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man: document systemd-nspawn
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Lennart Poettering
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@ -519,6 +519,7 @@ MANPAGES = \
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man/systemctl.1 \
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man/systemadm.1 \
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man/systemd-cgls.1 \
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man/systemd-nspawn.1 \
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man/systemd-tmpfiles.8 \
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man/systemd-notify.1 \
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man/sd_notify.3 \
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190
man/systemd-nspawn.xml
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190
man/systemd-nspawn.xml
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<?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 General Public License as published by
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the Free Software Foundation; either version 2 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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General Public License for more details.
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You should have received a copy of the GNU 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 <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="opt">COMMAND</arg> <arg choice="opt" rep="repeat">ARGS</arg></command>
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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 hierachy, 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>/selinux</filename>. Network interfaces and
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the system clock may not be changed from within the
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container. Device nodes may not be created. The host
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system cannot be rebooted and kernel modules may not
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be loaded from within the 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>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry> or <citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</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> 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>/dev/.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 seperation 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.</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>--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>--directory=</option></term>
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<term><option>--D</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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</variablelist>
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</refsect1>
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<refsect1>
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<title>Example 1</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 2</title>
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<programlisting># mock --init
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# systemd-nspawn -D /var/lib/mock/fedora-rawhide-x86_64/root/ /bin/systemd systemd.log_level=debug</programlisting>
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<para>This installs a minimal Fedora distribution into
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a subdirectory of <filename>/var/lib/mock/</filename>
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and then boots an OS in a namespace container in it,
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with systemd as init system, configured for debug
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logging.</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>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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<citerefentry><refentrytitle>mock</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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