1SYSTEMD-NSPAWN(1)               systemd-nspawn               SYSTEMD-NSPAWN(1)
2
3
4

NAME

6       systemd-nspawn - Spawn a command or OS in a light-weight container
7

SYNOPSIS

9       systemd-nspawn [OPTIONS...] [COMMAND [ARGS...]]
10
11       systemd-nspawn --boot [OPTIONS...] [ARGS...]
12

DESCRIPTION

14       systemd-nspawn may be used to run a command or OS in a light-weight
15       namespace container. In many ways it is similar to chroot(1), but more
16       powerful since it fully virtualizes the file system hierarchy, as well
17       as the process tree, the various IPC subsystems and the host and domain
18       name.
19
20       systemd-nspawn may be invoked on any directory tree containing an
21       operating system tree, using the --directory= command line option. By
22       using the --machine= option an OS tree is automatically searched for in
23       a couple of locations, most importantly in /var/lib/machines/, the
24       suggested directory to place OS container images installed on the
25       system.
26
27       In contrast to chroot(1) systemd-nspawn may be used to boot full
28       Linux-based operating systems in a container.
29
30       systemd-nspawn limits access to various kernel interfaces in the
31       container to read-only, such as /sys/, /proc/sys/ or /sys/fs/selinux/.
32       The host's network interfaces and the system clock may not be changed
33       from within the container. Device nodes may not be created. The host
34       system cannot be rebooted and kernel modules may not be loaded from
35       within the container.
36
37       Use a tool like dnf(8), debootstrap(8), or pacman(8) to set up an OS
38       directory tree suitable as file system hierarchy for systemd-nspawn
39       containers. See the Examples section below for details on suitable
40       invocation of these commands.
41
42       As a safety check systemd-nspawn will verify the existence of
43       /usr/lib/os-release or /etc/os-release in the container tree before
44       starting the container (see os-release(5)). It might be necessary to
45       add this file to the container tree manually if the OS of the container
46       is too old to contain this file out-of-the-box.
47
48       systemd-nspawn may be invoked directly from the interactive command
49       line or run as system service in the background. In this mode each
50       container instance runs as its own service instance; a default template
51       unit file systemd-nspawn@.service is provided to make this easy, taking
52       the container name as instance identifier. Note that different default
53       options apply when systemd-nspawn is invoked by the template unit file
54       than interactively on the command line. Most importantly the template
55       unit file makes use of the --boot which is not the default in case
56       systemd-nspawn is invoked from the interactive command line. Further
57       differences with the defaults are documented along with the various
58       supported options below.
59
60       The machinectl(1) tool may be used to execute a number of operations on
61       containers. In particular it provides easy-to-use commands to run
62       containers as system services using the systemd-nspawn@.service
63       template unit file.
64
65       Along with each container a settings file with the .nspawn suffix may
66       exist, containing additional settings to apply when running the
67       container. See systemd.nspawn(5) for details. Settings files override
68       the default options used by the systemd-nspawn@.service template unit
69       file, making it usually unnecessary to alter this template file
70       directly.
71
72       Note that systemd-nspawn will mount file systems private to the
73       container to /dev/, /run/ and similar. These will not be visible
74       outside of the container, and their contents will be lost when the
75       container exits.
76
77       Note that running two systemd-nspawn containers from the same directory
78       tree will not make processes in them see each other. The PID namespace
79       separation of the two containers is complete and the containers will
80       share very few runtime objects except for the underlying file system.
81       Use machinectl(1)'s login or shell commands to request an additional
82       login session in a running container.
83
84       systemd-nspawn implements the Container Interface[1] specification.
85
86       While running, containers invoked with systemd-nspawn are registered
87       with the systemd-machined(8) service that keeps track of running
88       containers, and provides programming interfaces to interact with them.
