man/systemd.resource-control.xml

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   9 <refentry id="systemd.resource-control">
  10   <refentryinfo>
  11     <title>systemd.resource-control</title>
  12     <productname>systemd</productname>
  13   </refentryinfo>
  14
  15   <refmeta>
  16     <refentrytitle>systemd.resource-control</refentrytitle>
  17     <manvolnum>5</manvolnum>
  18   </refmeta>
  19
  20   <refnamediv>
  21     <refname>systemd.resource-control</refname>
  22     <refpurpose>Resource control unit settings</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para>
  27       <filename><replaceable>slice</replaceable>.slice</filename>,
  28       <filename><replaceable>scope</replaceable>.scope</filename>,
  29       <filename><replaceable>service</replaceable>.service</filename>,
  30       <filename><replaceable>socket</replaceable>.socket</filename>,
  31       <filename><replaceable>mount</replaceable>.mount</filename>,
  32       <filename><replaceable>swap</replaceable>.swap</filename>
  33     </para>
  34   </refsynopsisdiv>
  35
  36   <refsect1>
  37     <title>Description</title>
  38
  39     <para>Unit configuration files for services, slices, scopes, sockets, mount points, and swap devices share a subset
  40     of configuration options for resource control of spawned processes. Internally, this relies on the Linux Control
  41     Groups (cgroups) kernel concept for organizing processes in a hierarchical tree of named groups for the purpose of
  42     resource management.</para>
  43
  44     <para>This man page lists the configuration options shared by
  45     those six unit types. See
  46     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  47     for the common options of all unit configuration files, and
  48     <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  49     <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  50     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51     <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  52     <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  53     and
  54     <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  55     for more information on the specific unit configuration files. The
  56     resource control configuration options are configured in the
  57     [Slice], [Scope], [Service], [Socket], [Mount], or [Swap]
  58     sections, depending on the unit type.</para>
  59
  60     <para>In addition, options which control resources available to programs
  61     <emphasis>executed</emphasis> by systemd are listed in
  62     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
  63     Those options complement options listed here.</para>
  64
  65     <para>See the <ulink
  66     url="https://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
  67     Control Group Interfaces</ulink> for an introduction on how to make
  68     use of resource control APIs from programs.</para>
  69   </refsect1>
  70
  71   <refsect1>
  72     <title>Implicit Dependencies</title>
  73
  74     <para>The following dependencies are implicitly added:</para>
  75
  76     <itemizedlist>
  77       <listitem><para>Units with the <varname>Slice=</varname> setting set automatically acquire
  78       <varname>Requires=</varname> and <varname>After=</varname> dependencies on the specified
  79       slice unit.</para></listitem>
  80     </itemizedlist>
  81   </refsect1>
  82
  83   <!-- We don't have any default dependency here. -->
  84
  85   <refsect1>
  86     <title>Unified and Legacy Control Group Hierarchies</title>
  87
  88     <para>The unified control group hierarchy is the new version of kernel control group interface, see <ulink
  89     url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>. Depending on the resource type,
  90     there are differences in resource control capabilities.  Also, because of interface changes, some resource types
  91     have separate set of options on the unified hierarchy.</para>
  92
  93     <para>
  94       <variablelist>
  95
  96         <varlistentry>
  97           <term><option>CPU</option></term>
  98           <listitem>
  99             <para><varname>CPUWeight=</varname> and <varname>StartupCPUWeight=</varname> replace
 100             <varname>CPUShares=</varname> and <varname>StartupCPUShares=</varname>, respectively.</para>
 101
 102             <para>The <literal>cpuacct</literal> controller does not exist separately on the unified hierarchy.</para>
 103           </listitem>
 104         </varlistentry>
 105
 106         <varlistentry>
 107           <term><option>Memory</option></term>
 108           <listitem>
 109             <para><varname>MemoryMax=</varname> replaces <varname>MemoryLimit=</varname>. <varname>MemoryLow=</varname>
 110             and <varname>MemoryHigh=</varname> are effective only on unified hierarchy.</para>
 111           </listitem>
 112         </varlistentry>
 113
 114         <varlistentry>
 115           <term><option>IO</option></term>
 116           <listitem>
 117             <para><varname>IO</varname> prefixed settings are a superset of and replace <varname>BlockIO</varname>
 118             prefixed ones. On unified hierarchy, IO resource control also applies to buffered writes.</para>
 119           </listitem>
 120         </varlistentry>
 121
 122       </variablelist>
 123     </para>
 124
 125     <para>To ease the transition, there is best-effort translation between the two versions of settings. For each
 126     controller, if any of the settings for the unified hierarchy are present, all settings for the legacy hierarchy are
 127     ignored. If the resulting settings are for the other type of hierarchy, the configurations are translated before
 128     application.</para>
 129
 130     <para>Legacy control group hierarchy (see <ulink
 131     url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>), also called cgroup-v1,
 132     doesn't allow safe delegation of controllers to unprivileged processes. If the system uses the legacy control group
 133     hierarchy, resource control is disabled for systemd user instance, see
 134     <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
 135     </para>
 136   </refsect1>
 137
 138   <refsect1>
 139     <title>Options</title>
 140
 141     <para>Units of the types listed above can have settings
 142     for resource control configuration:</para>
 143
 144     <variablelist class='unit-directives'>
 145
 146       <varlistentry>
 147         <term><varname>CPUAccounting=</varname></term>
 148
 149         <listitem>
 150           <para>Turn on CPU usage accounting for this unit. Takes a
 151           boolean argument. Note that turning on CPU accounting for
 152           one unit will also implicitly turn it on for all units
 153           contained in the same slice and for all its parent slices
 154           and the units contained therein. The system default for this
 155           setting may be controlled with
 156           <varname>DefaultCPUAccounting=</varname> in
 157           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 158         </listitem>
 159       </varlistentry>
 160
 161       <varlistentry>
 162         <term><varname>CPUWeight=<replaceable>weight</replaceable></varname></term>
 163         <term><varname>StartupCPUWeight=<replaceable>weight</replaceable></varname></term>
 164
 165         <listitem>
 166           <para>Assign the specified CPU time weight to the processes executed, if the unified control group hierarchy
 167           is used on the system. These options take an integer value and control the <literal>cpu.weight</literal>
 168           control group attribute. The allowed range is 1 to 10000. Defaults to 100. For details about this control
 169           group attribute, see <ulink
 170           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink> and <ulink
 171           url="https://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt">sched-design-CFS.txt</ulink>.
