man/systemd.exec.xml

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   7   This file is part of systemd.
   8
   9   Copyright 2010 Lennart Poettering
  10
  11   systemd is free software; you can redistribute it and/or modify it
  12   under the terms of the GNU Lesser General Public License as published by
  13   the Free Software Foundation; either version 2.1 of the License, or
  14   (at your option) any later version.
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  19   Lesser General Public License for more details.
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  24
  25 <refentry id="systemd.exec">
  26         <refentryinfo>
  27                 <title>systemd.exec</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd.exec</refentrytitle>
  42                 <manvolnum>5</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd.exec</refname>
  47                 <refpurpose>Execution environment configuration</refpurpose>
  48         </refnamediv>
  49
  50         <refsynopsisdiv>
  51                 <para><filename>systemd.service</filename>,
  52                 <filename>systemd.socket</filename>,
  53                 <filename>systemd.mount</filename>,
  54                 <filename>systemd.swap</filename></para>
  55         </refsynopsisdiv>
  56
  57         <refsect1>
  58                 <title>Description</title>
  59
  60                 <para>Unit configuration files for services, sockets,
  61                 mount points and swap devices share a subset of
  62                 configuration options which define the execution
  63                 environment of spawned processes.</para>
  64
  65                 <para>This man page lists the configuration options
  66                 shared by these four unit types. See
  67                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  68                 for the common options of all unit configuration
  69                 files, and
  70                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  71                 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  72                 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  73                 and
  74                 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  75                 for more information on the specific unit
  76                 configuration files. The execution specific
  77                 configuration options are configured in the [Service],
  78                 [Socket], [Mount], or [Swap] sections, depending on the unit
  79                 type.</para>
  80         </refsect1>
  81
  82         <refsect1>
  83                 <title>Options</title>
  84
  85                 <variablelist class='unit-directives'>
  86
  87                         <varlistentry>
  88                                 <term><varname>WorkingDirectory=</varname></term>
  89
  90                                 <listitem><para>Takes an absolute
  91                                 directory path. Sets the working
  92                                 directory for executed processes. If
  93                                 not set defaults to the root directory
  94                                 when systemd is running as a system
  95                                 instance and the respective user's
  96                                 home directory if run as
  97                                 user.</para></listitem>
  98                         </varlistentry>
  99
 100                         <varlistentry>
 101                                 <term><varname>RootDirectory=</varname></term>
 102
 103                                 <listitem><para>Takes an absolute
 104                                 directory path. Sets the root
 105                                 directory for executed processes, with
 106                                 the
 107                                 <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 108                                 system call. If this is used it must
 109                                 be ensured that the process and all
 110                                 its auxiliary files are available in
 111                                 the <function>chroot()</function>
 112                                 jail.</para></listitem>
 113                         </varlistentry>
 114
 115                         <varlistentry>
 116                                 <term><varname>User=</varname></term>
 117                                 <term><varname>Group=</varname></term>
 118
 119                                 <listitem><para>Sets the Unix user
 120                                 or group that the processes are executed
 121                                 as, respectively. Takes a single user or group
 122                                 name or ID as argument. If no group is
 123                                 set, the default group of the user is
 124                                 chosen.</para></listitem>
 125                         </varlistentry>
 126
 127                         <varlistentry>
 128                                 <term><varname>SupplementaryGroups=</varname></term>
 129
 130                                 <listitem><para>Sets the supplementary
 131                                 Unix groups the processes are executed
 132                                 as. This takes a space separated list
 133                                 of group names or IDs. This option may
 134                                 be specified more than once in which
 135                                 case all listed groups are set as
 136                                 supplementary groups. When the empty
 137                                 string is assigned the list of
 138                                 supplementary groups is reset, and all
 139                                 assignments prior to this one will
 140                                 have no effect. In any way, this
 141                                 option does not override, but extends
 142                                 the list of supplementary groups
 143                                 configured in the system group
 144                                 database for the
 145                                 user.</para></listitem>
 146                         </varlistentry>
 147
 148                         <varlistentry>
 149                                 <term><varname>Nice=</varname></term>
 150
 151                                 <listitem><para>Sets the default nice
 152                                 level (scheduling priority) for
 153                                 executed processes. Takes an integer
 154                                 between -20 (highest priority) and 19
 155                                 (lowest priority). See
 156                                 <citerefentry><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 157                                 for details.</para></listitem>
 158                         </varlistentry>
 159
 160                         <varlistentry>
 161                                 <term><varname>OOMScoreAdjust=</varname></term>
 162
 163                                 <listitem><para>Sets the adjustment
 164                                 level for the Out-Of-Memory killer for
 165                                 executed processes. Takes an integer
 166                                 between -1000 (to disable OOM killing
 167                                 for this process) and 1000 (to make
 168                                 killing of this process under memory
 169                                 pressure very likely). See <ulink
 170                                 url="http://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt</ulink>
 171                                 for details.</para></listitem>
 172                         </varlistentry>
 173
 174                         <varlistentry>
 175                                 <term><varname>IOSchedulingClass=</varname></term>
 176
 177                                 <listitem><para>Sets the IO scheduling
 178                                 class for executed processes. Takes an
 179                                 integer between 0 and 3 or one of the
 180                                 strings <option>none</option>,
 181                                 <option>realtime</option>,
 182                                 <option>best-effort</option> or
 183                                 <option>idle</option>. See
 184                                 <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 185                                 for details.</para></listitem>
 186                         </varlistentry>
 187
 188                         <varlistentry>
 189                                 <term><varname>IOSchedulingPriority=</varname></term>
 190
 191                                 <listitem><para>Sets the IO scheduling
 192                                 priority for executed processes. Takes
 193                                 an integer between 0 (highest
 194                                 priority) and 7 (lowest priority). The
 195                                 available priorities depend on the
 196                                 selected IO scheduling class (see
 197                                 above). See
 198                                 <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 199                                 for details.</para></listitem>
 200                         </varlistentry>
 201
 202                         <varlistentry>
 203                                 <term><varname>CPUSchedulingPolicy=</varname></term>
 204
 205                                 <listitem><para>Sets the CPU
 206                                 scheduling policy for executed
 207                                 processes. Takes one of
 208                                 <option>other</option>,
 209                                 <option>batch</option>,
 210                                 <option>idle</option>,
 211                                 <option>fifo</option> or
 212                                 <option>rr</option>. See
 213                                 <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 214                                 for details.</para></listitem>
 215                         </varlistentry>
 216
 217                         <varlistentry>
 218                                 <term><varname>CPUSchedulingPriority=</varname></term>
 219
 220                                 <listitem><para>Sets the CPU
 221                                 scheduling priority for executed
 222                                 processes. The available priority
 223                                 range depends on the selected CPU
 224                                 scheduling policy (see above). For
 225                                 real-time scheduling policies an
 226                                 integer between 1 (lowest priority)
 227                                 and 99 (highest priority) can be used.
