<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-release-21.05">
  <title>Release 21.05 (<quote>Okapi</quote>, 2021.05/31)</title>
  <para>
    Support is planned until the end of December 2021, handing over to
    21.11.
  </para>
  <section xml:id="sec-release-21.05-highlights">
    <title>Highlights</title>
    <para>
      In addition to numerous new and upgraded packages, this release
      has the following highlights:
    </para>
    <itemizedlist>
      <listitem>
        <para>
          Core version changes:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              gcc: 9.3.0 -&gt; 10.3.0
            </para>
          </listitem>
          <listitem>
            <para>
              glibc: 2.30 -&gt; 2.32
            </para>
          </listitem>
          <listitem>
            <para>
              default linux: 5.4 -&gt; 5.10, all supported kernels
              available
            </para>
          </listitem>
          <listitem>
            <para>
              mesa: 20.1.7 -&gt; 21.0.1
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
          Desktop Environments:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              GNOME: 3.36 -&gt; 40, see its
              <link xlink:href="https://help.gnome.org/misc/release-notes/40.0/">release
              notes</link>
            </para>
          </listitem>
          <listitem>
            <para>
              Plasma5: 5.18.5 -&gt; 5.21.3
            </para>
          </listitem>
          <listitem>
            <para>
              kdeApplications: 20.08.1 -&gt; 20.12.3
            </para>
          </listitem>
          <listitem>
            <para>
              cinnamon: 4.6 -&gt; 4.8.1
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
          Programming Languages and Frameworks:
        </para>
        <itemizedlist spacing="compact">
          <listitem>
            <para>
              Python optimizations were disabled again. Builds with
              optimizations enabled are not reproducible. Optimizations
              can now be enabled with an option.
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
          The linux_latest kernel was updated to the 5.12 series. It
          currently is not officially supported for use with the zfs
          filesystem. If you use zfs, you should use a different kernel
          version (either the LTS kernel, or track a specific one).
        </para>
      </listitem>
    </itemizedlist>
  </section>
  <section xml:id="sec-release-21.05-new-services">
    <title>New Services</title>
    <para>
      The following new services were added since the last release:
    </para>
    <itemizedlist>
      <listitem>
        <para>
          <link xlink:href="https://www.gnuradio.org/">GNURadio</link>
          3.8 was
          <link xlink:href="https://github.com/NixOS/nixpkgs/issues/82263">finally</link>
          packaged, along with a rewrite to the Nix expressions,
          allowing users to override the features upstream supports
          selecting to compile or not to. Additionally, the attribute
          <literal>gnuradio</literal> and <literal>gnuradio3_7</literal>
          now point to an externally wrapped by default derivations,
          that allow you to also add `extraPythonPackages` to the Python
          interpreter used by GNURadio. Missing environmental variables
          needed for operational GUI were also added
          (<link xlink:href="https://github.com/NixOS/nixpkgs/issues/75478">#75478</link>).
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://www.keycloak.org/">Keycloak</link>,
          an open source identity and access management server with
          support for
          <link xlink:href="https://openid.net/connect/">OpenID
          Connect</link>, <link xlink:href="https://oauth.net/2/">OAUTH
          2.0</link> and
          <link xlink:href="https://en.wikipedia.org/wiki/SAML_2.0">SAML
          2.0</link>.
        </para>
        <para>
          See the <link linkend="module-services-keycloak">Keycloak
          section of the NixOS manual</link> for more information.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-services.samba-wsdd.enable">services.samba-wsdd.enable</link>
          Web Services Dynamic Discovery host daemon
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://www.discourse.org/">Discourse</link>,
          a modern and open source discussion platform.
        </para>
        <para>
          See the <link linkend="module-services-discourse">Discourse
          section of the NixOS manual</link> for more information.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-services.nebula.networks">services.nebula.networks</link>
          <link xlink:href="https://github.com/slackhq/nebula">Nebula
          VPN</link>
        </para>
      </listitem>
    </itemizedlist>
  </section>
  <section xml:id="sec-release-21.05-incompatibilities">
    <title>Backward Incompatibilities</title>
    <para>
      When upgrading from a previous release, please be aware of the
      following incompatible changes:
    </para>
    <itemizedlist>
      <listitem>
        <para>
          GNOME desktop environment was upgraded to 40, see the release
          notes for
          <link xlink:href="https://help.gnome.org/misc/release-notes/40.0/">40.0</link>
          and
          <link xlink:href="https://help.gnome.org/misc/release-notes/3.38/">3.38</link>.
          The <literal>gnome3</literal> attribute set has been renamed
          to <literal>gnome</literal> and so have been the NixOS
          options.
        </para>
      </listitem>
      <listitem>
        <para>
          If you are using <literal>services.udev.extraRules</literal>
          to assign custom names to network interfaces, this may stop
          working due to a change in the initialisation of dhcpcd and
          systemd networkd. To avoid this, either move them to
          <literal>services.udev.initrdRules</literal> or see the new
          <link linkend="sec-custom-ifnames">Assigning custom
          names</link> section of the NixOS manual for an example using
          networkd links.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>security.hideProcessInformation</literal> module
          has been removed. It was broken since the switch to
          cgroups-v2.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>linuxPackages.ati_drivers_x11</literal> kernel
          modules have been removed. The drivers only supported kernels
          prior to 4.2, and thus have become obsolete.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>systemConfig</literal> kernel parameter is no
          longer added to boot loader entries. It has been unused since
          September 2010, but if do have a system generation from that
          era, you will now be unable to boot into them.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>systemd-journal2gelf</literal> no longer parses json
          and expects the receiving system to handle it. How to achieve
          this with Graylog is described in this
          <link xlink:href="https://github.com/parse-nl/SystemdJournal2Gelf/issues/10">GitHub
          issue</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          If the <literal>services.dbus</literal> module is enabled,
          then the user D-Bus session is now always socket activated.
          The associated options
          <literal>services.dbus.socketActivated</literal> and
          <literal>services.xserver.startDbusSession</literal> have
          therefore been removed and you will receive a warning if they
          are present in your configuration. This change makes the user
          D-Bus session available also for non-graphical logins.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>networking.wireless.iwd</literal> module now
          installs the upstream-provided 80-iwd.link file, which sets
          the NamePolicy= for all wlan devices to &quot;keep
          kernel&quot;, to avoid race conditions between iwd and
          networkd. If you don't want this, you can set
          <literal>systemd.network.links.&quot;80-iwd&quot; = lib.mkForce {}</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>rubyMinimal</literal> was removed due to being unused
          and unusable. The default ruby interpreter includes JIT
          support, which makes it reference it's compiler. Since JIT
          support is probably needed by some Gems, it was decided to
          enable this feature with all cc references by default, and
          allow to build a Ruby derivation without references to cc, by
          setting <literal>jitSupport = false;</literal> in an overlay.