89

OPTIONS

91       If option -b is specified, the arguments are used as arguments for the
92       init program. Otherwise, COMMAND specifies the program to launch in the
93       container, and the remaining arguments are used as arguments for this
94       program. If --boot is not used and no arguments are specified, a shell
95       is launched in the container.
96
97       The following options are understood:
98
99       -q, --quiet
100           Turns off any status output by the tool itself. When this switch is
101           used, the only output from nspawn will be the console output of the
102           container OS itself.
103
104       --settings=MODE
105           Controls whether systemd-nspawn shall search for and use additional
106           per-container settings from .nspawn files. Takes a boolean or the
107           special values override or trusted.
108
109           If enabled (the default), a settings file named after the machine
110           (as specified with the --machine= setting, or derived from the
111           directory or image file name) with the suffix .nspawn is searched
112           in /etc/systemd/nspawn/ and /run/systemd/nspawn/. If it is found
113           there, its settings are read and used. If it is not found there, it
114           is subsequently searched in the same directory as the image file or
115           in the immediate parent of the root directory of the container. In
116           this case, if the file is found, its settings will be also read and
117           used, but potentially unsafe settings are ignored. Note that in
118           both these cases, settings on the command line take precedence over
119           the corresponding settings from loaded .nspawn files, if both are
120           specified. Unsafe settings are considered all settings that elevate
121           the container's privileges or grant access to additional resources
122           such as files or directories of the host. For details about the
123           format and contents of .nspawn files, consult systemd.nspawn(5).
124
125           If this option is set to override, the file is searched, read and
126           used the same way, however, the order of precedence is reversed:
127           settings read from the .nspawn file will take precedence over the
128           corresponding command line options, if both are specified.
129
130           If this option is set to trusted, the file is searched, read and
131           used the same way, but regardless of being found in
132           /etc/systemd/nspawn/, /run/systemd/nspawn/ or next to the image
133           file or container root directory, all settings will take effect,
134           however, command line arguments still take precedence over
135           corresponding settings.
136
137           If disabled, no .nspawn file is read and no settings except the
138           ones on the command line are in effect.
139
140   Image Options
141       -D, --directory=
142           Directory to use as file system root for the container.
143
144           If neither --directory=, nor --image= is specified the directory is
145           determined by searching for a directory named the same as the
146           machine name specified with --machine=. See machinectl(1) section
147           "Files and Directories" for the precise search path.
148
149           If neither --directory=, --image=, nor --machine= are specified,
150           the current directory will be used. May not be specified together
151           with --image=.
152
153       --template=
154           Directory or "btrfs" subvolume to use as template for the
155           container's root directory. If this is specified and the
156           container's root directory (as configured by --directory=) does not
157           yet exist it is created as "btrfs" snapshot (if supported) or plain
158           directory (otherwise) and populated from this template tree.
159           Ideally, the specified template path refers to the root of a
160           "btrfs" subvolume, in which case a simple copy-on-write snapshot is
161           taken, and populating the root directory is instant. If the
162           specified template path does not refer to the root of a "btrfs"
163           subvolume (or not even to a "btrfs" file system at all), the tree
164           is copied (though possibly in a 'reflink' copy-on-write scheme — if
165           the file system supports that), which can be substantially more
166           time-consuming. Note that the snapshot taken is of the specified
167           directory or subvolume, including all subdirectories and subvolumes
168           below it, but excluding any sub-mounts. May not be specified
169           together with --image= or --ephemeral.
170
171           Note that this switch leaves hostname, machine ID and all other
172           settings that could identify the instance unmodified.
173
174       -x, --ephemeral
175           If specified, the container is run with a temporary snapshot of its
176           file system that is removed immediately when the container
177           terminates. May not be specified together with --template=.
178
179           Note that this switch leaves hostname, machine ID and all other
180           settings that could identify the instance unmodified. Please note
181           that — as with --template= — taking the temporary snapshot is more
182           efficient on file systems that support subvolume snapshots or
183           'reflinks' natively ("btrfs" or new "xfs") than on more traditional
184           file systems that do not ("ext4"). Note that the snapshot taken is
185           of the specified directory or subvolume, including all
186           subdirectories and subvolumes below it, but excluding any
187           sub-mounts.
