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1fd961211d
systemd-nspawn will now print the PID of the child. An example showing how to enter the container is added to the man page. Support for nsenter without an explicit command was added in https://github.com/karelzak/util-linux/commit/5758069 (post v2.22.2). So this example requires both a new kernel and the latest util-linux.
378 lines
18 KiB
XML
378 lines
18 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd-nspawn">
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<refentryinfo>
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<title>systemd-nspawn</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-nspawn</refentrytitle>
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<manvolnum>1</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-nspawn</refname>
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<refpurpose>Spawn a namespace container for debugging, testing and building</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>systemd-nspawn</command>
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<arg choice="opt" rep="repeat">OPTIONS</arg>
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<arg choice="opt">COMMAND</arg>
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<arg choice="opt" rep="repeat">ARGS</arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-nspawn</command> may be used to
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run a command or OS in a light-weight namespace
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container. In many ways it is similar to
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<citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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but more powerful since it fully virtualizes the file
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system hierarchy, as well as the process tree, the
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various IPC subsystems and the host and domain
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name.</para>
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<para><command>systemd-nspawn</command> limits access
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to various kernel interfaces in the container to
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read-only, such as <filename>/sys</filename>,
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<filename>/proc/sys</filename> or
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<filename>/sys/fs/selinux</filename>. Network
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interfaces and the system clock may not be changed
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from within the container. Device nodes may not be
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created. The host system cannot be rebooted and kernel
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modules may not be loaded from within the
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container.</para>
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<para>Note that even though these security precautions
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are taken <command>systemd-nspawn</command> is not
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suitable for secure container setups. Many of the
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security features may be circumvented and are hence
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primarily useful to avoid accidental changes to the
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host system from the container. The intended use of
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this program is debugging and testing as well as
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building of packages, distributions and software
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involved with boot and systems management.</para>
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<para>In contrast to
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<citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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<command>systemd-nspawn</command> may be used to boot
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full Linux-based operating systems in a
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container.</para>
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<para>Use a tool like
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<citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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or
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<citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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to set up an OS directory tree suitable as file system
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hierarchy for <command>systemd-nspawn</command>
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containers.</para>
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<para>Note that <command>systemd-nspawn</command> will
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mount file systems private to the container to
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<filename>/dev</filename>,
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<filename>/run</filename> and similar. These will
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not be visible outside of the container, and their
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contents will be lost when the container exits.</para>
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<para>Note that running two
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<command>systemd-nspawn</command> containers from the
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same directory tree will not make processes in them
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see each other. The PID namespace separation of the
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two containers is complete and the containers will
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share very few runtime objects except for the
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underlying file system. It is however possible to
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enter an existing container, see
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<link linkend='example-nsenter'>Example 4</link> below.
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</para>
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<para><command>systemd-nspawn</command> implements the
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<ulink
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url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
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Interface</ulink> specification.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>If no arguments are passed the container is set
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up and a shell started in it, otherwise the passed
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command and arguments are executed in it. The
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following options are understood:</para>
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<variablelist>
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<varlistentry>
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<term><option>-h</option></term>
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<term><option>--help</option></term>
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<listitem><para>Prints a short help
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text and exits.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--version</option></term>
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<listitem><para>Prints a version string
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and exits.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-D</option></term>
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<term><option>--directory=</option></term>
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<listitem><para>Directory to use as
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file system root for the namespace
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container. If omitted the current
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directory will be
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used.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-b</option></term>
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<term><option>--boot</option></term>
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<listitem><para>Automatically search
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for an init binary and invoke it
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instead of a shell or a user supplied
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program.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-u</option></term>
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<term><option>--user=</option></term>
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<listitem><para>Run the command
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under specified user, create home
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directory and cd into it. As rest
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of systemd-nspawn, this is not
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the security feature and limits
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against accidental changes only.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--uuid=</option></term>
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<listitem><para>Set the specified uuid
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for the container. The init system
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will initialize
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<filename>/etc/machine-id</filename>
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from this if this file is not set yet.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-C</option></term>
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<term><option>--controllers=</option></term>
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<listitem><para>Makes the container appear in
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other hierarchies than the name=systemd:/ one.