          See
          <link xlink:href="https://github.com/NixOS/nixpkgs/pull/90151">#90151</link>
          for more info.
        </para>
      </listitem>
      <listitem>
        <para>
          Setting
          <literal>services.openssh.authorizedKeysFiles</literal> now
          also affects which keys
          <literal>security.pam.enableSSHAgentAuth</literal> will use.
          WARNING: If you are using these options in combination do make
          sure that any key paths you use are present in
          <literal>services.openssh.authorizedKeysFiles</literal>!
        </para>
      </listitem>
      <listitem>
        <para>
          The option <literal>fonts.enableFontDir</literal> has been
          renamed to
          <link xlink:href="options.html#opt-fonts.fontDir.enable">fonts.fontDir.enable</link>.
          The path of font directory has also been changed to
          <literal>/run/current-system/sw/share/X11/fonts</literal>, for
          consistency with other X11 resources.
        </para>
      </listitem>
      <listitem>
        <para>
          A number of options have been renamed in the kicad interface.
          <literal>oceSupport</literal> has been renamed to
          <literal>withOCE</literal>, <literal>withOCCT</literal> has
          been renamed to <literal>withOCC</literal>,
          <literal>ngspiceSupport</literal> has been renamed to
          <literal>withNgspice</literal>, and
          <literal>scriptingSupport</literal> has been renamed to
          <literal>withScripting</literal>. Additionally,
          <literal>kicad/base.nix</literal> no longer provides default
          argument values since these are provided by
          <literal>kicad/default.nix</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The socket for the <literal>pdns-recursor</literal> module was
          moved from <literal>/var/lib/pdns-recursor</literal> to
          <literal>/run/pdns-recursor</literal> to match upstream.
        </para>
      </listitem>
      <listitem>
        <para>
          Paperwork was updated to version 2. The on-disk format
          slightly changed, and it is not possible to downgrade from
          Paperwork 2 back to Paperwork 1.3. Back your documents up
          before upgrading. See
          <link xlink:href="https://forum.openpaper.work/t/paperwork-2-0/112/5">this
          thread</link> for more details.
        </para>
      </listitem>
      <listitem>
        <para>
          PowerDNS has been updated from <literal>4.2.x</literal> to
          <literal>4.3.x</literal>. Please be sure to review the
          <link xlink:href="https://doc.powerdns.com/authoritative/upgrading.html#x-to-4-3-0">Upgrade
          Notes</link> provided by upstream before upgrading. Worth
          specifically noting is that the service now runs entirely as a
          dedicated <literal>pdns</literal> user, instead of starting as
          <literal>root</literal> and dropping privileges, as well as
          the default <literal>socket-dir</literal> location changing
          from <literal>/var/lib/powerdns</literal> to
          <literal>/run/pdns</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>mediatomb</literal> service is now using by
          default the new and maintained fork <literal>gerbera</literal>
          package instead of the unmaintained
          <literal>mediatomb</literal> package. If you want to keep the
          old behavior, you must declare it with:
        </para>
        <programlisting language="bash">
{
  services.mediatomb.package = pkgs.mediatomb;
}
</programlisting>
        <para>
          One new option <literal>openFirewall</literal> has been
          introduced which defaults to false. If you relied on the
          service declaration to add the firewall rules itself before,
          you should now declare it with:
        </para>
        <programlisting language="bash">
{
  services.mediatomb.openFirewall = true;
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          xfsprogs was update from 4.19 to 5.11. It now enables reflink
          support by default on filesystem creation. Support for
          reflinks was added with an experimental status to kernel 4.9
          and deemed stable in kernel 4.16. If you want to be able to
          mount XFS filesystems created with this release of xfsprogs on
          kernel releases older than those, you need to format them with
          <literal>mkfs.xfs -m reflink=0</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The uWSGI server is now built with POSIX capabilities. As a
          consequence, root is no longer required in emperor mode and
          the service defaults to running as the unprivileged
          <literal>uwsgi</literal> user. Any additional capability can
          be added via the new option
          <link xlink:href="options.html#opt-services.uwsgi.capabilities">services.uwsgi.capabilities</link>.
          The previous behaviour can be restored by setting:
        </para>
        <programlisting language="bash">
{
  services.uwsgi.user = &quot;root&quot;;
  services.uwsgi.group = &quot;root&quot;;
  services.uwsgi.instance =
    {
      uid = &quot;uwsgi&quot;;
      gid = &quot;uwsgi&quot;;
    };
}
</programlisting>
        <para>
          Another incompatibility from the previous release is that
          vassals running under a different user or group need to use
          <literal>immediate-{uid,gid}</literal> instead of the usual
          <literal>uid,gid</literal> options.
        </para>
      </listitem>
      <listitem>
        <para>
          btc1 has been abandoned upstream, and removed.
        </para>
      </listitem>
      <listitem>
        <para>
          cpp_ethereum (aleth) has been abandoned upstream, and removed.
        </para>
      </listitem>
      <listitem>
        <para>
          riak-cs package removed along with
          <literal>services.riak-cs</literal> module.
        </para>
      </listitem>
      <listitem>
        <para>
          stanchion package removed along with
          <literal>services.stanchion</literal> module.
        </para>
      </listitem>
      <listitem>
        <para>
          mutt has been updated to a new major version (2.x), which
          comes with some backward incompatible changes that are
          described in the
          <link xlink:href="http://www.mutt.org/relnotes/2.0/">release
          notes for Mutt 2.0</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>vim</literal> and <literal>neovim</literal> switched
          to Python 3, dropping all Python 2 support.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-networking.wireguard.interfaces">networking.wireguard.interfaces.&lt;name&gt;.generatePrivateKeyFile</link>,
          which is off by default, had a <literal>chmod</literal> race
          condition fixed. As an aside, the parent directory's
          permissions were widened, and the key files were made
          owner-writable. This only affects newly created keys. However,
          if the exact permissions are important for your setup, read
          <link xlink:href="https://github.com/NixOS/nixpkgs/pull/121294">#121294</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-boot.zfs.forceImportAll">boot.zfs.forceImportAll</link>
          previously did nothing, but has been fixed. However its
          default has been changed to <literal>false</literal> to
          preserve the existing default behaviour. If you have this
          explicitly set to <literal>true</literal>, please note that
          your non-root pools will now be forcibly imported.
