man/systemd-nspawn.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd-nspawn"
  25           xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27         <refentryinfo>
  28                 <title>systemd-nspawn</title>
  29                 <productname>systemd</productname>
  30
  31                 <authorgroup>
  32                         <author>
  33                                 <contrib>Developer</contrib>
  34                                 <firstname>Lennart</firstname>
  35                                 <surname>Poettering</surname>
  36                                 <email>lennart@poettering.net</email>
  37                         </author>
  38                 </authorgroup>
  39         </refentryinfo>
  40
  41         <refmeta>
  42                 <refentrytitle>systemd-nspawn</refentrytitle>
  43                 <manvolnum>1</manvolnum>
  44         </refmeta>
  45
  46         <refnamediv>
  47                 <refname>systemd-nspawn</refname>
  48                 <refpurpose>Spawn a namespace container for debugging, testing and building</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <cmdsynopsis>
  53                         <command>systemd-nspawn</command>
  54                         <arg choice="opt" rep="repeat">OPTIONS</arg>
  55                         <arg choice="opt"><replaceable>COMMAND</replaceable>
  56                         <arg choice="opt" rep="repeat">ARGS</arg>
  57                         </arg>
  58                 </cmdsynopsis>
  59                 <cmdsynopsis>
  60                         <command>systemd-nspawn</command>
  61                         <arg choice="plain">-b</arg>
  62                         <arg choice="opt" rep="repeat">OPTIONS</arg>
  63                         <arg choice="opt" rep="repeat">ARGS</arg>
  64                 </cmdsynopsis>
  65         </refsynopsisdiv>
  66
  67         <refsect1>
  68                 <title>Description</title>
  69
  70                 <para><command>systemd-nspawn</command> may be used to
  71                 run a command or OS in a light-weight namespace
  72                 container. In many ways it is similar to
  73                 <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  74                 but more powerful since it fully virtualizes the file
  75                 system hierarchy, as well as the process tree, the
  76                 various IPC subsystems and the host and domain
  77                 name.</para>
  78
  79                 <para><command>systemd-nspawn</command> limits access
  80                 to various kernel interfaces in the container to
  81                 read-only, such as <filename>/sys</filename>,
  82                 <filename>/proc/sys</filename> or
  83                 <filename>/sys/fs/selinux</filename>. Network
  84                 interfaces and the system clock may not be changed
  85                 from within the container. Device nodes may not be
  86                 created. The host system cannot be rebooted and kernel
  87                 modules may not be loaded from within the
  88                 container.</para>
  89
  90                 <para>Note that even though these security precautions
  91                 are taken <command>systemd-nspawn</command> is not
  92                 suitable for secure container setups. Many of the
  93                 security features may be circumvented and are hence
  94                 primarily useful to avoid accidental changes to the
  95                 host system from the container. The intended use of
  96                 this program is debugging and testing as well as
  97                 building of packages, distributions and software
  98                 involved with boot and systems management.</para>
  99
 100                 <para>In contrast to
 101                 <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry> <command>systemd-nspawn</command>
 102                 may be used to boot full Linux-based operating systems
 103                 in a container.</para>
 104
 105                 <para>Use a tool like
 106                 <citerefentry project='die-net'><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 107                 <citerefentry project='die-net'><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 108                 or
 109                 <citerefentry project='archlinux'><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 110                 to set up an OS directory tree suitable as file system
 111                 hierarchy for <command>systemd-nspawn</command>
 112                 containers.</para>
 113
 114                 <para>Note that <command>systemd-nspawn</command> will
 115                 mount file systems private to the container to
 116                 <filename>/dev</filename>,
 117                 <filename>/run</filename> and similar. These will
 118                 not be visible outside of the container, and their
 119                 contents will be lost when the container exits.</para>
 120
 121                 <para>Note that running two
 122                 <command>systemd-nspawn</command> containers from the
 123                 same directory tree will not make processes in them
 124                 see each other. The PID namespace separation of the
 125                 two containers is complete and the containers will
 126                 share very few runtime objects except for the
 127                 underlying file system. Use
 128                 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 129                 <command>login</command> command to request an
 130                 additional login prompt in a running container.</para>
 131
 132                 <para><command>systemd-nspawn</command> implements the
 133                 <ulink
 134                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 135                 Interface</ulink> specification.</para>
 136
 137                 <para>As a safety check