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Takes a comma-separated list of controllers.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--private-network</option></term>
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<listitem><para>Turn off networking in
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the container. This makes all network
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interfaces unavailable in the
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container, with the exception of the
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loopback device.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--read-only</option></term>
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<listitem><para>Mount the root file
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system read only for the
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container.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--capability=</option></term>
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<listitem><para>List one or more
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additional capabilities to grant the
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container. Takes a comma separated
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list of capability names, see
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<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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for more information. Note that the
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following capabilities will be granted
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in any way: CAP_CHOWN,
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CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
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CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
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CAP_KILL, CAP_LEASE,
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CAP_LINUX_IMMUTABLE,
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CAP_NET_BIND_SERVICE,
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CAP_NET_BROADCAST, CAP_NET_RAW,
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CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP,
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CAP_SETUID, CAP_SYS_ADMIN,
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CAP_SYS_CHROOT, CAP_SYS_NICE,
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CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
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CAP_SYS_RESOURCE, CAP_SYS_BOOT,
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CAP_AUDIT_WRITE,
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CAP_AUDIT_CONTROL.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--link-journal=</option></term>
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<listitem><para>Control whether the
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container's journal shall be made
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visible to the host system. If enabled
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allows viewing the container's journal
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files from the host (but not vice
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versa). Takes one of
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<literal>no</literal>,
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<literal>host</literal>,
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<literal>guest</literal>,
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<literal>auto</literal>. If
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<literal>no</literal>, the journal is
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not linked. If <literal>host</literal>,
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the journal files are stored on the
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host file system (beneath
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<filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
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and the subdirectory is bind-mounted
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into the container at the same
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location. If <literal>guest</literal>,
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the journal files are stored on the
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guest file system (beneath
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<filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
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and the subdirectory is symlinked into the host
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at the same location. If
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<literal>auto</literal> (the default),
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and the right subdirectory of
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<filename>/var/log/journal</filename>
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exists, it will be bind mounted
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into the container. If the
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subdirectory doesn't exist, no
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linking is performed. Effectively,
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booting a container once with
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<literal>guest</literal> or
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<literal>host</literal> will link the
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journal persistently if further on
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the default of <literal>auto</literal>
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is used.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-j</option></term>
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<listitem><para>Equivalent to
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<option>--link-journal=guest</option>.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Example 1</title>
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<programlisting># yum -y --releasever=19 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
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# systemd-nspawn -bD /srv/mycontainer</programlisting>
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<para>This installs a minimal Fedora distribution into
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the directory <filename>/srv/mycontainer/</filename> and
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then boots an OS in a namespace container in
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it.</para>
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</refsect1>
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<refsect1>
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<title>Example 2</title>
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<programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
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# systemd-nspawn -D ~/debian-tree/</programlisting>
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<para>This installs a minimal Debian unstable
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distribution into the directory
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<filename>~/debian-tree/</filename> and then spawns a
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shell in a namespace container in it.</para>
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</refsect1>
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<refsect1>
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<title>Example 3</title>
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<programlisting># pacstrap -c -d ~/arch-tree/ base
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# systemd-nspawn -bD ~/arch-tree/</programlisting>
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<para>This installs a mimimal Arch Linux distribution into
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the directory <filename>~/arch-tree/</filename> and then
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boots an OS in a namespace container in it.</para>
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</refsect1>
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<refsect1 id='example-nsenter'>
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<title>Example 4</title>
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<para>To enter the container, PID of one of the
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processes sharing the new namespaces must be used.
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<command>systemd-nspawn</command> prints the PID
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(as viewed from the outside) of the launched process,
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and it can be used to enter the container.</para>
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<programlisting># nsenter -muinpt $PID</programlisting>
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<para><citerefentry><refentrytitle>nsenter</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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is part of
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<ulink url="https://github.com/karelzak/util-linux">util-linux</ulink>.
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Kernel support for entering namespaces was added in
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Linux 3.8.</para>
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</refsect1>
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<refsect1>
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<title>Exit status</title>
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<para>The exit code of the program executed in the
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container is returned.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>unshare</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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