188
189           With this option no modifications of the container image are
190           retained. Use --volatile= (described below) for other mechanisms to
191           restrict persistency of container images during runtime.
192
193       -i, --image=
194           Disk image to mount the root directory for the container from.
195           Takes a path to a regular file or to a block device node. The file
196           or block device must contain either:
197
198           •   An MBR partition table with a single partition of type 0x83
199               that is marked bootable.
200
201           •   A GUID partition table (GPT) with a single partition of type
202               0fc63daf-8483-4772-8e79-3d69d8477de4.
203
204           •   A GUID partition table (GPT) with a marked root partition which
205               is mounted as the root directory of the container. Optionally,
206               GPT images may contain a home and/or a server data partition
207               which are mounted to the appropriate places in the container.
208               All these partitions must be identified by the partition types
209               defined by the Discoverable Partitions Specification[2].
210
211           •   No partition table, and a single file system spanning the whole
212               image.
213
214           On GPT images, if an EFI System Partition (ESP) is discovered, it
215           is automatically mounted to /efi (or /boot as fallback) in case a
216           directory by this name exists and is empty.
217
218           Partitions encrypted with LUKS are automatically decrypted. Also,
219           on GPT images dm-verity data integrity hash partitions are set up
220           if the root hash for them is specified using the --root-hash=
221           option.
222
223           Single file system images (i.e. file systems without a surrounding
224           partition table) can be opened using dm-verity if the integrity
225           data is passed using the --root-hash= and --verity-data= (and
226           optionally --root-hash-sig=) options.
227
228           Any other partitions, such as foreign partitions or swap partitions
229           are not mounted. May not be specified together with --directory=,
230           --template=.
231
232       --oci-bundle=
233           Takes the path to an OCI runtime bundle to invoke, as specified in
234           the OCI Runtime Specification[3]. In this case no .nspawn file is
235           loaded, and the root directory and various settings are read from
236           the OCI runtime JSON data (but data passed on the command line
237           takes precedence).
238
239       --read-only
240           Mount the container's root file system (and any other file systems
241           container in the container image) read-only. This has no effect on
242           additional mounts made with --bind=, --tmpfs= and similar options.
243           This mode is implied if the container image file or directory is
244           marked read-only itself. It is also implied if --volatile= is used.
245           In this case the container image on disk is strictly read-only,
246           while changes are permitted but kept non-persistently in memory
247           only. For further details, see below.
248
249       --volatile, --volatile=MODE
250           Boots the container in volatile mode. When no mode parameter is
251           passed or when mode is specified as yes, full volatile mode is
252           enabled. This means the root directory is mounted as a mostly
253           unpopulated "tmpfs" instance, and /usr/ from the OS tree is mounted
254           into it in read-only mode (the system thus starts up with read-only
255           OS image, but pristine state and configuration, any changes are
256           lost on shutdown). When the mode parameter is specified as state,
257           the OS tree is mounted read-only, but /var/ is mounted as a
258           writable "tmpfs" instance into it (the system thus starts up with
259           read-only OS resources and configuration, but pristine state, and
260           any changes to the latter are lost on shutdown). When the mode
261           parameter is specified as overlay the read-only root file system is
262           combined with a writable tmpfs instance through "overlayfs", so
263           that it appears at it normally would, but any changes are applied
264           to the temporary file system only and lost when the container is
265           terminated. When the mode parameter is specified as no (the
266           default), the whole OS tree is made available writable (unless
267           --read-only is specified, see above).