 138                 <command>systemd-nspawn</command> will verify the
 139                 existence of <filename>/usr/lib/os-release</filename>
 140                 or <filename>/etc/os-release</filename> in the
 141                 container tree before starting the container (see
 142                 <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>). It
 143                 might be necessary to add this file to the container
 144                 tree manually if the OS of the container is too old to
 145                 contain this file out-of-the-box.</para>
 146         </refsect1>
 147
 148         <refsect1>
 149                 <title>Options</title>
 150
 151                 <para>If option <option>-b</option> is specified, the
 152                 arguments are used as arguments for the init
 153                 binary. Otherwise, <replaceable>COMMAND</replaceable>
 154                 specifies the program to launch in the container, and
 155                 the remaining arguments are used as arguments for this
 156                 program. If <option>-b</option> is not used and no
 157                 arguments are specifed, a shell is launched in the
 158                 container.</para>
 159
 160                 <para>The following options are understood:</para>
 161
 162                 <variablelist>
 163                         <varlistentry>
 164                                 <term><option>-D</option></term>
 165                                 <term><option>--directory=</option></term>
 166
 167                                 <listitem><para>Directory to use as
 168                                 file system root for the container.</para>
 169
 170                                 <para>If neither
 171                                 <option>--directory=</option>, nor
 172                                 <option>--image=</option> is specified
 173                                 the directory is determined as
 174                                 <filename>/var/lib/container/</filename>
 175                                 suffixed by the machine name as
 176                                 specified with
 177                                 <option>--machine=</option>. If
 178                                 neither <option>--directory=</option>,
 179                                 <option>--image=</option>, nor
 180                                 <option>--machine=</option> are
 181                                 specified, the current directory will
 182                                 be used. May not be specified together
 183                                 with
 184                                 <option>--image=</option>.</para></listitem>
 185                         </varlistentry>
 186
 187                         <varlistentry>
 188                                 <term><option>--template=</option></term>
 189
 190                                 <listitem><para>Directory or
 191                                 <literal>btrfs</literal> subvolume to
 192                                 use as template for the container's
 193                                 root directory. If this is specified
 194                                 and the container's root directory (as
 195                                 configured by
 196                                 <option>--directory=</option>) does
 197                                 not yet exist it is created as
 198                                 <literal>btrfs</literal> subvolume and
 199                                 populated from this template
 200                                 tree. Ideally, the specified template
 201                                 path refers to the root of a
 202                                 <literal>btrfs</literal> subvolume, in
 203                                 which case a simple copy-on-write
 204                                 snapshot is taken, and populating the
 205                                 root directory is instant. If the
 206                                 specified template path does not refer
 207                                 to the root of a
 208                                 <literal>btrfs</literal> subvolume (or
 209                                 not even to a <literal>btrfs</literal>
 210                                 file system at all), the tree is
 211                                 copied, which can be substantially
 212                                 more time-consuming. Note that if this
 213                                 option is used the container's root
 214                                 directory (in contrast to the template
 215                                 directory!) must be located on a
 216                                 <literal>btrfs</literal> file system,
 217                                 so that the <literal>btrfs</literal>
 218                                 subvolume may be created. May not be
 219                                 specified together with
 220                                 <option>--image=</option> or
 221                                 <option>--ephemeral</option>.</para></listitem>
 222                         </varlistentry>
 223
 224                         <varlistentry>
 225                                 <term><option>-x</option></term>
 226                                 <term><option>--ephemeral</option></term>
 227
 228                                 <listitem><para>If specified, the
 229                                 container is run with a temporary
 230                                 <literal>btrfs</literal> snapshot of
 231                                 its root directory (as configured with
 232                                 <option>--directory=</option>), that
 233                                 is removed immediately when the
 234                                 container terminates. This option is
 235                                 only supported if the root file system
 236                                 is <literal>btrfs</literal>. May not