 228                                 See <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 229                                 for details.
 230                                 </para></listitem>
 231                         </varlistentry>
 232
 233                         <varlistentry>
 234                                 <term><varname>CPUSchedulingResetOnFork=</varname></term>
 235
 236                                 <listitem><para>Takes a boolean
 237                                 argument. If true elevated CPU
 238                                 scheduling priorities and policies
 239                                 will be reset when the executed
 240                                 processes fork, and can hence not leak
 241                                 into child processes. See
 242                                 <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 243                                 for details. Defaults to false.</para></listitem>
 244                         </varlistentry>
 245
 246                         <varlistentry>
 247                                 <term><varname>CPUAffinity=</varname></term>
 248
 249                                 <listitem><para>Controls the CPU
 250                                 affinity of the executed
 251                                 processes. Takes a space-separated
 252                                 list of CPU indexes. This option may
 253                                 be specified more than once in which
 254                                 case the specificed CPU affinity masks
 255                                 are merged. If the empty string is
 256                                 assigned the mask is reset, all
 257                                 assignments prior to this will have no
 258                                 effect. See
 259                                 <citerefentry><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 260                                 for details.</para></listitem>
 261                         </varlistentry>
 262
 263                         <varlistentry>
 264                                 <term><varname>UMask=</varname></term>
 265
 266                                 <listitem><para>Controls the file mode
 267                                 creation mask. Takes an access mode in
 268                                 octal notation. See
 269                                 <citerefentry><refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 270                                 for details. Defaults to
 271                                 0022.</para></listitem>
 272                         </varlistentry>
 273
 274                         <varlistentry>
 275                                 <term><varname>Environment=</varname></term>
 276
 277                                 <listitem><para>Sets environment
 278                                 variables for executed
 279                                 processes. Takes a space-separated
 280                                 list of variable assignments. This
 281                                 option may be specified more than once
 282                                 in which case all listed variables
 283                                 will be set. If the same variable is
 284                                 set twice the later setting will
 285                                 override the earlier setting. If the
 286                                 empty string is assigned to this
 287                                 option the list of environment
 288                                 variables is reset, all prior
 289                                 assignments have no effect.
 290                                 Variable expansion is not performed
 291                                 inside the strings, and $ has no special
 292                                 meaning.
 293                                 If you need to assign a value containing spaces
 294                                 to a variable, use double quotes (")
 295                                 for the assignment.</para>
 296
 297                                 <para>Example:
 298                                 <programlisting>Environment="VAR1=word1 word2" VAR2=word3 "VAR3=word 5 6"</programlisting>
 299                                 gives three variables <literal>VAR1</literal>,
 300                                 <literal>VAR2</literal>, <literal>VAR3</literal>.
 301                                 </para>
 302
 303                                 <para>
 304                                 See
 305                                 <citerefentry><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 306                                 for details about environment variables.</para></listitem>
 307                         </varlistentry>
 308                         <varlistentry>
 309                                 <term><varname>EnvironmentFile=</varname></term>
 310                                 <listitem><para>Similar to
 311                                 <varname>Environment=</varname> but
 312                                 reads the environment variables from a
 313                                 text file. The text file should
 314                                 contain new-line separated variable
 315                                 assignments. Empty lines and lines
 316                                 starting with ; or # will be ignored,
 317                                 which may be used for commenting. A line
 318                                 ending with a backslash will be concatenated
 319                                 with the following one, allowing multiline variable
 320                                 definitions. The parser strips leading
 321                                 and trailing whitespace from the values
 322                                 of assignments, unless you use
 323                                 double quotes (").</para>
 324
 325                                 <para>The argument passed should be an
 326                                 absolute file name or wildcard
 327                                 expression, optionally prefixed with
 328                                 "-", which indicates that if the file
 329                                 does not exist it won't be read and no
 330                                 error or warning message is logged.
 331                                 This option may be specified more than
 332                                 once in which case all specified files
 333                                 are read. If the empty string is
 334                                 assigned to this option the list of
 335                                 file to read is reset, all prior
 336                                 assignments have no effect.</para>
 337
 338                                 <para>The files listed with this
 339                                 directive will be read shortly before
 340                                 the process is executed. Settings from
 341                                 these files override settings made
 342                                 with
 343                                 <varname>Environment=</varname>. If
 344                                 the same variable is set twice from
 345                                 these files the files will be read in
 346                                 the order they are specified and the
 347                                 later setting will override the
 348                                 earlier setting.</para></listitem>
 349                         </varlistentry>
 350
 351                         <varlistentry>
 352                                 <term><varname>StandardInput=</varname></term>
 353                                 <listitem><para>Controls where file
 354                                 descriptor 0 (STDIN) of the executed
 355                                 processes is connected to. Takes one
 356                                 of <option>null</option>,
 357                                 <option>tty</option>,
 358                                 <option>tty-force</option>,
 359                                 <option>tty-fail</option> or
 360                                 <option>socket</option>. If
 361                                 <option>null</option> is selected
 362                                 standard input will be connected to
 363                                 <filename>/dev/null</filename>,
 364                                 i.e. all read attempts by the process
 365                                 will result in immediate EOF. If
 366                                 <option>tty</option> is selected
 367                                 standard input is connected to a TTY
 368                                 (as configured by
 369                                 <varname>TTYPath=</varname>, see
 370                                 below) and the executed process
 371                                 becomes the controlling process of the
 372                                 terminal. If the terminal is already
 373                                 being controlled by another process the
 374                                 executed process waits until the current
 375                                 controlling process releases the
 376                                 terminal.
