systemd/man/systemd.resource-control.xml

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<refentry id="systemd.resource-control" xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>systemd.resource-control</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.resource-control</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.resource-control</refname>
    <refpurpose>Resource control unit settings</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para>
      <filename><replaceable>slice</replaceable>.slice</filename>,
      <filename><replaceable>scope</replaceable>.scope</filename>,
      <filename><replaceable>service</replaceable>.service</filename>,
      <filename><replaceable>socket</replaceable>.socket</filename>,
      <filename><replaceable>mount</replaceable>.mount</filename>,
      <filename><replaceable>swap</replaceable>.swap</filename>
    </para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Unit configuration files for services, slices, scopes, sockets, mount points, and swap devices share a subset
    of configuration options for resource control of spawned processes. Internally, this relies on the Linux Control
    Groups (cgroups) kernel concept for organizing processes in a hierarchical tree of named groups for the purpose of
    resource management.</para>

    <para>This man page lists the configuration options shared by
    those six unit types. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for the common options of all unit configuration files, and
    <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
    and
    <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for more information on the specific unit configuration files. The
    resource control configuration options are configured in the
    [Slice], [Scope], [Service], [Socket], [Mount], or [Swap]
    sections, depending on the unit type.</para>

    <para>In addition, options which control resources available to programs
    <emphasis>executed</emphasis> by systemd are listed in
    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
    Those options complement options listed here.</para>

    <para>See the <ulink
    url="https://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
    Control Group Interfaces</ulink> for an introduction on how to make
    use of resource control APIs from programs.</para>

    <refsect2>
      <title>Setting resource controls for a group of related units</title>

      <para>As described in
      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, the
      settings listed here may be set through the main file of a unit and drop-in snippets in
      <filename index="false">*.d/</filename> directories. The list of directories searched for drop-ins
      includes names formed by repeatedly truncating the unit name after all dashes. This is particularly
      convenient to set resource limits for a group of units with similar names.</para>

      <para>For example, every user gets their own slice
      <filename>user-<replaceable>nnn</replaceable>.slice</filename>. Drop-ins with local configuration that
      affect user 1000 may be placed in
      <filename index="false">/etc/systemd/system/user-1000.slice</filename>,
      <filename index="false">/etc/systemd/system/user-1000.slice.d/*.conf</filename>, but also
      <filename index="false">/etc/systemd/system/user-.slice.d/*.conf</filename>. This last directory
      applies to all user slices.</para>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Implicit Dependencies</title>

    <para>The following dependencies are implicitly added:</para>

    <itemizedlist>
      <listitem><para>Units with the <varname>Slice=</varname> setting set automatically acquire
      <varname>Requires=</varname> and <varname>After=</varname> dependencies on the specified
      slice unit.</para></listitem>
    </itemizedlist>
  </refsect1>

  <!-- We don't have any default dependency here. -->

  <refsect1>
    <title>Unified and Legacy Control Group Hierarchies</title>

    <para>The unified control group hierarchy is the new version of kernel control group interface, see
    <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">Control Groups v2</ulink>.
    Depending on the resource type, there are differences in resource control capabilities. Also, because of
    interface changes, some resource types have separate set of options on the unified hierarchy.</para>

    <para>
      <variablelist>

        <varlistentry>
          <term>CPU</term>
          <listitem>
            <para><varname>CPUWeight=</varname> and <varname>StartupCPUWeight=</varname> replace
            <varname>CPUShares=</varname> and <varname>StartupCPUShares=</varname>, respectively.</para>

            <para>The <literal>cpuacct</literal> controller does not exist separately on the unified hierarchy.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>Memory</term>
          <listitem>
            <para><varname>MemoryMax=</varname> replaces <varname>MemoryLimit=</varname>. <varname>MemoryLow=</varname>
            and <varname>MemoryHigh=</varname> are effective only on unified hierarchy.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>IO</term>
          <listitem>
            <para><literal>IO</literal>-prefixed settings are a superset of and replace
            <literal>BlockIO</literal>-prefixed ones. On unified hierarchy, IO resource control also applies
            to buffered writes.</para>
          </listitem>
        </varlistentry>

      </variablelist>
    </para>

    <para>To ease the transition, there is best-effort translation between the two versions of settings. For each
    controller, if any of the settings for the unified hierarchy are present, all settings for the legacy hierarchy are
    ignored. If the resulting settings are for the other type of hierarchy, the configurations are translated before
    application.</para>

    <para>Legacy control group hierarchy (see <ulink
    url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/">Control Groups version 1</ulink>),
    also called cgroup-v1, doesn't allow safe delegation of controllers to unprivileged processes. If the
    system uses the legacy control group hierarchy, resource control is disabled for the systemd user
    instance, see
    <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>Units of the types listed above can have settings
    for resource control configuration:</para>

    <variablelist class='unit-directives'>

      <varlistentry>
        <term><varname>CPUAccounting=</varname></term>

        <listitem>
          <para>Turn on CPU usage accounting for this unit. Takes a
          boolean argument. Note that turning on CPU accounting for
          one unit will also implicitly turn it on for all units
          contained in the same slice and for all its parent slices
          and the units contained therein. The system default for this
          setting may be controlled with
          <varname>DefaultCPUAccounting=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUWeight=<replaceable>weight</replaceable></varname></term>
        <term><varname>StartupCPUWeight=<replaceable>weight</replaceable></varname></term>

        <listitem>
          <para>Assign the specified CPU time weight to the processes executed, if the unified control group
          hierarchy is used on the system. These options take an integer value and control the
          <literal>cpu.weight</literal> control group attribute. The allowed range is 1 to 10000. Defaults to
          100. For details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">Control Groups v2</ulink>
          and <ulink url="https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html">CFS
          Scheduler</ulink>.  The available CPU time is split up among all units within one slice relative to
          their CPU time weight. A higher weight means more CPU time, a lower weight means less.</para>

          <para>While <varname>StartupCPUWeight=</varname> applies to the startup and shutdown phases of the system,
          <varname>CPUWeight=</varname> applies to normal runtime of the system, and if the former is not set also to
          the startup and shutdown phases. Using <varname>StartupCPUWeight=</varname> allows prioritizing specific services at
          boot-up and shutdown differently than during normal runtime.</para>

          <para>These settings replace <varname>CPUShares=</varname> and <varname>StartupCPUShares=</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUQuota=</varname></term>

        <listitem>
          <para>Assign the specified CPU time quota to the processes executed. Takes a percentage value, suffixed with
          "%". The percentage specifies how much CPU time the unit shall get at maximum, relative to the total CPU time
          available on one CPU. Use values &gt; 100% for allotting CPU time on more than one CPU. This controls the
          <literal>cpu.max</literal> attribute on the unified control group hierarchy and
          <literal>cpu.cfs_quota_us</literal> on legacy. For details about these control group attributes, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">Control Groups v2</ulink> and <ulink
          url="https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt">sched-bwc.txt</ulink>.
          Setting <varname>CPUQuota=</varname> to an empty value unsets the quota.</para>

