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systemd/man/systemd-nspawn.xml
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<?xml version='1.0'?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY fedora_latest_version "32">
<!ENTITY fedora_cloud_release "1.6">
]>
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="systemd-nspawn"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>systemd-nspawn</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-nspawn</refentrytitle>
<manvolnum>1</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-nspawn</refname>
<refpurpose>Spawn a command or OS in a light-weight container</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>systemd-nspawn</command>
<arg choice="opt" rep="repeat">OPTIONS</arg>
<arg choice="opt"><replaceable>COMMAND</replaceable>
<arg choice="opt" rep="repeat">ARGS</arg>
</arg>
</cmdsynopsis>
<cmdsynopsis>
<command>systemd-nspawn</command>
<arg choice="plain">--boot</arg>
<arg choice="opt" rep="repeat">OPTIONS</arg>
<arg choice="opt" rep="repeat">ARGS</arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><command>systemd-nspawn</command> may be used to run a command or OS in a light-weight namespace
container. In many ways it is similar to <citerefentry
project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>, but more powerful
since it fully virtualizes the file system hierarchy, as well as the process tree, the various IPC subsystems and
the host and domain name.</para>
<para><command>systemd-nspawn</command> may be invoked on any directory tree containing an operating system tree,
using the <option>--directory=</option> command line option. By using the <option>--machine=</option> option an OS
tree is automatically searched for in a couple of locations, most importantly in
<filename>/var/lib/machines</filename>, the suggested directory to place OS container images installed on the
system.</para>
<para>In contrast to <citerefentry
project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry> <command>systemd-nspawn</command>
may be used to boot full Linux-based operating systems in a container.</para>
<para><command>systemd-nspawn</command> limits access to various kernel interfaces in the container to read-only,
such as <filename>/sys</filename>, <filename>/proc/sys</filename> or <filename>/sys/fs/selinux</filename>. The
host's network interfaces and the system clock may not be changed from within the container. Device nodes may not
be created. The host system cannot be rebooted and kernel modules may not be loaded from within the
container.</para>
<para>Use a tool like <citerefentry
project='mankier'><refentrytitle>dnf</refentrytitle><manvolnum>8</manvolnum></citerefentry>, <citerefentry
project='die-net'><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>, or
<citerefentry project='archlinux'><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry> to
set up an OS directory tree suitable as file system hierarchy for <command>systemd-nspawn</command> containers. See
the Examples section below for details on suitable invocation of these commands.</para>
<para>As a safety check <command>systemd-nspawn</command> will verify the existence of
<filename>/usr/lib/os-release</filename> or <filename>/etc/os-release</filename> in the container tree before
starting the container (see
<citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>). It might be
necessary to add this file to the container tree manually if the OS of the container is too old to contain this
file out-of-the-box.</para>
<para><command>systemd-nspawn</command> may be invoked directly from the interactive command line or run as system
service in the background. In this mode each container instance runs as its own service instance; a default
template unit file <filename>systemd-nspawn@.service</filename> is provided to make this easy, taking the container
name as instance identifier. Note that different default options apply when <command>systemd-nspawn</command> is
invoked by the template unit file than interactively on the command line. Most importantly the template unit file
makes use of the <option>--boot</option> which is not the default in case <command>systemd-nspawn</command> is
invoked from the interactive command line. Further differences with the defaults are documented along with the
various supported options below.</para>
<para>The <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool may
be used to execute a number of operations on containers. In particular it provides easy-to-use commands to run
containers as system services using the <filename>systemd-nspawn@.service</filename> template unit
file.</para>
<para>Along with each container a settings file with the <filename>.nspawn</filename> suffix may exist, containing
additional settings to apply when running the container. See
<citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details. Settings files override the default options used by the <filename>systemd-nspawn@.service</filename>
template unit file, making it usually unnecessary to alter this template file directly.</para>
<para>Note that <command>systemd-nspawn</command> will mount file systems private to the container to
<filename>/dev</filename>, <filename>/run</filename> and similar. These will not be visible outside of the
container, and their contents will be lost when the container exits.</para>
<para>Note that running two <command>systemd-nspawn</command> containers from the same directory tree will not make
processes in them see each other. The PID namespace separation of the two containers is complete and the containers
will share very few runtime objects except for the underlying file system. Use
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<command>login</command> or <command>shell</command> commands to request an additional login session in a running
container.</para>
<para><command>systemd-nspawn</command> implements the <ulink
url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink> specification.</para>
<para>While running, containers invoked with <command>systemd-nspawn</command> are registered with the
<citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry> service that
keeps track of running containers, and provides programming interfaces to interact with them.</para>
</refsect1>
<refsect1>
<title>Options</title>
<para>If option <option>-b</option> is specified, the arguments
are used as arguments for the init program. Otherwise,
<replaceable>COMMAND</replaceable> specifies the program to launch
in the container, and the remaining arguments are used as
arguments for this program. If <option>--boot</option> is not used and
no arguments are specified, a shell is launched in the
container.</para>
<para>The following options are understood:</para>
<variablelist>
<varlistentry>
<term><option>-q</option></term>
<term><option>--quiet</option></term>
<listitem><para>Turns off any status output by the tool
itself. When this switch is used, the only output from nspawn
will be the console output of the container OS
itself.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--settings=</option><replaceable>MODE</replaceable></term>
<listitem><para>Controls whether
<command>systemd-nspawn</command> shall search for and use
additional per-container settings from
<filename>.nspawn</filename> files. Takes a boolean or the
special values <option>override</option> or
<option>trusted</option>.</para>
<para>If enabled (the default), a settings file named after the
machine (as specified with the <option>--machine=</option>
setting, or derived from the directory or image file name)
with the suffix <filename>.nspawn</filename> is searched in
<filename>/etc/systemd/nspawn/</filename> and
<filename>/run/systemd/nspawn/</filename>. If it is found
there, its settings are read and used. If it is not found
there, it is subsequently searched in the same directory as the
image file or in the immediate parent of the root directory of
the container. In this case, if the file is found, its settings
will be also read and used, but potentially unsafe settings
are ignored. Note that in both these cases, settings on the
command line take precedence over the corresponding settings
from loaded <filename>.nspawn</filename> files, if both are
specified. Unsafe settings are considered all settings that
elevate the container's privileges or grant access to
additional resources such as files or directories of the
host. For details about the format and contents of
<filename>.nspawn</filename> files, consult
<citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>If this option is set to <option>override</option>, the
file is searched, read and used the same way, however, the order of
precedence is reversed: settings read from the
<filename>.nspawn</filename> file will take precedence over
the corresponding command line options, if both are
specified.</para>
<para>If this option is set to <option>trusted</option>, the
file is searched, read and used the same way, but regardless
of being found in <filename>/etc/systemd/nspawn/</filename>,
<filename>/run/systemd/nspawn/</filename> or next to the image
file or container root directory, all settings will take
effect, however, command line arguments still take precedence
over corresponding settings.</para>
<para>If disabled, no <filename>.nspawn</filename> file is read
and no settings except the ones on the command line are in
effect.</para></listitem>
</varlistentry>
</variablelist>
<refsect2>
<title>Image Options</title>
<variablelist>
<varlistentry>
<term><option>-D</option></term>
<term><option>--directory=</option></term>