 377                                 <option>tty-force</option>
 378                                 is similar to <option>tty</option>,
 379                                 but the executed process is forcefully
 380                                 and immediately made the controlling
 381                                 process of the terminal, potentially
 382                                 removing previous controlling
 383                                 processes from the
 384                                 terminal. <option>tty-fail</option> is
 385                                 similar to <option>tty</option> but if
 386                                 the terminal already has a controlling
 387                                 process start-up of the executed
 388                                 process fails.  The
 389                                 <option>socket</option> option is only
 390                                 valid in socket-activated services,
 391                                 and only when the socket configuration
 392                                 file (see
 393                                 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 394                                 for details) specifies a single socket
 395                                 only. If this option is set standard
 396                                 input will be connected to the socket
 397                                 the service was activated from, which
 398                                 is primarily useful for compatibility
 399                                 with daemons designed for use with the
 400                                 traditional
 401                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 402                                 daemon. This setting defaults to
 403                                 <option>null</option>.</para></listitem>
 404                         </varlistentry>
 405                         <varlistentry>
 406                                 <term><varname>StandardOutput=</varname></term>
 407                                 <listitem><para>Controls where file
 408                                 descriptor 1 (STDOUT) of the executed
 409                                 processes is connected to. Takes one
 410                                 of <option>inherit</option>,
 411                                 <option>null</option>,
 412                                 <option>tty</option>,
 413                                 <option>syslog</option>,
 414                                 <option>kmsg</option>,
 415                                 <option>journal</option>,
 416                                 <option>syslog+console</option>,
 417                                 <option>kmsg+console</option>,
 418                                 <option>journal+console</option> or
 419                                 <option>socket</option>. If set to
 420                                 <option>inherit</option> the file
 421                                 descriptor of standard input is
 422                                 duplicated for standard output. If set
 423                                 to <option>null</option> standard
 424                                 output will be connected to
 425                                 <filename>/dev/null</filename>,
 426                                 i.e. everything written to it will be
 427                                 lost. If set to <option>tty</option>
 428                                 standard output will be connected to a
 429                                 tty (as configured via
 430                                 <varname>TTYPath=</varname>, see
 431                                 below). If the TTY is used for output
 432                                 only the executed process will not
 433                                 become the controlling process of the
 434                                 terminal, and will not fail or wait
 435                                 for other processes to release the
 436                                 terminal. <option>syslog</option>
 437                                 connects standard output to the
 438                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 439                                 system syslog
 440                                 service. <option>kmsg</option>
 441                                 connects it with the kernel log buffer
 442                                 which is accessible via
 443                                 <citerefentry><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <option>journal</option>
 444                                 connects it with the journal which is
 445                                 accessible via
 446                                 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 447                                 (Note that everything that is written
 448                                 to syslog or kmsg is implicitly stored
 449                                 in the journal as well, those options
 450                                 are hence supersets of this
 451                                 one). <option>syslog+console</option>,
 452                                 <option>journal+console</option> and
 453                                 <option>kmsg+console</option> work
 454                                 similarly but copy the output to the
 455                                 system console as
 456                                 well. <option>socket</option> connects
 457                                 standard output to a socket from
 458                                 socket activation, semantics are
 459                                 similar to the respective option of
 460                                 <varname>StandardInput=</varname>.
 461                                 This setting defaults to the value set
 462                                 with
 463                                 <option>DefaultStandardOutput=</option>
 464                                 in
 465                                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 466                                 which defaults to
 467                                 <option>journal</option>.</para></listitem>
 468                         </varlistentry>
 469                         <varlistentry>
 470                                 <term><varname>StandardError=</varname></term>
 471                                 <listitem><para>Controls where file
 472                                 descriptor 2 (STDERR) of the executed
 473                                 processes is connected to. The
 474                                 available options are identical to
 475                                 those of
 476                                 <varname>StandardOutput=</varname>,
 477                                 with one exception: if set to
 478                                 <option>inherit</option> the file
 479                                 descriptor used for standard output is
 480                                 duplicated for standard error. This
 481                                 setting defaults to the value set with
 482                                 <option>DefaultStandardError=</option>
 483                                 in
 484                                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 485                                 which defaults to
 486                                 <option>inherit</option>.</para></listitem>
 487                         </varlistentry>
 488                         <varlistentry>
 489                                 <term><varname>TTYPath=</varname></term>
 490                                 <listitem><para>Sets the terminal
 491                                 device node to use if standard input,
 492                                 output or stderr are connected to a
 493                                 TTY (see above). Defaults to
 494                                 <filename>/dev/console</filename>.</para></listitem>
 495                         </varlistentry>
 496                         <varlistentry>
 497                                 <term><varname>TTYReset=</varname></term>
 498                                 <listitem><para>Reset the terminal
 499                                 device specified with
 500                                 <varname>TTYPath=</varname> before and
 501                                 after execution. Defaults to
 502                                 <literal>no</literal>.</para></listitem>
 503                         </varlistentry>
 504                         <varlistentry>
 505                                 <term><varname>TTYVHangup=</varname></term>
 506                                 <listitem><para>Disconnect all clients
 507                                 which have opened the terminal device
 508                                 specified with
 509                                 <varname>TTYPath=</varname>
 510                                 before and after execution. Defaults
 511                                 to
 512                                 <literal>no</literal>.</para></listitem>