 172           The available CPU time is split up among all units within one slice relative to their CPU time weight.</para>
 173
 174           <para>While <varname>StartupCPUWeight=</varname> only applies to the startup phase of the system,
 175           <varname>CPUWeight=</varname> applies to normal runtime of the system, and if the former is not set also to
 176           the startup phase. Using <varname>StartupCPUWeight=</varname> allows prioritizing specific services at
 177           boot-up differently than during normal runtime.</para>
 178
 179           <para>These settings replace <varname>CPUShares=</varname> and <varname>StartupCPUShares=</varname>.</para>
 180         </listitem>
 181       </varlistentry>
 182
 183       <varlistentry>
 184         <term><varname>CPUQuota=</varname></term>
 185
 186         <listitem>
 187           <para>Assign the specified CPU time quota to the processes executed. Takes a percentage value, suffixed with
 188           "%". The percentage specifies how much CPU time the unit shall get at maximum, relative to the total CPU time
 189           available on one CPU. Use values &gt; 100% for allotting CPU time on more than one CPU. This controls the
 190           <literal>cpu.max</literal> attribute on the unified control group hierarchy and
 191           <literal>cpu.cfs_quota_us</literal> on legacy. For details about these control group attributes, see <ulink
 192           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink> and <ulink
 193           url="https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt">sched-bwc.txt</ulink>.</para>
 194
 195           <para>Example: <varname>CPUQuota=20%</varname> ensures that the executed processes will never get more than
 196           20% CPU time on one CPU.</para>
 197
 198         </listitem>
 199       </varlistentry>
 200
 201       <varlistentry>
 202         <term><varname>CPUQuotaPeriodSec=</varname></term>
 203
 204         <listitem>
 205           <para>Assign the duration over which the CPU time quota specified by <varname>CPUQuota=</varname> is measured.
 206           Takes a time duration value in seconds, with an optional suffix such as "ms" for milliseconds (or "s" for seconds.)
 207           The default setting is 100ms. The period is clamped to the range supported by the kernel, which is [1ms, 1000ms].
 208           Additionally, the period is adjusted up so that the quota interval is also at least 1ms.
 209           Setting <varname>CPUQuotaPeriodSec=</varname> to an empty value resets it to the default.</para>
 210
 211           <para>This controls the second field of <literal>cpu.max</literal> attribute on the unified control group hierarchy
 212           and <literal>cpu.cfs_period_us</literal> on legacy. For details about these control group attributes, see
 213           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink> and
 214           <ulink url="https://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt">sched-design-CFS.txt</ulink>.</para>
 215
 216           <para>Example: <varname>CPUQuotaPeriodSec=10ms</varname> to request that the CPU quota is measured in periods of 10ms.</para>
 217         </listitem>
 218       </varlistentry>
 219
 220       <varlistentry>
 221         <term><varname>MemoryAccounting=</varname></term>
 222
 223         <listitem>
 224           <para>Turn on process and kernel memory accounting for this
 225           unit. Takes a boolean argument. Note that turning on memory
 226           accounting for one unit will also implicitly turn it on for
 227           all units contained in the same slice and for all its parent
 228           slices and the units contained therein. The system default
 229           for this setting may be controlled with
 230           <varname>DefaultMemoryAccounting=</varname> in
 231           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 232         </listitem>
 233       </varlistentry>
 234
 235       <varlistentry>
 236         <term><varname>MemoryMin=<replaceable>bytes</replaceable></varname></term>
 237
 238         <listitem>
 239           <para>Specify the memory usage protection of the executed processes in this unit. If the memory usages of
 240           this unit and all its ancestors are below their minimum boundaries, this unit's memory won't be reclaimed.</para>
 241
 242           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
 243           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
 244           percentage value may be specified, which is taken relative to the installed physical memory on the
 245           system. This controls the <literal>memory.min</literal> control group attribute. For details about this
 246           control group attribute, see <ulink
 247           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 248
 249           <para>This setting is supported only if the unified control group hierarchy is used and disables
 250           <varname>MemoryLimit=</varname>.</para>
 251         </listitem>
 252       </varlistentry>
 253
 254       <varlistentry>
 255         <term><varname>MemoryLow=<replaceable>bytes</replaceable></varname></term>
 256
 257         <listitem>
 258           <para>Specify the best-effort memory usage protection of the executed processes in this unit. If the memory
 259           usages of this unit and all its ancestors are below their low boundaries, this unit's memory won't be
 260           reclaimed as long as memory can be reclaimed from unprotected units.</para>
 261
 262           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
 263           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
 264           percentage value may be specified, which is taken relative to the installed physical memory on the
 265           system. This controls the <literal>memory.low</literal> control group attribute. For details about this
 266           control group attribute, see <ulink
 267           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 268
 269           <para>This setting is supported only if the unified control group hierarchy is used and disables
 270           <varname>MemoryLimit=</varname>.</para>
 271         </listitem>
 272       </varlistentry>
 273
 274       <varlistentry>
 275         <term><varname>MemoryHigh=<replaceable>bytes</replaceable></varname></term>