          <para>Example: <varname>CPUQuota=20%</varname> ensures that the executed processes will never get more than
          20% CPU time on one CPU.</para>

        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>CPUQuotaPeriodSec=</varname></term>

        <listitem>
          <para>Assign the duration over which the CPU time quota specified by <varname>CPUQuota=</varname> is measured.
          Takes a time duration value in seconds, with an optional suffix such as "ms" for milliseconds (or "s" for seconds.)
          The default setting is 100ms. The period is clamped to the range supported by the kernel, which is [1ms, 1000ms].
          Additionally, the period is adjusted up so that the quota interval is also at least 1ms.
          Setting <varname>CPUQuotaPeriodSec=</varname> to an empty value resets it to the default.</para>

          <para>This controls the second field of <literal>cpu.max</literal> attribute on the unified control group hierarchy
          and <literal>cpu.cfs_period_us</literal> on legacy. For details about these control group attributes, see
          <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">Control Groups v2</ulink> and
          <ulink url="https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html">CFS Scheduler</ulink>.</para>

          <para>Example: <varname>CPUQuotaPeriodSec=10ms</varname> to request that the CPU quota is measured in periods of 10ms.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AllowedCPUs=</varname></term>
        <term><varname>StartupAllowedCPUs=</varname></term>

        <listitem>
          <para>Restrict processes to be executed on specific CPUs. Takes a list of CPU indices or ranges separated by either
          whitespace or commas. CPU ranges are specified by the lower and upper CPU indices separated by a dash.</para>

          <para>Setting <varname>AllowedCPUs=</varname> or <varname>StartupAllowedCPUs=</varname> doesn't guarantee that all
          of the CPUs will be used by the processes as it may be limited by parent units. The effective configuration is
          reported as <varname>EffectiveCPUs=</varname>.</para>

          <para>While <varname>StartupAllowedCPUs=</varname> applies to the startup and shutdown phases of the system,
          <varname>AllowedCPUs=</varname> applies to normal runtime of the system, and if the former is not set also to
          the startup and shutdown phases. Using <varname>StartupAllowedCPUs=</varname> allows prioritizing specific services at
          boot-up and shutdown differently than during normal runtime.</para>

          <para>This setting is supported only with the unified control group hierarchy.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>AllowedMemoryNodes=</varname></term>
        <term><varname>StartupAllowedMemoryNodes=</varname></term>

        <listitem>
          <para>Restrict processes to be executed on specific memory NUMA nodes. Takes a list of memory NUMA nodes indices
          or ranges separated by either whitespace or commas. Memory NUMA nodes ranges are specified by the lower and upper
          NUMA nodes indices separated by a dash.</para>

          <para>Setting <varname>AllowedMemoryNodes=</varname> or <varname>StartupAllowedMemoryNodes=</varname> doesn't
          guarantee that all of the memory NUMA nodes will be used by the processes as it may be limited by parent units.
          The effective configuration is reported as <varname>EffectiveMemoryNodes=</varname>.</para>

          <para>While <varname>StartupAllowedMemoryNodes=</varname> applies to the startup and shutdown phases of the system,
          <varname>AllowedMemoryNodes=</varname> applies to normal runtime of the system, and if the former is not set also to
          the startup and shutdown phases. Using <varname>StartupAllowedMemoryNodes=</varname> allows prioritizing specific services at
          boot-up and shutdown differently than during normal runtime.</para>

          <para>This setting is supported only with the unified control group hierarchy.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryAccounting=</varname></term>

        <listitem>
          <para>Turn on process and kernel memory accounting for this
          unit. Takes a boolean argument. Note that turning on memory
          accounting for one unit will also implicitly turn it on for
          all units contained in the same slice and for all its parent
          slices and the units contained therein. The system default
          for this setting may be controlled with
          <varname>DefaultMemoryAccounting=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryMin=<replaceable>bytes</replaceable></varname>, <varname>MemoryLow=<replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Specify the memory usage protection of the executed processes in this unit.
          When reclaiming memory, the unit is treated as if it was using less memory resulting in memory
          to be preferentially reclaimed from unprotected units.
          Using <varname>MemoryLow=</varname> results in a weaker protection where memory may still
          be reclaimed to avoid invoking the OOM killer in case there is no other reclaimable memory.</para>
          <para>
          For a protection to be effective, it is generally required to set a corresponding
          allocation on all ancestors, which is then distributed between children
          (with the exception of the root slice).
          Any <varname>MemoryMin=</varname> or <varname>MemoryLow=</varname> allocation that is not
          explicitly distributed to specific children is used to create a shared protection for all children.
          As this is a shared protection, the children will freely compete for the memory.</para>

          <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
          percentage value may be specified, which is taken relative to the installed physical memory on the
          system. If assigned the special value <literal>infinity</literal>, all available memory is protected, which may be
          useful in order to always inherit all of the protection afforded by ancestors.
          This controls the <literal>memory.min</literal> or <literal>memory.low</literal> control group attribute.
          For details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#memory-interface-files">Memory Interface Files</ulink>.</para>

          <para>This setting is supported only if the unified control group hierarchy is used and disables
          <varname>MemoryLimit=</varname>.</para>

          <para>Units may have their children use a default <literal>memory.min</literal> or
          <literal>memory.low</literal> value by specifying <varname>DefaultMemoryMin=</varname> or
          <varname>DefaultMemoryLow=</varname>, which has the same semantics as
          <varname>MemoryMin=</varname> and <varname>MemoryLow=</varname>.
          This setting does not affect <literal>memory.min</literal> or <literal>memory.low</literal>
          in the unit itself.
          Using it to set a default child allocation is only useful on kernels older than 5.7,
          which do not support the <literal>memory_recursiveprot</literal> cgroup2 mount option.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryHigh=<replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Specify the throttling limit on memory usage of the executed processes in this unit. Memory usage may go
          above the limit if unavoidable, but the processes are heavily slowed down and memory is taken away
          aggressively in such cases. This is the main mechanism to control memory usage of a unit.</para>

          <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
          percentage value may be specified, which is taken relative to the installed physical memory on the
          system. If assigned the
          special value <literal>infinity</literal>, no memory throttling is applied. This controls the
          <literal>memory.high</literal> control group attribute. For details about this control group attribute, see
          <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#memory-interface-files">Memory Interface Files</ulink>.</para>

          <para>This setting is supported only if the unified control group hierarchy is used and disables
          <varname>MemoryLimit=</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryMax=<replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Specify the absolute limit on memory usage of the executed processes in this unit. If memory usage
          cannot be contained under the limit, out-of-memory killer is invoked inside the unit. It is recommended to
          use <varname>MemoryHigh=</varname> as the main control mechanism and use <varname>MemoryMax=</varname> as the
          last line of defense.</para>