 513                         </varlistentry>
 514                         <varlistentry>
 515                                 <term><varname>TTYVTDisallocate=</varname></term>
 516                                 <listitem><para>If the terminal
 517                                 device specified with
 518                                 <varname>TTYPath=</varname> is a
 519                                 virtual console terminal try to
 520                                 deallocate the TTY before and after
 521                                 execution. This ensures that the
 522                                 screen and scrollback buffer is
 523                                 cleared. Defaults to
 524                                 <literal>no</literal>.</para></listitem>
 525                         </varlistentry>
 526                         <varlistentry>
 527                                 <term><varname>SyslogIdentifier=</varname></term>
 528                                 <listitem><para>Sets the process name
 529                                 to prefix log lines sent to syslog or
 530                                 the kernel log buffer with. If not set
 531                                 defaults to the process name of the
 532                                 executed process. This option is only
 533                                 useful when
 534                                 <varname>StandardOutput=</varname> or
 535                                 <varname>StandardError=</varname> are
 536                                 set to <option>syslog</option> or
 537                                 <option>kmsg</option>.</para></listitem>
 538                         </varlistentry>
 539                         <varlistentry>
 540                                 <term><varname>SyslogFacility=</varname></term>
 541                                 <listitem><para>Sets the syslog
 542                                 facility to use when logging to
 543                                 syslog. One of <option>kern</option>,
 544                                 <option>user</option>,
 545                                 <option>mail</option>,
 546                                 <option>daemon</option>,
 547                                 <option>auth</option>,
 548                                 <option>syslog</option>,
 549                                 <option>lpr</option>,
 550                                 <option>news</option>,
 551                                 <option>uucp</option>,
 552                                 <option>cron</option>,
 553                                 <option>authpriv</option>,
 554                                 <option>ftp</option>,
 555                                 <option>local0</option>,
 556                                 <option>local1</option>,
 557                                 <option>local2</option>,
 558                                 <option>local3</option>,
 559                                 <option>local4</option>,
 560                                 <option>local5</option>,
 561                                 <option>local6</option> or
 562                                 <option>local7</option>. See
 563                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 564                                 for details. This option is only
 565                                 useful when
 566                                 <varname>StandardOutput=</varname> or
 567                                 <varname>StandardError=</varname> are
 568                                 set to <option>syslog</option>.
 569                                 Defaults to
 570                                 <option>daemon</option>.</para></listitem>
 571                         </varlistentry>
 572                         <varlistentry>
 573                                 <term><varname>SyslogLevel=</varname></term>
 574                                 <listitem><para>Default syslog level
 575                                 to use when logging to syslog or the
 576                                 kernel log buffer. One of
 577                                 <option>emerg</option>,
 578                                 <option>alert</option>,
 579                                 <option>crit</option>,
 580                                 <option>err</option>,
 581                                 <option>warning</option>,
 582                                 <option>notice</option>,
 583                                 <option>info</option>,
 584                                 <option>debug</option>. See
 585                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 586                                 for details. This option is only
 587                                 useful when
 588                                 <varname>StandardOutput=</varname> or
 589                                 <varname>StandardError=</varname> are
 590                                 set to <option>syslog</option> or
 591                                 <option>kmsg</option>. Note that
 592                                 individual lines output by the daemon
 593                                 might be prefixed with a different log
 594                                 level which can be used to override
 595                                 the default log level specified
 596                                 here. The interpretation of these
 597                                 prefixes may be disabled with
 598                                 <varname>SyslogLevelPrefix=</varname>,
 599                                 see below. For details see
 600                                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 601
 602                                 Defaults to
 603                                 <option>info</option>.</para></listitem>
 604                         </varlistentry>
 605
 606                         <varlistentry>
 607                                 <term><varname>SyslogLevelPrefix=</varname></term>
 608                                 <listitem><para>Takes a boolean
 609                                 argument. If true and
 610                                 <varname>StandardOutput=</varname> or
 611                                 <varname>StandardError=</varname> are
 612                                 set to <option>syslog</option>,
 613                                 <option>kmsg</option> or
 614                                 <option>journal</option>, log lines
 615                                 written by the executed process that
 616                                 are prefixed with a log level will be
 617                                 passed on to syslog with this log
 618                                 level set but the prefix removed. If
 619                                 set to false, the interpretation of
 620                                 these prefixes is disabled and the
 621                                 logged lines are passed on as-is. For
 622                                 details about this prefixing see
 623                                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 624                                 Defaults to true.</para></listitem>
 625                         </varlistentry>
 626
 627                         <varlistentry>
 628                                 <term><varname>TimerSlackNSec=</varname></term>
 629                                 <listitem><para>Sets the timer slack
 630                                 in nanoseconds for the executed
 631                                 processes. The timer slack controls
 632                                 the accuracy of wake-ups triggered by
 633                                 timers. See
 634                                 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 635                                 for more information. Note that in
 636                                 contrast to most other time span
 637                                 definitions this parameter takes an
 638                                 integer value in nano-seconds if no
 639                                 unit is specified. The usual time
 640                                 units are understood
 641                                 too.</para></listitem>
 642                         </varlistentry>
 643
 644                         <varlistentry>
 645                                 <term><varname>LimitCPU=</varname></term>
 646                                 <term><varname>LimitFSIZE=</varname></term>
 647                                 <term><varname>LimitDATA=</varname></term>
 648                                 <term><varname>LimitSTACK=</varname></term>
 649                                 <term><varname>LimitCORE=</varname></term>
 650                                 <term><varname>LimitRSS=</varname></term>
 651                                 <term><varname>LimitNOFILE=</varname></term>
 652                                 <term><varname>LimitAS=</varname></term>
 653                                 <term><varname>LimitNPROC=</varname></term>
 654                                 <term><varname>LimitMEMLOCK=</varname></term>
