=+1>RFFDG</font></tt> If set, the invoker’s file descriptor table (see <i>intro</i>(<i>))</i>
is copied; otherwise the two processes share a single table.
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File descriptors in a shared file descriptor table are kept open
until either they are explicitly closed or all processes sharing
the table exit.
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If <tt><font size=+1>RFPROC</font></tt> is set, the value returned in the parent process is
the process id of the child process; the value returned in the
child is zero. Without <tt><font size=+1>RFPROC</font></tt>, the return value is zero. Process
ids range from 1 to the maximum integer (<tt><font size=+1>int</font></tt>) value. <i>Rfork</i> will
sleep, if necessary, until required process resources are available.
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Calling <tt><font size=+1>rfork(RFFDG|RFPROC)</font></tt> is equivalent to calling <a href="../man2/fork.html"><i>fork</i>(2)</a>.<br>
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<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/lib9/rfork.c<br>
</font></tt>
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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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<i>Rfork</i> sets <i>errstr</i>.<br>
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