          <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
          percentage value may be specified, which is taken relative to the installed physical memory on the system. If
          assigned the special value <literal>infinity</literal>, no memory limit is applied. This controls the
          <literal>memory.max</literal> control group attribute. For details about this control group attribute, see
          <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#memory-interface-files">Memory Interface Files</ulink>.</para>

          <para>This setting replaces <varname>MemoryLimit=</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemorySwapMax=<replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Specify the absolute limit on swap usage of the executed processes in this unit.</para>

          <para>Takes a swap size in bytes. If the value is suffixed with K, M, G or T, the specified swap size is
          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. If assigned the
          special value <literal>infinity</literal>, no swap limit is applied. This controls the
          <literal>memory.swap.max</literal> control group attribute. For details about this control group attribute,
          see <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#memory-interface-files">Memory Interface Files</ulink>.</para>

          <para>This setting is supported only if the unified control group hierarchy is used and disables
          <varname>MemoryLimit=</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TasksAccounting=</varname></term>

        <listitem>
          <para>Turn on task accounting for this unit. Takes a
          boolean argument. If enabled, the system manager will keep
          track of the number of tasks in the unit. The number of
          tasks accounted this way includes both kernel threads and
          userspace processes, with each thread counting
          individually. Note that turning on tasks accounting for one
          unit will also implicitly turn it on for all units contained
          in the same slice and for all its parent slices and the
          units contained therein. The system default for this setting
          may be controlled with
          <varname>DefaultTasksAccounting=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>TasksMax=<replaceable>N</replaceable></varname></term>

        <listitem>
          <para>Specify the maximum number of tasks that may be created in the unit. This ensures that the number of
          tasks accounted for the unit (see above) stays below a specific limit. This either takes an absolute number
          of tasks or a percentage value that is taken relative to the configured maximum number of tasks on the
          system.  If assigned the special value <literal>infinity</literal>, no tasks limit is applied. This controls
          the <literal>pids.max</literal> control group attribute. For details about this control group attribute, see
          <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/pids.html">Process Number Controller</ulink>.
          </para>

          <para>The system default for this setting may be controlled with
          <varname>DefaultTasksMax=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOAccounting=</varname></term>

        <listitem>
          <para>Turn on Block I/O accounting for this unit, if the unified control group hierarchy is used on the
          system. Takes a boolean argument. Note that turning on block I/O accounting for one unit will also implicitly
          turn it on for all units contained in the same slice and all for its parent slices and the units contained
          therein. The system default for this setting may be controlled with <varname>DefaultIOAccounting=</varname>
          in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

          <para>This setting replaces <varname>BlockIOAccounting=</varname> and disables settings prefixed with
          <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOWeight=<replaceable>weight</replaceable></varname></term>
        <term><varname>StartupIOWeight=<replaceable>weight</replaceable></varname></term>

        <listitem>
          <para>Set the default overall block I/O weight for the executed processes, if the unified control
          group hierarchy is used on the system. Takes a single weight value (between 1 and 10000) to set the
          default block I/O weight. This controls the <literal>io.weight</literal> control group attribute,
          which defaults to 100. For details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files">IO
          Interface Files</ulink>.  The available I/O bandwidth is split up among all units within one slice
          relative to their block I/O weight. A higher weight means more I/O bandwidth, a lower weight means
          less.</para>

          <para>While <varname>StartupIOWeight=</varname> applies
          to the startup and shutdown phases of the system,
          <varname>IOWeight=</varname> applies to the later runtime of
          the system, and if the former is not set also to the startup
          and shutdown phases. This allows prioritizing specific services at boot-up
          and shutdown differently than during runtime.</para>

          <para>These settings replace <varname>BlockIOWeight=</varname> and <varname>StartupBlockIOWeight=</varname>
          and disable settings prefixed with <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IODeviceWeight=<replaceable>device</replaceable> <replaceable>weight</replaceable></varname></term>

        <listitem>
          <para>Set the per-device overall block I/O weight for the executed processes, if the unified control group
          hierarchy is used on the system. Takes a space-separated pair of a file path and a weight value to specify
          the device specific weight value, between 1 and 10000. (Example: <literal>/dev/sda 1000</literal>). The file
          path may be specified as path to a block device node or as any other file, in which case the backing block
          device of the file system of the file is determined. This controls the <literal>io.weight</literal> control
          group attribute, which defaults to 100. Use this option multiple times to set weights for multiple devices.
          For details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files">IO Interface Files</ulink>.</para>

          <para>This setting replaces <varname>BlockIODeviceWeight=</varname> and disables settings prefixed with
          <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>

          <para>The specified device node should reference a block device that has an I/O scheduler
          associated, i.e. should not refer to partition or loopback block devices, but to the originating,
          physical device. When a path to a regular file or directory is specified it is attempted to
          discover the correct originating device backing the file system of the specified path. This works
          correctly only for simpler cases, where the file system is directly placed on a partition or
          physical block device, or where simple 1:1 encryption using dm-crypt/LUKS is used. This discovery
          does not cover complex storage and in particular RAID and volume management storage devices.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOReadBandwidthMax=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
        <term><varname>IOWriteBandwidthMax=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Set the per-device overall block I/O bandwidth maximum limit for the executed processes, if the unified
          control group hierarchy is used on the system. This limit is not work-conserving and the executed processes
          are not allowed to use more even if the device has idle capacity.  Takes a space-separated pair of a file
          path and a bandwidth value (in bytes per second) to specify the device specific bandwidth. The file path may
          be a path to a block device node, or as any other file in which case the backing block device of the file
          system of the file is used. If the bandwidth is suffixed with K, M, G, or T, the specified bandwidth is
          parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes, respectively, to the base of 1000. (Example:
          "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This controls the <literal>io.max</literal> control
          group attributes. Use this option multiple times to set bandwidth limits for multiple devices. For details
          about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files">IO Interface Files</ulink>.
          </para>

          <para>These settings replace <varname>BlockIOReadBandwidth=</varname> and
          <varname>BlockIOWriteBandwidth=</varname> and disable settings prefixed with <varname>BlockIO</varname> or
          <varname>StartupBlockIO</varname>.</para>

          <para>Similar restrictions on block device discovery as for <varname>IODeviceWeight=</varname> apply, see above.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IOReadIOPSMax=<replaceable>device</replaceable> <replaceable>IOPS</replaceable></varname></term>
        <term><varname>IOWriteIOPSMax=<replaceable>device</replaceable> <replaceable>IOPS</replaceable></varname></term>

        <listitem>
          <para>Set the per-device overall block I/O IOs-Per-Second maximum limit for the executed processes, if the
          unified control group hierarchy is used on the system. This limit is not work-conserving and the executed
          processes are not allowed to use more even if the device has idle capacity.  Takes a space-separated pair of
          a file path and an IOPS value to specify the device specific IOPS. The file path may be a path to a block
          device node, or as any other file in which case the backing block device of the file system of the file is
          used. If the IOPS is suffixed with K, M, G, or T, the specified IOPS is parsed as KiloIOPS, MegaIOPS,
          GigaIOPS, or TeraIOPS, respectively, to the base of 1000. (Example:
          "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 1K"). This controls the <literal>io.max</literal> control
          group attributes. Use this option multiple times to set IOPS limits for multiple devices. For details about
          this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files">IO Interface Files</ulink>.
          </para>