<listitem><para>Directory to use as file system root for the
container.</para>
<para>If neither <option>--directory=</option>, nor
<option>--image=</option> is specified the directory is
determined by searching for a directory named the same as the
machine name specified with <option>--machine=</option>. See
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
section "Files and Directories" for the precise search path.</para>
<para>If neither <option>--directory=</option>,
<option>--image=</option>, nor <option>--machine=</option>
are specified, the current directory will
be used. May not be specified together with
<option>--image=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--template=</option></term>
<listitem><para>Directory or <literal>btrfs</literal> subvolume to use as template for the
container's root directory. If this is specified and the container's root directory (as configured by
<option>--directory=</option>) does not yet exist it is created as <literal>btrfs</literal> snapshot
(if supported) or plain directory (otherwise) and populated from this template tree. Ideally, the
specified template path refers to the root of a <literal>btrfs</literal> subvolume, in which case a
simple copy-on-write snapshot is taken, and populating the root directory is instant. If the
specified template path does not refer to the root of a <literal>btrfs</literal> subvolume (or not
even to a <literal>btrfs</literal> file system at all), the tree is copied (though possibly in a
'reflink' copy-on-write scheme — if the file system supports that), which can be substantially more
time-consuming. Note that the snapshot taken is of the specified directory or subvolume, including
all subdirectories and subvolumes below it, but excluding any sub-mounts. May not be specified
together with <option>--image=</option> or <option>--ephemeral</option>.</para>
<para>Note that this switch leaves hostname, machine ID and
all other settings that could identify the instance
unmodified.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-x</option></term>
<term><option>--ephemeral</option></term>
<listitem><para>If specified, the container is run with a temporary snapshot of its file system that is removed
immediately when the container terminates. May not be specified together with
<option>--template=</option>.</para>
<para>Note that this switch leaves hostname, machine ID and all other settings that could identify
the instance unmodified. Please note that — as with <option>--template=</option> — taking the
temporary snapshot is more efficient on file systems that support subvolume snapshots or 'reflinks'
natively (<literal>btrfs</literal> or new <literal>xfs</literal>) than on more traditional file
systems that do not (<literal>ext4</literal>). Note that the snapshot taken is of the specified
directory or subvolume, including all subdirectories and subvolumes below it, but excluding any
sub-mounts.</para>
<para>With this option no modifications of the container image are retained. Use
<option>--volatile=</option> (described below) for other mechanisms to restrict persistency of
container images during runtime.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-i</option></term>
<term><option>--image=</option></term>
<listitem><para>Disk image to mount the root directory for the
container from. Takes a path to a regular file or to a block
device node. The file or block device must contain
either:</para>
<itemizedlist>
<listitem><para>An MBR partition table with a single
partition of type 0x83 that is marked
bootable.</para></listitem>
<listitem><para>A GUID partition table (GPT) with a single
partition of type
0fc63daf-8483-4772-8e79-3d69d8477de4.</para></listitem>
<listitem><para>A GUID partition table (GPT) with a marked
root partition which is mounted as the root directory of the
container. Optionally, GPT images may contain a home and/or
a server data partition which are mounted to the appropriate
places in the container. All these partitions must be
identified by the partition types defined by the <ulink
url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable
Partitions Specification</ulink>.</para></listitem>
<listitem><para>No partition table, and a single file system spanning the whole image.</para></listitem>
</itemizedlist>
<para>On GPT images, if an EFI System Partition (ESP) is discovered, it is automatically mounted to
<filename>/efi</filename> (or <filename>/boot</filename> as fallback) in case a directory by this name exists
and is empty.</para>
<para>Partitions encrypted with LUKS are automatically decrypted. Also, on GPT images dm-verity data integrity
hash partitions are set up if the root hash for them is specified using the <option>--root-hash=</option>
option.</para>
<para>Single file system images (i.e. file systems without a surrounding partition table) can be opened using
dm-verity if the integrity data is passed using the <option>--root-hash=</option> and
<option>--verity-data=</option> (and optionally <option>--root-hash-sig=</option>) options.</para>
<para>Any other partitions, such as foreign partitions or swap partitions are not mounted. May not be specified
together with <option>--directory=</option>, <option>--template=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--oci-bundle=</option></term>
<listitem><para>Takes the path to an OCI runtime bundle to invoke, as specified in the <ulink
url="https://github.com/opencontainers/runtime-spec/blob/master/spec.md">OCI Runtime Specification</ulink>. In
this case no <filename>.nspawn</filename> file is loaded, and the root directory and various settings are read
from the OCI runtime JSON data (but data passed on the command line takes precedence).</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--read-only</option></term>
<listitem><para>Mount the container's root file system (and any other file systems container in the container
image) read-only. This has no effect on additional mounts made with <option>--bind=</option>,
<option>--tmpfs=</option> and similar options. This mode is implied if the container image file or directory is
marked read-only itself. It is also implied if <option>--volatile=</option> is used. In this case the container
image on disk is strictly read-only, while changes are permitted but kept non-persistently in memory only. For
further details, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--volatile</option></term>
<term><option>--volatile=</option><replaceable>MODE</replaceable></term>
<listitem><para>Boots the container in volatile mode. When no mode parameter is passed or when mode is
specified as <option>yes</option>, full volatile mode is enabled. This means the root directory is mounted as a
mostly unpopulated <literal>tmpfs</literal> instance, and <filename>/usr/</filename> from the OS tree is
mounted into it in read-only mode (the system thus starts up with read-only OS image, but pristine state and
configuration, any changes are lost on shutdown). When the mode parameter is specified as
<option>state</option>, the OS tree is mounted read-only, but <filename>/var/</filename> is mounted as a
writable <literal>tmpfs</literal> instance into it (the system thus starts up with read-only OS resources and
configuration, but pristine state, and any changes to the latter are lost on shutdown). When the mode parameter
is specified as <option>overlay</option> the read-only root file system is combined with a writable
<filename>tmpfs</filename> instance through <literal>overlayfs</literal>, so that it appears at it normally
would, but any changes are applied to the temporary file system only and lost when the container is
terminated. When the mode parameter is specified as <option>no</option> (the default), the whole OS tree is
made available writable (unless <option>--read-only</option> is specified, see above).</para>
<para>Note that if one of the volatile modes is chosen, its effect is limited to the root file system (or
<filename>/var/</filename> in case of <option>state</option>), and any other mounts placed in the hierarchy are
unaffected — regardless if they are established automatically (e.g. the EFI system partition that might be
mounted to <filename>/efi/</filename> or <filename>/boot/</filename>) or explicitly (e.g. through an additional
command line option such as <option>--bind=</option>, see below). This means, even if
<option>--volatile=overlay</option> is used changes to <filename>/efi/</filename> or
<filename>/boot/</filename> are prohibited in case such a partition exists in the container image operated on,
and even if <option>--volatile=state</option> is used the hypothetical file <filename>/etc/foobar</filename> is
potentially writable if <option>--bind=/etc/foobar</option> if used to mount it from outside the read-only
container <filename>/etc</filename> directory.</para>
<para>The <option>--ephemeral</option> option is closely related to this setting, and provides similar
behaviour by making a temporary, ephemeral copy of the whole OS image and executing that. For further details,
see above.</para>
<para>The <option>--tmpfs=</option> and <option>--overlay=</option> options provide similar functionality, but
for specific sub-directories of the OS image only. For details, see below.</para>
<para>This option provides similar functionality for containers as the <literal>systemd.volatile=</literal>
kernel command line switch provides for host systems. See
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details.</para>
<para>Note that setting this option to <option>yes</option> or <option>state</option> will only work