268
269           Note that if one of the volatile modes is chosen, its effect is
270           limited to the root file system (or /var/ in case of state), and
271           any other mounts placed in the hierarchy are unaffected —
272           regardless if they are established automatically (e.g. the EFI
273           system partition that might be mounted to /efi/ or /boot/) or
274           explicitly (e.g. through an additional command line option such as
275           --bind=, see below). This means, even if --volatile=overlay is used
276           changes to /efi/ or /boot/ are prohibited in case such a partition
277           exists in the container image operated on, and even if
278           --volatile=state is used the hypothetical file /etc/foobar is
279           potentially writable if --bind=/etc/foobar if used to mount it from
280           outside the read-only container /etc/ directory.
281
282           The --ephemeral option is closely related to this setting, and
283           provides similar behaviour by making a temporary, ephemeral copy of
284           the whole OS image and executing that. For further details, see
285           above.
286
287           The --tmpfs= and --overlay= options provide similar functionality,
288           but for specific sub-directories of the OS image only. For details,
289           see below.
290
291           This option provides similar functionality for containers as the
292           "systemd.volatile=" kernel command line switch provides for host
293           systems. See kernel-command-line(7) for details.
294
295           Note that setting this option to yes or state will only work
296           correctly with operating systems in the container that can boot up
297           with only /usr/ mounted, and are able to automatically populate
298           /var/ (and /etc/ in case of "--volatile=yes"). Specifically, this
299           means that operating systems that follow the historic split of
300           /bin/ and /lib/ (and related directories) from /usr/ (i.e. where
301           the former are not symlinks into the latter) are not supported by
302           "--volatile=yes" as container payload. The overlay option does not
303           require any particular preparations in the OS, but do note that
304           "overlayfs" behaviour differs from regular file systems in a number
305           of ways, and hence compatibility is limited.
306
307       --root-hash=
308           Takes a data integrity (dm-verity) root hash specified in
309           hexadecimal. This option enables data integrity checks using
310           dm-verity, if the used image contains the appropriate integrity
311           data (see above). The specified hash must match the root hash of
312           integrity data, and is usually at least 256 bits (and hence 64
313           formatted hexadecimal characters) long (in case of SHA256 for
314           example). If this option is not specified, but the image file
315           carries the "user.verity.roothash" extended file attribute (see
316           xattr(7)), then the root hash is read from it, also as formatted
317           hexadecimal characters. If the extended file attribute is not found
318           (or is not supported by the underlying file system), but a file
319           with the .roothash suffix is found next to the image file, bearing
320           otherwise the same name (except if the image has the .raw suffix,
321           in which case the root hash file must not have it in its name), the
322           root hash is read from it and automatically used, also as formatted
323           hexadecimal characters.
324
325           Note that this configures the root hash for the root file system.
326           Disk images may also contain separate file systems for the /usr/
327           hierarchy, which may be Verity protected as well. The root hash for
328           this protection may be configured via the "user.verity.usrhash"
329           extended file attribute or via a .usrhash file adjacent to the disk
330           image, following the same format and logic as for the root hash for
331           the root file system described here. Note that there's currently no
332           switch to configure the root hash for the /usr/ from the command
333           line.
334
335           Also see the RootHash= option in systemd.exec(5).
336
337       --root-hash-sig=
338           Takes a PKCS7 signature of the --root-hash= option. The semantics
339           are the same as for the RootHashSignature= option, see
340           systemd.exec(5).
341
342       --verity-data=
343           Takes the path to a data integrity (dm-verity) file. This option
344           enables data integrity checks using dm-verity, if a root-hash is
345           passed and if the used image itself does not contains the integrity
346           data. The integrity data must be matched by the root hash. If this
347           option is not specified, but a file with the .verity suffix is
348           found next to the image file, bearing otherwise the same name
349           (except if the image has the .raw suffix, in which case the verity
350           data file must not have it in its name), the verity data is read
351           from it and automatically used.
352
353       --pivot-root=
354           Pivot the specified directory to / inside the container, and either
355           unmount the container's old root, or pivot it to another specified
356           directory. Takes one of: a path argument — in which case the
357           specified path will be pivoted to / and the old root will be
358           unmounted; or a colon-separated pair of new root path and pivot
359           destination for the old root. The new root path will be pivoted to
360           /, and the old / will be pivoted to the other directory. Both paths
361           must be absolute, and are resolved in the container's file system
362           namespace.