          <para>These settings are supported only if the unified control group hierarchy is used and disable settings
          prefixed with <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>

          <para>Similar restrictions on block device discovery as for <varname>IODeviceWeight=</varname> apply, see above.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IODeviceLatencyTargetSec=<replaceable>device</replaceable> <replaceable>target</replaceable></varname></term>

        <listitem>
          <para>Set the per-device average target I/O latency for the executed processes, if the unified control group
          hierarchy is used on the system. Takes a file path and a timespan separated by a space to specify
          the device specific latency target. (Example: "/dev/sda 25ms"). The file path may be specified
          as path to a block device node or as any other file, in which case the backing block device of the file
          system of the file is determined. This controls the <literal>io.latency</literal> control group
          attribute. Use this option multiple times to set latency target for multiple devices. For details about this
          control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#io-interface-files">IO Interface Files</ulink>.</para>

          <para>Implies <literal>IOAccounting=yes</literal>.</para>

          <para>These settings are supported only if the unified control group hierarchy is used.</para>

          <para>Similar restrictions on block device discovery as for <varname>IODeviceWeight=</varname> apply, see above.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IPAccounting=</varname></term>

        <listitem>
          <para>Takes a boolean argument. If true, turns on IPv4 and IPv6 network traffic accounting for packets sent
          or received by the unit. When this option is turned on, all IPv4 and IPv6 sockets created by any process of
          the unit are accounted for.</para>

          <para>When this option is used in socket units, it applies to all IPv4 and IPv6 sockets
          associated with it (including both listening and connection sockets where this applies). Note that for
          socket-activated services, this configuration setting and the accounting data of the service unit and the
          socket unit are kept separate, and displayed separately. No propagation of the setting and the collected
          statistics is done, in either direction. Moreover, any traffic sent or received on any of the socket unit's
          sockets is accounted to the socket unit — and never to the service unit it might have activated, even if the
          socket is used by it.</para>

          <para>The system default for this setting may be controlled with <varname>DefaultIPAccounting=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IPAddressAllow=<replaceable>ADDRESS[/PREFIXLENGTH]…</replaceable></varname></term>
        <term><varname>IPAddressDeny=<replaceable>ADDRESS[/PREFIXLENGTH]…</replaceable></varname></term>

        <listitem>
          <para>Turn on network traffic filtering for IP packets sent and received over
          <constant>AF_INET</constant> and <constant>AF_INET6</constant> sockets. Both directives take a
          space separated list of IPv4 or IPv6 addresses, each optionally suffixed with an address prefix
          length in bits after a <literal>/</literal> character. If the suffix is omitted, the address is
          considered a host address, i.e. the filter covers the whole address (32 bits for IPv4, 128 bits for
          IPv6).</para>

          <para>The access lists configured with this option are applied to all sockets created by processes
          of this unit (or in the case of socket units, associated with it). The lists are implicitly
          combined with any lists configured for any of the parent slice units this unit might be a member
          of. By default both access lists are empty. Both ingress and egress traffic is filtered by these
          settings. In case of ingress traffic the source IP address is checked against these access lists,
          in case of egress traffic the destination IP address is checked. The following rules are applied in
          turn:</para>

          <itemizedlist>
            <listitem><para>Access is granted when the checked IP address matches an entry in the
            <varname>IPAddressAllow=</varname> list.</para></listitem>

            <listitem><para>Otherwise, access is denied when the checked IP address matches an entry in the
            <varname>IPAddressDeny=</varname> list.</para></listitem>

            <listitem><para>Otherwise, access is granted.</para></listitem>
          </itemizedlist>

          <para>In order to implement an allow-listing IP firewall, it is recommended to use a
          <varname>IPAddressDeny=</varname><constant>any</constant> setting on an upper-level slice unit
          (such as the root slice <filename>-.slice</filename> or the slice containing all system services
          <filename>system.slice</filename> – see
          <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
          for details on these slice units), plus individual per-service <varname>IPAddressAllow=</varname>
          lines permitting network access to relevant services, and only them.</para>

          <para>Note that for socket-activated services, the IP access list configured on the socket unit
          applies to all sockets associated with it directly, but not to any sockets created by the
          ultimately activated services for it. Conversely, the IP access list configured for the service is
          not applied to any sockets passed into the service via socket activation. Thus, it is usually a
          good idea to replicate the IP access lists on both the socket and the service unit. Nevertheless,
          it may make sense to maintain one list more open and the other one more restricted, depending on
          the usecase.</para>

          <para>If these settings are used multiple times in the same unit the specified lists are combined. If an
          empty string is assigned to these settings the specific access list is reset and all previous settings undone.</para>

          <para>In place of explicit IPv4 or IPv6 address and prefix length specifications a small set of symbolic
          names may be used. The following names are defined:</para>

          <table>
            <title>Special address/network names</title>

            <tgroup cols='3'>
              <colspec colname='name'/>
              <colspec colname='definition'/>
              <colspec colname='meaning'/>

              <thead>
                <row>
                  <entry>Symbolic Name</entry>
                  <entry>Definition</entry>
                  <entry>Meaning</entry>
                </row>
              </thead>

            <tbody>
              <row>
                <entry><constant>any</constant></entry>
                <entry>0.0.0.0/0 ::/0</entry>
                <entry>Any host</entry>
              </row>

              <row>
                <entry><constant>localhost</constant></entry>
                <entry>127.0.0.0/8 ::1/128</entry>
                <entry>All addresses on the local loopback</entry>
              </row>

              <row>
                <entry><constant>link-local</constant></entry>
                <entry>169.254.0.0/16 fe80::/64</entry>
                <entry>All link-local IP addresses</entry>
              </row>

              <row>
                <entry><constant>multicast</constant></entry>
                <entry>224.0.0.0/4 ff00::/8</entry>
                <entry>All IP multicasting addresses</entry>
              </row>
            </tbody>
            </tgroup>
          </table>

          <para>Note that these settings might not be supported on some systems (for example if eBPF control group
          support is not enabled in the underlying kernel or container manager). These settings will have no effect in
          that case. If compatibility with such systems is desired it is hence recommended to not exclusively rely on
          them for IP security.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>IPIngressFilterPath=<replaceable>BPF_FS_PROGRAM_PATH</replaceable></varname></term>
        <term><varname>IPEgressFilterPath=<replaceable>BPF_FS_PROGRAM_PATH</replaceable></varname></term>