 655                                 <term><varname>LimitLOCKS=</varname></term>
 656                                 <term><varname>LimitSIGPENDING=</varname></term>
 657                                 <term><varname>LimitMSGQUEUE=</varname></term>
 658                                 <term><varname>LimitNICE=</varname></term>
 659                                 <term><varname>LimitRTPRIO=</varname></term>
 660                                 <term><varname>LimitRTTIME=</varname></term>
 661                                 <listitem><para>These settings control
 662                                 various resource limits for executed
 663                                 processes. See
 664                                 <citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 665                                 for details. Use the string
 666                                 <varname>infinity</varname> to
 667                                 configure no limit on a specific
 668                                 resource.</para></listitem>
 669                         </varlistentry>
 670
 671                         <varlistentry>
 672                                 <term><varname>PAMName=</varname></term>
 673                                 <listitem><para>Sets the PAM service
 674                                 name to set up a session as. If set
 675                                 the executed process will be
 676                                 registered as a PAM session under the
 677                                 specified service name. This is only
 678                                 useful in conjunction with the
 679                                 <varname>User=</varname> setting. If
 680                                 not set no PAM session will be opened
 681                                 for the executed processes. See
 682                                 <citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 683                                 for details.</para></listitem>
 684                         </varlistentry>
 685
 686                         <varlistentry>
 687                                 <term><varname>TCPWrapName=</varname></term>
 688                                 <listitem><para>If this is a
 689                                 socket-activated service this sets the
 690                                 tcpwrap service name to check the
 691                                 permission for the current connection
 692                                 with. This is only useful in
 693                                 conjunction with socket-activated
 694                                 services, and stream sockets (TCP) in
 695                                 particular. It has no effect on other
 696                                 socket types (e.g. datagram/UDP) and
 697                                 on processes unrelated to socket-based
 698                                 activation. If the tcpwrap
 699                                 verification fails daemon start-up
 700                                 will fail and the connection is
 701                                 terminated. See
 702                                 <citerefentry><refentrytitle>tcpd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 703                                 for details. Note that this option may
 704                                 be used to do access control checks
 705                                 only. Shell commands and commands
 706                                 described in
 707                                 <citerefentry><refentrytitle>hosts_options</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 708                                 are not supported.</para></listitem>
 709                         </varlistentry>
 710
 711                         <varlistentry>
 712                                 <term><varname>CapabilityBoundingSet=</varname></term>
 713
 714                                 <listitem><para>Controls which
 715                                 capabilities to include in the
 716                                 capability bounding set for the
 717                                 executed process. See
 718                                 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 719                                 for details. Takes a whitespace
 720                                 separated list of capability names as
 721                                 read by
 722                                 <citerefentry><refentrytitle>cap_from_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 723                                 Capabilities listed will be included
 724                                 in the bounding set, all others are
 725                                 removed. If the list of capabilities
 726                                 is prefixed with ~ all but the listed
 727                                 capabilities will be included, the
 728                                 effect of the assignment
 729                                 inverted. Note that this option also
 730                                 effects the respective capabilities in
 731                                 the effective, permitted and
 732                                 inheritable capability sets, on top of
 733                                 what <varname>Capabilities=</varname>
 734                                 does. If this option is not used the
 735                                 capability bounding set is not
 736                                 modified on process execution, hence
 737                                 no limits on the capabilities of the
 738                                 process are enforced. This option may
 739                                 appear more than once in which case
 740                                 the bounding sets are merged. If the empty
 741                                 string is assigned to this option the
 742                                 bounding set is reset, and all prior
 743                                 settings have no
 744                                 effect.</para></listitem>
 745                         </varlistentry>
 746
 747                         <varlistentry>
 748                                 <term><varname>SecureBits=</varname></term>
 749                                 <listitem><para>Controls the secure
 750                                 bits set for the executed process. See
 751                                 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 752                                 for details. Takes a list of strings:
 753                                 <option>keep-caps</option>,
 754                                 <option>keep-caps-locked</option>,
 755                                 <option>no-setuid-fixup</option>,
 756                                 <option>no-setuid-fixup-locked</option>,
 757                                 <option>noroot</option> and/or
 758                                 <option>noroot-locked</option>. This
 759                                 option may appear more than once in
 760                                 which case the secure bits are
 761                                 ORed. If the empty string is assigned
 762                                 to this option the bits are reset to
 763                                 0.</para></listitem>
 764                         </varlistentry>
 765
 766                         <varlistentry>
 767                                 <term><varname>Capabilities=</varname></term>
 768                                 <listitem><para>Controls the
 769                                 <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 770                                 set for the executed process. Take a
 771                                 capability string describing the
 772                                 effective, permitted and inherited
 773                                 capability sets as documented in
 774                                 <citerefentry><refentrytitle>cap_from_text</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 775                                 Note that these capability sets are
 776                                 usually influenced by the capabilities
 777                                 attached to the executed file. Due to
 778                                 that
 779                                 <varname>CapabilityBoundingSet=</varname>
 780                                 is probably the much more useful
 781                                 setting.</para></listitem>
 782                         </varlistentry>
 783
 784                         <varlistentry>
 785                                 <term><varname>ControlGroup=</varname></term>
 786
 787                                 <listitem><para>Controls the control
 788                                 groups the executed processes shall be
 789                                 made members of. Takes a
 790                                 space-separated list of cgroup
 791                                 identifiers. A cgroup identifier is
 792                                 formatted like
