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82 lines
4.3 KiB
XML
82 lines
4.3 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd-nsresourced.service" conditional='ENABLE_NSRESOURCED'>
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<refentryinfo>
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<title>systemd-nsresourced.service</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-nsresourced.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-nsresourced.service</refname>
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<refname>systemd-nsresourced</refname>
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<refpurpose>User Namespace Resource Delegation Service</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-nsresourced.service</filename></para>
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<para><filename>/usr/lib/systemd/systemd-nsresourced</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><command>systemd-nsresourced</command> is a system service that permits transient delegation of a
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UID/GID range to a user namespace (see <citerefentry
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project='man-pages'><refentrytitle>user_namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>)
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allocated by a client, via a Varlink IPC API.</para>
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<para>Unprivileged clients may allocate a user namespace, and then request a UID/GID range to be assigned
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to it via this service. The user namespace may then be used to run containers and other sandboxes, and/or
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apply it to an id-mapped mount.</para>
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<para>Allocations of UIDs/GIDs this way are transient: when a user namespace goes away, its UID/GID range
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is returned to the pool of available ranges. In order to ensure that clients cannot gain persistency in
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their transient UID/GID range a BPF-LSM based policy is enforced that ensures that user namespaces set up
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this way can only write to file systems they allocate themselves or that are explicitly allowlisted via
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<command>systemd-nsresourced</command>.</para>
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<para><command>systemd-nsresourced</command> automatically ensures that any registered UID ranges show up
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in the system's NSS database via the <ulink url="https://systemd.io/USER_GROUP_API">User/Group Record
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Lookup API via Varlink</ulink>.</para>
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<para>Currently, only UID/GID ranges consisting of either exactly 1 or exactly 65536 UIDs/GIDs can be
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registered with this service. Moreover, UIDs and GIDs are always allocated together, and
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symmetrically.</para>
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<para>The service provides API calls to allowlist mounts (referenced via their mount file descriptors as
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per Linux <function>fsmount()</function> API), to pass ownership of a cgroup subtree to the user
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namespace and to delegate a virtual Ethernet device pair to the user namespace. When used in combination
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this is sufficient to implement fully unprivileged container environments, as implemented by
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<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>, fully
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unprivileged <varname>RootImage=</varname> (see
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or
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fully unprivileged disk image tools such as
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<citerefentry><refentrytitle>systemd-dissect</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
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<para>This service provides one <ulink url="https://varlink.org/">Varlink</ulink> service:
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<constant>io.systemd.NamespaceResource</constant> allows registering user namespaces, and assign mounts,
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cgroups and network interfaces to it.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-mountfsd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-dissect</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>user_namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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