<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
-<!--
- SPDX-License-Identifier: LGPL-2.1+
--->
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="daemon">
<function>setsid()</function> to detach from any terminal and
create an independent session.</para></listitem>
- <listitem><para>In the child, call <function>fork()</function>
- again, to ensure that the daemon can never re-acquire a
- terminal again.</para></listitem>
+ <listitem><para>In the child, call <function>fork()</function> again, to ensure that the daemon can
+ never re-acquire a terminal again. (This relevant if the program — and all its dependencies — does
+ not carefully specify `O_NOCTTY` on each and every single `open()` call that might potentially open a
+ TTY device node.)</para></listitem>
<listitem><para>Call <function>exit()</function> in the first
child, so that only the second child (the actual daemon
and
<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+ <listitem><para>As new-style daemons are invoked without a controlling TTY (but as their own session
+ leaders) care should be taken to always specify `O_NOCTTY` on `open()` calls that possibly reference
+ a TTY device node, so that no controlling TTY is accidentally acquired.</para></listitem>
+
</orderedlist>
<para>These recommendations are similar but not identical to the