        <listitem>
          <para>Add custom network traffic filters implemented as BPF programs, applying to all IP packets
          sent and received over <constant>AF_INET</constant> and <constant>AF_INET6</constant> sockets.
          Takes an absolute path to a pinned BPF program in the BPF virtual filesystem (<filename>/sys/fs/bpf/</filename>).
          </para>

          <para>The filters configured with this option are applied to all sockets created by processes
          of this unit (or in the case of socket units, associated with it). The filters are loaded in addition
          to filters any of the parent slice units this unit might be a member of as well as any
          <varname>IPAddressAllow=</varname> and <varname>IPAddressDeny=</varname> filters in any of these units.
          By default there are no filters specified.</para>

          <para>If these settings are used multiple times in the same unit all the specified programs are attached. If an
          empty string is assigned to these settings the program list is reset and all previous specified programs ignored.</para>

          <para>If the path <replaceable>BPF_FS_PROGRAM_PATH</replaceable> in <varname>IPIngressFilterPath=</varname> assignment
          is already being handled by <varname>BPFProgram=</varname> ingress hook, e.g.
          <varname>BPFProgram=</varname><constant>ingress</constant>:<replaceable>BPF_FS_PROGRAM_PATH</replaceable>,
          the assignment will be still considered valid and the program will be attached to a cgroup. Same for
          <varname>IPEgressFilterPath=</varname> path and <constant>egress</constant> hook.</para>

          <para>Note that for socket-activated services, the IP filter programs configured on the socket unit apply to
          all sockets associated with it directly, but not to any sockets created by the ultimately activated services
          for it. Conversely, the IP filter programs configured for the service are not applied to any sockets passed into
          the service via socket activation. Thus, it is usually a good idea, to replicate the IP filter programs on both
          the socket and the service unit, however it often makes sense to maintain one configuration more open and the other
          one more restricted, depending on the usecase.</para>

          <para>Note that these settings might not be supported on some systems (for example if eBPF control group
          support is not enabled in the underlying kernel or container manager). These settings will fail the service in
          that case. If compatibility with such systems is desired it is hence recommended to attach your filter manually
          (requires <varname>Delegate=</varname><constant>yes</constant>) instead of using this setting.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BPFProgram=<replaceable>type</replaceable><constant>:</constant><replaceable>program-path</replaceable></varname></term>
        <listitem>
          <para>Add a custom cgroup BPF program.</para>

          <para><varname>BPFProgram=</varname> allows attaching BPF hooks to the cgroup of a systemd unit.
          (This generalizes the functionality exposed via <varname>IPEgressFilterPath=</varname> for egress and
          <varname>IPIngressFilterPath=</varname> for ingress.)
          Cgroup-bpf hooks in the form of BPF programs loaded to the BPF filesystem are attached with cgroup-bpf attach
          flags determined by the unit. For details about attachment types and flags see <ulink
          url="https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/include/uapi/linux/bpf.h"/>.
          For general BPF documentation please refer to <ulink url="https://www.kernel.org/doc/html/latest/bpf/index.html"/>.</para>

          <para>The specification of BPF program consists of a <replaceable>type</replaceable> followed by a
          <replaceable>program-path</replaceable> with <literal>:</literal> as the separator:
          <replaceable>type</replaceable><constant>:</constant><replaceable>program-path</replaceable>.</para>

          <para><replaceable>type</replaceable> is the string name of BPF attach type also used in
          <command>bpftool</command>. <replaceable>type</replaceable> can be one of <constant>egress</constant>,
          <constant>ingress</constant>, <constant>sock_create</constant>, <constant>sock_ops</constant>,
          <constant>device</constant>, <constant>bind4</constant>, <constant>bind6</constant>,
          <constant>connect4</constant>, <constant>connect6</constant>, <constant>post_bind4</constant>,
          <constant>post_bind6</constant>, <constant>sendmsg4</constant>, <constant>sendmsg6</constant>,
          <constant>sysctl</constant>, <constant>recvmsg4</constant>, <constant>recvmsg6</constant>,
          <constant>getsockopt</constant>, <constant>setsockopt</constant>.</para>

          <para>Setting <varname>BPFProgram=</varname> to an empty value makes previous assignments ineffective.</para>
          <para>Multiple assignments of the same <replaceable>type</replaceable>:<replaceable>program-path</replaceable>
          value have the same effect as a single assignment: the program with the path <replaceable>program-path</replaceable>
          will be attached to cgroup hook <replaceable>type</replaceable> just once.</para>
          <para>If BPF <constant>egress</constant> pinned to <replaceable>program-path</replaceable> path is already being
          handled by <varname>IPEgressFilterPath=</varname>, <varname>BPFProgram=</varname>
          assignment will be considered valid and <varname>BPFProgram=</varname> will be attached to a cgroup.
          Similarly for <constant>ingress</constant> hook and <varname>IPIngressFilterPath=</varname> assignment.</para>

          <para>BPF programs passed with <varname>BPFProgram=</varname> are attached to the cgroup of a unit with BPF
          attach flag <constant>multi</constant>, that allows further attachments of the same
          <replaceable>type</replaceable> within cgroup hierarchy topped by the unit cgroup.</para>

          <para>Examples:<programlisting>
BPFProgram=egress:/sys/fs/bpf/egress-hook
BPFProgram=bind6:/sys/fs/bpf/sock-addr-hook
</programlisting></para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>SocketBindAllow=<replaceable>bind-rule</replaceable></varname></term>
        <term><varname>SocketBindDeny=<replaceable>bind-rule</replaceable></varname></term>

        <listitem>
          <para>Allow or deny binding a socket address to a socket by matching it with the <replaceable>bind-rule</replaceable> and
          applying a corresponding action if there is a match.</para>

          <para><replaceable>bind-rule</replaceable> describes socket properties such as <replaceable>address-family</replaceable>,
          <replaceable>transport-protocol</replaceable> and <replaceable>ip-ports</replaceable>.</para>

          <para><replaceable>bind-rule</replaceable> :=
          { [<replaceable>address-family</replaceable><constant>:</constant>][<replaceable>transport-protocol</replaceable><constant>:</constant>][<replaceable>ip-ports</replaceable>] | <constant>any</constant> }</para>

          <para><replaceable>address-family</replaceable> := { <constant>ipv4</constant> | <constant>ipv6</constant> }</para>

          <para><replaceable>transport-protocol</replaceable> := { <constant>tcp</constant> | <constant>udp</constant> }</para>

          <para><replaceable>ip-ports</replaceable> := { <replaceable>ip-port</replaceable> | <replaceable>ip-port-range</replaceable> }</para>

          <para>An optional <replaceable>address-family</replaceable> expects <constant>ipv4</constant> or <constant>ipv6</constant> values.
          If not specified, a rule will be matched for both IPv4 and IPv6 addresses and applied depending on other socket fields, e.g. <replaceable>transport-protocol</replaceable>,
          <replaceable>ip-port</replaceable>.</para>