correctly with operating systems in the container that can boot up with only
<filename>/usr/</filename> mounted, and are able to automatically populate <filename>/var/</filename>
(and <filename>/etc/</filename> in case of <literal>--volatile=yes</literal>). Specifically, this
means that operating systems that follow the historic split of <filename>/bin/</filename> and
<filename>/lib/</filename> (and related directories) from <filename>/usr/</filename> (i.e. where the
former are not symlinks into the latter) are not supported by <literal>--volatile=yes</literal> as
container payload. The <option>overlay</option> option does not require any particular preparations
in the OS, but do note that <literal>overlayfs</literal> behaviour differs from regular file systems
in a number of ways, and hence compatibility is limited.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--root-hash=</option></term>
<listitem><para>Takes a data integrity (dm-verity) root hash specified in hexadecimal. This option enables data
integrity checks using dm-verity, if the used image contains the appropriate integrity data (see above). The
specified hash must match the root hash of integrity data, and is usually at least 256 bits (and hence 64
formatted hexadecimal characters) long (in case of SHA256 for example). If this option is not specified, but
the image file carries the <literal>user.verity.roothash</literal> extended file attribute (see <citerefentry
project='man-pages'><refentrytitle>xattr</refentrytitle><manvolnum>7</manvolnum></citerefentry>), then the root
hash is read from it, also as formatted hexadecimal characters. If the extended file attribute is not found (or
is not supported by the underlying file system), but a file with the <filename>.roothash</filename> suffix is
found next to the image file, bearing otherwise the same name (except if the image has the
<filename>.raw</filename> suffix, in which case the root hash file must not have it in its name), the root hash
is read from it and automatically used, also as formatted hexadecimal characters.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--root-hash-sig=</option></term>
<listitem><para>Takes a PKCS7 formatted binary signature of the <option>--root-hash=</option> option as a path
to a DER encoded signature file or as an ASCII base64 string encoding of the DER encoded signature, prefixed
by <literal>base64:</literal>. The dm-verity volume will only be opened if the signature of the root hash hex
string is valid and done by a public key present in the kernel keyring. If this option is not specified, but a
file with the <filename>.roothash.p7s</filename> suffix is found next to the image file, bearing otherwise the
same name (except if the image has the <filename>.raw</filename> suffix, in which case the signature file must
not have it in its name), the signature is read from it and automatically used.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--verity-data=</option></term>
<listitem><para>Takes the path to a data integrity (dm-verity) file. This option enables data integrity checks
using dm-verity, if a root-hash is passed and if the used image itself does not contains the integrity data.
The integrity data must be matched by the root hash. If this option is not specified, but a file with the
<filename>.verity</filename> suffix is found next to the image file, bearing otherwise the same name (except if
the image has the <filename>.raw</filename> suffix, in which case the verity data file must not have it in its name),
the verity data is read from it and automatically used.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--pivot-root=</option></term>
<listitem><para>Pivot the specified directory to <filename>/</filename> inside the container, and either unmount the
container's old root, or pivot it to another specified directory. Takes one of: a path argument — in which case the
specified path will be pivoted to <filename>/</filename> and the old root will be unmounted; or a colon-separated pair
of new root path and pivot destination for the old root. The new root path will be pivoted to <filename>/</filename>,
and the old <filename>/</filename> will be pivoted to the other directory. Both paths must be absolute, and are resolved
in the container's file system namespace.</para>
<para>This is for containers which have several bootable directories in them; for example, several
<ulink url="https://ostree.readthedocs.io/en/latest/">OSTree</ulink> deployments. It emulates the behavior of
the boot loader and initial RAM disk which normally select which directory to mount as the root and start the
container's PID 1 in.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Execution Options</title>
<variablelist>
<varlistentry>
<term><option>-a</option></term>
<term><option>--as-pid2</option></term>
<listitem><para>Invoke the shell or specified program as process ID (PID) 2 instead of PID 1 (init). By
default, if neither this option nor <option>--boot</option> is used, the selected program is run as the process
with PID 1, a mode only suitable for programs that are aware of the special semantics that the process with
PID 1 has on UNIX. For example, it needs to reap all processes reparented to it, and should implement
<command>sysvinit</command> compatible signal handling (specifically: it needs to reboot on SIGINT, reexecute
on SIGTERM, reload configuration on SIGHUP, and so on). With <option>--as-pid2</option> a minimal stub init
process is run as PID 1 and the selected program is executed as PID 2 (and hence does not need to implement any
special semantics). The stub init process will reap processes as necessary and react appropriately to
signals. It is recommended to use this mode to invoke arbitrary commands in containers, unless they have been
modified to run correctly as PID 1. Or in other words: this switch should be used for pretty much all commands,
except when the command refers to an init or shell implementation, as these are generally capable of running
correctly as PID 1. This option may not be combined with <option>--boot</option>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-b</option></term>
<term><option>--boot</option></term>
<listitem><para>Automatically search for an init program and invoke it as PID 1, instead of a shell or a user
supplied program. If this option is used, arguments specified on the command line are used as arguments for the
init program. This option may not be combined with <option>--as-pid2</option>.</para>
<para>The following table explains the different modes of invocation and relationship to
<option>--as-pid2</option> (see above):</para>
<table>
<title>Invocation Mode</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<colspec colname="switch" />
<colspec colname="explanation" />
<thead>
<row>
<entry>Switch</entry>
<entry>Explanation</entry>
</row>
</thead>
<tbody>
<row>
<entry>Neither <option>--as-pid2</option> nor <option>--boot</option> specified</entry>
<entry>The passed parameters are interpreted as the command line, which is executed as PID 1 in the container.</entry>
</row>
<row>
<entry><option>--as-pid2</option> specified</entry>
<entry>The passed parameters are interpreted as the command line, which is executed as PID 2 in the container. A stub init process is run as PID 1.</entry>
</row>
<row>
<entry><option>--boot</option> specified</entry>
<entry>An init program is automatically searched for and run as PID 1 in the container. The passed parameters are used as invocation parameters for this process.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>Note that <option>--boot</option> is the default mode of operation if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--chdir=</option></term>
<listitem><para>Change to the specified working directory before invoking the process in the container. Expects
an absolute path in the container's file system namespace.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-E <replaceable>NAME</replaceable>=<replaceable>VALUE</replaceable></option></term>
<term><option>--setenv=<replaceable>NAME</replaceable>=<replaceable>VALUE</replaceable></option></term>
<listitem><para>Specifies an environment variable assignment
to pass to the init process in the container, in the format
<literal>NAME=VALUE</literal>. This may be used to override
the default variables or to set additional variables. This
parameter may be used more than once.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-u</option></term>
<term><option>--user=</option></term>
<listitem><para>After transitioning into the container, change to the specified user defined in the
container's user database. Like all other systemd-nspawn features, this is not a security feature and
provides protection against accidental destructive operations only.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--kill-signal=</option></term>
<listitem><para>Specify the process signal to send to the container's PID 1 when nspawn itself receives
<constant>SIGTERM</constant>, in order to trigger an orderly shutdown of the container. Defaults to
<constant>SIGRTMIN+3</constant> if <option>--boot</option> is used (on systemd-compatible init systems
<constant>SIGRTMIN+3</constant> triggers an orderly shutdown). If <option>--boot</option> is not used and this
option is not specified the container's processes are terminated abruptly via <constant>SIGKILL</constant>. For
a list of valid signals, see <citerefentry
project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--notify-ready=</option></term>
<listitem><para>Configures support for notifications from the container's init process.