 276
 277         <listitem>
 278           <para>Specify the high limit on memory usage of the executed processes in this unit. Memory usage may go
 279           above the limit if unavoidable, but the processes are heavily slowed down and memory is taken away
 280           aggressively in such cases. This is the main mechanism to control memory usage of a unit.</para>
 281
 282           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
 283           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
 284           percentage value may be specified, which is taken relative to the installed physical memory on the
 285           system. If assigned the
 286           special value <literal>infinity</literal>, no memory limit is applied. This controls the
 287           <literal>memory.high</literal> control group attribute. For details about this control group attribute, see
 288           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 289
 290           <para>This setting is supported only if the unified control group hierarchy is used and disables
 291           <varname>MemoryLimit=</varname>.</para>
 292         </listitem>
 293       </varlistentry>
 294
 295       <varlistentry>
 296         <term><varname>MemoryMax=<replaceable>bytes</replaceable></varname></term>
 297
 298         <listitem>
 299           <para>Specify the absolute limit on memory usage of the executed processes in this unit. If memory usage
 300           cannot be contained under the limit, out-of-memory killer is invoked inside the unit. It is recommended to
 301           use <varname>MemoryHigh=</varname> as the main control mechanism and use <varname>MemoryMax=</varname> as the
 302           last line of defense.</para>
 303
 304           <para>Takes a memory size in bytes. If the value is suffixed with K, M, G or T, the specified memory size is
 305           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. Alternatively, a
 306           percentage value may be specified, which is taken relative to the installed physical memory on the system. If
 307           assigned the special value <literal>infinity</literal>, no memory limit is applied. This controls the
 308           <literal>memory.max</literal> control group attribute. For details about this control group attribute, see
 309           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 310
 311           <para>This setting replaces <varname>MemoryLimit=</varname>.</para>
 312         </listitem>
 313       </varlistentry>
 314
 315       <varlistentry>
 316         <term><varname>MemorySwapMax=<replaceable>bytes</replaceable></varname></term>
 317
 318         <listitem>
 319           <para>Specify the absolute limit on swap usage of the executed processes in this unit.</para>
 320
 321           <para>Takes a swap size in bytes. If the value is suffixed with K, M, G or T, the specified swap size is
 322           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base 1024), respectively. If assigned the
 323           special value <literal>infinity</literal>, no swap limit is applied. This controls the
 324           <literal>memory.swap.max</literal> control group attribute. For details about this control group attribute,
 325           see <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 326
 327           <para>This setting is supported only if the unified control group hierarchy is used and disables
 328           <varname>MemoryLimit=</varname>.</para>
 329         </listitem>
 330       </varlistentry>
 331
 332       <varlistentry>
 333         <term><varname>TasksAccounting=</varname></term>
 334
 335         <listitem>
 336           <para>Turn on task accounting for this unit. Takes a
 337           boolean argument. If enabled, the system manager will keep
 338           track of the number of tasks in the unit. The number of
 339           tasks accounted this way includes both kernel threads and
 340           userspace processes, with each thread counting
 341           individually. Note that turning on tasks accounting for one
 342           unit will also implicitly turn it on for all units contained
 343           in the same slice and for all its parent slices and the
 344           units contained therein. The system default for this setting
 345           may be controlled with
 346           <varname>DefaultTasksAccounting=</varname> in
 347           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 348         </listitem>
 349       </varlistentry>
 350
 351       <varlistentry>
 352         <term><varname>TasksMax=<replaceable>N</replaceable></varname></term>
 353
 354         <listitem>
 355           <para>Specify the maximum number of tasks that may be created in the unit. This ensures that the number of
 356           tasks accounted for the unit (see above) stays below a specific limit. This either takes an absolute number
 357           of tasks or a percentage value that is taken relative to the configured maximum number of tasks on the
 358           system.  If assigned the special value <literal>infinity</literal>, no tasks limit is applied. This controls
 359           the <literal>pids.max</literal> control group attribute. For details about this control group attribute, see
 360           <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/pids.txt">pids.txt</ulink>.</para>
 361
 362           <para>The
 363           system default for this setting may be controlled with
 364           <varname>DefaultTasksMax=</varname> in
 365           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 366         </listitem>
 367       </varlistentry>
 368
 369       <varlistentry>
 370         <term><varname>IOAccounting=</varname></term>
 371
 372         <listitem>
 373           <para>Turn on Block I/O accounting for this unit, if the unified control group hierarchy is used on the
 374           system. Takes a boolean argument. Note that turning on block I/O accounting for one unit will also implicitly
 375           turn it on for all units contained in the same slice and all for its parent slices and the units contained
 376           therein. The system default for this setting may be controlled with <varname>DefaultIOAccounting=</varname>
 377           in
 378           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 379
