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systemd/man/systemd.nspawn.xml
Lennart Poettering 960e4569e1 nspawn: implement configurable syscall whitelisting/blacklisting 
Now that we have ported nspawn's seccomp code to the generic code in
seccomp-util, let's extend it to support whitelisting and blacklisting
of specific additional syscalls.

This uses similar syntax as PID1's support for system call filtering,
but in contrast to that always implements a blacklist (and not a
whitelist), as we prepopulate the filter with a blacklist, and the
unit's system call filter logic does not come with anything
prepopulated.

(Later on we might actually want to invert the logic here, and
whitelist rather than blacklist things, but at this point let's not do
that. In case we switch this over later, the syscall add/remove logic of
this commit should be compatible conceptually.)

Fixes: #5163

Replaces: #5944
2017-09-12 14:06:21 +02:00

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<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [
<!ENTITY % entities SYSTEM "custom-entities.ent" >
%entities;
]>
<!--
This file is part of systemd.
Copyright 2015 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="systemd.nspawn">
<refentryinfo>
<title>systemd.nspawn</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.nspawn</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.nspawn</refname>
<refpurpose>Container settings</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/etc/systemd/nspawn/<replaceable>machine</replaceable>.nspawn</filename></para>
<para><filename>/run/systemd/nspawn/<replaceable>machine</replaceable>.nspawn</filename></para>
<para><filename>/var/lib/machines/<replaceable>machine</replaceable>.nspawn</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>An nspawn container settings file (suffix
<filename>.nspawn</filename>) encodes additional runtime
information about a local container, and is searched, read and
used by
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
when starting a container. Files of this type are named after the
containers they define settings for. They are optional, and only
required for containers whose execution environment shall differ
from the defaults. Files of this type mostly contain settings that
may also be set on the <command>systemd-nspawn</command> command
line, and make it easier to persistently attach specific settings
to specific containers. The syntax of these files is inspired by
<filename>.desktop</filename> files following the <ulink
url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
Desktop Entry Specification</ulink>, which in turn are inspired by
Microsoft Windows <filename>.ini</filename> files.</para>
<para>Boolean arguments used in these settings files can be
written in various formats. For positive settings, the strings
<option>1</option>, <option>yes</option>, <option>true</option>
and <option>on</option> are equivalent. For negative settings, the
strings <option>0</option>, <option>no</option>,
<option>false</option> and <option>off</option> are
equivalent.</para>
<para>Empty lines and lines starting with # or ; are
ignored. This may be used for commenting. Lines ending
in a backslash are concatenated with the following
line while reading and the backslash is replaced by a
space character. This may be used to wrap long lines.</para>
</refsect1>
<refsect1>
<title><filename>.nspawn</filename> File Discovery</title>
<para>Files are searched by appending the
<filename>.nspawn</filename> suffix to the machine name of the
container, as specified with the <option>--machine=</option>
switch of <command>systemd-nspawn</command>, or derived from the
directory or image file name. This file is first searched in
<filename>/etc/systemd/nspawn/</filename> and
<filename>/run/systemd/nspawn/</filename>. If found in these
directories, its settings are read and all of them take full effect
(but are possibly overridden by corresponding command line
arguments). If not found, the file will then be searched next to
the image file or in the immediate parent of the root directory of
the container. If the file is found there, only a subset of the
settings will take effect however. All settings that possibly
elevate privileges or grant additional access to resources of the
host (such as files or directories) are ignored. To which options
this applies is documented below.</para>
<para>Persistent settings files created and maintained by the
administrator (and thus trusted) should be placed in
<filename>/etc/systemd/nspawn/</filename>, while automatically
downloaded (and thus potentially untrusted) settings files are
placed in <filename>/var/lib/machines/</filename> instead (next to
the container images), where their security impact is limited. In
order to add privileged settings to <filename>.nspawn</filename>
files acquired from the image vendor, it is recommended to copy the
settings files into <filename>/etc/systemd/nspawn/</filename> and
edit them there, so that the privileged options become
available. The precise algorithm for how the files are searched and
interpreted may be configured with
<command>systemd-nspawn</command>'s <option>--settings=</option>
switch, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for details.</para>
</refsect1>
<refsect1>
<title>[Exec] Section Options</title>
<para>Settings files may include an <literal>[Exec]</literal>
section, which carries various execution parameters:</para>
<variablelist>
<varlistentry>
<term><varname>Boot=</varname></term>
<listitem><para>Takes a boolean argument, which defaults to off. If enabled, <command>systemd-nspawn</command>
will automatically search for an <filename>init</filename> executable and invoke it. In this case, the
specified parameters using <varname>Parameters=</varname> are passed as additional arguments to the
<filename>init</filename> process. This setting corresponds to the <option>--boot</option> switch on the
<command>systemd-nspawn</command> command line. This option may not be combined with
<varname>ProcessTwo=yes</varname>. This option is the default if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProcessTwo=</varname></term>