        </para>
      </listitem>
      <listitem>
        <para>
          openafs now points to openafs_1_8, which is the new stable
          release. OpenAFS 1.6 was removed.
        </para>
      </listitem>
      <listitem>
        <para>
          The WireGuard module gained a new option
          <literal>networking.wireguard.interfaces.&lt;name&gt;.peers.*.dynamicEndpointRefreshSeconds</literal>
          that implements refreshing the IP of DNS-based endpoints
          periodically (which WireGuard itself
          <link xlink:href="https://lists.zx2c4.com/pipermail/wireguard/2017-November/002028.html">cannot
          do</link>).
        </para>
      </listitem>
      <listitem>
        <para>
          MariaDB has been updated to 10.5. Before you upgrade, it would
          be best to take a backup of your database and read
          <link xlink:href="https://mariadb.com/kb/en/upgrading-from-mariadb-104-to-mariadb-105/#incompatible-changes-between-104-and-105">
          Incompatible Changes Between 10.4 and 10.5</link>. After the
          upgrade you will need to run <literal>mysql_upgrade</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The TokuDB storage engine dropped in mariadb 10.5 and removed
          in mariadb 10.6. It is recommended to switch to RocksDB. See
          also
          <link xlink:href="https://mariadb.com/kb/en/tokudb/">TokuDB</link>
          and
          <link xlink:href="https://jira.mariadb.org/browse/MDEV-19780">MDEV-19780:
          Remove the TokuDB storage engine</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>openldap</literal> module now has support for
          OLC-style configuration, users of the
          <literal>configDir</literal> option may wish to migrate. If
          you continue to use <literal>configDir</literal>, ensure that
          <literal>olcPidFile</literal> is set to
          <literal>/run/slapd/slapd.pid</literal>.
        </para>
        <para>
          As a result, <literal>extraConfig</literal> and
          <literal>extraDatabaseConfig</literal> are removed. To help
          with migration, you can convert your
          <literal>slapd.conf</literal> file to OLC configuration with
          the following script (find the location of this configuration
          file by running <literal>systemctl status openldap</literal>,
          it is the <literal>-f</literal> option.
        </para>
        <programlisting>
$ TMPDIR=$(mktemp -d)
$ slaptest -f /path/to/slapd.conf -F $TMPDIR
$ slapcat -F $TMPDIR -n0 -H 'ldap:///???(!(objectClass=olcSchemaConfig))'
</programlisting>
        <para>
          This will dump your current configuration in LDIF format,
          which should be straightforward to convert into Nix settings.
          This does not show your schema configuration, as this is
          unnecessarily verbose for users of the default schemas and
          <literal>slaptest</literal> is buggy with schemas directly in
          the config file.
        </para>
      </listitem>
      <listitem>
        <para>
          Amazon EC2 and OpenStack Compute (nova) images now re-fetch
          instance meta data and user data from the instance metadata
          service (IMDS) on each boot. For example: stopping an EC2
          instance, changing its user data, and restarting the instance
          will now cause it to fetch and apply the new user data.
        </para>
        <warning>
          <para>
            Specifically, <literal>/etc/ec2-metadata</literal> is
            re-populated on each boot. Some NixOS scripts that read from
            this directory are guarded to only run if the files they
            want to manipulate do not already exist, and so will not
            re-apply their changes if the IMDS response changes.
            Examples: <literal>root</literal>'s SSH key is only added if
            <literal>/root/.ssh/authorized_keys</literal> does not
            exist, and SSH host keys are only set from user data if they
            do not exist in <literal>/etc/ssh</literal>.
          </para>
        </warning>
      </listitem>
      <listitem>
        <para>
          The <literal>rspamd</literal> services is now sandboxed. It is
          run as a dynamic user instead of root, so secrets and other
          files may have to be moved or their permissions may have to be
          fixed. The sockets are now located in
          <literal>/run/rspamd</literal> instead of
          <literal>/run</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          Enabling the Tor client no longer silently also enables and
          configures Privoxy, and the
          <literal>services.tor.client.privoxy.enable</literal> option
          has been removed. To enable Privoxy, and to configure it to
          use Tor's faster port, use the following configuration:
        </para>
        <programlisting language="bash">
{
  opt-services.privoxy.enable = true;
  opt-services.privoxy.enableTor = true;
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          The <literal>services.tor</literal> module has a new
          exhaustively typed
          <link xlink:href="options.html#opt-services.tor.settings">services.tor.settings</link>
          option following RFC 0042; backward compatibility with old
          options has been preserved when aliasing was possible. The
          corresponding systemd service has been hardened, but there is
          a chance that the service still requires more permissions, so
          please report any related trouble on the bugtracker. Onion
          services v3 are now supported in
          <link xlink:href="options.html#opt-services.tor.relay.onionServices">services.tor.relay.onionServices</link>.
          A new
          <link xlink:href="options.html#opt-services.tor.openFirewall">services.tor.openFirewall</link>
          option as been introduced for allowing connections on all the
          TCP ports configured.
        </para>
      </listitem>
      <listitem>
        <para>
          The options
          <literal>services.slurm.dbdserver.storagePass</literal> and
          <literal>services.slurm.dbdserver.configFile</literal> have
          been removed. Use
          <literal>services.slurm.dbdserver.storagePassFile</literal>
          instead to provide the database password. Extra config options
          can be given via the option
          <literal>services.slurm.dbdserver.extraConfig</literal>. The
          actual configuration file is created on the fly on startup of
          the service. This avoids that the password gets exposed in the
          nix store.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>wafHook</literal> hook does not wrap Python
          anymore. Packages depending on <literal>wafHook</literal> need
          to include any Python into their
          <literal>nativeBuildInputs</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          Starting with version 1.7.0, the project formerly named
          <literal>CodiMD</literal> is now named
          <literal>HedgeDoc</literal>. New installations will no longer
          use the old name for users, state directories and such, this
          needs to be considered when moving state to a more recent
          NixOS installation. Based on
          <link xlink:href="options.html#opt-system.stateVersion">system.stateVersion</link>,
          existing installations will continue to work.
        </para>
      </listitem>
      <listitem>
        <para>
          The fish-foreign-env package has been replaced with
          fishPlugins.foreign-env, in which the fish functions have been
          relocated to the <literal>vendor_functions.d</literal>
          directory to be loaded automatically.