 380           <para>This setting replaces <varname>BlockIOAccounting=</varname> and disables settings prefixed with
 381           <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
 382         </listitem>
 383       </varlistentry>
 384
 385       <varlistentry>
 386         <term><varname>IOWeight=<replaceable>weight</replaceable></varname></term>
 387         <term><varname>StartupIOWeight=<replaceable>weight</replaceable></varname></term>
 388
 389         <listitem>
 390           <para>Set the default overall block I/O weight for the executed processes, if the unified control group
 391           hierarchy is used on the system. Takes a single weight value (between 1 and 10000) to set the default block
 392           I/O weight. This controls the <literal>io.weight</literal> control group attribute, which defaults to
 393           100. For details about this control group attribute, see <ulink
 394           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.  The available I/O
 395           bandwidth is split up among all units within one slice relative to their block I/O weight.</para>
 396
 397           <para>While <varname>StartupIOWeight=</varname> only applies
 398           to the startup phase of the system,
 399           <varname>IOWeight=</varname> applies to the later runtime of
 400           the system, and if the former is not set also to the startup
 401           phase. This allows prioritizing specific services at boot-up
 402           differently than during runtime.</para>
 403
 404           <para>These settings replace <varname>BlockIOWeight=</varname> and <varname>StartupBlockIOWeight=</varname>
 405           and disable settings prefixed with <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
 406         </listitem>
 407       </varlistentry>
 408
 409       <varlistentry>
 410         <term><varname>IODeviceWeight=<replaceable>device</replaceable> <replaceable>weight</replaceable></varname></term>
 411
 412         <listitem>
 413           <para>Set the per-device overall block I/O weight for the executed processes, if the unified control group
 414           hierarchy is used on the system. Takes a space-separated pair of a file path and a weight value to specify
 415           the device specific weight value, between 1 and 10000. (Example: <literal>/dev/sda 1000</literal>). The file
 416           path may be specified as path to a block device node or as any other file, in which case the backing block
 417           device of the file system of the file is determined. This controls the <literal>io.weight</literal> control
 418           group attribute, which defaults to 100. Use this option multiple times to set weights for multiple devices.
 419           For details about this control group attribute, see <ulink
 420           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 421
 422           <para>This setting replaces <varname>BlockIODeviceWeight=</varname> and disables settings prefixed with
 423           <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
 424         </listitem>
 425       </varlistentry>
 426
 427       <varlistentry>
 428         <term><varname>IOReadBandwidthMax=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
 429         <term><varname>IOWriteBandwidthMax=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
 430
 431         <listitem>
 432           <para>Set the per-device overall block I/O bandwidth maximum limit for the executed processes, if the unified
 433           control group hierarchy is used on the system. This limit is not work-conserving and the executed processes
 434           are not allowed to use more even if the device has idle capacity.  Takes a space-separated pair of a file
 435           path and a bandwidth value (in bytes per second) to specify the device specific bandwidth. The file path may
 436           be a path to a block device node, or as any other file in which case the backing block device of the file
 437           system of the file is used. If the bandwidth is suffixed with K, M, G, or T, the specified bandwidth is
 438           parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes, respectively, to the base of 1000. (Example:
 439           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This controls the <literal>io.max</literal> control
 440           group attributes. Use this option multiple times to set bandwidth limits for multiple devices. For details
 441           about this control group attribute, see <ulink
 442           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.
 443           </para>
 444
 445           <para>These settings replace <varname>BlockIOReadBandwidth=</varname> and
 446           <varname>BlockIOWriteBandwidth=</varname> and disable settings prefixed with <varname>BlockIO</varname> or
 447           <varname>StartupBlockIO</varname>.</para>
 448         </listitem>
 449       </varlistentry>
 450
 451       <varlistentry>
 452         <term><varname>IOReadIOPSMax=<replaceable>device</replaceable> <replaceable>IOPS</replaceable></varname></term>
 453         <term><varname>IOWriteIOPSMax=<replaceable>device</replaceable> <replaceable>IOPS</replaceable></varname></term>
 454
 455         <listitem>
 456           <para>Set the per-device overall block I/O IOs-Per-Second maximum limit for the executed processes, if the
 457           unified control group hierarchy is used on the system. This limit is not work-conserving and the executed
 458           processes are not allowed to use more even if the device has idle capacity.  Takes a space-separated pair of
 459           a file path and an IOPS value to specify the device specific IOPS. The file path may be a path to a block
 460           device node, or as any other file in which case the backing block device of the file system of the file is
 461           used. If the IOPS is suffixed with K, M, G, or T, the specified IOPS is parsed as KiloIOPS, MegaIOPS,
 462           GigaIOPS, or TeraIOPS, respectively, to the base of 1000. (Example:
 463           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 1K"). This controls the <literal>io.max</literal> control
 464           group attributes. Use this option multiple times to set IOPS limits for multiple devices. For details about
 465           this control group attribute, see <ulink
 466           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.