 237                                 be specified together with
 238                                 <option>--image=</option> or
 239                                 <option>--template=</option>.</para></listitem>
 240                         </varlistentry>
 241
 242                         <varlistentry>
 243                                 <term><option>-i</option></term>
 244                                 <term><option>--image=</option></term>
 245
 246                                 <listitem><para>Disk image to mount
 247                                 the root directory for the container
 248                                 from. Takes a path to a regular file
 249                                 or to a block device node. The file or
 250                                 block device must contain a GUID
 251                                 Partition Table with a root partition
 252                                 which is mounted as the root directory
 253                                 of the container. Optionally, it may
 254                                 contain a home and/or a server data
 255                                 partition which are mounted to the
 256                                 appropriate places in the
 257                                 container. All these partitions must
 258                                 be identified by the partition types
 259                                 defined by the <ulink
 260                                 url="http://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Discoverable
 261                                 Partitions Specification</ulink>. Any
 262                                 other partitions, such as foreign
 263                                 partitions, swap partitions or EFI
 264                                 system partitions are not mounted. May
 265                                 not be specified together with
 266                                 <option>--directory=</option>,
 267                                 <option>--template=</option> or
 268                                 <option>--ephemeral</option>.</para></listitem>
 269                         </varlistentry>
 270
 271                         <varlistentry>
 272                                 <term><option>-b</option></term>
 273                                 <term><option>--boot</option></term>
 274
 275                                 <listitem><para>Automatically search
 276                                 for an init binary and invoke it
 277                                 instead of a shell or a user supplied
 278                                 program. If this option is used,
 279                                 arguments specified on the command
 280                                 line are used as arguments for the
 281                                 init binary. This option may not be
 282                                 combined with
 283                                 <option>--share-system</option>.
 284                                 </para></listitem>
 285                         </varlistentry>
 286
 287                         <varlistentry>
 288                                 <term><option>-u</option></term>
 289                                 <term><option>--user=</option></term>
 290
 291                                 <listitem><para>After transitioning
 292                                 into the container, change to the
 293                                 specified user-defined in the
 294                                 container's user database. Like all
 295                                 other systemd-nspawn features, this is
 296                                 not a security feature and provides
 297                                 protection against accidental
 298                                 destructive operations
 299                                 only.</para></listitem>
 300                         </varlistentry>
 301
 302                         <varlistentry>
 303                                 <term><option>-M</option></term>
 304                                 <term><option>--machine=</option></term>
 305
 306                                 <listitem><para>Sets the machine name
 307                                 for this container. This name may be
 308                                 used to identify this container during
 309                                 its runtime (for example in tools like
 310                                 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 311                                 and similar), and is used to
 312                                 initialize the container's hostname
 313                                 (which the container can choose to
 314                                 override, however). If not specified,
 315                                 the last component of the root
 316                                 directory path of the container is
 317                                 used, possibly suffixed with a random
 318                                 identifier in case
 319                                 <option>--ephemeral</option> mode is
 320                                 selected. If the root directory
 321                                 selected is the host's root directory
 322                                 the host's hostname is used as default
 323                                 instead.</para></listitem>
 324                         </varlistentry>
 325
 326                         <varlistentry>
 327                                 <term><option>--uuid=</option></term>
 328
 329                                 <listitem><para>Set the specified UUID
 330                                 for the container. The init system
 331                                 will initialize
 332                                 <filename>/etc/machine-id</filename>
 333                                 from this if this file is not set yet.