          <para>An optional <replaceable>transport-protocol</replaceable> expects <constant>tcp</constant> or <constant>udp</constant> transport protocol names.
          If not specified, a rule will be matched for any transport protocol.</para>

          <para>An optional <replaceable>ip-port</replaceable> value must lie within 1…65535 interval inclusively, i.e.
          dynamic port <constant>0</constant> is not allowed. A range of sequential ports is described by
          <replaceable>ip-port-range</replaceable> := <replaceable>ip-port-low</replaceable><constant>-</constant><replaceable>ip-port-high</replaceable>,
          where <replaceable>ip-port-low</replaceable> is smaller than or equal to <replaceable>ip-port-high</replaceable>
          and both are within 1…65535 inclusively.</para>

          <para>A special value <constant>any</constant> can be used to apply a rule to any address family, transport protocol and any port with a positive value.</para>

          <para>To allow multiple rules assign <varname>SocketBindAllow=</varname> or <varname>SocketBindDeny=</varname> multiple times.
          To clear the existing assignments pass an empty <varname>SocketBindAllow=</varname> or <varname>SocketBindDeny=</varname>
          assignment.</para>

          <para>For each of <varname>SocketBindAllow=</varname> and <varname>SocketBindDeny=</varname>, maximum allowed number of assignments is
          <constant>128</constant>.</para>

          <itemizedlist>
            <listitem><para>Binding to a socket is allowed when a socket address matches an entry in the
            <varname>SocketBindAllow=</varname> list.</para></listitem>

            <listitem><para>Otherwise, binding is denied when the socket address matches an entry in the
            <varname>SocketBindDeny=</varname> list.</para></listitem>

            <listitem><para>Otherwise, binding is allowed.</para></listitem>
          </itemizedlist>

          <para>The feature is implemented with <constant>cgroup/bind4</constant> and <constant>cgroup/bind6</constant> cgroup-bpf hooks.</para>
          <para>Examples:<programlisting>…
# Allow binding IPv6 socket addresses with a port greater than or equal to 10000.
[Service]
SocketBindAllow=ipv6:10000-65535
SocketBindDeny=any
…
# Allow binding IPv4 and IPv6 socket addresses with 1234 and 4321 ports.
[Service]
SocketBindAllow=1234
SocketBindAllow=4321
SocketBindDeny=any
…
# Deny binding IPv6 socket addresses.
[Service]
SocketBindDeny=ipv6
…
# Deny binding IPv4 and IPv6 socket addresses.
[Service]
SocketBindDeny=any
…
# Allow binding only over TCP
[Service]
SocketBindAllow=tcp
SocketBindDeny=any
…
# Allow binding only over IPv6/TCP
[Service]
SocketBindAllow=ipv6:tcp
SocketBindDeny=any
…
# Allow binding ports within 10000-65535 range over IPv4/UDP.
[Service]
SocketBindAllow=ipv4:udp:10000-65535
SocketBindDeny=any
…</programlisting></para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>RestrictNetworkInterfaces=</varname></term>

        <listitem>
          <para>Takes a list of space-separated network interface names. This option restricts the network
          interfaces that processes of this unit can use. By default processes can only use the network interfaces
          listed (allow-list). If the first character of the rule is <literal>~</literal>, the effect is inverted:
          the processes can only use network interfaces not listed (deny-list).
          </para>

          <para>This option can appear multiple times, in which case the network interface names are merged. If the
          empty string is assigned the set is reset, all prior assignments will have not effect.
          </para>

          <para>If you specify both types of this option (i.e. allow-listing and deny-listing), the first encountered
          will take precedence and will dictate the default action (allow vs deny). Then the next occurrences of this
          option will add or delete the listed network interface names from the set, depending of its type and the
          default action.
          </para>

          <para>The loopback interface ("lo") is not treated in any special way, you have to configure it explicitly
          in the unit file.
          </para>
          <para>Example 1: allow-list
          <programlisting>
RestrictNetworkInterfaces=eth1
RestrictNetworkInterfaces=eth2</programlisting>
          Programs in the unit will be only able to use the eth1 and eth2 network
          interfaces.
          </para>

          <para>Example 2: deny-list
          <programlisting>
RestrictNetworkInterfaces=~eth1 eth2</programlisting>
          Programs in the unit will be able to use any network interface but eth1 and eth2.
          </para>

          <para>Example 3: mixed
          <programlisting>
RestrictNetworkInterfaces=eth1 eth2
RestrictNetworkInterfaces=~eth1</programlisting>
          Programs in the unit will be only able to use the eth2 network interface.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DeviceAllow=</varname></term>

        <listitem>
          <para>Control access to specific device nodes by the executed processes. Takes two space-separated
          strings: a device node specifier followed by a combination of <constant>r</constant>,
          <constant>w</constant>, <constant>m</constant> to control <emphasis>r</emphasis>eading,
          <emphasis>w</emphasis>riting, or creation of the specific device node(s) by the unit
          (<emphasis>m</emphasis>knod), respectively. On cgroup-v1 this controls the
          <literal>devices.allow</literal> control group attribute. For details about this control group
          attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/devices.html">Device Whitelist Controller</ulink>.
          In the unified cgroup hierarchy this functionality is implemented using eBPF filtering.</para>

          <para>When access to <emphasis>all</emphasis> physical devices should be disallowed,
          <varname>PrivateDevices=</varname> may be used instead. See
          <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
          </para>

          <para>The device node specifier is either a path to a device node in the file system, starting with
          <filename>/dev/</filename>, or a string starting with either <literal>char-</literal> or
          <literal>block-</literal> followed by a device group name, as listed in
          <filename>/proc/devices</filename>. The latter is useful to allow-list all current and future
          devices belonging to a specific device group at once. The device group is matched according to
          filename globbing rules, you may hence use the <literal>*</literal> and <literal>?</literal>
          wildcards. (Note that such globbing wildcards are not available for device node path
          specifications!) In order to match device nodes by numeric major/minor, use device node paths in
          the <filename>/dev/char/</filename> and <filename>/dev/block/</filename> directories. However,
          matching devices by major/minor is generally not recommended as assignments are neither stable nor
          portable between systems or different kernel versions.</para>

          <para>Examples: <filename>/dev/sda5</filename> is a path to a device node, referring to an ATA or
          SCSI block device. <literal>char-pts</literal> and <literal>char-alsa</literal> are specifiers for
          all pseudo TTYs and all ALSA sound devices, respectively. <literal>char-cpu/*</literal> is a
          specifier matching all CPU related device groups.</para>

          <para>Note that allow lists defined this way should only reference device groups which are
          resolvable at the time the unit is started. Any device groups not resolvable then are not added to
          the device allow list. In order to work around this limitation, consider extending service units
          with a pair of <command>After=modprobe@xyz.service</command> and
          <command>Wants=modprobe@xyz.service</command> lines that load the necessary kernel module
          implementing the device group if missing.
          Example: <programlisting>…
[Unit]
Wants=modprobe@loop.service
After=modprobe@loop.service

