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man: document the new --resolv-conf= options

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Lennart Poettering 2020-04-21 18:56:30 +02:00
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man/systemd-nspawn.xml
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@ -1099,29 +1099,60 @@
<varlistentry>
<term><option>--resolv-conf=</option></term>
<listitem><para>Configures how <filename>/etc/resolv.conf</filename> inside of the container (i.e. DNS
configuration synchronization from host to container) shall be handled. Takes one of <literal>off</literal>,
<literal>copy-host</literal>, <literal>copy-static</literal>, <literal>bind-host</literal>,
<literal>bind-static</literal>, <literal>delete</literal> or <literal>auto</literal>. If set to
<literal>off</literal> the <filename>/etc/resolv.conf</filename> file in the container is left as it is
included in the image, and neither modified nor bind mounted over. If set to <literal>copy-host</literal>, the
<filename>/etc/resolv.conf</filename> file from the host is copied into the container. Similar, if
<literal>bind-host</literal> is used, the file is bind mounted from the host into the container. If set to
<literal>copy-static</literal> the static <filename>resolv.conf</filename> file supplied with
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> is
copied into the container, and correspondingly <literal>bind-static</literal> bind mounts it there. If set to
<literal>delete</literal> the <filename>/etc/resolv.conf</filename> file in the container is deleted if it
exists. Finally, if set to <literal>auto</literal> the file is left as it is if private networking is turned on
(see <option>--private-network</option>). Otherwise, if <filename>systemd-resolved.service</filename> is
connectible its static <filename>resolv.conf</filename> file is used, and if not the host's
<filename>/etc/resolv.conf</filename> file is used. In the latter cases the file is copied if the image is
writable, and bind mounted otherwise. It's recommended to use <literal>copy</literal> if the container shall be
able to make changes to the DNS configuration on its own, deviating from the host's settings. Otherwise
<literal>bind</literal> is preferable, as it means direct changes to <filename>/etc/resolv.conf</filename> in
the container are not allowed, as it is a read-only bind mount (but note that if the container has enough
privileges, it might simply go ahead and unmount the bind mount anyway). Note that both if the file is bind
mounted and if it is copied no further propagation of configuration is generally done after the one-time early
initialization (this is because the file is usually updated through copying and renaming). Defaults to
<listitem><para>Configures how <filename>/etc/resolv.conf</filename> inside of the container shall be
handled (i.e. DNS configuration synchronization from host to container). Takes one of
<literal>off</literal>, <literal>copy-host</literal>, <literal>copy-static</literal>,
<literal>copy-uplink</literal>, <literal>copy-stub</literal>, <literal>replace-host</literal>,
<literal>replace-static</literal>, <literal>replace-uplink</literal>,
<literal>replace-stub</literal>, <literal>bind-host</literal>, <literal>bind-static</literal>,
<literal>bind-uplink</literal>, <literal>bind-stub</literal>, <literal>delete</literal> or
<literal>auto</literal>.</para>
<para>If set to <literal>off</literal> the <filename>/etc/resolv.conf</filename> file in the
container is left as it is included in the image, and neither modified nor bind mounted over.</para>
<para>If set to <literal>copy-host</literal>, the <filename>/etc/resolv.conf</filename> file from the
host is copied into the container, unless the file exists already and is not a regular file (e.g. a
symlink). Similar, if <literal>replace-host</literal> is used the file is copied, replacing any
existing inode, including symlinks. Similar, if <literal>bind-host</literal> is used, the file is
bind mounted from the host into the container.</para>
<para>If set to <literal>copy-static</literal>, <literal>replace-static</literal> or
<literal>bind-static</literal> the static <filename>resolv.conf</filename> file supplied with
<citerefentry><refentrytitle>systemd-resolved.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
(specifically: <filename>/usr/lib/systemd/resolv.conf</filename>) is copied or bind mounted into the
container.</para>
<para>If set to <literal>copy-uplink</literal>, <literal>replace-uplink</literal> or
<literal>bind-uplink</literal> the uplink <filename>resolv.conf</filename> file managed by
<filename>systemd-resolved.service</filename> (specifically:
<filename>/run/systemd/resolve/resolv.conf</filename>) is copied or bind mounted into the
container.</para>
<para>If set to <literal>copy-stub</literal>, <literal>replace-stub</literal> or
<literal>bind-stub</literal> the stub <filename>resolv.conf</filename> file managed by
<filename>systemd-resolved.service</filename> (specifically:
<filename>/run/systemd/resolve/stub-resolv.conf</filename>) is copied or bind mounted into the
container.</para>
<para>If set to <literal>delete</literal> the <filename>/etc/resolv.conf</filename> file in the
container is deleted if it exists.</para>
<para>Finally, if set to <literal>auto</literal> the file is left as it is if private networking is
turned on (see <option>--private-network</option>). Otherwise, if
<filename>systemd-resolved.service</filename> is connectible its stub
<filename>resolv.conf</filename> file is used, and if not the host's
<filename>/etc/resolv.conf</filename> file is used. In the latter cases the file is copied if the
image is writable, and bind mounted otherwise.</para>
<para>It's recommended to use <literal>copy-…</literal> or <literal>replace-…</literal> if the
container shall be able to make changes to the DNS configuration on its own, deviating from the
host's settings. Otherwise <literal>bind</literal> is preferable, as it means direct changes to
<filename>/etc/resolv.conf</filename> in the container are not allowed, as it is a read-only bind
mount (but note that if the container has enough privileges, it might simply go ahead and unmount the
bind mount anyway). Note that both if the file is bind mounted and if it is copied no further
propagation of configuration is generally done after the one-time early initialization (this is
because the file is usually updated through copying and renaming). Defaults to
<literal>auto</literal>.</para></listitem>
</varlistentry>