<?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 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>