 467           </para>
 468
 469           <para>These settings are supported only if the unified control group hierarchy is used and disable settings
 470           prefixed with <varname>BlockIO</varname> or <varname>StartupBlockIO</varname>.</para>
 471         </listitem>
 472       </varlistentry>
 473
 474       <varlistentry>
 475         <term><varname>IODeviceLatencyTargetSec=<replaceable>device</replaceable> <replaceable>target</replaceable></varname></term>
 476
 477         <listitem>
 478           <para>Set the per-device average target I/O latency for the executed processes, if the unified control group
 479           hierarchy is used on the system. Takes a file path and a timespan separated by a space to specify
 480           the device specific latency target. (Example: "/dev/sda 25ms"). The file path may be specified
 481           as path to a block device node or as any other file, in which case the backing block device of the file
 482           system of the file is determined. This controls the <literal>io.latency</literal> control group
 483           attribute. Use this option multiple times to set latency target for multiple devices. For details about this
 484           control group attribute, see <ulink
 485           url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">cgroup-v2.txt</ulink>.</para>
 486
 487           <para>Implies <literal>IOAccounting=yes</literal>.</para>
 488
 489           <para>These settings are supported only if the unified control group hierarchy is used.</para>
 490         </listitem>
 491       </varlistentry>
 492
 493       <varlistentry>
 494         <term><varname>IPAccounting=</varname></term>
 495
 496         <listitem>
 497           <para>Takes a boolean argument. If true, turns on IPv4 and IPv6 network traffic accounting for packets sent
 498           or received by the unit. When this option is turned on, all IPv4 and IPv6 sockets created by any process of
 499           the unit are accounted for.</para>
 500
 501           <para>When this option is used in socket units, it applies to all IPv4 and IPv6 sockets
 502           associated with it (including both listening and connection sockets where this applies). Note that for
 503           socket-activated services, this configuration setting and the accounting data of the service unit and the
 504           socket unit are kept separate, and displayed separately. No propagation of the setting and the collected
 505           statistics is done, in either direction. Moreover, any traffic sent or received on any of the socket unit's
 506           sockets is accounted to the socket unit — and never to the service unit it might have activated, even if the
 507           socket is used by it.</para>
 508
 509           <para>The system default for this setting may be controlled with <varname>DefaultIPAccounting=</varname> in
 510           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 511         </listitem>
 512       </varlistentry>
 513
 514       <varlistentry>
 515         <term><varname>IPAddressAllow=<replaceable>ADDRESS[/PREFIXLENGTH]…</replaceable></varname></term>
 516         <term><varname>IPAddressDeny=<replaceable>ADDRESS[/PREFIXLENGTH]…</replaceable></varname></term>
 517
 518         <listitem>
 519           <para>Turn on address range network traffic filtering for packets sent and received over AF_INET and AF_INET6
 520           sockets.  Both directives take a space separated list of IPv4 or IPv6 addresses, each optionally suffixed
 521           with an address prefix length (separated by a <literal>/</literal> character). If the latter is omitted, the
 522           address is considered a host address, i.e. the prefix covers the whole address (32 for IPv4, 128 for IPv6).
 523           </para>
 524
 525           <para>The access lists configured with this option are applied to all sockets created by processes of this
 526           unit (or in the case of socket units, associated with it). The lists are implicitly combined with any lists
 527           configured for any of the parent slice units this unit might be a member of. By default all access lists are
 528           empty. When configured the lists are enforced as follows:</para>
 529
 530           <itemizedlist>
 531             <listitem><para>Access will be granted in case its destination/source address matches any entry in the
 532             <varname>IPAddressAllow=</varname> setting.</para></listitem>
 533
 534             <listitem><para>Otherwise, access will be denied in case its destination/source address matches any entry
 535             in the <varname>IPAddressDeny=</varname> setting.</para></listitem>
 536
 537             <listitem><para>Otherwise, access will be granted.</para></listitem>
 538           </itemizedlist>
 539
 540           <para>In order to implement a whitelisting IP firewall, it is recommended to use a
 541           <varname>IPAddressDeny=</varname><constant>any</constant> setting on an upper-level slice unit (such as the
 542           root slice <filename>-.slice</filename> or the slice containing all system services
 543           <filename>system.slice</filename> – see
 544           <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
 545           details on these slice units), plus individual per-service <varname>IPAddressAllow=</varname> lines
 546           permitting network access to relevant services, and only them.</para>
 547
 548           <para>Note that for socket-activated services, the IP access list configured on the socket unit applies to
 549           all sockets associated with it directly, but not to any sockets created by the ultimately activated services
 550           for it. Conversely, the IP access list configured for the service is not applied to any sockets passed into
 551           the service via socket activation. Thus, it is usually a good idea, to replicate the IP access lists on both
 552           the socket and the service unit, however it often makes sense to maintain one list more open and the other
 553           one more restricted, depending on the usecase.</para>
 554
 555           <para>If these settings are used multiple times in the same unit the specified lists are combined. If an
 556           empty string is assigned to these settings the specific access list is reset and all previous settings undone.</para>
 557
 558           <para>In place of explicit IPv4 or IPv6 address and prefix length specifications a small set of symbolic
 559           names may be used. The following names are defined:</para>
 560
 561           <table>
 562             <title>Special address/network names</title>
 563
 564             <tgroup cols='3'>
 565               <colspec colname='name'/>
 566               <colspec colname='definition'/>
 567               <colspec colname='meaning'/>
 568
 569               <thead>
 570                 <row>
 571                   <entry>Symbolic Name</entry>
 572                   <entry>Definition</entry>
 573                   <entry>Meaning</entry>
 574                 </row>
 575               </thead>
 576
 577             <tbody>
 578               <row>
 579                 <entry><constant>any</constant></entry>
 580                 <entry>0.0.0.0/0 ::/0</entry>
 581                 <entry>Any host</entry>
 582               </row>
 583
 584               <row>
 585                 <entry><constant>localhost</constant></entry>
 586                 <entry>127.0.0.0/8 ::1/128</entry>
 587                 <entry>All addresses on the local loopback</entry>
 588               </row>
 589
 590               <row>
 591                 <entry><constant>link-local</constant></entry>
 592                 <entry>169.254.0.0/16 fe80::/64</entry>