 334                                 </para></listitem>
 335                         </varlistentry>
 336
 337                         <varlistentry>
 338                                 <term><option>--slice=</option></term>
 339
 340                                 <listitem><para>Make the container
 341                                 part of the specified slice, instead
 342                                 of the default
 343                                 <filename>machine.slice</filename>.</para>
 344                                 </listitem>
 345                         </varlistentry>
 346
 347                         <varlistentry>
 348                                 <term><option>--private-network</option></term>
 349
 350                                 <listitem><para>Disconnect networking
 351                                 of the container from the host. This
 352                                 makes all network interfaces
 353                                 unavailable in the container, with the
 354                                 exception of the loopback device and
 355                                 those specified with
 356                                 <option>--network-interface=</option>
 357                                 and configured with
 358                                 <option>--network-veth</option>. If
 359                                 this option is specified, the
 360                                 CAP_NET_ADMIN capability will be added
 361                                 to the set of capabilities the
 362                                 container retains. The latter may be
 363                                 disabled by using
 364                                 <option>--drop-capability=</option>.</para></listitem>
 365                         </varlistentry>
 366
 367                         <varlistentry>
 368                                 <term><option>--network-interface=</option></term>
 369
 370                                 <listitem><para>Assign the specified
 371                                 network interface to the
 372                                 container. This will remove the
 373                                 specified interface from the calling
 374                                 namespace and place it in the
 375                                 container. When the container
 376                                 terminates, it is moved back to the
 377                                 host namespace. Note that
 378                                 <option>--network-interface=</option>
 379                                 implies
 380                                 <option>--private-network</option>. This
 381                                 option may be used more than once to
 382                                 add multiple network interfaces to the
 383                                 container.</para></listitem>
 384                         </varlistentry>
 385
 386                         <varlistentry>
 387                                 <term><option>--network-macvlan=</option></term>
 388
 389                                 <listitem><para>Create a
 390                                 <literal>macvlan</literal> interface
 391                                 of the specified Ethernet network
 392                                 interface and add it to the
 393                                 container. A
 394                                 <literal>macvlan</literal> interface
 395                                 is a virtual interface that adds a
 396                                 second MAC address to an existing
 397                                 physical Ethernet link. The interface
 398                                 in the container will be named after
 399                                 the interface on the host, prefixed
 400                                 with <literal>mv-</literal>. Note that
 401                                 <option>--network-macvlan=</option>
 402                                 implies
 403                                 <option>--private-network</option>. This
 404                                 option may be used more than once to
 405                                 add multiple network interfaces to the
 406                                 container.</para></listitem>
 407                         </varlistentry>
 408
 409                         <varlistentry>
 410                                 <term><option>--network-veth</option></term>
 411
 412                                 <listitem><para>Create a virtual
 413                                 Ethernet link
 414                                 (<literal>veth</literal>) between host
 415                                 and container. The host side of the
 416                                 Ethernet link will be available as a
 417                                 network interface named after the
 418                                 container's name (as specified with
 419                                 <option>--machine=</option>), prefixed
 420                                 with <literal>ve-</literal>. The
 421                                 container side of the Ethernet
 422                                 link will be named
 423                                 <literal>host0</literal>. Note that
 424                                 <option>--network-veth</option>
 425                                 implies
 426                                 <option>--private-network</option>.</para></listitem>
 427                         </varlistentry>
 428
 429                         <varlistentry>
 430                                 <term><option>--network-bridge=</option></term>
 431
 432                                 <listitem><para>Adds the host side of
 433                                 the Ethernet link created with
 434                                 <option>--network-veth</option> to the
 435                                 specified bridge. Note that
 436                                 <option>--network-bridge=</option>
 437                                 implies
 438                                 <option>--network-veth</option>. If
 439                                 this option is used, the host side of
 440                                 the Ethernet link will use the
 441                                 <literal>vb-</literal> prefix instead
 442                                 of <literal>ve-</literal>.</para></listitem>
 443                         </varlistentry>
 444
 445                         <varlistentry>
 446                                 <term><option>-p</option></term>
 447                                 <term><option>--port=</option></term>
 448
 449                                 <listitem><para>If private networking
 450                                 is enabled, maps an IP port on the
 451                                 host onto an IP port on the
 452                                 container. Takes a protocol specifier
 453                                 (either <literal>tcp</literal> or
 454                                 <literal>udp</literal>), separated by
 455                                 a colon from a host port number in the
 456                                 range 1 to 65535, separated by a colon
 457                                 from a container port number in the
 458                                 range from 1 to 65535. The protocol
 459                                 specifier and its separating colon may
 460                                 be omitted, in which case
 461                                 <literal>tcp</literal> is assumed.