 793                                 <filename>cpu:/foo/bar</filename>,
 794                                 where "cpu" indicates the kernel
 795                                 control group controller used, and
 796                                 <filename>/foo/bar</filename> is the
 797                                 control group path. The controller
 798                                 name and ":" may be omitted in which
 799                                 case the named systemd control group
 800                                 hierarchy is implied. Alternatively,
 801                                 the path and ":" may be omitted, in
 802                                 which case the default control group
 803                                 path for this unit is implied.</para>
 804
 805                                 <para>This option may be used to place
 806                                 executed processes in arbitrary groups
 807                                 in arbitrary hierarchies -- which may
 808                                 then be externally configured with
 809                                 additional execution limits. By
 810                                 default systemd will place all
 811                                 executed processes in separate
 812                                 per-unit control groups (named after
 813                                 the unit) in the systemd named
 814                                 hierarchy. This option is primarily
 815                                 intended to place executed processes
 816                                 in specific paths in specific kernel
 817                                 controller hierarchies. It is not
 818                                 recommended to manipulate the service
 819                                 control group path in the systemd
 820                                 named hierarchy. For details about
 821                                 control groups see <ulink
 822                                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>.</para>
 823
 824                                 <para>This option may appear more than
 825                                 once, in which case the list of
 826                                 control group assignments is
 827                                 merged. If the same hierarchy gets two
 828                                 different paths assigned only the
 829                                 later setting will take effect. If the
 830                                 empty string is assigned to this
 831                                 option the list of control group
 832                                 assignments is reset, all previous
 833                                 assignments will have no
 834                                 effect.</para>
 835
 836                                 <para>Note that the list of control
 837                                 group assignments of a unit is
 838                                 extended implicitly based on the
 839                                 settings of
 840                                 <varname>DefaultControllers=</varname>
 841                                 of
 842                                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 843                                 but a unit's
 844                                 <varname>ControlGroup=</varname>
 845                                 setting for a specific controller
 846                                 takes precedence.</para></listitem>
 847                         </varlistentry>
 848
 849                         <varlistentry>
 850                                 <term><varname>ControlGroupModify=</varname></term>
 851                                 <listitem><para>Takes a boolean
 852                                 argument. If true, the control groups
 853                                 created for this unit will be owned by
 854                                 the user specified with
 855                                 <varname>User=</varname> (and the
 856                                 appropriate group), and he/she can create
 857                                 subgroups as well as add processes to
 858                                 the group.</para></listitem>
 859                         </varlistentry>
 860
 861                         <varlistentry>
 862                                 <term><varname>ControlGroupPersistent=</varname></term>
 863                                 <listitem><para>Takes a boolean
 864                                 argument. If true, the control groups
 865                                 created for this unit will be marked
 866                                 to be persistent, i.e. systemd will
 867                                 not remove them when stopping the
 868                                 unit. The default is false, meaning
 869                                 that the control groups will be
 870                                 removed when the unit is stopped. For
 871                                 details about the semantics of this
 872                                 logic see <ulink
 873                                 url="http://www.freedesktop.org/wiki/Software/systemd/PaxControlGroups">PaxControlGroups</ulink>.</para></listitem>
 874                         </varlistentry>
 875
 876                         <varlistentry>
 877                                 <term><varname>ControlGroupAttribute=</varname></term>
 878
 879                                 <listitem><para>Set a specific control
 880                                 group attribute for executed
 881                                 processes, and (if needed) add the
 882                                 executed processes to a cgroup in the
 883                                 hierarchy of the controller the
 884                                 attribute belongs to. Takes two
 885                                 space-separated arguments: the
 886                                 attribute name (syntax is
 887                                 <literal>cpu.shares</literal> where
 888                                 <literal>cpu</literal> refers to a
 889                                 specific controller and
 890                                 <literal>shares</literal> to the
 891                                 attribute name), and the attribute
 892                                 value. Example:
 893                                 <literal>ControlGroupAttribute=cpu.shares
 894                                 512</literal>. If this option is used
 895                                 for an attribute that belongs to a
 896                                 kernel controller hierarchy the unit
 897                                 is not already configured to be added
 898                                 to (for example via the
 899                                 <literal>ControlGroup=</literal>
 900                                 option) then the unit will be added to
 901                                 the controller and the default unit
 902                                 cgroup path is implied. Thus, using
 903                                 <varname>ControlGroupAttribute=</varname>
 904                                 is in most cases sufficient to make
 905                                 use of control group enforcements,
 906                                 explicit
 907                                 <varname>ControlGroup=</varname> are
 908                                 only necessary in case the implied
 909                                 default control group path for a
 910                                 service is not desirable. For details
 911                                 about control group attributes see
 912                                 <ulink
 913                                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>. This
 914                                 option may appear more than once, in
 915                                 order to set multiple control group
 916                                 attributes. If this option is used
 917                                 multiple times for the same cgroup
 918                                 attribute only the later setting takes
 919                                 effect. If the empty string is
 920                                 assigned to this option the list of
 921                                 attributes is reset, all previous
 922                                 cgroup attribute settings have no
 923                                 effect, including those done with
 924                                 <varname>CPUShares=</varname>,
 925                                 <varname>MemoryLimit=</varname>,
 926                                 <varname>MemorySoftLimit</varname>,
 927                                 <varname>DeviceAllow=</varname>,
 928                                 <varname>DeviceDeny=</varname>,
 929                                 <varname>BlockIOWeight=</varname>,
 930                                 <varname>BlockIOReadBandwidth=</varname>,
 931                                 <varname>BlockIOWriteBandwidth=</varname>.