<option>--notify-ready=</option> takes a boolean (<option>no</option> and <option>yes</option>).
With option <option>no</option> systemd-nspawn notifies systemd
with a <literal>READY=1</literal> message when the init process is created.
With option <option>yes</option> systemd-nspawn waits for the
<literal>READY=1</literal> message from the init process in the container
before sending its own to systemd. For more details about notifications
see <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>System Identity Options</title>
<variablelist>
<varlistentry>
<term><option>-M</option></term>
<term><option>--machine=</option></term>
<listitem><para>Sets the machine name for this container. This
name may be used to identify this container during its runtime
(for example in tools like
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and similar), and is used to initialize the container's
hostname (which the container can choose to override,
however). If not specified, the last component of the root
directory path of the container is used, possibly suffixed
with a random identifier in case <option>--ephemeral</option>
mode is selected. If the root directory selected is the host's
root directory the host's hostname is used as default
instead.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--hostname=</option></term>
<listitem><para>Controls the hostname to set within the container, if different from the machine name. Expects
a valid hostname as argument. If this option is used, the kernel hostname of the container will be set to this
value, otherwise it will be initialized to the machine name as controlled by the <option>--machine=</option>
option described above. The machine name is used for various aspect of identification of the container from the
outside, the kernel hostname configurable with this option is useful for the container to identify itself from
the inside. It is usually a good idea to keep both forms of identification synchronized, in order to avoid
confusion. It is hence recommended to avoid usage of this option, and use <option>--machine=</option>
exclusively. Note that regardless whether the container's hostname is initialized from the name set with
<option>--hostname=</option> or the one set with <option>--machine=</option>, the container can later override
its kernel hostname freely on its own as well.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--uuid=</option></term>
<listitem><para>Set the specified UUID for the container. The
init system will initialize
<filename>/etc/machine-id</filename> from this if this file is
not set yet. Note that this option takes effect only if
<filename>/etc/machine-id</filename> in the container is
unpopulated.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Property Options</title>
<variablelist>
<varlistentry>
<term><option>-S</option></term>
<term><option>--slice=</option></term>
<listitem><para>Make the container part of the specified slice, instead of the default
<filename>machine.slice</filename>. This applies only if the machine is run in its own scope unit, i.e. if
<option>--keep-unit</option> isn't used.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--property=</option></term>
<listitem><para>Set a unit property on the scope unit to register for the machine. This applies only if the
machine is run in its own scope unit, i.e. if <option>--keep-unit</option> isn't used. Takes unit property
assignments in the same format as <command>systemctl set-property</command>. This is useful to set memory
limits and similar for container.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--register=</option></term>
<listitem><para>Controls whether the container is registered with
<citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes a
boolean argument, which defaults to <literal>yes</literal>. This option should be enabled when the container
runs a full Operating System (more specifically: a system and service manager as PID 1), and is useful to
ensure that the container is accessible via
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry> and shown by
tools such as <citerefentry
project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>. If the container
does not run a service manager, it is recommended to set this option to
<literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--keep-unit</option></term>
<listitem><para>Instead of creating a transient scope unit to run the container in, simply use the service or
scope unit <command>systemd-nspawn</command> has been invoked in. If <option>--register=yes</option> is set
this unit is registered with
<citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. This
switch should be used if <command>systemd-nspawn</command> is invoked from within a service unit, and the
service unit's sole purpose is to run a single <command>systemd-nspawn</command> container. This option is not
available if run from a user session.</para>
<para>Note that passing <option>--keep-unit</option> disables the effect of <option>--slice=</option> and
<option>--property=</option>. Use <option>--keep-unit</option> and <option>--register=no</option> in
combination to disable any kind of unit allocation or registration with
<command>systemd-machined</command>.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>User Namespacing Options</title>
<variablelist>
<varlistentry>
<term><option>--private-users=</option></term>
<listitem><para>Controls user namespacing. If enabled, the container will run with its own private set of UNIX
user and group ids (UIDs and GIDs). This involves mapping the private UIDs/GIDs used in the container (starting
with the container's root user 0 and up) to a range of UIDs/GIDs on the host that are not used for other
purposes (usually in the range beyond the host's UID/GID 65536). The parameter may be specified as follows:</para>
<orderedlist>
<listitem><para>If one or two colon-separated numbers are specified, user namespacing is turned on. The first
parameter specifies the first host UID/GID to assign to the container, the second parameter specifies the
number of host UIDs/GIDs to assign to the container. If the second parameter is omitted, 65536 UIDs/GIDs are
assigned.</para></listitem>
<listitem><para>If the parameter is omitted, or true, user namespacing is turned on. The UID/GID range to
use is determined automatically from the file ownership of the root directory of the container's directory
tree. To use this option, make sure to prepare the directory tree in advance, and ensure that all files and
directories in it are owned by UIDs/GIDs in the range you'd like to use. Also, make sure that used file ACLs
exclusively reference UIDs/GIDs in the appropriate range. If this mode is used the number of UIDs/GIDs
assigned to the container for use is 65536, and the UID/GID of the root directory must be a multiple of
65536.</para></listitem>
<listitem><para>If the parameter is false, user namespacing is turned off. This is the default.</para>
</listitem>
<listitem><para>The special value <literal>pick</literal> turns on user namespacing. In this case the UID/GID
range is automatically chosen. As first step, the file owner of the root directory of the container's
directory tree is read, and it is checked that it is currently not used by the system otherwise (in
particular, that no other container is using it). If this check is successful, the UID/GID range determined
this way is used, similar to the behavior if "yes" is specified. If the check is not successful (and thus
the UID/GID range indicated in the root directory's file owner is already used elsewhere) a new – currently
unused – UID/GID range of 65536 UIDs/GIDs is randomly chosen between the host UID/GIDs of 524288 and
1878982656, always starting at a multiple of 65536. This setting implies
<option>--private-users-chown</option> (see below), which has the effect that the files and directories in
the container's directory tree will be owned by the appropriate users of the range picked. Using this option
makes user namespace behavior fully automatic. Note that the first invocation of a previously unused
container image might result in picking a new UID/GID range for it, and thus in the (possibly expensive) file
ownership adjustment operation. However, subsequent invocations of the container will be cheap (unless of
course the picked UID/GID range is assigned to a different use by then).</para></listitem>
</orderedlist>
<para>It is recommended to assign at least 65536 UIDs/GIDs to each container, so that the usable UID/GID range in the
container covers 16 bit. For best security, do not assign overlapping UID/GID ranges to multiple containers. It is
hence a good idea to use the upper 16 bit of the host 32-bit UIDs/GIDs as container identifier, while the lower 16
bit encode the container UID/GID used. This is in fact the behavior enforced by the
<option>--private-users=pick</option> option.</para>
<para>When user namespaces are used, the GID range assigned to each container is always chosen identical to the
UID range.</para>
<para>In most cases, using <option>--private-users=pick</option> is the recommended option as it enhances
container security massively and operates fully automatically in most cases.</para>
<para>Note that the picked UID/GID range is not written to <filename>/etc/passwd</filename> or
<filename>/etc/group</filename>. In fact, the allocation of the range is not stored persistently anywhere,
except in the file ownership of the files and directories of the container.</para>
<para>Note that when user namespacing is used file ownership on disk reflects this, and all of the container's
files and directories are owned by the container's effective user and group IDs. This means that copying files
from and to the container image requires correction of the numeric UID/GID values, according to the UID/GID
shift applied.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--private-users-chown</option></term>
<listitem><para>If specified, all files and directories in the container's directory tree will be
adjusted so that they are owned by the appropriate UIDs/GIDs selected for the container (see above).