 593                 <entry>All link-local IP addresses</entry>
 594               </row>
 595
 596               <row>
 597                 <entry><constant>multicast</constant></entry>
 598                 <entry>224.0.0.0/4 ff00::/8</entry>
 599                 <entry>All IP multicasting addresses</entry>
 600               </row>
 601             </tbody>
 602             </tgroup>
 603           </table>
 604
 605           <para>Note that these settings might not be supported on some systems (for example if eBPF control group
 606           support is not enabled in the underlying kernel or container manager). These settings will have no effect in
 607           that case. If compatibility with such systems is desired it is hence recommended to not exclusively rely on
 608           them for IP security.</para>
 609         </listitem>
 610       </varlistentry>
 611
 612       <varlistentry>
 613         <term><varname>DeviceAllow=</varname></term>
 614
 615         <listitem>
 616           <para>Control access to specific device nodes by the
 617           executed processes. Takes two space-separated strings: a
 618           device node specifier followed by a combination of
 619           <constant>r</constant>, <constant>w</constant>,
 620           <constant>m</constant> to control
 621           <emphasis>r</emphasis>eading, <emphasis>w</emphasis>riting,
 622           or creation of the specific device node(s) by the unit
 623           (<emphasis>m</emphasis>knod), respectively. This controls
 624           the <literal>devices.allow</literal> and
 625           <literal>devices.deny</literal> control group
 626           attributes. For details about these control group
 627           attributes, see <ulink
 628           url="https://www.kernel.org/doc/Documentation/cgroup-v1/devices.txt">devices.txt</ulink>.</para>
 629
 630           <para>The device node specifier is either a path to a device
 631           node in the file system, starting with
 632           <filename>/dev/</filename>, or a string starting with either
 633           <literal>char-</literal> or <literal>block-</literal>
 634           followed by a device group name, as listed in
 635           <filename>/proc/devices</filename>. The latter is useful to
 636           whitelist all current and future devices belonging to a
 637           specific device group at once. The device group is matched
 638           according to filename globbing rules, you may hence use the
 639           <literal>*</literal> and <literal>?</literal>
 640           wildcards. Examples: <filename>/dev/sda5</filename> is a
 641           path to a device node, referring to an ATA or SCSI block
 642           device. <literal>char-pts</literal> and
 643           <literal>char-alsa</literal> are specifiers for all pseudo
 644           TTYs and all ALSA sound devices,
 645           respectively. <literal>char-cpu/*</literal> is a specifier
 646           matching all CPU related device groups.</para>
 647         </listitem>
 648       </varlistentry>
 649
 650       <varlistentry>
 651         <term><varname>DevicePolicy=auto|closed|strict</varname></term>
 652
 653         <listitem>
 654           <para>
 655             Control the policy for allowing device access:
 656           </para>
 657           <variablelist>
 658             <varlistentry>
 659               <term><option>strict</option></term>
 660               <listitem>
 661                 <para>means to only allow types of access that are
 662                 explicitly specified.</para>
 663               </listitem>
 664             </varlistentry>
 665
 666             <varlistentry>
 667               <term><option>closed</option></term>
 668               <listitem>
 669                 <para>in addition, allows access to standard pseudo
 670                 devices including
 671                 <filename>/dev/null</filename>,
 672                 <filename>/dev/zero</filename>,
 673                 <filename>/dev/full</filename>,
 674                 <filename>/dev/random</filename>, and
 675                 <filename>/dev/urandom</filename>.
 676                 </para>
 677               </listitem>
 678             </varlistentry>
 679
 680             <varlistentry>
 681               <term><option>auto</option></term>
 682               <listitem>
 683                 <para>
 684                   in addition, allows access to all devices if no
 685                   explicit <varname>DeviceAllow=</varname> is present.
 686                   This is the default.
 687                 </para>
 688               </listitem>
 689             </varlistentry>
 690           </variablelist>
 691         </listitem>
 692       </varlistentry>
 693
 694       <varlistentry>
 695         <term><varname>Slice=</varname></term>
 696
 697         <listitem>
 698           <para>The name of the slice unit to place the unit
 699           in. Defaults to <filename>system.slice</filename> for all
 700           non-instantiated units of all unit types (except for slice
 701           units themselves see below). Instance units are by default
 702           placed in a subslice of <filename>system.slice</filename>
 703           that is named after the template name.</para>
 704
 705           <para>This option may be used to arrange systemd units in a
 706           hierarchy of slices each of which might have resource
 707           settings applied.</para>
 708
 709           <para>For units of type slice, the only accepted value for
 710           this setting is the parent slice. Since the name of a slice
 711           unit implies the parent slice, it is hence redundant to ever
 712           set this parameter directly for slice units.</para>
 713
 714           <para>Special care should be taken when relying on the default slice assignment in templated service units
 715           that have <varname>DefaultDependencies=no</varname> set, see
 716           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, section
 717           "Default Dependencies" for details.</para>
 718
 719         </listitem>
 720       </varlistentry>
 721
 722       <varlistentry>
 723         <term><varname>Delegate=</varname></term>
 724
 725         <listitem>
 726           <para>Turns on delegation of further resource control partitioning to processes of the unit. Units where this
 727           is enabled may create and manage their own private subhierarchy of control groups below the control group of
 728           the unit itself. For unprivileged services (i.e. those using the <varname>User=</varname> setting) the unit's
 729           control group will be made accessible to the relevant user. When enabled the service manager will refrain
 730           from manipulating control groups or moving processes below the unit's control group, so that a clear concept
 731           of ownership is established: the control group tree above the unit's control group (i.e. towards the root
 732           control group) is owned and managed by the service manager of the host, while the control group tree below
 733           the unit's control group is owned and managed by the unit itself. Takes either a boolean argument or a list
 734           of control group controller names. If true, delegation is turned on, and all supported controllers are
 735           enabled for the unit, making them available to the unit's processes for management. If false, delegation is
 736           turned off entirely (and no additional controllers are enabled). If set to a list of controllers, delegation
 737           is turned on, and the specified controllers are enabled for the unit. Note that additional controllers than