 462                                 The container port number and its
 463                                 colon may be ommitted, in which case
 464                                 the same port as the host port is
 465                                 implied. This option is only supported
 466                                 if private networking is used, such as
 467                                 <option>--network-veth</option> or
 468                                 <option>--network-bridge=</option>.</para></listitem>
 469                         </varlistentry>
 470
 471                         <varlistentry>
 472                                 <term><option>-Z</option></term>
 473                                 <term><option>--selinux-context=</option></term>
 474
 475                                 <listitem><para>Sets the SELinux
 476                                 security context to be used to label
 477                                 processes in the container.</para>
 478                                 </listitem>
 479                         </varlistentry>
 480
 481                         <varlistentry>
 482                                 <term><option>-L</option></term>
 483                                 <term><option>--selinux-apifs-context=</option></term>
 484
 485                                 <listitem><para>Sets the SELinux security
 486                                 context to be used to label files in
 487                                 the virtual API file systems in the
 488                                 container.</para>
 489                                 </listitem>
 490                         </varlistentry>
 491
 492                         <varlistentry>
 493                                 <term><option>--capability=</option></term>
 494
 495                                 <listitem><para>List one or more
 496                                 additional capabilities to grant the
 497                                 container. Takes a comma-separated
 498                                 list of capability names, see
 499                                 <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 500                                 for more information. Note that the
 501                                 following capabilities will be granted
 502                                 in any way: CAP_CHOWN,
 503                                 CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
 504                                 CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER,
 505                                 CAP_KILL, CAP_LEASE,
 506                                 CAP_LINUX_IMMUTABLE,
 507                                 CAP_NET_BIND_SERVICE,
 508                                 CAP_NET_BROADCAST, CAP_NET_RAW,
 509                                 CAP_SETGID, CAP_SETFCAP, CAP_SETPCAP,
 510                                 CAP_SETUID, CAP_SYS_ADMIN,
 511                                 CAP_SYS_CHROOT, CAP_SYS_NICE,
 512                                 CAP_SYS_PTRACE, CAP_SYS_TTY_CONFIG,
 513                                 CAP_SYS_RESOURCE, CAP_SYS_BOOT,
 514                                 CAP_AUDIT_WRITE,
 515                                 CAP_AUDIT_CONTROL. Also CAP_NET_ADMIN
 516                                 is retained if
 517                                 <option>--private-network</option> is
 518                                 specified. If the special value
 519                                 <literal>all</literal> is passed, all
 520                                 capabilities are
 521                                 retained.</para></listitem>
 522                         </varlistentry>
 523
 524                         <varlistentry>
 525                                 <term><option>--drop-capability=</option></term>
 526
 527                                 <listitem><para>Specify one or more
 528                                 additional capabilities to drop for
 529                                 the container. This allows running the
 530                                 container with fewer capabilities than
 531                                 the default (see above).</para></listitem>
 532                         </varlistentry>
 533
 534                         <varlistentry>
 535                                 <term><option>--link-journal=</option></term>
 536
 537                                 <listitem><para>Control whether the
 538                                 container's journal shall be made
 539                                 visible to the host system. If enabled,
 540                                 allows viewing the container's journal
 541                                 files from the host (but not vice
 542                                 versa). Takes one of
 543                                 <literal>no</literal>,
 544                                 <literal>host</literal>,
 545                                 <literal>try-host</literal>,
 546                                 <literal>guest</literal>,
 547                                 <literal>try-guest</literal>,
 548                                 <literal>auto</literal>. If
 549                                 <literal>no</literal>, the journal is
 550                                 not linked. If <literal>host</literal>,
 551                                 the journal files are stored on the
 552                                 host file system (beneath
 553                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
 554                                 and the subdirectory is bind-mounted
 555                                 into the container at the same
 556                                 location. If <literal>guest</literal>,
 557                                 the journal files are stored on the
 558                                 guest file system (beneath
 559                                 <filename>/var/log/journal/<replaceable>machine-id</replaceable></filename>)
 560                                 and the subdirectory is symlinked into the host
 561                                 at the same location. <literal>try-host</literal>
 562                                 and <literal>try-guest</literal> do the same
 563                                 but do not fail if the host does not have
 564                                 persistent journalling enabled.