This operation is potentially expensive, as it involves iterating through the full directory tree of
the container. Besides actual file ownership, file ACLs are adjusted as well.</para>
<para>This option is implied if <option>--private-users=pick</option> is used. This option has no effect if
user namespacing is not used.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-U</option></term>
<listitem><para>If the kernel supports the user namespaces feature, equivalent to
<option>--private-users=pick --private-users-chown</option>, otherwise equivalent to
<option>--private-users=no</option>.</para>
<para>Note that <option>-U</option> is the default if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para>
<para>Note: it is possible to undo the effect of <option>--private-users-chown</option> (or
<option>-U</option>) on the file system by redoing the operation with the first UID of 0:</para>
<programlisting>systemd-nspawn … --private-users=0 --private-users-chown</programlisting>
</listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Networking Options</title>
<variablelist>
<varlistentry>
<term><option>--private-network</option></term>
<listitem><para>Disconnect networking of the container from
the host. This makes all network interfaces unavailable in the
container, with the exception of the loopback device and those
specified with <option>--network-interface=</option> and
configured with <option>--network-veth</option>. If this
option is specified, the <constant>CAP_NET_ADMIN</constant> capability will be
added to the set of capabilities the container retains. The
latter may be disabled by using <option>--drop-capability=</option>.
If this option is not specified (or implied by one of the options
listed below), the container will have full access to the host network.
</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--network-interface=</option></term>
<listitem><para>Assign the specified network interface to the
container. This will remove the specified interface from the
calling namespace and place it in the container. When the
container terminates, it is moved back to the host namespace.
Note that <option>--network-interface=</option> implies
<option>--private-network</option>. This option may be used
more than once to add multiple network interfaces to the
container.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--network-macvlan=</option></term>
<listitem><para>Create a <literal>macvlan</literal> interface
of the specified Ethernet network interface and add it to the
container. A <literal>macvlan</literal> interface is a virtual
interface that adds a second MAC address to an existing
physical Ethernet link. The interface in the container will be
named after the interface on the host, prefixed with
<literal>mv-</literal>. Note that
<option>--network-macvlan=</option> implies
<option>--private-network</option>. This option may be used
more than once to add multiple network interfaces to the
container.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--network-ipvlan=</option></term>
<listitem><para>Create an <literal>ipvlan</literal> interface
of the specified Ethernet network interface and add it to the
container. An <literal>ipvlan</literal> interface is a virtual
interface, similar to a <literal>macvlan</literal> interface,
which uses the same MAC address as the underlying interface.
The interface in the container will be named after the
interface on the host, prefixed with <literal>iv-</literal>.
Note that <option>--network-ipvlan=</option> implies
<option>--private-network</option>. This option may be used
more than once to add multiple network interfaces to the
container.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-n</option></term>
<term><option>--network-veth</option></term>
<listitem><para>Create a virtual Ethernet link (<literal>veth</literal>) between host and container. The host
side of the Ethernet link will be available as a network interface named after the container's name (as
specified with <option>--machine=</option>), prefixed with <literal>ve-</literal>. The container side of the
Ethernet link will be named <literal>host0</literal>. The <option>--network-veth</option> option implies
<option>--private-network</option>.</para>
<para>Note that
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
includes by default a network file <filename>/usr/lib/systemd/network/80-container-ve.network</filename>
matching the host-side interfaces created this way, which contains settings to enable automatic address
provisioning on the created virtual link via DHCP, as well as automatic IP routing onto the host's external
network interfaces. It also contains <filename>/usr/lib/systemd/network/80-container-host0.network</filename>
matching the container-side interface created this way, containing settings to enable client side address
assignment via DHCP. In case <filename>systemd-networkd</filename> is running on both the host and inside the
container, automatic IP communication from the container to the host is thus available, with further
connectivity to the external network.</para>
<para>Note that <option>--network-veth</option> is the default if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para>
<para>Note that on Linux network interface names may have a length of 15 characters at maximum, while
container names may have a length up to 64 characters. As this option derives the host-side interface
name from the container name the name is possibly truncated. Thus, care needs to be taken to ensure
that interface names remain unique in this case, or even better container names are generally not
chosen longer than 12 characters, to avoid the truncation. If the name is truncated,
<command>systemd-nspawn</command> will automatically append a 4-digit hash value to the name to
reduce the chance of collisions. However, the hash algorithm is not collision-free. (See
<citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details on older naming algorithms for this interface). Alternatively, the
<option>--network-veth-extra=</option> option may be used, which allows free configuration of the
host-side interface name independently of the container name — but might require a bit more
additional configuration in case bridging in a fashion similar to <option>--network-bridge=</option>
is desired.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--network-veth-extra=</option></term>
<listitem><para>Adds an additional virtual Ethernet link
between host and container. Takes a colon-separated pair of
host interface name and container interface name. The latter
may be omitted in which case the container and host sides will
be assigned the same name. This switch is independent of
<option>--network-veth</option>, and — in contrast — may be
used multiple times, and allows configuration of the network
interface names. Note that <option>--network-bridge=</option>
has no effect on interfaces created with
<option>--network-veth-extra=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--network-bridge=</option></term>
<listitem><para>Adds the host side of the Ethernet link created with <option>--network-veth</option>
to the specified Ethernet bridge interface. Expects a valid network interface name of a bridge device
as argument. Note that <option>--network-bridge=</option> implies <option>--network-veth</option>. If
this option is used, the host side of the Ethernet link will use the <literal>vb-</literal> prefix
instead of <literal>ve-</literal>. Regardless of the used naming prefix the same network interface
name length limits imposed by Linux apply, along with the complications this creates (for details see
above).</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--network-zone=</option></term>
<listitem><para>Creates a virtual Ethernet link (<literal>veth</literal>) to the container and adds it to an
automatically managed Ethernet bridge interface. The bridge interface is named after the passed argument,
prefixed with <literal>vz-</literal>. The bridge interface is automatically created when the first container
configured for its name is started, and is automatically removed when the last container configured for its
name exits. Hence, each bridge interface configured this way exists only as long as there's at least one
container referencing it running. This option is very similar to <option>--network-bridge=</option>, besides
this automatic creation/removal of the bridge device.</para>
<para>This setting makes it easy to place multiple related containers on a common, virtual Ethernet-based
broadcast domain, here called a "zone". Each container may only be part of one zone, but each zone may contain
any number of containers. Each zone is referenced by its name. Names may be chosen freely (as long as they form
valid network interface names when prefixed with <literal>vz-</literal>), and it is sufficient to pass the same
name to the <option>--network-zone=</option> switch of the various concurrently running containers to join
them in one zone.</para>
<para>Note that
<citerefentry><refentrytitle>systemd-networkd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
includes by default a network file <filename>/usr/lib/systemd/network/80-container-vz.network</filename>
matching the bridge interfaces created this way, which contains settings to enable automatic address
provisioning on the created virtual network via DHCP, as well as automatic IP routing onto the host's external
network interfaces. Using <option>--network-zone=</option> is hence in most cases fully automatic and
sufficient to connect multiple local containers in a joined broadcast domain to the host, with further
connectivity to the external network.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--network-namespace-path=</option></term>
<listitem><para>Takes the path to a file representing a kernel
network namespace that the container shall run in. The specified path
should refer to a (possibly bind-mounted) network namespace file, as
exposed by the kernel below <filename>/proc/$PID/ns/net</filename>.