363
364           This is for containers which have several bootable directories in
365           them; for example, several OSTree[4] deployments. It emulates the
366           behavior of the boot loader and initial RAM disk which normally
367           select which directory to mount as the root and start the
368           container's PID 1 in.
369
370   Execution Options
371       -a, --as-pid2
372           Invoke the shell or specified program as process ID (PID) 2 instead
373           of PID 1 (init). By default, if neither this option nor --boot is
374           used, the selected program is run as the process with PID 1, a mode
375           only suitable for programs that are aware of the special semantics
376           that the process with PID 1 has on UNIX. For example, it needs to
377           reap all processes reparented to it, and should implement sysvinit
378           compatible signal handling (specifically: it needs to reboot on
379           SIGINT, reexecute on SIGTERM, reload configuration on SIGHUP, and
380           so on). With --as-pid2 a minimal stub init process is run as PID 1
381           and the selected program is executed as PID 2 (and hence does not
382           need to implement any special semantics). The stub init process
383           will reap processes as necessary and react appropriately to
384           signals. It is recommended to use this mode to invoke arbitrary
385           commands in containers, unless they have been modified to run
386           correctly as PID 1. Or in other words: this switch should be used
387           for pretty much all commands, except when the command refers to an
388           init or shell implementation, as these are generally capable of
389           running correctly as PID 1. This option may not be combined with
390           --boot.
391
392       -b, --boot
393           Automatically search for an init program and invoke it as PID 1,
394           instead of a shell or a user supplied program. If this option is
395           used, arguments specified on the command line are used as arguments
396           for the init program. This option may not be combined with
397           --as-pid2.
398
399           The following table explains the different modes of invocation and
400           relationship to --as-pid2 (see above):
401
402           Table 1. Invocation Mode
403           ┌──────────────────────┬────────────────────────────┐
404Switch                Explanation                
405           ├──────────────────────┼────────────────────────────┤
406           │Neither --as-pid2 nor │ The passed parameters are  │
407--boot specified      │ interpreted as the command │
408           │                      │ line, which is executed as │
409           │                      │ PID 1 in the container.    │
410           ├──────────────────────┼────────────────────────────┤
411--as-pid2 specified   │ The passed parameters are  │
412           │                      │ interpreted as the command │
413           │                      │ line, which is executed as │
414           │                      │ PID 2 in the container. A  │
415           │                      │ stub init process is run   │
416           │                      │ as PID 1.                  │
417           ├──────────────────────┼────────────────────────────┤
418--boot specified      │ An init program is         │
419           │                      │ automatically searched for │
420           │                      │ and run as PID 1 in the    │
421           │                      │ container. The passed      │
422           │                      │ parameters are used as     │
423           │                      │ invocation parameters for  │
424           │                      │ this process.              │
425           └──────────────────────┴────────────────────────────┘
426           Note that --boot is the default mode of operation if the
427           systemd-nspawn@.service template unit file is used.
428
429       --chdir=
430           Change to the specified working directory before invoking the
431           process in the container. Expects an absolute path in the
432           container's file system namespace.
433
434       -E NAME=VALUE, --setenv=NAME=VALUE
435           Specifies an environment variable assignment to pass to the init
436           process in the container, in the format "NAME=VALUE". This may be
437           used to override the default variables or to set additional
438           variables. This parameter may be used more than once.
439
440       -u, --user=
441           After transitioning into the container, change to the specified
442           user defined in the container's user database. Like all other
443           systemd-nspawn features, this is not a security feature and
444           provides protection against accidental destructive operations only.
