networkd-wait-online: improve interoptability and enable by default

To make sure we don't delay boot on systems where (some) network links are managed by someone else
we don't block if something else has successfully brought up a link.

We will still block until all links we are aware of that are  managed by networkd have been
configured, but if no such links exist, and someone else have configured a link sufficiently
that it has a carrier, it may be that the link is ready so we should no longer block.

Note that in all likelyhood the link is not ready (no addresses/routes configured),
so whatever network managment daemon configured it should provide a similar wait-online
service to block network-online.target until it is ready.

The aim is to block as long as we know networking is not fully configured, but no longer. This
will allow systemd-networkd-wait-online.service to be enabled on any system, even if we don't
know whether networkd is the main/only network manager.

Even in the case networking is fully configured by networkd, the default behavior may not be
sufficient: if two links need to be configured, but the first is fully configured before the
second one appears we will assume the network is up. To work around that, we allow specifying
specific devices to wait for before considering the network up.

This unit is enabled by default, just like systemd-networkd, but will only be pulled in if
anyone pulls in network-online.target.

1 files changed, 81 insertions, 0 deletions

diff --git a/man/systemd-networkd-wait-online.service.xml b/man/systemd-networkd-wait-online.service.xml
new file mode 100644
index 0000000000..d8f2226552
--- /dev/null
+++ b/man/systemd-networkd-wait-online.service.xml
@@ -0,0 +1,81 @@
+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2014 Tom Gundersen
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="systemd-networkd-wait-online.service" conditional='ENABLE_NETWORKD'>
+
+        <refentryinfo>
+                <title>systemd-networkd.service</title>
+                <productname>systemd</productname>
+
+                <authorgroup>
+                        <author>
+                                <contrib>Developer</contrib>
+                                <firstname>Tom</firstname>
+                                <surname>Gundersen</surname>
+                                <email>teg@jklm.no</email>
+                        </author>
+                </authorgroup>
+        </refentryinfo>
+
+        <refmeta>
+                <refentrytitle>systemd-networkd-wait-online.service</refentrytitle>
+                <manvolnum>8</manvolnum>
+        </refmeta>
+
+        <refnamediv>
+                <refname>systemd-networkd-wait-online.service</refname>
+                <refname>systemd-networkd-wait-online</refname>
+                <refpurpose>Wait for network to become online</refpurpose>
+        </refnamediv>
+
+        <refsynopsisdiv>
+                <para><filename>systemd-networkd-wait-online.service</filename></para>
+                <para><filename>/usr/lib/systemd/systemd-networkd-wait-online</filename></para>
+        </refsynopsisdiv>
+
+        <refsect1>
+                <title>Description</title>
+
+                <para><command>systemd-networkd-wait-online</command> is a
+                one-shot system service that waits for the network to be configured.
+                It will wait for all links managed by
+                <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+                to be fully configured. It will wait for at least one link managed by
+                systemd-networkd to appear, or for a link to be brought up by someone else.
+
+                To wait for a specific set of links, see
+                <citerefentry><refentrytitle>systemd-networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+                This may be necessary on systems with more than one active link.
+                </para>
+        </refsect1>
+
+        <refsect1>
+                <title>See Also</title>
+                <para>
+                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>systemd-networkd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+                </para>
+        </refsect1>
+
+</refentry>