This makes the container enter the given network namespace. One of the
typical use cases is to give a network namespace under
<filename>/run/netns</filename> created by <citerefentry
project='man-pages'><refentrytitle>ip-netns</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
for example, <option>--network-namespace-path=/run/netns/foo</option>.
Note that this option cannot be used together with other
network-related options, such as <option>--private-network</option>
or <option>--network-interface=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-p</option></term>
<term><option>--port=</option></term>
<listitem><para>If private networking is enabled, maps an IP
port on the host onto an IP port on the container. Takes a
protocol specifier (either <literal>tcp</literal> or
<literal>udp</literal>), separated by a colon from a host port
number in the range 1 to 65535, separated by a colon from a
container port number in the range from 1 to 65535. The
protocol specifier and its separating colon may be omitted, in
which case <literal>tcp</literal> is assumed. The container
port number and its colon may be omitted, in which case the
same port as the host port is implied. This option is only
supported if private networking is used, such as with
<option>--network-veth</option>, <option>--network-zone=</option>
<option>--network-bridge=</option>.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Security Options</title>
<variablelist>
<varlistentry>
<term><option>--capability=</option></term>
<listitem><para>List one or more additional capabilities to grant the container. Takes a
comma-separated list of capability names, see <citerefentry
project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for more information. Note that the following capabilities will be granted in any way:
<constant>CAP_AUDIT_CONTROL</constant>, <constant>CAP_AUDIT_WRITE</constant>,
<constant>CAP_CHOWN</constant>, <constant>CAP_DAC_OVERRIDE</constant>,
<constant>CAP_DAC_READ_SEARCH</constant>, <constant>CAP_FOWNER</constant>,
<constant>CAP_FSETID</constant>, <constant>CAP_IPC_OWNER</constant>, <constant>CAP_KILL</constant>,
<constant>CAP_LEASE</constant>, <constant>CAP_LINUX_IMMUTABLE</constant>,
<constant>CAP_MKNOD</constant>, <constant>CAP_NET_BIND_SERVICE</constant>,
<constant>CAP_NET_BROADCAST</constant>, <constant>CAP_NET_RAW</constant>,
<constant>CAP_SETFCAP</constant>, <constant>CAP_SETGID</constant>, <constant>CAP_SETPCAP</constant>,
<constant>CAP_SETUID</constant>, <constant>CAP_SYS_ADMIN</constant>,
<constant>CAP_SYS_BOOT</constant>, <constant>CAP_SYS_CHROOT</constant>,
<constant>CAP_SYS_NICE</constant>, <constant>CAP_SYS_PTRACE</constant>,
<constant>CAP_SYS_RESOURCE</constant>, <constant>CAP_SYS_TTY_CONFIG</constant>. Also
<constant>CAP_NET_ADMIN</constant> is retained if <option>--private-network</option> is specified.
If the special value <literal>all</literal> is passed, all capabilities are retained.</para>
<para>If the special value of <literal>help</literal> is passed, the program will print known
capability names and exit.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--drop-capability=</option></term>
<listitem><para>Specify one or more additional capabilities to
drop for the container. This allows running the container with
fewer capabilities than the default (see
above).</para>
<para>If the special value of <literal>help</literal> is passed, the program will print known
capability names and exit.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--no-new-privileges=</option></term>
<listitem><para>Takes a boolean argument. Specifies the value of the
<constant>PR_SET_NO_NEW_PRIVS</constant> flag for the container payload. Defaults to off. When turned
on the payload code of the container cannot acquire new privileges, i.e. the "setuid" file bit as
well as file system capabilities will not have an effect anymore. See <citerefentry
project='man-pages'><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details about this flag. </para></listitem>
</varlistentry>
<varlistentry>
<term><option>--system-call-filter=</option></term> <listitem><para>Alter the system call filter
applied to containers. Takes a space-separated list of system call names or group names (the latter
prefixed with <literal>@</literal>, as listed by the <command>syscall-filter</command> command of
<citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>). Passed
system calls will be permitted. The list may optionally be prefixed by <literal>~</literal>, in which
case all listed system calls are prohibited. If this command line option is used multiple times the
configured lists are combined. If both a positive and a negative list (that is one system call list
without and one with the <literal>~</literal> prefix) are configured, the negative list takes
precedence over the positive list. Note that <command>systemd-nspawn</command> always implements a
system call allow list (as opposed to a deny list!), and this command line option hence adds or
removes entries from the default allow list, depending on the <literal>~</literal> prefix. Note that
the applied system call filter is also altered implicitly if additional capabilities are passed using
the <command>--capabilities=</command>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-Z</option></term>
<term><option>--selinux-context=</option></term>
<listitem><para>Sets the SELinux security context to be used
to label processes in the container.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-L</option></term>
<term><option>--selinux-apifs-context=</option></term>
<listitem><para>Sets the SELinux security context to be used
to label files in the virtual API file systems in the
container.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Resource Options</title>
<variablelist>
<varlistentry>
<term><option>--rlimit=</option></term>
<listitem><para>Sets the specified POSIX resource limit for the container payload. Expects an assignment of the
form
<literal><replaceable>LIMIT</replaceable>=<replaceable>SOFT</replaceable>:<replaceable>HARD</replaceable></literal>
or <literal><replaceable>LIMIT</replaceable>=<replaceable>VALUE</replaceable></literal>, where
<replaceable>LIMIT</replaceable> should refer to a resource limit type, such as
<constant>RLIMIT_NOFILE</constant> or <constant>RLIMIT_NICE</constant>. The <replaceable>SOFT</replaceable> and
<replaceable>HARD</replaceable> fields should refer to the numeric soft and hard resource limit values. If the
second form is used, <replaceable>VALUE</replaceable> may specify a value that is used both as soft and hard
limit. In place of a numeric value the special string <literal>infinity</literal> may be used to turn off
resource limiting for the specific type of resource. This command line option may be used multiple times to
control limits on multiple limit types. If used multiple times for the same limit type, the last use
wins. For details about resource limits see <citerefentry
project='man-pages'><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>. By default
resource limits for the container's init process (PID 1) are set to the same values the Linux kernel originally
passed to the host init system. Note that some resource limits are enforced on resources counted per user, in
particular <constant>RLIMIT_NPROC</constant>. This means that unless user namespacing is deployed
(i.e. <option>--private-users=</option> is used, see above), any limits set will be applied to the resource
usage of the same user on all local containers as well as the host. This means particular care needs to be
taken with these limits as they might be triggered by possibly less trusted code. Example:
<literal>--rlimit=RLIMIT_NOFILE=8192:16384</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--oom-score-adjust=</option></term>
<listitem><para>Changes the OOM ("Out Of Memory") score adjustment value for the container payload. This controls
<filename>/proc/self/oom_score_adj</filename> which influences the preference with which this container is
terminated when memory becomes scarce. For details see <citerefentry
project='man-pages'><refentrytitle>proc</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Takes an