<listitem><para>Takes a boolean argument, which defaults to off. If enabled, the specified program is run as
PID 2. A stub init process is run as PID 1. This setting corresponds to the <option>--as-pid2</option> switch
on the <command>systemd-nspawn</command> command line. This option may not be combined with
<varname>Boot=yes</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Parameters=</varname></term>
<listitem><para>Takes a space-separated list of
arguments. This is either a command line, beginning with the
binary name to execute, or – if <varname>Boot=</varname> is
enabled – the list of arguments to pass to the init
process. This setting corresponds to the command line
parameters passed on the <command>systemd-nspawn</command>
command line.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Environment=</varname></term>
<listitem><para>Takes an environment variable assignment
consisting of key and value, separated by
<literal>=</literal>. Sets an environment variable for the
main process invoked in the container. This setting may be
used multiple times to set multiple environment variables. It
corresponds to the <option>--setenv=</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>User=</varname></term>
<listitem><para>Takes a UNIX user name. Specifies the user
name to invoke the main process of the container as. This user
must be known in the container's user database. This
corresponds to the <option>--user=</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>WorkingDirectory=</varname></term>
<listitem><para>Selects the working directory for the process invoked in the container. Expects an absolute
path in the container's file system namespace. This corresponds to the <option>--chdir=</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PivotRoot=</varname></term>
<listitem><para>Selects a directory to pivot to <filename>/</filename> inside the container when starting up.
Takes a single path, or a pair of two paths separated by a colon. Both paths must be absolute, and are resolved
in the container's file system namespace. This corresponds to the <option>--pivot-root=</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Capability=</varname></term>
<term><varname>DropCapability=</varname></term>
<listitem><para>Takes a space-separated list of Linux process
capabilities (see
<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details). The <varname>Capability=</varname> setting
specifies additional capabilities to pass on top of the
default set of capabilities. The
<varname>DropCapability=</varname> setting specifies
capabilities to drop from the default set. These settings
correspond to the <option>--capability=</option> and
<option>--drop-capability=</option> command line
switches. Note that <varname>Capability=</varname> is a
privileged setting, and only takes effect in
<filename>.nspawn</filename> files in
<filename>/etc/systemd/nspawn/</filename> and
<filename>/run/system/nspawn/</filename> (see above). On the
other hand, <varname>DropCapability=</varname> takes effect in
all cases.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>KillSignal=</varname></term>
<listitem><para>Specify the process signal to send to the
container's PID 1 when nspawn itself receives SIGTERM, in
order to trigger an orderly shutdown of the container.
Defaults to SIGRTMIN+3 if <option>Boot=</option> is used
(on systemd-compatible init systems SIGRTMIN+3 triggers an
orderly shutdown). For a list of valid signals, see
<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Personality=</varname></term>
<listitem><para>Configures the kernel personality for the
container. This is equivalent to the
<option>--personality=</option> switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MachineID=</varname></term>
<listitem><para>Configures the 128-bit machine ID (UUID) to pass to
the container. This is equivalent to the
<option>--uuid=</option> command line switch. This option is
privileged (see above). </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateUsers=</varname></term>
<listitem><para>Configures support for usernamespacing. This is equivalent to the
<option>--private-users=</option> command line switch, and takes the same options. This option is privileged
(see above). This option is the default if the <filename>systemd-nspawn@.service</filename> template unit file
is used.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NotifyReady=</varname></term>
<listitem><para>Configures support for notifications from the container's init process. This is equivalent to
the <option>--notify-ready=</option> command line switch, and takes the same paramaters. See
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry> for details
about the specific options supported.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallFilter=</varname></term>
<listitem><para>Configures the system call filter applied to containers. This is equivalent to the
<option>--system-call-filter=</option> command line switch, and takes the same list parameter. See
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[Files] Section Options</title>
<para>Settings files may include a <literal>[Files]</literal>
section, which carries various parameters configuring the file
system of the container:</para>
<variablelist>
<varlistentry>
<term><varname>ReadOnly=</varname></term>
<listitem><para>Takes a boolean argument, which defaults to off. If
specified, the container will be run with a read-only file
system. This setting corresponds to the
<option>--read-only</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Volatile=</varname></term>
<listitem><para>Takes a boolean argument, or the special value
<literal>state</literal>. This configures whether to run the
container with volatile state and/or configuration. This
option is equivalent to <option>--volatile=</option>, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for details about the specific options
supported.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Bind=</varname></term>