 738           the ones specified might be made available as well, depending on configuration of the containing slice unit
 739           or other units contained in it. Note that assigning the empty string will enable delegation, but reset the
 740           list of controllers, all assignments prior to this will have no effect.  Defaults to false.</para>
 741
 742           <para>Note that controller delegation to less privileged code is only safe on the unified control group
 743           hierarchy. Accordingly, access to the specified controllers will not be granted to unprivileged services on
 744           the legacy hierarchy, even when requested.</para>
 745
 746           <para>The following controller names may be specified: <option>cpu</option>, <option>cpuacct</option>,
 747           <option>io</option>, <option>blkio</option>, <option>memory</option>, <option>devices</option>,
 748           <option>pids</option>. Not all of these controllers are available on all kernels however, and some are
 749           specific to the unified hierarchy while others are specific to the legacy hierarchy. Also note that the
 750           kernel might support further controllers, which aren't covered here yet as delegation is either not supported
 751           at all for them or not defined cleanly.</para>
 752
 753           <para>For further details on the delegation model consult <ulink
 754           url="https://systemd.io/CGROUP_DELEGATION">Control Group APIs and Delegation</ulink>.</para>
 755         </listitem>
 756       </varlistentry>
 757
 758       <varlistentry>
 759         <term><varname>DisableControllers=</varname></term>
 760
 761         <listitem>
 762           <para>Disables controllers from being enabled for a unit's children. If a controller listed is already in use
 763           in its subtree, the controller will be removed from the subtree. This can be used to avoid child units being
 764           able to implicitly or explicitly enable a controller. Defaults to not disabling any controllers.</para>
 765
 766           <para>It may not be possible to successfully disable a controller if the unit or any child of the unit in
 767           question delegates controllers to its children, as any delegated subtree of the cgroup hierarchy is unmanaged
 768           by systemd.</para>
 769
 770           <para>Multiple controllers may be specified, separated by spaces. You may also pass
 771           <varname>DisableControllers=</varname> multiple times, in which case each new instance adds another controller
 772           to disable. Passing <varname>DisableControllers=</varname> by itself with no controller name present resets
 773           the disabled controller list.</para>
 774
 775           <para>Valid controllers are <option>cpu</option>, <option>cpuacct</option>, <option>io</option>,
 776           <option>blkio</option>, <option>memory</option>, <option>devices</option>, and <option>pids</option>.</para>
 777         </listitem>
 778       </varlistentry>
 779     </variablelist>
 780   </refsect1>
 781
 782   <refsect1>
 783     <title>Deprecated Options</title>
 784
 785     <para>The following options are deprecated. Use the indicated superseding options instead:</para>
 786
 787     <variablelist class='unit-directives'>
 788
 789       <varlistentry>
 790         <term><varname>CPUShares=<replaceable>weight</replaceable></varname></term>
 791         <term><varname>StartupCPUShares=<replaceable>weight</replaceable></varname></term>
 792
 793         <listitem>
 794           <para>Assign the specified CPU time share weight to the processes executed. These options take an integer
 795           value and control the <literal>cpu.shares</literal> control group attribute. The allowed range is 2 to
 796           262144. Defaults to 1024. For details about this control group attribute, see <ulink
 797           url="https://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt">sched-design-CFS.txt</ulink>.
 798           The available CPU time is split up among all units within one slice relative to their CPU time share
 799           weight.</para>
 800
 801           <para>While <varname>StartupCPUShares=</varname> only applies to the startup phase of the system,
 802           <varname>CPUShares=</varname> applies to normal runtime of the system, and if the former is not set also to
 803           the startup phase. Using <varname>StartupCPUShares=</varname> allows prioritizing specific services at
 804           boot-up differently than during normal runtime.</para>
 805
 806           <para>Implies <literal>CPUAccounting=yes</literal>.</para>
 807
 808           <para>These settings are deprecated. Use <varname>CPUWeight=</varname> and
 809           <varname>StartupCPUWeight=</varname> instead.</para>
 810         </listitem>
 811       </varlistentry>
 812
 813       <varlistentry>
 814         <term><varname>MemoryLimit=<replaceable>bytes</replaceable></varname></term>
 815
 816         <listitem>
 817           <para>Specify the limit on maximum memory usage of the executed processes. The limit specifies how much
 818           process and kernel memory can be used by tasks in this unit. Takes a memory size in bytes. If the value is
 819           suffixed with K, M, G or T, the specified memory size is parsed as Kilobytes, Megabytes, Gigabytes, or
 820           Terabytes (with the base 1024), respectively. Alternatively, a percentage value may be specified, which is
 821           taken relative to the installed physical memory on the system. If assigned the special value
 822           <literal>infinity</literal>, no memory limit is applied. This controls the
 823           <literal>memory.limit_in_bytes</literal> control group attribute. For details about this control group
 824           attribute, see <ulink
 825           url="https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt">memory.txt</ulink>.</para>
 826
 827           <para>Implies <literal>MemoryAccounting=yes</literal>.</para>
 828
 829           <para>This setting is deprecated. Use <varname>MemoryMax=</varname> instead.</para>
 830         </listitem>
 831       </varlistentry>
 832
 833       <varlistentry>
 834         <term><varname>BlockIOAccounting=</varname></term>
 835
 836         <listitem>
 837           <para>Turn on Block I/O accounting for this unit, if the legacy control group hierarchy is used on the
 838           system. Takes a boolean argument. Note that turning on block I/O accounting for one unit will also implicitly
 839           turn it on for all units contained in the same slice and all for its parent slices and the units contained
 840           therein. The system default for this setting may be controlled with
 841           <varname>DefaultBlockIOAccounting=</varname> in
 842           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 843
 844           <para>This setting is deprecated. Use <varname>IOAccounting=</varname> instead.</para>
 845         </listitem>
 846       </varlistentry>
 847
 848       <varlistentry>
 849         <term><varname>BlockIOWeight=<replaceable>weight</replaceable></varname></term>
 850         <term><varname>StartupBlockIOWeight=<replaceable>weight</replaceable></varname></term>
 851
 852         <listitem><para>Set the default overall block I/O weight for the executed processes, if the legacy control
 853         group hierarchy is used on the system. Takes a single weight value (between 10 and 1000) to set the default
 854         block I/O weight. This controls the <literal>blkio.weight</literal> control group attribute, which defaults to
 855         500. For details about this control group attribute, see <ulink
 856         url="https://www.kernel.org/doc/Documentation/cgroup-v1/blkio-controller.txt">blkio-controller.txt</ulink>.