integer in the range -1000…1000.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--cpu-affinity=</option></term>
<listitem><para>Controls the CPU affinity of the container payload. Takes a comma separated list of CPU numbers
or number ranges (the latter's start and end value separated by dashes). See <citerefentry
project='man-pages'><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--personality=</option></term>
<listitem><para>Control the architecture ("personality")
reported by
<citerefentry project='man-pages'><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
in the container. Currently, only <literal>x86</literal> and
<literal>x86-64</literal> are supported. This is useful when
running a 32-bit container on a 64-bit host. If this setting
is not used, the personality reported in the container is the
same as the one reported on the host.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Integration Options</title>
<variablelist>
<varlistentry>
<term><option>--resolv-conf=</option></term>
<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 running its stub <filename>resolv.conf</filename>
file is used, and if not the host's <filename>/etc/resolv.conf</filename> file. 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>
<varlistentry>
<term><option>--timezone=</option></term>
<listitem><para>Configures how <filename>/etc/localtime</filename> inside of the container
(i.e. local timezone synchronization from host to container) shall be handled. Takes one of
<literal>off</literal>, <literal>copy</literal>, <literal>bind</literal>, <literal>symlink</literal>,
<literal>delete</literal> or <literal>auto</literal>. If set to <literal>off</literal> the
<filename>/etc/localtime</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</literal> the
<filename>/etc/localtime</filename> file of the host is copied into the container. Similarly, if
<literal>bind</literal> is used, the file is bind mounted from the host into the container. If set to
<literal>symlink</literal>, a symlink is created pointing from <filename>/etc/localtime</filename> in
the container to the timezone file in the container that matches the timezone setting on the host. If
set to <literal>delete</literal>, the file in the container is deleted, should it exist. If set to
<literal>auto</literal> and the <filename>/etc/localtime</filename> file of the host is a symlink,
then <literal>symlink</literal> mode is used, and <literal>copy</literal> otherwise, except if the
image is read-only in which case <literal>bind</literal> is used instead. Defaults to
<literal>auto</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--link-journal=</option></term>
<listitem><para>Control whether the container's journal shall
be made visible to the host system. If enabled, allows viewing
the container's journal files from the host (but not vice
versa). Takes one of <literal>no</literal>,
<literal>host</literal>, <literal>try-host</literal>,
<literal>guest</literal>, <literal>try-guest</literal>,
<literal>auto</literal>. If <literal>no</literal>, the journal
is not linked. If <literal>host</literal>, the journal files
are stored on the host file system (beneath
<filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
and the subdirectory is bind-mounted into the container at the
same location. If <literal>guest</literal>, the journal files
are stored on the guest file system (beneath
<filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
and the subdirectory is symlinked into the host at the same
location. <literal>try-host</literal> and
<literal>try-guest</literal> do the same but do not fail if
the host does not have persistent journaling enabled. If
<literal>auto</literal> (the default), and the right
subdirectory of <filename>/var/log/journal</filename> exists,
it will be bind mounted into the container. If the
subdirectory does not exist, no linking is performed.
Effectively, booting a container once with
<literal>guest</literal> or <literal>host</literal> will link
the journal persistently if further on the default of
<literal>auto</literal> is used.</para>
<para>Note that <option>--link-journal=try-guest</option> is the default if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>-j</option></term>
<listitem><para>Equivalent to
<option>--link-journal=try-guest</option>.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Mount Options</title>
<variablelist>
<varlistentry>
<term><option>--bind=</option></term>
<term><option>--bind-ro=</option></term>
<listitem><para>Bind mount a file or directory from the host into the container. Takes one of: a path
argument — in which case the specified path will be mounted from the host to the same path in the container, or
a colon-separated pair of paths — in which case the first specified path is the source in the host, and the
second path is the destination in the container, or a colon-separated triple of source path, destination path
and mount options. The source path may optionally be prefixed with a <literal>+</literal> character. If so, the
source path is taken relative to the image's root directory. This permits setting up bind mounts within the
container image. The source path may be specified as empty string, in which case a temporary directory below
the host's <filename>/var/tmp</filename> directory is used. It is automatically removed when the container is
shut down. Mount options are comma-separated and currently, only <option>rbind</option> and
<option>norbind</option> are allowed, controlling whether to create a recursive or a regular bind
mount. Defaults to "rbind". Backslash escapes are interpreted, so <literal>\:</literal> may be used to embed
colons in either path. This option may be specified multiple times for creating multiple independent bind
mount points. The <option>--bind-ro=</option> option creates read-only bind mounts.</para>
<para>Note that when this option is used in combination with <option>--private-users</option>, the resulting
mount points will be owned by the <constant>nobody</constant> user. That's because the mount and its files and
directories continue to be owned by the relevant host users and groups, which do not exist in the container,
and thus show up under the wildcard UID 65534 (nobody). If such bind mounts are created, it is recommended to
make them read-only, using <option>--bind-ro=</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--inaccessible=</option></term>
<listitem><para>Make the specified path inaccessible in the container. This over-mounts the specified path
(which must exist in the container) with a file node of the same type that is empty and has the most
restrictive access mode supported. This is an effective way to mask files, directories and other file system
objects from the container payload. This option may be used more than once in case all specified paths are
masked.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--tmpfs=</option></term>
<listitem><para>Mount a tmpfs file system into the container. Takes a single absolute path argument that
specifies where to mount the tmpfs instance to (in which case the directory access mode will be chosen as 0755,
owned by root/root), or optionally a colon-separated pair of path and mount option string that is used for
mounting (in which case the kernel default for access mode and owner will be chosen, unless otherwise
specified). Backslash escapes are interpreted in the path, so <literal>\:</literal> may be used to embed colons
in the path.</para>
<para>Note that this option cannot be used to replace the root file system of the container with a temporary
file system. However, the <option>--volatile=</option> option described below provides similar
functionality, with a focus on implementing stateless operating system images.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--overlay=</option></term>
<term><option>--overlay-ro=</option></term>
<listitem><para>Combine multiple directory trees into one
overlay file system and mount it into the container. Takes a
list of colon-separated paths to the directory trees to
combine and the destination mount point.</para>
<para>Backslash escapes are interpreted in the paths, so
<literal>\:</literal> may be used to embed colons in the paths.