 932                                 </para></listitem>
 933                         </varlistentry>
 934
 935                         <varlistentry>
 936                                 <term><varname>CPUShares=</varname></term>
 937
 938                                 <listitem><para>Assign the specified
 939                                 overall CPU time shares to the
 940                                 processes executed. Takes an integer
 941                                 value. This controls the
 942                                 <literal>cpu.shares</literal> control
 943                                 group attribute, which defaults to
 944                                 1024. For details about this control
 945                                 group attribute see <ulink
 946                                 url="http://www.kernel.org/doc/Documentation/scheduler/sched-design-CFS.txt">sched-design-CFS.txt</ulink>.</para></listitem>
 947                         </varlistentry>
 948
 949                         <varlistentry>
 950                                 <term><varname>MemoryLimit=</varname></term>
 951                                 <term><varname>MemorySoftLimit=</varname></term>
 952
 953                                 <listitem><para>Limit the overall memory usage
 954                                 of the executed processes to a certain
 955                                 size. Takes a memory size in bytes. If
 956                                 the value is suffixed with K, M, G or
 957                                 T the specified memory size is parsed
 958                                 as Kilobytes, Megabytes, Gigabytes,
 959                                 or Terabytes (to the base
 960                                 1024), respectively. This controls the
 961                                 <literal>memory.limit_in_bytes</literal>
 962                                 and
 963                                 <literal>memory.soft_limit_in_bytes</literal>
 964                                 control group attributes. For details
 965                                 about these control group attributes
 966                                 see <ulink
 967                                 url="http://www.kernel.org/doc/Documentation/cgroups/memory.txt">memory.txt</ulink>.</para></listitem>
 968                         </varlistentry>
 969
 970                         <varlistentry>
 971                                 <term><varname>DeviceAllow=</varname></term>
 972                                 <term><varname>DeviceDeny=</varname></term>
 973
 974                                 <listitem><para>Control access to
 975                                 specific device nodes by the executed processes. Takes two
 976                                 space separated strings: a device node
 977                                 path (such as
 978                                 <filename>/dev/null</filename>)
 979                                 followed by a combination of r, w, m
 980                                 to control reading, writing, or
 981                                 creating of the specific device node
 982                                 by the unit, respectively. This controls the
 983                                 <literal>devices.allow</literal>
 984                                 and
 985                                 <literal>devices.deny</literal>
 986                                 control group attributes. For details
 987                                 about these control group attributes
 988                                 see <ulink
 989                                 url="http://www.kernel.org/doc/Documentation/cgroups/devices.txt">devices.txt</ulink>.</para></listitem>
 990                         </varlistentry>
 991
 992                         <varlistentry>
 993                                 <term><varname>BlockIOWeight=</varname></term>
 994
 995                                 <listitem><para>Set the default or
 996                                 per-device overall block IO weight
 997                                 value for the executed
 998                                 processes. Takes either a single
 999                                 weight value (between 10 and 1000) to
1000                                 set the default block IO weight, or a
1001                                 space separated pair of a file path
1002                                 and a weight value to specify the
1003                                 device specific weight value (Example:
1004                                 "/dev/sda 500"). The file path may be
1005                                 specified as path to a block device
1006                                 node or as any other file in which
1007                                 case the backing block device of the
1008                                 file system of the file is
1009                                 determined. This controls the
1010                                 <literal>blkio.weight</literal> and
1011                                 <literal>blkio.weight_device</literal>
1012                                 control group attributes, which
1013                                 default to 1000. Use this option
1014                                 multiple times to set weights for
1015                                 multiple devices. For details about
1016                                 these control group attributes see
1017                                 <ulink
1018                                 url="http://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt">blkio-controller.txt</ulink>.</para></listitem>
1019                         </varlistentry>
1020
1021                         <varlistentry>
1022                                 <term><varname>BlockIOReadBandwidth=</varname></term>
1023                                 <term><varname>BlockIOWriteBandwidth=</varname></term>
1024
1025                                 <listitem><para>Set the per-device
1026                                 overall block IO bandwidth limit for
1027                                 the executed processes. Takes a space
1028                                 separated pair of a file path and a
1029                                 bandwidth value (in bytes per second)
1030                                 to specify the device specific
1031                                 bandwidth. The file path may be
1032                                 specified as path to a block device
1033                                 node or as any other file in which
1034                                 case the backing block device of the
1035                                 file system of the file is determined.
1036                                 If the bandwidth is suffixed with K, M,
1037                                 G, or T the specified bandwidth is
1038                                 parsed as Kilobytes, Megabytes,
1039                                 Gigabytes, or Terabytes, respectively (Example:
1040                                 "/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0
1041                                 5M"). This controls the
1042                                 <literal>blkio.read_bps_device</literal>
1043                                 and
1044                                 <literal>blkio.write_bps_device</literal>
1045                                 control group attributes. Use this
1046                                 option multiple times to set bandwidth
1047                                 limits for multiple devices. For
1048                                 details about these control group
1049                                 attributes see <ulink
1050                                 url="http://www.kernel.org/doc/Documentation/cgroups/blkio-controller.txt">blkio-controller.txt</ulink>.</para></listitem>
1051                         </varlistentry>
1052
1053                         <varlistentry>
1054                                 <term><varname>ReadWriteDirectories=</varname></term>
1055                                 <term><varname>ReadOnlyDirectories=</varname></term>
1056                                 <term><varname>InaccessibleDirectories=</varname></term>
1057
1058                                 <listitem><para>Sets up a new
1059                                 file-system name space for executed
1060                                 processes. These options may be used
1061                                 to limit access a process might have
1062                                 to the main file-system
1063                                 hierarchy. Each setting takes a
1064                                 space-separated list of absolute
1065                                 directory paths. Directories listed in
1066                                 <varname>ReadWriteDirectories=</varname>
1067                                 are accessible from within the
1068                                 namespace with the same access rights
1069                                 as from outside. Directories listed in
1070                                 <varname>ReadOnlyDirectories=</varname>
1071                                 are accessible for reading only,
1072                                 writing will be refused even if the
1073                                 usual file access controls would
1074                                 permit this. Directories listed in
1075                                 <varname>InaccessibleDirectories=</varname>
1076                                 will be made inaccessible for
1077                                 processes inside the namespace. Note
1078                                 that restricting access with these
1079                                 options does not extend to submounts
1080                                 of a directory. You must list
1081                                 submounts separately in these settings
1082                                 to ensure the same limited
1083                                 access. These options may be specified
1084                                 more than once in which case all
1085                                 directories listed will have limited
1086                                 access from within the namespace. If
1087                                 the empty string is assigned to this
1088                                 option the specific list is reset, and
1089                                 all prior assignments have no
1090                                 effect.</para></listitem>
1091                         </varlistentry>
1092
1093                         <varlistentry>
1094                                 <term><varname>PrivateTmp=</varname></term>
1095
1096                                 <listitem><para>Takes a boolean
1097                                 argument. If true sets up a new file
1098                                 system namespace for the executed
1099                                 processes and mounts private
1100                                 <filename>/tmp</filename> and
1101                                 <filename>/var/tmp</filename> directories
1102                                 inside it, that are not shared by
1103                                 processes outside of the
1104                                 namespace. This is useful to secure
1105                                 access to temporary files of the
1106                                 process, but makes sharing between
1107                                 processes via
1108                                 <filename>/tmp</filename> or
1109                                 <filename>/var/tmp</filename>
1110                                 impossible. Defaults to
1111                                 false.</para></listitem>
1112                         </varlistentry>
1113
1114                         <varlistentry>
1115                                 <term><varname>PrivateNetwork=</varname></term>
1116
1117                                 <listitem><para>Takes a boolean
1118                                 argument. If true sets up a new
1119                                 network namespace for the executed
1120                                 processes and configures only the
1121                                 loopback network device
1122                                 <literal>lo</literal> inside it. No
1123                                 other network devices will be
1124                                 available to the executed process.