 565                                 If <literal>auto</literal> (the default),
 566                                 and the right subdirectory of
 567                                 <filename>/var/log/journal</filename>
 568                                 exists, it will be bind mounted
 569                                 into the container. If the
 570                                 subdirectory does not exist, no
 571                                 linking is performed. Effectively,
 572                                 booting a container once with
 573                                 <literal>guest</literal> or
 574                                 <literal>host</literal> will link the
 575                                 journal persistently if further on
 576                                 the default of <literal>auto</literal>
 577                                 is used.</para></listitem>
 578                         </varlistentry>
 579
 580                         <varlistentry>
 581                                 <term><option>-j</option></term>
 582
 583                                 <listitem><para>Equivalent to
 584                                 <option>--link-journal=try-guest</option>.</para></listitem>
 585                         </varlistentry>
 586
 587                         <varlistentry>
 588                                 <term><option>--read-only</option></term>
 589
 590                                 <listitem><para>Mount the root file
 591                                 system read-only for the
 592                                 container.</para></listitem>
 593                         </varlistentry>
 594
 595                         <varlistentry>
 596                                 <term><option>--bind=</option></term>
 597                                 <term><option>--bind-ro=</option></term>
 598
 599                                 <listitem><para>Bind mount a file or
 600                                 directory from the host into the
 601                                 container. Either takes a path
 602                                 argument -- in which case the
 603                                 specified path will be mounted from
 604                                 the host to the same path in the
 605                                 container --, or a colon-separated
 606                                 pair of paths -- in which case the
 607                                 first specified path is the source in
 608                                 the host, and the second path is the
 609                                 destination in the container. The
 610                                 <option>--bind-ro=</option> option
 611                                 creates read-only bind
 612                                 mounts.</para></listitem>
 613                         </varlistentry>
 614
 615                         <varlistentry>
 616                                 <term><option>--tmpfs=</option></term>
 617
 618                                 <listitem><para>Mount a tmpfs file
 619                                 system into the container. Takes a
 620                                 single absolute path argument that
 621                                 specifies where to mount the tmpfs
 622                                 instance to (in which case the
 623                                 directory access mode will be chosen
 624                                 as 0755, owned by root/root), or
 625                                 optionally a colon-separated pair of
 626                                 path and mount option string, that is
 627                                 used for mounting (in which case the
 628                                 kernel default for access mode and
 629                                 owner will be chosen, unless otherwise
 630                                 specified). This option is
 631                                 particularly useful for mounting
 632                                 directories such as
 633                                 <filename>/var</filename> as tmpfs, to
 634                                 allow state-less systems, in
 635                                 particular when combined with
 636                                 <option>--read-only</option>.</para></listitem>
 637                         </varlistentry>
 638
 639                         <varlistentry>
 640                                 <term><option>--setenv=</option></term>
 641
 642                                 <listitem><para>Specifies an
 643                                 environment variable assignment to
 644                                 pass to the init process in the
 645                                 container, in the format
 646                                 <literal>NAME=VALUE</literal>. This
 647                                 may be used to override the default
 648                                 variables or to set additional
 649                                 variables. This parameter may be used
 650                                 more than once.</para></listitem>
 651                         </varlistentry>
 652
 653                         <varlistentry>
 654                                 <term><option>--share-system</option></term>
 655
 656                                 <listitem><para>Allows the container
 657                                 to share certain system facilities
 658                                 with the host. More specifically, this
 659                                 turns off PID namespacing, UTS
 660                                 namespacing and IPC namespacing, and
 661                                 thus allows the guest to see and
 662                                 interact more easily with processes
 663                                 outside of the container. Note that
 664                                 using this option makes it impossible
 665                                 to start up a full Operating System in
 666                                 the container, as an init system
 667                                 cannot operate in this mode. It is
 668                                 only useful to run specific programs
 669                                 or applications this way, without
 670                                 involving an init system in the
 671                                 container. This option implies
 672                                 <option>--register=no</option>. This
 673                                 option may not be combined with
 674                                 <option>--boot</option>.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><option>--register=</option></term>
 679
 680                                 <listitem><para>Controls whether the
 681                                 container is registered with
 682                                 <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes
 683                                 a boolean argument, defaults to
 684                                 <literal>yes</literal>. This option
 685                                 should be enabled when the container
 686                                 runs a full Operating System (more
 687                                 specifically: an init system), and is
 688                                 useful to ensure that the container is
 689                                 accessible via
 690                                 <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 691                                 and shown by tools such as
 692                                 <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>. If
 693                                 the container does not run an init
 694                                 system, it is recommended to set this
 695                                 option to <literal>no</literal>. Note
 696                                 that <option>--share-system</option>
 697                                 implies
 698                                 <option>--register=no</option>.