<term><varname>BindReadOnly=</varname></term>
<listitem><para>Adds a bind mount from the host into the
container. Takes a single path, a pair of two paths separated
by a colon, or a triplet of two paths plus an option string
separated by colons. This option may be used multiple times to
configure multiple bind mounts. This option is equivalent to
the command line switches <option>--bind=</option> and
<option>--bind-ro=</option>, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for details about the specific options supported. This setting
is privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TemporaryFileSystem=</varname></term>
<listitem><para>Adds a <literal>tmpfs</literal> mount to the
container. Takes a path or a pair of path and option string,
separated by a colon. This option may be used multiple times to
configure multiple <literal>tmpfs</literal> mounts. This
option is equivalent to the command line switch
<option>--tmpfs=</option>, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for details about the specific options supported. This setting
is privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Overlay=</varname></term>
<term><varname>OverlayReadOnly=</varname></term>
<listitem><para>Adds an overlay mount point. Takes a colon-separated list of paths. This option may be used
multiple times to configure multiple overlay mounts. This option is equivalent to the command line switches
<option>--overlay=</option> and <option>--overlay-ro=</option>, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry> for details
about the specific options supported. This setting is privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateUsersChown=</varname></term>
<listitem><para>Configures whether the ownership of the files and directories in the container tree shall be
adjusted to the UID/GID range used, if necessary and user namespacing is enabled. This is equivalent to the
<option>--private-users-chown</option> command line switch. This option is privileged (see
above). </para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>[Network] Section Options</title>
<para>Settings files may include a <literal>[Network]</literal>
section, which carries various parameters configuring the network
connectivity of the container:</para>
<variablelist>
<varlistentry>
<term><varname>Private=</varname></term>
<listitem><para>Takes a boolean argument, which defaults to off. If
enabled, the container will run in its own network namespace
and not share network interfaces and configuration with the
host. This setting corresponds to the
<option>--private-network</option> command line
switch.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>VirtualEthernet=</varname></term>
<listitem><para>Takes a boolean argument. Configures whether to create a virtual Ethernet connection
(<literal>veth</literal>) between host and the container. This setting implies
<varname>Private=yes</varname>. This setting corresponds to the <option>--network-veth</option> command line
switch. This option is privileged (see above). This option is the default if the
<filename>systemd-nspawn@.service</filename> template unit file is used.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>VirtualEthernetExtra=</varname></term>
<listitem><para>Takes a colon-separated pair of interface
names. Configures an additional virtual Ethernet connection
(<literal>veth</literal>) between host and the container. The
first specified name is the interface name on the host, the
second the interface name in the container. The latter may be
omitted in which case it is set to the same name as the host
side interface. This setting implies
<varname>Private=yes</varname>. This setting corresponds to
the <option>--network-veth-extra=</option> command line
switch, and maybe be used multiple times. It is independent of
<varname>VirtualEthernet=</varname>. This option is privileged
(see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Interface=</varname></term>
<listitem><para>Takes a space-separated list of interfaces to
add to the container. This option corresponds to the
<option>--network-interface=</option> command line switch and
implies <varname>Private=yes</varname>. This option is
privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MACVLAN=</varname></term>
<term><varname>IPVLAN=</varname></term>
<listitem><para>Takes a space-separated list of interfaces to
add MACLVAN or IPVLAN interfaces to, which are then added to
the container. These options correspond to the
<option>--network-macvlan=</option> and
<option>--network-ipvlan=</option> command line switches and
imply <varname>Private=yes</varname>. These options are
privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Bridge=</varname></term>
<listitem><para>Takes an interface name. This setting implies
<varname>VirtualEthernet=yes</varname> and
<varname>Private=yes</varname> and has the effect that the
host side of the created virtual Ethernet link is connected to
the specified bridge interface. This option corresponds to the
<option>--network-bridge=</option> command line switch. This
option is privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Zone=</varname></term>
<listitem><para>Takes a network zone name. This setting implies <varname>VirtualEthernet=yes</varname> and
<varname>Private=yes</varname> and has the effect that the host side of the created virtual Ethernet link is
connected to an automatically managed bridge interface named after the passed argument, prefixed with
<literal>vz-</literal>. This option corresponds to the <option>--network-zone=</option> command line
switch. This option is privileged (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Port=</varname></term>
<listitem><para>Exposes a TCP or UDP port of the container on
the host. This option corresponds to the
<option>--port=</option> command line switch, see
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>
for the precise syntax of the argument this option takes. This
option is privileged (see above).</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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