 857         The available I/O bandwidth is split up among all units within one slice relative to their block I/O
 858         weight.</para>
 859
 860         <para>While <varname>StartupBlockIOWeight=</varname> only
 861         applies to the startup phase of the system,
 862         <varname>BlockIOWeight=</varname> applies to the later runtime
 863         of the system, and if the former is not set also to the
 864         startup phase. This allows prioritizing specific services at
 865         boot-up differently than during runtime.</para>
 866
 867         <para>Implies
 868         <literal>BlockIOAccounting=yes</literal>.</para>
 869
 870         <para>These settings are deprecated. Use <varname>IOWeight=</varname> and <varname>StartupIOWeight=</varname>
 871         instead.</para>
 872
 873       </listitem>
 874       </varlistentry>
 875
 876       <varlistentry>
 877         <term><varname>BlockIODeviceWeight=<replaceable>device</replaceable> <replaceable>weight</replaceable></varname></term>
 878
 879         <listitem>
 880           <para>Set the per-device overall block I/O weight for the executed processes, if the legacy control group
 881           hierarchy is used on the system. Takes a space-separated pair of a file path and a weight value to specify
 882           the device specific weight value, between 10 and 1000. (Example: "/dev/sda 500"). The file path may be
 883           specified as path to a block device node or as any other file, in which case the backing block device of the
 884           file system of the file is determined. This controls the <literal>blkio.weight_device</literal> control group
 885           attribute, which defaults to 1000. Use this option multiple times to set weights for multiple devices. For
 886           details about this control group attribute, see <ulink
 887           url="https://www.kernel.org/doc/Documentation/cgroup-v1/blkio-controller.txt">blkio-controller.txt</ulink>.</para>
 888
 889           <para>Implies
 890           <literal>BlockIOAccounting=yes</literal>.</para>
 891
 892           <para>This setting is deprecated. Use <varname>IODeviceWeight=</varname> instead.</para>
 893         </listitem>
 894       </varlistentry>
 895
 896       <varlistentry>
 897         <term><varname>BlockIOReadBandwidth=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
 898         <term><varname>BlockIOWriteBandwidth=<replaceable>device</replaceable> <replaceable>bytes</replaceable></varname></term>
 899
 900         <listitem>
 901           <para>Set the per-device overall block I/O bandwidth limit for the executed processes, if the legacy control
 902           group hierarchy is used on the system. Takes a space-separated pair of a file path and a bandwidth value (in
 903           bytes per second) to specify the device specific bandwidth. The file path may be a path to a block device
 904           node, or as any other file in which case the backing block device of the file system of the file is used. If
 905           the bandwidth is suffixed with K, M, G, or T, the specified bandwidth is parsed as Kilobytes, Megabytes,
 906           Gigabytes, or Terabytes, respectively, to the base of 1000. (Example:
 907           "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0 5M"). This controls the
 908           <literal>blkio.throttle.read_bps_device</literal> and <literal>blkio.throttle.write_bps_device</literal>
 909           control group attributes. Use this option multiple times to set bandwidth limits for multiple devices. For
 910           details about these control group attributes, see <ulink
 911           url="https://www.kernel.org/doc/Documentation/cgroup-v1/blkio-controller.txt">blkio-controller.txt</ulink>.
 912           </para>
 913
 914           <para>Implies
 915           <literal>BlockIOAccounting=yes</literal>.</para>
 916
 917           <para>These settings are deprecated. Use <varname>IOReadBandwidthMax=</varname> and
 918           <varname>IOWriteBandwidthMax=</varname> instead.</para>
 919         </listitem>
 920       </varlistentry>
 921
 922     </variablelist>
 923   </refsect1>
 924
 925   <refsect1>
 926     <title>See Also</title>
 927     <para>
 928       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 929       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 930       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 931       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 932       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 933       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 934       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 935       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 936       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 937       <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 938       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 939       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 940       The documentation for control groups and specific controllers in the Linux kernel:
 941       <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>,
 942       <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/cpuacct.txt">cpuacct.txt</ulink>,
 943       <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt">memory.txt</ulink>,
 944       <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/blkio-controller.txt">blkio-controller.txt</ulink>.
 945       <ulink url="https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt">sched-bwc.txt</ulink>.
 946     </para>
 947   </refsect1>
 948 </refentry>