        </para>
      </listitem>
      <listitem>
        <para>
          The prometheus json exporter is now managed by the prometheus
          community. Together with additional features some backwards
          incompatibilities were introduced. Most importantly the
          exporter no longer accepts a fixed command-line parameter to
          specify the URL of the endpoint serving JSON. It now expects
          this URL to be passed as an URL parameter, when scraping the
          exporter's <literal>/probe</literal> endpoint. In the
          prometheus scrape configuration the scrape target might look
          like this:
        </para>
        <programlisting>
http://some.json-exporter.host:7979/probe?target=https://example.com/some/json/endpoint
</programlisting>
        <para>
          Existing configuration for the exporter needs to be updated,
          but can partially be re-used. Documentation is available in
          the upstream repository and a small example for NixOS is
          available in the corresponding NixOS test.
        </para>
        <para>
          These changes also affect
          <link xlink:href="options.html#opt-services.prometheus.exporters.rspamd.enable">services.prometheus.exporters.rspamd.enable</link>,
          which is just a preconfigured instance of the json exporter.
        </para>
        <para>
          For more information, take a look at the
          <link xlink:href="https://github.com/prometheus-community/json_exporter">
          official documentation</link> of the json_exporter.
        </para>
      </listitem>
      <listitem>
        <para>
          Androidenv was updated, removing the
          <literal>includeDocs</literal> and
          <literal>lldbVersions</literal> arguments. Docs only covered a
          single version of the Android SDK, LLDB is now bundled with
          the NDK, and both are no longer available to download from the
          Android package repositories. Additionally, since the package
          lists have been updated, some older versions of Android
          packages may not be bundled. If you depend on older versions
          of Android packages, we recommend overriding the repo.
        </para>
        <para>
          Android packages are now loaded from a repo.json file created
          by parsing Android repo XML files. The arguments
          <literal>repoJson</literal> and <literal>repoXmls</literal>
          have been added to allow overriding the built-in androidenv
          repo.json with your own. Additionally, license files are now
          written to allow compatibility with Gradle-based tools, and
          the <literal>extraLicenses</literal> argument has been added
          to accept more SDK licenses if your project requires it. See
          the androidenv documentation for more details.
        </para>
      </listitem>
      <listitem>
        <para>
          The attribute <literal>mpi</literal> is now consistently used
          to provide a default, system-wide MPI implementation. The
          default implementation is openmpi, which has been used before
          by all derivations affects by this change. Note that all
          packages that have used <literal>mpi ? null</literal> in the
          input for optional MPI builds, have been changed to the
          boolean input paramater <literal>useMpi</literal> to enable
          building with MPI. Building all packages with
          <literal>mpich</literal> instead of the default
          <literal>openmpi</literal> can now be achived like this:
        </para>
        <programlisting language="bash">
self: super:
{
  mpi = super.mpich;
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          The Searx module has been updated with the ability to
          configure the service declaratively and uWSGI integration. The
          option <literal>services.searx.configFile</literal> has been
          renamed to
          <link xlink:href="options.html#opt-services.searx.settingsFile">services.searx.settingsFile</link>
          for consistency with the new
          <link xlink:href="options.html#opt-services.searx.settings">services.searx.settings</link>.
          In addition, the <literal>searx</literal> uid and gid
          reservations have been removed since they were not necessary:
          the service is now running with a dynamically allocated uid.
        </para>
      </listitem>
      <listitem>
        <para>
          The libinput module has been updated with the ability to
          configure mouse and touchpad settings separately. The options
          in <literal>services.xserver.libinput</literal> have been
          renamed to
          <literal>services.xserver.libinput.touchpad</literal>, while
          there is a new
          <literal>services.xserver.libinput.mouse</literal> for mouse
          related configuration.
        </para>
        <para>
          Since touchpad options no longer apply to all devices, you may
          want to replicate your touchpad configuration in mouse
          section.
        </para>
      </listitem>
      <listitem>
        <para>
          ALSA OSS emulation
          (<literal>sound.enableOSSEmulation</literal>) is now disabled
          by default.
        </para>
      </listitem>
      <listitem>
        <para>
          Thinkfan as been updated to <literal>1.2.x</literal>, which
          comes with a new YAML based configuration format. For this
          reason, several NixOS options of the thinkfan module have been
          changed to non-backward compatible types. In addition, a new
          <link xlink:href="options.html#opt-services.thinkfan.settings">services.thinkfan.settings</link>
          option has been added.
        </para>
        <para>
          Please read the
          <link xlink:href="https://github.com/vmatare/thinkfan#readme">
          thinkfan documentation</link> before updating.
        </para>
      </listitem>
      <listitem>
        <para>
          Adobe Flash Player support has been dropped from the tree. In
          particular, the following packages no longer support it:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              chromium
            </para>
          </listitem>
          <listitem>
            <para>
              firefox
            </para>
          </listitem>
          <listitem>
            <para>
              qt48
            </para>
          </listitem>
          <listitem>
            <para>
              qt5.qtwebkit
            </para>
          </listitem>
        </itemizedlist>
        <para>
          Additionally, packages flashplayer and hal-flash were removed
          along with the <literal>services.flashpolicyd</literal>
          module.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>security.rngd</literal> module has been removed.
          It was disabled by default in 20.09 as it was functionally
          redundant with krngd in the linux kernel. It is not necessary
          for any device that the kernel recognises as an hardware RNG,
          as it will automatically run the krngd task to periodically
          collect random data from the device and mix it into the
          kernel's RNG.
        </para>
        <para>
          The default SMTP port for GitLab has been changed to
          <literal>25</literal> from its previous default of
          <literal>465</literal>. If you depended on this default, you
          should now set the
          <link xlink:href="options.html#opt-services.gitlab.smtp.port">services.gitlab.smtp.port</link>
          option.
        </para>
      </listitem>
      <listitem>
        <para>
          The default version of ImageMagick has been updated from 6 to
          7. You can use imagemagick6, imagemagick6_light, and
          imagemagick6Big if you need the older version.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-services.xserver.videoDrivers">services.xserver.videoDrivers</link>
          no longer uses the deprecated <literal>cirrus</literal> and
          <literal>vesa</literal> device dependent X drivers by default.
          It also enables both <literal>amdgpu</literal> and
          <literal>nouveau</literal> drivers by default now.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>kindlegen</literal> package is gone, because it
          is no longer supported or hosted by Amazon. Sadly, its
          replacement, Kindle Previewer, has no Linux support. However,
          there are other ways to generate MOBI files. See
          <link xlink:href="https://github.com/NixOS/nixpkgs/issues/96439">the
          discussion</link> for more info.