</para>
<para>If three or more paths are specified, then the last
specified path is the destination mount point in the
container, all paths specified before refer to directory trees
on the host and are combined in the specified order into one
overlay file system. The left-most path is hence the lowest
directory tree, the second-to-last path the highest directory
tree in the stacking order. If <option>--overlay-ro=</option>
is used instead of <option>--overlay=</option>, a read-only
overlay file system is created. If a writable overlay file
system is created, all changes made to it are written to the
highest directory tree in the stacking order, i.e. the
second-to-last specified.</para>
<para>If only two paths are specified, then the second
specified path is used both as the top-level directory tree in
the stacking order as seen from the host, as well as the mount
point for the overlay file system in the container. At least
two paths have to be specified.</para>
<para>The source paths may optionally be prefixed with <literal>+</literal> character. If so they are taken
relative to the image's root directory. The uppermost source path may also be specified as empty string, in
which case a temporary directory below the host's <filename>/var/tmp</filename> is used. The directory is
removed automatically when the container is shut down. This behaviour is useful in order to make read-only
container directories writable while the container is running. For example, use the
<literal>--overlay=+/var::/var</literal> option in order to automatically overlay a writable temporary
directory on a read-only <filename>/var</filename> directory.</para>
<para>For details about overlay file systems, see <ulink
url="https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt">overlayfs.txt</ulink>. Note
that the semantics of overlay file systems are substantially
different from normal file systems, in particular regarding
reported device and inode information. Device and inode
information may change for a file while it is being written
to, and processes might see out-of-date versions of files at
times. Note that this switch automatically derives the
<literal>workdir=</literal> mount option for the overlay file
system from the top-level directory tree, making it a sibling
of it. It is hence essential that the top-level directory tree
is not a mount point itself (since the working directory must
be on the same file system as the top-most directory
tree). Also note that the <literal>lowerdir=</literal> mount
option receives the paths to stack in the opposite order of
this switch.</para>
<para>Note that this option cannot be used to replace the root file system of the container with an overlay
file system. However, the <option>--volatile=</option> option described above provides similar functionality,
with a focus on implementing stateless operating system images.</para></listitem>
</varlistentry>
</variablelist>
</refsect2><refsect2>
<title>Input/Output Options</title>
<variablelist>
<varlistentry>
<term><option>--console=</option><replaceable>MODE</replaceable></term>
<listitem><para>Configures how to set up standard input, output and error output for the container
payload, as well as the <filename>/dev/console</filename> device for the container. Takes one of
<option>interactive</option>, <option>read-only</option>, <option>passive</option>, or
<option>pipe</option>. If <option>interactive</option>, a pseudo-TTY is allocated and made available
as <filename>/dev/console</filename> in the container. It is then bi-directionally connected to the
standard input and output passed to <command>systemd-nspawn</command>. <option>read-only</option> is
similar but only the output of the container is propagated and no input from the caller is read. If
<option>passive</option>, a pseudo TTY is allocated, but it is not connected anywhere. Finally, in
<option>pipe</option> mode no pseudo TTY is allocated, but the standard input, output and error
output file descriptors passed to <command>systemd-nspawn</command> are passed on — as they are — to
the container payload, see the following paragraph. Defaults to <option>interactive</option> if
<command>systemd-nspawn</command> is invoked from a terminal, and <option>read-only</option>
otherwise.</para>
<para>In <option>pipe</option> mode, <filename>/dev/console</filename> will not exist in the
container. This means that the container payload generally cannot be a full init system as init
systems tend to require <filename>/dev/console</filename> to be available. On the other hand, in this
mode container invocations can be used within shell pipelines. This is because intermediary pseudo
TTYs do not permit independent bidirectional propagation of the end-of-file (EOF) condition, which is
necessary for shell pipelines to work correctly. <emphasis>Note that the <option>pipe</option> mode
should be used carefully</emphasis>, as passing arbitrary file descriptors to less trusted container
payloads might open up unwanted interfaces for access by the container payload. For example, if a
passed file descriptor refers to a TTY of some form, APIs such as <constant>TIOCSTI</constant> may be
used to synthesize input that might be used for escaping the container. Hence <option>pipe</option>
mode should only be used if the payload is sufficiently trusted or when the standard
input/output/error output file descriptors are known safe, for example pipes.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--pipe</option></term>
<term><option>-P</option></term>
<listitem><para>Equivalent to <option>--console=pipe</option>.</para></listitem>
</varlistentry>
<xi:include href="standard-options.xml" xpointer="no-pager" />
<xi:include href="standard-options.xml" xpointer="help" />
<xi:include href="standard-options.xml" xpointer="version" />
</variablelist>
</refsect2>
</refsect1>
<xi:include href="less-variables.xml" />
<refsect1>
<title>Examples</title>
<example>
<title>Download a
<ulink url="https://getfedora.org">Fedora</ulink> image and start a shell in it</title>
<programlisting># machinectl pull-raw --verify=no \
https://download.fedoraproject.org/pub/fedora/linux/releases/&fedora_latest_version;/Cloud/x86_64/images/Fedora-Cloud-Base-&fedora_latest_version;-&fedora_cloud_release;.x86_64.raw.xz \
Fedora-Cloud-Base-&fedora_latest_version;-&fedora_cloud_release;.x86-64
# systemd-nspawn -M Fedora-Cloud-Base-&fedora_latest_version;-&fedora_cloud_release;.x86-64</programlisting>
<para>This downloads an image using
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and opens a shell in it.</para>
</example>
<example>
<title>Build and boot a minimal Fedora distribution in a container</title>
<programlisting># dnf -y --releasever=&fedora_latest_version; --installroot=/var/lib/machines/f&fedora_latest_version; \
--disablerepo='*' --enablerepo=fedora --enablerepo=updates install \
systemd passwd dnf fedora-release vim-minimal glibc-minimal-langpack
# systemd-nspawn -bD /var/lib/machines/f&fedora_latest_version;</programlisting>
<para>This installs a minimal Fedora distribution into the
directory <filename index="false">/var/lib/machines/f&fedora_latest_version;</filename>
and then boots that OS in a namespace container. Because the installation
is located underneath the standard <filename>/var/lib/machines/</filename>
directory, it is also possible to start the machine using
<command>systemd-nspawn -M f&fedora_latest_version;</command>.</para>
</example>
<example>
<title>Spawn a shell in a container of a minimal Debian unstable distribution</title>
<programlisting># debootstrap unstable ~/debian-tree/
# systemd-nspawn -D ~/debian-tree/</programlisting>
<para>This installs a minimal Debian unstable distribution into
the directory <filename>~/debian-tree/</filename> and then
spawns a shell from this image in a namespace container.</para>
<para><command>debootstrap</command> supports
<ulink url="https://www.debian.org">Debian</ulink>,
<ulink url="https://www.ubuntu.com">Ubuntu</ulink>,
and <ulink url="https://www.tanglu.org">Tanglu</ulink>
out of the box, so the same command can be used to install any of those. For other
distributions from the Debian family, a mirror has to be specified, see
<citerefentry project='die-net'><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para>
</example>
<example>
<title>Boot a minimal
<ulink url="https://www.archlinux.org">Arch Linux</ulink> distribution in a container</title>
<programlisting># pacstrap -c ~/arch-tree/ base
# systemd-nspawn -bD ~/arch-tree/</programlisting>
<para>This installs a minimal Arch Linux distribution into the
directory <filename>~/arch-tree/</filename> and then boots an OS
in a namespace container in it.</para>
</example>
<example>
<title>Install the
<ulink url="https://software.opensuse.org/distributions/tumbleweed">OpenSUSE Tumbleweed</ulink>
rolling distribution</title>
<programlisting># zypper --root=/var/lib/machines/tumbleweed ar -c \
https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
# zypper --root=/var/lib/machines/tumbleweed refresh
# zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
systemd shadow zypper openSUSE-release vim
# systemd-nspawn -M tumbleweed passwd root
# systemd-nspawn -M tumbleweed -b</programlisting>
</example>
<example>
<title>Boot into an ephemeral snapshot of the host system</title>
<programlisting># systemd-nspawn -D / -xb</programlisting>
<para>This runs a copy of the host system in a snapshot which is removed immediately when the container
exits. All file system changes made during runtime will be lost on shutdown, hence.</para>
</example>
<example>
<title>Run a container with SELinux sandbox security contexts</title>
<programlisting># chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
# systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 \
-Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh</programlisting>
</example>
<example>
<title>Run a container with an OSTree deployment</title>
<programlisting># systemd-nspawn -b -i ~/image.raw \
--pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
--bind=+/sysroot/ostree/deploy/$OS/var:/var</programlisting>
</example>
</refsect1>
<refsect1>
<title>Exit status</title>
<para>The exit code of the program executed in the container is
returned.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.nspawn</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='mankier'><refentrytitle>dnf</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='archlinux'><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry project='mankier'><refentrytitle>zypper</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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