 699                                 </para></listitem>
 700                         </varlistentry>
 701
 702                         <varlistentry>
 703                                 <term><option>--keep-unit</option></term>
 704
 705                                 <listitem><para>Instead of creating a
 706                                 transient scope unit to run the
 707                                 container in, simply register the
 708                                 service or scope unit
 709                                 <command>systemd-nspawn</command> has
 710                                 been invoked in with
 711                                 <citerefentry><refentrytitle>systemd-machined</refentrytitle><manvolnum>8</manvolnum></citerefentry>. This
 712                                 has no effect if
 713                                 <option>--register=no</option> is
 714                                 used. This switch should be used if
 715                                 <command>systemd-nspawn</command> is
 716                                 invoked from within a service unit,
 717                                 and the service unit's sole purpose
 718                                 is to run a single
 719                                 <command>systemd-nspawn</command>
 720                                 container. This option is not
 721                                 available if run from a user
 722                                 session.</para></listitem>
 723                         </varlistentry>
 724
 725                         <varlistentry>
 726                                 <term><option>--personality=</option></term>
 727
 728                                 <listitem><para>Control the
 729                                 architecture ("personality") reported
 730                                 by
 731                                 <citerefentry><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 732                                 in the container. Currently, only
 733                                 <literal>x86</literal> and
 734                                 <literal>x86-64</literal> are
 735                                 supported. This is useful when running
 736                                 a 32-bit container on a 64-bit
 737                                 host. If this setting is not used,
 738                                 the personality reported in the
 739                                 container is the same as the one
 740                                 reported on the
 741                                 host.</para></listitem>
 742                         </varlistentry>
 743
 744                         <varlistentry>
 745                                 <term><option>-q</option></term>
 746                                 <term><option>--quiet</option></term>
 747
 748                                 <listitem><para>Turns off any status
 749                                 output by the tool itself. When this
 750                                 switch is used, the only output
 751                                 from nspawn will be the console output
 752                                 of the container OS itself.</para></listitem>
 753                         </varlistentry>
 754
 755                         <varlistentry>
 756                                 <term><option>--volatile</option><replaceable>=MODE</replaceable></term>
 757
 758                                 <listitem><para>Boots the container in
 759                                 volatile mode. When no mode parameter
 760                                 is passed or when mode is specified as
 761                                 <literal>yes</literal> full volatile
 762                                 mode is enabled. This means the root
 763                                 directory is mounted as mostly
 764                                 unpopulated <literal>tmpfs</literal>
 765                                 instance, and
 766                                 <filename>/usr</filename> from the OS
 767                                 tree is mounted into it, read-only
 768                                 (the system thus starts up with
 769                                 read-only OS resources, but pristine
 770                                 state and configuration, any changes
 771                                 to the either are lost on
 772                                 shutdown). When the mode parameter is
 773                                 specified as <literal>state</literal>
 774                                 the OS tree is mounted read-only, but
 775                                 <filename>/var</filename> is mounted
 776                                 as <literal>tmpfs</literal> instance
 777                                 into it (the system thus starts up
 778                                 with read-only OS resources and
 779                                 configuration, but pristine state, any
 780                                 changes to the latter are lost on
 781                                 shutdown). When the mode parameter is
 782                                 specified as <literal>no</literal>
 783                                 (the default) the whole OS tree is
 784                                 made available writable.</para>
 785
 786                                 <para>Note that setting this to
 787                                 <literal>yes</literal> or
 788                                 <literal>state</literal> will only