[Service]
DeviceAllow=block-loop
DeviceAllow=/dev/loop-control
…</programlisting></para>

        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DevicePolicy=auto|closed|strict</varname></term>

        <listitem>
          <para>
            Control the policy for allowing device access:
          </para>
          <variablelist>
            <varlistentry>
              <term><option>strict</option></term>
              <listitem>
                <para>means to only allow types of access that are
                explicitly specified.</para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>closed</option></term>
              <listitem>
                <para>in addition, allows access to standard pseudo
                devices including
                <filename>/dev/null</filename>,
                <filename>/dev/zero</filename>,
                <filename>/dev/full</filename>,
                <filename>/dev/random</filename>, and
                <filename>/dev/urandom</filename>.
                </para>
              </listitem>
            </varlistentry>

            <varlistentry>
              <term><option>auto</option></term>
              <listitem>
                <para>
                  in addition, allows access to all devices if no
                  explicit <varname>DeviceAllow=</varname> is present.
                  This is the default.
                </para>
              </listitem>
            </varlistentry>
          </variablelist>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Slice=</varname></term>

        <listitem>
          <para>The name of the slice unit to place the unit
          in. Defaults to <filename>system.slice</filename> for all
          non-instantiated units of all unit types (except for slice
          units themselves see below). Instance units are by default
          placed in a subslice of <filename>system.slice</filename>
          that is named after the template name.</para>

          <para>This option may be used to arrange systemd units in a
          hierarchy of slices each of which might have resource
          settings applied.</para>

          <para>For units of type slice, the only accepted value for
          this setting is the parent slice. Since the name of a slice
          unit implies the parent slice, it is hence redundant to ever
          set this parameter directly for slice units.</para>

          <para>Special care should be taken when relying on the default slice assignment in templated service units
          that have <varname>DefaultDependencies=no</varname> set, see
          <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, section
          "Default Dependencies" for details.</para>

        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>Delegate=</varname></term>

        <listitem>
          <para>Turns on delegation of further resource control partitioning to processes of the unit. Units where this
          is enabled may create and manage their own private subhierarchy of control groups below the control group of
          the unit itself. For unprivileged services (i.e. those using the <varname>User=</varname> setting) the unit's
          control group will be made accessible to the relevant user. When enabled the service manager will refrain
          from manipulating control groups or moving processes below the unit's control group, so that a clear concept
          of ownership is established: the control group tree above the unit's control group (i.e. towards the root
          control group) is owned and managed by the service manager of the host, while the control group tree below
          the unit's control group is owned and managed by the unit itself. Takes either a boolean argument or a list
          of control group controller names. If true, delegation is turned on, and all supported controllers are
          enabled for the unit, making them available to the unit's processes for management. If false, delegation is
          turned off entirely (and no additional controllers are enabled). If set to a list of controllers, delegation
          is turned on, and the specified controllers are enabled for the unit. Note that additional controllers than
          the ones specified might be made available as well, depending on configuration of the containing slice unit
          or other units contained in it. Note that assigning the empty string will enable delegation, but reset the
          list of controllers, all assignments prior to this will have no effect.  Defaults to false.</para>

          <para>Note that controller delegation to less privileged code is only safe on the unified control group
          hierarchy. Accordingly, access to the specified controllers will not be granted to unprivileged services on
          the legacy hierarchy, even when requested.</para>

          <xi:include href="supported-controllers.xml"  xpointer="controllers-text" />

          <para>Not all of these controllers are available on all kernels however, and some are
          specific to the unified hierarchy while others are specific to the legacy hierarchy. Also note that the
          kernel might support further controllers, which aren't covered here yet as delegation is either not supported
          at all for them or not defined cleanly.</para>

          <para>For further details on the delegation model consult <ulink
          url="https://systemd.io/CGROUP_DELEGATION">Control Group APIs and Delegation</ulink>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>DisableControllers=</varname></term>

        <listitem>
          <para>Disables controllers from being enabled for a unit's children. If a controller listed is already in use
          in its subtree, the controller will be removed from the subtree. This can be used to avoid child units being
          able to implicitly or explicitly enable a controller. Defaults to not disabling any controllers.</para>

          <para>It may not be possible to successfully disable a controller if the unit or any child of the unit in
          question delegates controllers to its children, as any delegated subtree of the cgroup hierarchy is unmanaged
          by systemd.</para>

          <para>Multiple controllers may be specified, separated by spaces. You may also pass
          <varname>DisableControllers=</varname> multiple times, in which case each new instance adds another controller
          to disable. Passing <varname>DisableControllers=</varname> by itself with no controller name present resets
          the disabled controller list.</para>

          <xi:include href="supported-controllers.xml"  xpointer="controllers-text" />
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ManagedOOMSwap=auto|kill</varname></term>
        <term><varname>ManagedOOMMemoryPressure=auto|kill</varname></term>

        <listitem>
          <para>Specifies how
          <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
          will act on this unit's cgroups. Defaults to <option>auto</option>.</para>

          <para>When set to <option>kill</option>, <command>systemd-oomd</command> will actively monitor this unit's
          cgroup metrics to decide whether it needs to act. If the cgroup passes the limits set by
          <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> or its
          overrides, <command>systemd-oomd</command> will send a <constant>SIGKILL</constant> to all of the processes
          under the chosen candidate cgroup. Note that only descendant cgroups can be eligible candidates for killing;
          the unit that set its property to <option>kill</option> is not a candidate (unless one of its ancestors set
          their property to <option>kill</option>). You can find more details on candidates and kill behavior at
          <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
          and <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Setting
          either of these properties to <option>kill</option> will also automatically acquire
          <varname>After=</varname> and <varname>Wants=</varname> dependencies on
          <filename>systemd-oomd.service</filename> unless <varname>DefaultDependencies=no</varname>.
        </para>

          <para>When set to <option>auto</option>, <command>systemd-oomd</command> will not actively use this cgroup's
          data for monitoring and detection. However, if an ancestor cgroup has one of these properties set to
          <option>kill</option>, a unit with <option>auto</option> can still be an eligible candidate for
          <command>systemd-oomd</command> to act on.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ManagedOOMMemoryPressureLimit=</varname></term>

        <listitem>
          <para>Overrides the default memory pressure limit set by
          <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
          this unit (cgroup). Takes a percentage value between 0% and 100%, inclusive. This property is
          ignored unless <varname>ManagedOOMMemoryPressure=</varname><option>kill</option>. Defaults to 0%,
          which means to use the default set by
          <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
          </para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>ManagedOOMPreference=none|avoid|omit</varname></term>

        <listitem>
          <para>Allows deprioritizing or omitting this unit's cgroup as a candidate when
          <command>systemd-oomd</command> needs to act. Requires support for extended attributes (see
          <citerefentry project='man-pages'><refentrytitle>xattr</refentrytitle><manvolnum>7</manvolnum></citerefentry>)
          in order to use <option>avoid</option> or <option>omit</option>. Additionally,
          <command>systemd-oomd</command> will ignore these extended attributes if the unit's cgroup is not
          owned by the root user.</para>