        </para>
      </listitem>
      <listitem>
        <para>
          The apacheKafka packages are now built with version-matched
          JREs. Versions 2.6 and above, the ones that recommend it, use
          jdk11, while versions below remain on jdk8. The NixOS service
          has been adjusted to start the service using the same version
          as the package, adjustable with the new
          <link xlink:href="options.html#opt-services.apache-kafka.jre">services.apache-kafka.jre</link>
          option. Furthermore, the default list of
          <link xlink:href="options.html#opt-services.apache-kafka.jvmOptions">services.apache-kafka.jvmOptions</link>
          have been removed. You should set your own according to the
          <link xlink:href="https://kafka.apache.org/documentation/#java">upstream
          documentation</link> for your Kafka version.
        </para>
      </listitem>
      <listitem>
        <para>
          The kodi package has been modified to allow concise addon
          management. Consider the following configuration from previous
          releases of NixOS to install kodi, including the
          kodiPackages.inputstream-adaptive and kodiPackages.vfs-sftp
          addons:
        </para>
        <programlisting language="bash">
{
  environment.systemPackages = [
    pkgs.kodi
  ];

  nixpkgs.config.kodi = {
    enableInputStreamAdaptive = true;
    enableVFSSFTP = true;
  };
}
</programlisting>
        <para>
          All Kodi <literal>config</literal> flags have been removed,
          and as a result the above configuration should now be written
          as:
        </para>
        <programlisting language="bash">
{
  environment.systemPackages = [
    (pkgs.kodi.withPackages (p: with p; [
      inputstream-adaptive
      vfs-sftp
    ]))
  ];
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          <literal>environment.defaultPackages</literal> now includes
          the nano package. If pkgs.nano is not added to the list, make
          sure another editor is installed and the
          <literal>EDITOR</literal> environment variable is set to it.
          Environment variables can be set using
          <literal>environment.variables</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>services.minio.dataDir</literal> changed type to a
          list of paths, required for specifiyng multiple data
          directories for using with erasure coding. Currently, the
          service doesn't enforce nor checks the correct number of paths
          to correspond to minio requirements.
        </para>
      </listitem>
      <listitem>
        <para>
          All CUDA toolkit versions prior to CUDA 10 have been removed.
        </para>
      </listitem>
      <listitem>
        <para>
          The kbdKeymaps package was removed since dvp and neo are now
          included in kbd. If you want to use the Programmer Dvorak
          Keyboard Layout, you have to use
          <literal>dvorak-programmer</literal> in
          <literal>console.keyMap</literal> now instead of
          <literal>dvp</literal>. In
          <literal>services.xserver.xkbVariant</literal> it's still
          <literal>dvp</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The babeld service is now being run as an unprivileged user.
          To achieve that the module configures
          <literal>skip-kernel-setup true</literal> and takes care of
          setting forwarding and rp_filter sysctls by itself as well as
          for each interface in
          <literal>services.babeld.interfaces</literal>.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>services.zigbee2mqtt.config</literal> option has
          been renamed to
          <literal>services.zigbee2mqtt.settings</literal> and now
          follows
          <link xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md">RFC
          0042</link>.
        </para>
      </listitem>
    </itemizedlist>
    <para>
      The yadm dotfile manager has been updated from 2.x to 3.x, which
      has new (XDG) default locations for some data/state files. Most
      yadm commands will fail and print a legacy path warning (which
      describes how to upgrade/migrate your repository). If you have
      scripts, daemons, scheduled jobs, shell profiles, etc. that invoke
      yadm, expect them to fail or misbehave until you perform this
      migration and prepare accordingly.
    </para>
    <itemizedlist>
      <listitem>
        <para>
          Instead of determining
          <literal>services.radicale.package</literal> automatically
          based on <literal>system.stateVersion</literal>, the latest
          version is always used because old versions are not officially
          supported.
        </para>
        <para>
          Furthermore, Radicale's systemd unit was hardened which might
          break some deployments. In particular, a non-default
          <literal>filesystem_folder</literal> has to be added to
          <literal>systemd.services.radicale.serviceConfig.ReadWritePaths</literal>
          if the deprecated <literal>services.radicale.config</literal>
          is used.
        </para>
      </listitem>
      <listitem>
        <para>
          In the <literal>security.acme</literal> module, use of
          <literal>--reuse-key</literal> parameter for Lego has been
          removed. It was introduced for HKPK, but this security feature
          is now deprecated. It is a better security practice to rotate
          key pairs instead of always keeping the same. If you need to
          keep this parameter, you can add it back using
          <literal>extraLegoRenewFlags</literal> as an option for the
          appropriate certificate.
        </para>
      </listitem>
    </itemizedlist>
  </section>
  <section xml:id="sec-release-21.05-notable-changes">
    <title>Other Notable Changes</title>
    <itemizedlist>
      <listitem>
        <para>
          <literal>stdenv.lib</literal> has been deprecated and will
          break eval in 21.11. Please use <literal>pkgs.lib</literal>
          instead. See
          <link xlink:href="https://github.com/NixOS/nixpkgs/issues/108938">#108938</link>
          for details.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://www.gnuradio.org/">GNURadio</link>
          has a <literal>pkgs</literal> attribute set, and there's a
          <literal>gnuradio.callPackage</literal> function that extends
          <literal>pkgs</literal> with a
          <literal>mkDerivation</literal>, and a
          <literal>mkDerivationWith</literal>, like Qt5. Now all
          <literal>gnuradio.pkgs</literal> are defined with
          <literal>gnuradio.callPackage</literal> and some packages that
          depend on gnuradio are defined with this as well.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://www.privoxy.org/">Privoxy</link> has
          been updated to version 3.0.32 (See
          <link xlink:href="https://lists.privoxy.org/pipermail/privoxy-announce/2021-February/000007.html">announcement</link>).
          Compared to the previous release, Privoxy has gained support
          for HTTPS inspection (still experimental), Brotli
          decompression, several new filters and lots of bug fixes,
          including security ones. In addition, the package is now built
          with compression and external filters support, which were
          previously disabled.
        </para>
        <para>
          Regarding the NixOS module, new options for HTTPS inspection
          have been added and
          <literal>services.privoxy.extraConfig</literal> has been
          replaced by the new
          <link xlink:href="options.html#opt-services.privoxy.settings">services.privoxy.settings</link>
          (See
          <link xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md">RFC
          0042</link> for the motivation).