1125                                 This is useful to securely turn off
1126                                 network access by the executed
1127                                 process. Defaults to
1128                                 false.</para></listitem>
1129                         </varlistentry>
1130
1131                         <varlistentry>
1132                                 <term><varname>MountFlags=</varname></term>
1133
1134                                 <listitem><para>Takes a mount
1135                                 propagation flag:
1136                                 <option>shared</option>,
1137                                 <option>slave</option> or
1138                                 <option>private</option>, which
1139                                 control whether the file system
1140                                 namespace set up for this unit's
1141                                 processes will receive or propagate
1142                                 new mounts. See
1143                                 <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1144                                 for details. Default to
1145                                 <option>shared</option>.</para></listitem>
1146                         </varlistentry>
1147
1148                         <varlistentry>
1149                                 <term><varname>UtmpIdentifier=</varname></term>
1150
1151                                 <listitem><para>Takes a four
1152                                 character identifier string for an
1153                                 utmp/wtmp entry for this service. This
1154                                 should only be set for services such
1155                                 as <command>getty</command>
1156                                 implementations where utmp/wtmp
1157                                 entries must be created and cleared
1158                                 before and after execution. If the
1159                                 configured string is longer than four
1160                                 characters it is truncated and the
1161                                 terminal four characters are
1162                                 used. This setting interprets %I style
1163                                 string replacements. This setting is
1164                                 unset by default, i.e. no utmp/wtmp
1165                                 entries are created or cleaned up for
1166                                 this service.</para></listitem>
1167                         </varlistentry>
1168
1169                         <varlistentry>
1170                                 <term><varname>IgnoreSIGPIPE=</varname></term>
1171
1172                                 <listitem><para>Takes a boolean
1173                                 argument. If true causes SIGPIPE to be
1174                                 ignored in the executed
1175                                 process. Defaults to true, since
1176                                 SIGPIPE generally is useful only in
1177                                 shell pipelines.</para></listitem>
1178                         </varlistentry>
1179
1180                         <varlistentry>
1181                                 <term><varname>NoNewPrivileges=</varname></term>
1182
1183                                 <listitem><para>Takes a boolean
1184                                 argument. If true ensures that the
1185                                 service process and all its children
1186                                 can never gain new privileges. This
1187                                 option is more powerful than the respective
1188                                 secure bits flags (see above), as it
1189                                 also prohibits UID changes of any
1190                                 kind. This is the simplest, most
1191                                 effective way to ensure that a process
1192                                 and its children can never elevate
1193                                 privileges again.</para></listitem>
1194                         </varlistentry>
1195
1196                         <varlistentry>
1197                                 <term><varname>SystemCallFilter=</varname></term>
1198
1199                                 <listitem><para>Takes a space
1200                                 separated list of system call
1201                                 names. If this setting is used all
1202                                 system calls executed by the unit
1203                                 process except for the listed ones
1204                                 will result in immediate process
1205                                 termination with the SIGSYS signal
1206                                 (whitelisting). If the first character
1207                                 of the list is <literal>~</literal>
1208                                 the effect is inverted: only the
1209                                 listed system calls will result in
1210                                 immediate process termination
1211                                 (blacklisting). If this option is used
1212                                 <varname>NoNewPrivileges=yes</varname>
1213                                 is implied. This feature makes use of
1214                                 the Secure Computing Mode 2 interfaces
1215                                 of the kernel ('seccomp filtering')
1216                                 and is useful for enforcing a minimal
1217                                 sandboxing environment. Note that the
1218                                 <function>execve</function>,
1219                                 <function>rt_sigreturn</function>,
1220                                 <function>sigreturn</function>,
1221                                 <function>exit_group</function>,
1222                                 <function>exit</function> system calls
1223                                 are implicitly whitelisted and don't
1224                                 need to be listed explicitly. This
1225                                 option may be specified more than once
1226                                 in which case the filter masks are
1227                                 merged. If the empty string is
1228                                 assigned the filter is reset, all
1229                                 prior assignments will have no
1230                                 effect.</para></listitem>
1231                         </varlistentry>
1232
1233                 </variablelist>
1234         </refsect1>
1235
1236         <refsect1>
1237                   <title>See Also</title>
1238                   <para>
1239                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1240                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1241                           <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1242                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1243                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1244                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1245                           <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1246                           <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1247                           <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1248                           <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1249                   </para>
1250         </refsect1>
1251
1252 </refentry>