 789                                 work correctly with operating systems
 790                                 in the container that can boot up with
 791                                 only <filename>/usr</filename>
 792                                 mounted, and are able to populate
 793                                 <filename>/var</filename>
 794                                 automatically, as
 795                                 needed.</para></listitem>
 796                         </varlistentry>
 797
 798                         <xi:include href="standard-options.xml" xpointer="help" />
 799                         <xi:include href="standard-options.xml" xpointer="version" />
 800                 </variablelist>
 801
 802         </refsect1>
 803
 804         <refsect1>
 805                 <title>Examples</title>
 806                 <example>
 807                         <title>Boot a minimal Fedora distribution in a container</title>
 808
 809                         <programlisting># yum -y --releasever=21 --nogpg --installroot=/srv/mycontainer --disablerepo='*' --enablerepo=fedora install systemd passwd yum fedora-release vim-minimal
 810 # systemd-nspawn -bD /srv/mycontainer</programlisting>
 811
 812                         <para>This installs a minimal Fedora distribution into
 813                         the directory <filename noindex='true'>/srv/mycontainer/</filename> and
 814                         then boots an OS in a namespace container in
 815                         it.</para>
 816                 </example>
 817
 818                 <example>
 819                         <title>Spawn a shell in a container of a minimal Debian unstable distribution</title>
 820
 821                         <programlisting># debootstrap --arch=amd64 unstable ~/debian-tree/
 822 # systemd-nspawn -D ~/debian-tree/</programlisting>
 823
 824                         <para>This installs a minimal Debian unstable
 825                         distribution into the directory
 826                         <filename>~/debian-tree/</filename> and then spawns a
 827                         shell in a namespace container in it.</para>
 828                 </example>
 829
 830                 <example>
 831                         <title>Boot a minimal Arch Linux distribution in a container</title>
 832
 833                         <programlisting># pacstrap -c -d ~/arch-tree/ base
 834 # systemd-nspawn -bD ~/arch-tree/</programlisting>
 835
 836                         <para>This installs a mimimal Arch Linux distribution into
 837                         the directory <filename>~/arch-tree/</filename> and then
 838                         boots an OS in a namespace container in it.</para>
 839                 </example>
 840
 841                 <example>
 842                         <title>Enable Arch Linux container on boot</title>
 843
 844                         <programlisting># mv ~/arch-tree /var/lib/container/arch
 845 # systemctl enable systemd-nspawn@arch.service
 846 # systemctl start systemd-nspawn@arch.service</programlisting>
 847
 848                         <para>This makes the Arch Linux container part of the
 849                         <filename>multi-user.target</filename> on the host.
 850                         </para>
 851                 </example>
 852
 853                 <example>
 854                         <title>Boot into an ephemeral <literal>btrfs</literal> snapshot of the host system</title>
 855
 856                         <programlisting># systemd-nspawn -D / -xb</programlisting>
 857
 858                         <para>This runs a copy of the host system in a
 859                         <literal>btrfs</literal> snapshot which is
 860                         removed immediately when the container
 861                         exits. All file system changes made during
 862                         runtime will be lost on shutdown,
 863                         hence.</para>
 864                 </example>
 865
 866                 <example>
 867                         <title>Run a container with SELinux sandbox security contexts</title>
 868
 869                         <programlisting># chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
 870 # systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh</programlisting>
 871                 </example>
 872         </refsect1>
 873
 874         <refsect1>
 875                 <title>Exit status</title>
 876
 877                 <para>The exit code of the program executed in the
 878                 container is returned.</para>
 879         </refsect1>
 880
 881         <refsect1>
 882                 <title>See Also</title>
 883                 <para>
 884                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 885                         <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 886                         <citerefentry project='die-net'><refentrytitle>yum</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 887                         <citerefentry project='die-net'><refentrytitle>debootstrap</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 888                         <citerefentry project='archlinux'><refentrytitle>pacman</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 889                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 890                         <citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 891                         <citerefentry><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 892                 </para>
 893         </refsect1>
 894
 895 </refentry>