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://kodi.tv/">Kodi</link> has been
          updated to version 19.1 &quot;Matrix&quot;. See the
          <link xlink:href="https://kodi.tv/article/kodi-190-matrix-release">announcement</link>
          for further details.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>services.packagekit.backend</literal> option has
          been removed as it only supported a single setting which would
          always be the default. Instead new
          <link xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md">RFC
          0042</link> compliant
          <link xlink:href="options.html#opt-services.packagekit.settings">services.packagekit.settings</link>
          and
          <link xlink:href="options.html#opt-services.packagekit.vendorSettings">services.packagekit.vendorSettings</link>
          options have been introduced.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://nginx.org">Nginx</link> has been
          updated to stable version 1.20.0. Now nginx uses the zlib-ng
          library by default.
        </para>
      </listitem>
      <listitem>
        <para>
          KDE Gear (formerly KDE Applications) is upgraded to 21.04, see
          its
          <link xlink:href="https://kde.org/announcements/gear/21.04/">release
          notes</link> for details.
        </para>
        <para>
          The <literal>kdeApplications</literal> package set is now
          <literal>kdeGear</literal>, in keeping with the new name. The
          old name remains for compatibility, but it is deprecated.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://libreswan.org/">Libreswan</link> has
          been updated to version 4.4. The package now includes example
          configurations and manual pages by default. The NixOS module
          has been changed to use the upstream systemd units and write
          the configuration in the <literal>/etc/ipsec.d/ </literal>
          directory. In addition, two new options have been added to
          specify connection policies
          (<link xlink:href="options.html#opt-services.libreswan.policies">services.libreswan.policies</link>)
          and disable send/receive redirects
          (<link xlink:href="options.html#opt-services.libreswan.disableRedirects">services.libreswan.disableRedirects</link>).
        </para>
      </listitem>
      <listitem>
        <para>
          The Mailman NixOS module (<literal>services.mailman</literal>)
          has a new option
          <link xlink:href="options.html#opt-services.mailman.enablePostfix">services.mailman.enablePostfix</link>,
          defaulting to true, that controls integration with Postfix.
        </para>
        <para>
          If this option is disabled, default MTA config becomes not set
          and you should set the options in
          <literal>services.mailman.settings.mta</literal> according to
          the desired configuration as described in
          <link xlink:href="https://mailman.readthedocs.io/en/latest/src/mailman/docs/mta.html">Mailman
          documentation</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          The default-version of <literal>nextcloud</literal> is
          nextcloud21. Please note that it's <emphasis>not</emphasis>
          possible to upgrade <literal>nextcloud</literal> across
          multiple major versions! This means that it's e.g. not
          possible to upgrade from nextcloud18 to nextcloud20 in a
          single deploy and most <literal>20.09</literal> users will
          have to upgrade to nextcloud20 first.
        </para>
        <para>
          The package can be manually upgraded by setting
          <link xlink:href="options.html#opt-services.nextcloud.package">services.nextcloud.package</link>
          to nextcloud21.
        </para>
      </listitem>
      <listitem>
        <para>
          The setting
          <link xlink:href="options.html#opt-services.redis.bind">services.redis.bind</link>
          defaults to <literal>127.0.0.1</literal> now, making Redis
          listen on the loopback interface only, and not all public
          network interfaces.
        </para>
      </listitem>
      <listitem>
        <para>
          NixOS now emits a deprecation warning if systemd's
          <literal>StartLimitInterval</literal> setting is used in a
          <literal>serviceConfig</literal> section instead of in a
          <literal>unitConfig</literal>; that setting is deprecated and
          now undocumented for the service section by systemd upstream,
          but still effective and somewhat buggy there, which can be
          confusing. See
          <link xlink:href="https://github.com/NixOS/nixpkgs/issues/45785">#45785</link>
          for details.
        </para>
        <para>
          All services should use
          <link xlink:href="options.html#opt-systemd.services._name_.startLimitIntervalSec">systemd.services.<emphasis>name</emphasis>.startLimitIntervalSec</link>
          or <literal>StartLimitIntervalSec</literal> in
          <link xlink:href="options.html#opt-systemd.services._name_.unitConfig">systemd.services.<emphasis>name</emphasis>.unitConfig</link>
          instead.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>mediatomb</literal> service declares new options.
          It also adapts existing options so the configuration
          generation is now lazy. The existing option
          <literal>customCfg</literal> (defaults to false), when
          enabled, stops the service configuration generation
          completely. It then expects the users to provide their own
          correct configuration at the right location (whereas the
          configuration was generated and not used at all before). The
          new option <literal>transcodingOption</literal> (defaults to
          no) allows a generated configuration. It makes the mediatomb
          service pulls the necessary runtime dependencies in the nix
          store (whereas it was generated with hardcoded values before).
          The new option <literal>mediaDirectories</literal> allows the
          users to declare autoscan media directories from their nixos
          configuration:
        </para>
        <programlisting language="bash">
{
  services.mediatomb.mediaDirectories = [
    { path = &quot;/var/lib/mediatomb/pictures&quot;; recursive = false; hidden-files = false; }
    { path = &quot;/var/lib/mediatomb/audio&quot;; recursive = true; hidden-files = false; }
  ];
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          The Unbound DNS resolver service
          (<literal>services.unbound</literal>) has been refactored to
          allow reloading, control sockets and to fix startup ordering
          issues.
        </para>
        <para>
          It is now possible to enable a local UNIX control socket for
          unbound by setting the
          <link xlink:href="options.html#opt-services.unbound.localControlSocketPath">services.unbound.localControlSocketPath</link>
          option.
        </para>
        <para>
          Previously we just applied a very minimal set of restrictions
          and trusted unbound to properly drop root privs and
          capabilities.
        </para>
        <para>
          As of this we are (for the most part) just using the upstream
          example unit file for unbound. The main difference is that we
          start unbound as <literal>unbound</literal> user with the
          required capabilities instead of letting unbound do the chroot
          &amp; uid/gid changes.
        </para>
        <para>
          The upstream unit configuration this is based on is a lot
          stricter with all kinds of permissions then our previous
          variant. It also came with the default of having the
          <literal>Type</literal> set to <literal>notify</literal>,
          therefore we are now also using the
          <literal>unbound-with-systemd</literal> package here. Unbound
          will start up, read the configuration files and start
          listening on the configured ports before systemd will declare
          the unit <literal>active (running)</literal>. This will likely
          help with startup order and the occasional race condition
          during system activation where the DNS service is started but
          not yet ready to answer queries. Services depending on
          <literal>nss-lookup.target</literal> or
          <literal>unbound.service</literal> are now be able to use
          unbound when those targets have been reached.