445
446       --kill-signal=
447           Specify the process signal to send to the container's PID 1 when
448           nspawn itself receives SIGTERM, in order to trigger an orderly
449           shutdown of the container. Defaults to SIGRTMIN+3 if --boot is used
450           (on systemd-compatible init systems SIGRTMIN+3 triggers an orderly
451           shutdown). If --boot is not used and this option is not specified
452           the container's processes are terminated abruptly via SIGKILL. For
453           a list of valid signals, see signal(7).
454
455       --notify-ready=
456           Configures support for notifications from the container's init
457           process.  --notify-ready= takes a boolean (no and yes). With option
458           no systemd-nspawn notifies systemd with a "READY=1" message when
459           the init process is created. With option yes systemd-nspawn waits
460           for the "READY=1" message from the init process in the container
461           before sending its own to systemd. For more details about
462           notifications see sd_notify(3).
463
464   System Identity Options
465       -M, --machine=
466           Sets the machine name for this container. This name may be used to
467           identify this container during its runtime (for example in tools
468           like machinectl(1) and similar), and is used to initialize the
469           container's hostname (which the container can choose to override,
470           however). If not specified, the last component of the root
471           directory path of the container is used, possibly suffixed with a
472           random identifier in case --ephemeral mode is selected. If the root
473           directory selected is the host's root directory the host's hostname
474           is used as default instead.
475
476       --hostname=
477           Controls the hostname to set within the container, if different
478           from the machine name. Expects a valid hostname as argument. If
479           this option is used, the kernel hostname of the container will be
480           set to this value, otherwise it will be initialized to the machine
481           name as controlled by the --machine= option described above. The
482           machine name is used for various aspect of identification of the
483           container from the outside, the kernel hostname configurable with
484           this option is useful for the container to identify itself from the
485           inside. It is usually a good idea to keep both forms of
486           identification synchronized, in order to avoid confusion. It is
487           hence recommended to avoid usage of this option, and use --machine=
488           exclusively. Note that regardless whether the container's hostname
489           is initialized from the name set with --hostname= or the one set
490           with --machine=, the container can later override its kernel
491           hostname freely on its own as well.
492
493       --uuid=
494           Set the specified UUID for the container. The init system will
495           initialize /etc/machine-id from this if this file is not set yet.
496           Note that this option takes effect only if /etc/machine-id in the
497           container is unpopulated.
498
499   Property Options
500       -S, --slice=
501           Make the container part of the specified slice, instead of the
502           default machine.slice. This applies only if the machine is run in
503           its own scope unit, i.e. if --keep-unit isn't used.
504
505       --property=
506           Set a unit property on the scope unit to register for the machine.
507           This applies only if the machine is run in its own scope unit, i.e.
508           if --keep-unit isn't used. Takes unit property assignments in the
509           same format as systemctl set-property. This is useful to set memory
510           limits and similar for container.
511
512       --register=
513           Controls whether the container is registered with systemd-
514           machined(8). Takes a boolean argument, which defaults to "yes".
515           This option should be enabled when the container runs a full
516           Operating System (more specifically: a system and service manager
517           as PID 1), and is useful to ensure that the container is accessible
518           via machinectl(1) and shown by tools such as ps(1). If the
519           container does not run a service manager, it is recommended to set
520           this option to "no".
521
522       --keep-unit
523           Instead of creating a transient scope unit to run the container in,
524           simply use the service or scope unit systemd-nspawn has been
525           invoked in. If --register=yes is set this unit is registered with
526           systemd-machined(8). This switch should be used if systemd-nspawn
527           is invoked from within a service unit, and the service unit's sole
528           purpose is to run a single systemd-nspawn container. This option is
529           not available if run from a user session.
530
531           Note that passing --keep-unit disables the effect of --slice= and
532           --property=. Use --keep-unit and --register=no in combination to
533           disable any kind of unit allocation or registration with
534           systemd-machined.
535
536   User Namespacing Options
537       --private-users=
538           Controls user namespacing. If enabled, the container will run with
539           its own private set of UNIX user and group ids (UIDs and GIDs).