          <para>If this property is set to <option>avoid</option>, the service manager will convey this to
          <command>systemd-oomd</command>, which will only select this cgroup if there are no other viable
          candidates.</para>

          <para>If this property is set to <option>omit</option>, the service manager will convey this to
          <command>systemd-oomd</command>, which will ignore this cgroup as a candidate and will not perform
          any actions on it.</para>

          <para>It is recommended to use <option>avoid</option> and <option>omit</option> sparingly, as it
          can adversely affect <command>systemd-oomd</command>'s kill behavior. Also note that these extended
          attributes are not applied recursively to cgroups under this unit's cgroup.</para>

          <para>Defaults to <option>none</option> which means <command>systemd-oomd</command> will rank this
          unit's cgroup as defined in
          <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
          and <citerefentry><refentrytitle>oomd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
          </para>
        </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Deprecated Options</title>

    <para>The following options are deprecated. Use the indicated superseding options instead:</para>

    <variablelist class='unit-directives'>

      <varlistentry>
        <term><varname>CPUShares=<replaceable>weight</replaceable></varname></term>
        <term><varname>StartupCPUShares=<replaceable>weight</replaceable></varname></term>

        <listitem>
          <para>Assign the specified CPU time share weight to the processes executed. These options take an integer
          value and control the <literal>cpu.shares</literal> control group attribute. The allowed range is 2 to
          262144. Defaults to 1024. For details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html">CFS Scheduler</ulink>.
          The available CPU time is split up among all units within one slice relative to their CPU time share
          weight.</para>

          <para>While <varname>StartupCPUShares=</varname> applies to the startup and shutdown phases of the system,
          <varname>CPUShares=</varname> applies to normal runtime of the system, and if the former is not set also to
          the startup and shutdown phases. Using <varname>StartupCPUShares=</varname> allows prioritizing specific services at
          boot-up and shutdown differently than during normal runtime.</para>

          <para>Implies <literal>CPUAccounting=yes</literal>.</para>

          <para>These settings are deprecated. Use <varname>CPUWeight=</varname> and
          <varname>StartupCPUWeight=</varname> instead.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>MemoryLimit=<replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Specify the limit on maximum memory usage of the executed processes. The limit specifies how much
          process and kernel memory can be used by tasks in this unit. Takes a memory size in bytes. If the value is
          suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or
          Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is
          taken relative to the installed physical memory on the system. If assigned the special value
          <literal>infinity</literal>, no memory limit is applied. This controls the
          <literal>memory.limit_in_bytes</literal> control group attribute. For details about this control group
          attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/memory.html">Memory Resource Controller</ulink>.</para>

          <para>Implies <literal>MemoryAccounting=yes</literal>.</para>

          <para>This setting is deprecated. Use <varname>MemoryMax=</varname> instead.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BlockIOAccounting=</varname></term>

        <listitem>
          <para>Turn on Block I/O accounting for this unit, if the legacy control group hierarchy is used on the
          system. Takes a boolean argument. Note that turning on block I/O accounting for one unit will also implicitly
          turn it on for all units contained in the same slice and all for its parent slices and the units contained
          therein. The system default for this setting may be controlled with
          <varname>DefaultBlockIOAccounting=</varname> in
          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

          <para>This setting is deprecated. Use <varname>IOAccounting=</varname> instead.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BlockIOWeight=<replaceable>weight</replaceable></varname></term>
        <term><varname>StartupBlockIOWeight=<replaceable>weight</replaceable></varname></term>

        <listitem><para>Set the default overall block I/O weight for the executed processes, if the legacy control
        group hierarchy is used on the system. Takes a single weight value (between 10 and 1000) to set the default
        block I/O weight. This controls the <literal>blkio.weight</literal> control group attribute, which defaults to
        500. For details about this control group attribute, see <ulink
        url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html">Block IO Controller</ulink>.
        The available I/O bandwidth is split up among all units within one slice relative to their block I/O
        weight.</para>

        <para>While <varname>StartupBlockIOWeight=</varname> only
        applies to the startup and shutdown phases of the system,
        <varname>BlockIOWeight=</varname> applies to the later runtime
        of the system, and if the former is not set also to the
        startup and shutdown phases. This allows prioritizing specific services at
        boot-up and shutdown differently than during runtime.</para>

        <para>Implies
        <literal>BlockIOAccounting=yes</literal>.</para>

        <para>These settings are deprecated. Use <varname>IOWeight=</varname> and <varname>StartupIOWeight=</varname>
        instead.</para>

      </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BlockIODeviceWeight=<replaceable>device</replaceable> <replaceable>weight</replaceable></varname></term>

        <listitem>
          <para>Set the per-device overall block I/O weight for the executed processes, if the legacy control group
          hierarchy is used on the system. Takes a space-separated pair of a file path and a weight value to specify
          the device specific weight value, between 10 and 1000. (Example: "/dev/sda 500"). The file path may be
          specified as path to a block device node or as any other file, in which case the backing block device of the
          file system of the file is determined. This controls the <literal>blkio.weight_device</literal> control group
          attribute, which defaults to 1000. Use this option multiple times to set weights for multiple devices. For
          details about this control group attribute, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html">Block IO Controller</ulink>.</para>

          <para>Implies
          <literal>BlockIOAccounting=yes</literal>.</para>

          <para>This setting is deprecated. Use <varname>IODeviceWeight=</varname> instead.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>BlockIOReadBandwidth=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
        <term><varname>BlockIOWriteBandwidth=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>

        <listitem>
          <para>Set the per-device overall block I/O bandwidth limit for the executed processes, if the legacy control
          group hierarchy is used on the system. Takes a space-separated pair of a file path and a bandwidth value (in
          bytes per second) to specify the device specific bandwidth. The file path may be a path to a block device
          node, or as any other file in which case the backing block device of the file system of the file is used. If
          the bandwidth is suffixed with K, M, G, or T, the specified bandwidth is parsed as Kilobytes, Megabytes,
          Gigabytes, or Terabytes, respectively, to the base of 1000. (Example:
          "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This controls the
          <literal>blkio.throttle.read_bps_device</literal> and <literal>blkio.throttle.write_bps_device</literal>
          control group attributes. Use this option multiple times to set bandwidth limits for multiple devices. For
          details about these control group attributes, see <ulink
          url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html">Block IO Controller</ulink>.
          </para>

          <para>Implies
          <literal>BlockIOAccounting=yes</literal>.</para>

          <para>These settings are deprecated. Use <varname>IOReadBandwidthMax=</varname> and
          <varname>IOWriteBandwidthMax=</varname> instead.</para>
        </listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-oomd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      The documentation for control groups and specific controllers in the Linux kernel:
      <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">Control Groups v2</ulink>.
    </para>
  </refsect1>
</refentry>