        </para>
        <para>
          Additionally to the much stricter runtime environment the
          <literal>/dev/urandom</literal> mount lines we previously had
          in the code (that randomly failed during the stop-phase) have
          been removed as systemd will take care of those for us.
        </para>
        <para>
          The <literal>preStart</literal> script is now only required if
          we enabled the trust anchor updates (which are still enabled
          by default).
        </para>
        <para>
          Another benefit of the refactoring is that we can now issue
          reloads via either <literal>pkill -HUP unbound</literal> and
          <literal>systemctl reload unbound</literal> to reload the
          running configuration without taking the daemon offline. A
          prerequisite of this was that unbound configuration is
          available on a well known path on the file system. We are
          using the path <literal>/etc/unbound/unbound.conf</literal> as
          that is the default in the CLI tooling which in turn enables
          us to use <literal>unbound-control</literal> without passing a
          custom configuration location.
        </para>
        <para>
          The module has also been reworked to be
          <link xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0042-config-option.md">RFC
          0042</link> compliant. As such,
          <literal>sevices.unbound.extraConfig</literal> has been
          removed and replaced by
          <link xlink:href="options.html#opt-services.unbound.settings">services.unbound.settings</link>.
          <literal>services.unbound.interfaces</literal> has been
          renamed to
          <literal>services.unbound.settings.server.interface</literal>.
        </para>
        <para>
          <literal>services.unbound.forwardAddresses</literal> and
          <literal>services.unbound.allowedAccess</literal> have also
          been changed to use the new settings interface. You can follow
          the instructions when executing
          <literal>nixos-rebuild</literal> to upgrade your configuration
          to use the new interface.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>services.dnscrypt-proxy2</literal> module now
          takes the upstream's example configuration and updates it with
          the user's settings. An option has been added to restore the
          old behaviour if you prefer to declare the configuration from
          scratch.
        </para>
      </listitem>
      <listitem>
        <para>
          NixOS now defaults to the unified cgroup hierarchy
          (cgroupsv2). See the
          <link xlink:href="https://www.redhat.com/sysadmin/fedora-31-control-group-v2">Fedora
          Article for 31</link> for details on why this is desirable,
          and how it impacts containers.
        </para>
        <para>
          If you want to run containers with a runtime that does not yet
          support cgroupsv2, you can switch back to the old behaviour by
          setting
          <link xlink:href="options.html#opt-systemd.enableUnifiedCgroupHierarchy">systemd.enableUnifiedCgroupHierarchy</link>
          = <literal>false</literal>; and rebooting.
        </para>
      </listitem>
      <listitem>
        <para>
          PulseAudio was upgraded to 14.0, with changes to the handling
          of default sinks. See its
          <link xlink:href="https://www.freedesktop.org/wiki/Software/PulseAudio/Notes/14.0/">release
          notes</link>.
        </para>
      </listitem>
      <listitem>
        <para>
          GNOME users may wish to delete their
          <literal>~/.config/pulse</literal> due to the changes to
          stream routing logic. See
          <link xlink:href="https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues/832">PulseAudio
          bug 832</link> for more information.
        </para>
      </listitem>
      <listitem>
        <para>
          The zookeeper package does not provide
          <literal>zooInspector.sh</literal> anymore, as that
          &quot;contrib&quot; has been dropped from upstream releases.
        </para>
      </listitem>
      <listitem>
        <para>
          In the ACME module, the data used to build the hash for the
          account directory has changed to accomodate new features to
          reduce account rate limit issues. This will trigger new
          account creation on the first rebuild following this update.
          No issues are expected to arise from this, thanks to the new
          account creation handling.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="options.html#opt-users.users._name_.createHome">users.users.<emphasis>name</emphasis>.createHome</link>
          now always ensures home directory permissions to be
          <literal>0700</literal>. Permissions had previously been
          ignored for already existing home directories, possibly
          leaving them readable by others. The option's description was
          incorrect regarding ownership management and has been
          simplified greatly.
        </para>
      </listitem>
      <listitem>
        <para>
          When defining a new user, one of
          <link xlink:href="options.html#opt-users.users._name_.isNormalUser">users.users.<emphasis>name</emphasis>.isNormalUser</link>
          and
          <link xlink:href="options.html#opt-users.users._name_.isSystemUser">users.users.<emphasis>name</emphasis>.isSystemUser</link>
          is now required. This is to prevent accidentally giving a UID
          above 1000 to system users, which could have unexpected
          consequences, like running user activation scripts for system
          users. Note that users defined with an explicit UID below 500
          are exempted from this check, as
          <link xlink:href="options.html#opt-users.users._name_.isSystemUser">users.users.<emphasis>name</emphasis>.isSystemUser</link>
          has no effect for those.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>security.apparmor</literal> module, for the
          <link xlink:href="https://gitlab.com/apparmor/apparmor/-/wikis/Documentation">AppArmor</link>
          Mandatory Access Control system, has been substantialy
          improved along with related tools, so that module maintainers
          can now more easily write AppArmor profiles for NixOS. The
          most notable change on the user-side is the new option
          <link xlink:href="options.html#opt-security.apparmor.policies">security.apparmor.policies</link>,
          replacing the previous <literal>profiles</literal> option to
          provide a way to disable a profile and to select whether to
          confine in enforce mode (default) or in complain mode (see
          <literal>journalctl -b --grep apparmor</literal>).
          Security-minded users may also want to enable
          <link xlink:href="options.html#opt-security.apparmor.killUnconfinedConfinables">security.apparmor.killUnconfinedConfinables</link>,
          at the cost of having some of their processes killed when
          updating to a NixOS version introducing new AppArmor profiles.
        </para>
      </listitem>
      <listitem>
        <para>
          The GNOME desktop manager once again installs gnome.epiphany
          by default.
        </para>
      </listitem>
      <listitem>
        <para>
          NixOS now generates empty <literal>/etc/netgroup</literal>.
          <literal>/etc/netgroup</literal> defines network-wide groups
          and may affect to setups using NIS.
        </para>
      </listitem>
      <listitem>
        <para>
          Platforms, like <literal>stdenv.hostPlatform</literal>, no
          longer have a <literal>platform</literal> attribute. It has
          been (mostly) flattened away:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              <literal>platform.gcc</literal> is now
              <literal>gcc</literal>
            </para>
          </listitem>
          <listitem>
            <para>
              <literal>platform.kernel*</literal> is now
              <literal>linux-kernel.*</literal>
            </para>
          </listitem>
        </itemizedlist>
        <para>
          Additionally, <literal>platform.kernelArch</literal> moved to
          the top level as <literal>linuxArch</literal> to match the
          other <literal>*Arch</literal> variables.
