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