        </para>
        <para>
          The <literal>platform</literal> grouping of these things never
          meant anything, and was just a historial/implementation
          artifact that was overdue removal.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>services.restic</literal> now uses a dedicated cache
          directory for every backup defined in
          <literal>services.restic.backups</literal>. The old global
          cache directory, <literal>/root/.cache/restic</literal>, is
          now unused and can be removed to free up disk space.
        </para>
      </listitem>
      <listitem>
        <para>
          <literal>isync</literal>: The <literal>isync</literal>
          compatibility wrapper was removed and the Master/Slave
          terminology has been deprecated and should be replaced with
          Far/Near in the configuration file.
        </para>
      </listitem>
      <listitem>
        <para>
          The nix-gc service now accepts randomizedDelaySec (default: 0)
          and persistent (default: true) parameters. By default nix-gc
          will now run immediately if it would have been triggered at
          least once during the time when the timer was inactive.
        </para>
      </listitem>
      <listitem>
        <para>
          The <literal>rustPlatform.buildRustPackage</literal> function
          is split into several hooks: cargoSetupHook to set up
          vendoring for Cargo-based projects, cargoBuildHook to build a
          project using Cargo, cargoInstallHook to install a project
          using Cargo, and cargoCheckHook to run tests in Cargo-based
          projects. With this change, mixed-language projects can use
          the relevant hooks within builders other than
          <literal>buildRustPackage</literal>. However, these changes
          also required several API changes to
          <literal>buildRustPackage</literal> itself:
        </para>
        <itemizedlist>
          <listitem>
            <para>
              The <literal>target</literal> argument was removed.
              Instead, <literal>buildRustPackage</literal> will always
              use the same target as the C/C++ compiler that is used.
            </para>
          </listitem>
          <listitem>
            <para>
              The <literal>cargoParallelTestThreads</literal> argument
              was removed. Parallel tests are now disabled through
              <literal>dontUseCargoParallelTests</literal>.
            </para>
          </listitem>
        </itemizedlist>
      </listitem>
      <listitem>
        <para>
          The <literal>rustPlatform.maturinBuildHook</literal> hook was
          added. This hook can be used with
          <literal>buildPythonPackage</literal> to build Python packages
          that are written in Rust and use Maturin as their build tool.
        </para>
      </listitem>
      <listitem>
        <para>
          Kubernetes has
          <link xlink:href="https://kubernetes.io/blog/2020/12/02/dont-panic-kubernetes-and-docker/">deprecated
          docker</link> as container runtime. As a consequence, the
          Kubernetes module now has support for configuration of custom
          remote container runtimes and enables containerd by default.
          Note that containerd is more strict regarding container image
          OCI-compliance. As an example, images with CMD or ENTRYPOINT
          defined as strings (not lists) will fail on containerd, while
          working fine on docker. Please test your setup and container
          images with containerd prior to upgrading.
        </para>
      </listitem>
      <listitem>
        <para>
          The GitLab module now has support for automatic backups. A
          schedule can be set with the
          <link xlink:href="options.html#opt-services.gitlab.backup.startAt">services.gitlab.backup.startAt</link>
          option.
        </para>
      </listitem>
      <listitem>
        <para>
          Prior to this release, systemd would also read system units
          from an undocumented
          <literal>/etc/systemd-mutable/system</literal> path. This path
          has been dropped from the defaults. That path (or others) can
          be re-enabled by adding it to the
          <link xlink:href="options.html#opt-boot.extraSystemdUnitPaths">boot.extraSystemdUnitPaths</link>
          list.
        </para>
      </listitem>
      <listitem>
        <para>
          PostgreSQL 9.5 is scheduled EOL during the 21.05 life cycle
          and has been removed.
        </para>
      </listitem>
      <listitem>
        <para>
          <link xlink:href="https://www.xfce.org/">Xfce4</link> relies
          on GIO/GVfs for userspace virtual filesystem access in
          applications like
          <link xlink:href="https://docs.xfce.org/xfce/thunar/">thunar</link>
          and
          <link xlink:href="https://docs.xfce.org/apps/gigolo/">gigolo</link>.
          For that to work, the gvfs nixos service is enabled by
          default, and it can be configured with the specific package
          that provides GVfs. Until now Xfce4 was setting it to use a
          lighter version of GVfs (without support for samba). To avoid
          conflicts with other desktop environments this setting has
          been dropped. Users that still want it should add the
          following to their system configuration:
        </para>
        <programlisting language="bash">
{
  services.gvfs.package = pkgs.gvfs.override { samba = null; };
}
</programlisting>
      </listitem>
      <listitem>
        <para>
          The newly enabled <literal>systemd-pstore.service</literal>
          now automatically evacuates crashdumps and panic logs from the
          persistent storage to
          <literal>/var/lib/systemd/pstore</literal>. This prevents
          NVRAM from filling up, which ensures the latest diagnostic
          data is always stored and alleviates problems with writing new
          boot configurations.
        </para>
      </listitem>
      <listitem>
        <para>
          Nixpkgs now contains
          <link xlink:href="https://github.com/NixOS/nixpkgs/pull/118232">automatically
          packaged GNOME Shell extensions</link> from the
          <link xlink:href="https://extensions.gnome.org/">GNOME
          Extensions</link> portal. You can find them, filed by their
          UUID, under <literal>gnome38Extensions</literal> attribute for
          GNOME 3.38 and under <literal>gnome40Extensions</literal> for
          GNOME 40. Finally, the <literal>gnomeExtensions</literal>
          attribute contains extensions for the latest GNOME Shell
          version in Nixpkgs, listed under a more human-friendly name.
          The unqualified attribute scope also contains manually
          packaged extensions. Note that the automatically packaged
          extensions are provided for convenience and are not checked or
          guaranteed to work.
        </para>
      </listitem>
      <listitem>
        <para>
          Erlang/OTP versions older than R21 got dropped. We also
          dropped the cuter package, as it was purely an example of how
          to build a package. We also dropped <literal>lfe_1_2</literal>
          as it could not build with R21+. Moving forward, we expect to
          only support 3 yearly releases of OTP.
        </para>
      </listitem>
    </itemizedlist>
  </section>
</section>