540           This involves mapping the private UIDs/GIDs used in the container
541           (starting with the container's root user 0 and up) to a range of
542           UIDs/GIDs on the host that are not used for other purposes (usually
543           in the range beyond the host's UID/GID 65536). The parameter may be
544           specified as follows:
545
546            1. If one or two colon-separated numbers are specified, user
547               namespacing is turned on. The first parameter specifies the
548               first host UID/GID to assign to the container, the second
549               parameter specifies the number of host UIDs/GIDs to assign to
550               the container. If the second parameter is omitted, 65536
551               UIDs/GIDs are assigned.
552
553            2. If the parameter is omitted, or true, user namespacing is
554               turned on. The UID/GID range to use is determined automatically
555               from the file ownership of the root directory of the
556               container's directory tree. To use this option, make sure to
557               prepare the directory tree in advance, and ensure that all
558               files and directories in it are owned by UIDs/GIDs in the range
559               you'd like to use. Also, make sure that used file ACLs
560               exclusively reference UIDs/GIDs in the appropriate range. If
561               this mode is used the number of UIDs/GIDs assigned to the
562               container for use is 65536, and the UID/GID of the root
563               directory must be a multiple of 65536.
564
565            3. If the parameter is false, user namespacing is turned off. This
566               is the default.
567
568            4. The special value "pick" turns on user namespacing. In this
569               case the UID/GID range is automatically chosen. As first step,
570               the file owner of the root directory of the container's
571               directory tree is read, and it is checked that it is currently
572               not used by the system otherwise (in particular, that no other
573               container is using it). If this check is successful, the
574               UID/GID range determined this way is used, similar to the
575               behavior if "yes" is specified. If the check is not successful
576               (and thus the UID/GID range indicated in the root directory's
577               file owner is already used elsewhere) a new – currently unused
578               – UID/GID range of 65536 UIDs/GIDs is randomly chosen between
579               the host UID/GIDs of 524288 and 1878982656, always starting at
580               a multiple of 65536, and, if possible, consistently hashed from
581               the machine name. This setting implies --private-users-chown
582               (see below), which has the effect that the files and
583               directories in the container's directory tree will be owned by
584               the appropriate users of the range picked. Using this option
585               makes user namespace behavior fully automatic. Note that the
586               first invocation of a previously unused container image might
587               result in picking a new UID/GID range for it, and thus in the
588               (possibly expensive) file ownership adjustment operation.
589               However, subsequent invocations of the container will be cheap
590               (unless of course the picked UID/GID range is assigned to a
591               different use by then).
592
593           It is recommended to assign at least 65536 UIDs/GIDs to each
594           container, so that the usable UID/GID range in the container covers
595           16 bit. For best security, do not assign overlapping UID/GID ranges
596           to multiple containers. It is hence a good idea to use the upper 16
597           bit of the host 32-bit UIDs/GIDs as container identifier, while the
598           lower 16 bit encode the container UID/GID used. This is in fact the
599           behavior enforced by the --private-users=pick option.
600
601           When user namespaces are used, the GID range assigned to each
602           container is always chosen identical to the UID range.
603
604           In most cases, using --private-users=pick is the recommended option
605           as it enhances container security massively and operates fully
606           automatically in most cases.
607
608           Note that the picked UID/GID range is not written to /etc/passwd or
609           /etc/group. In fact, the allocation of the range is not stored
610           persistently anywhere, except in the file ownership of the files
611           and directories of the container.
612
613           Note that when user namespacing is used file ownership on disk
614           reflects this, and all of the container's files and directories are
615           owned by the container's effective user and group IDs. This means
616           that copying files from and to the container image requires
617           correction of the numeric UID/GID values, according to the UID/GID
618           shift applied.
619
620       --private-users-chown
621           If specified, all files and directories in the container's
622           directory tree will be adjusted so that they are owned by the
623           appropriate UIDs/GIDs selected for the container (see above). This
624           operation is potentially expensive, as it involves iterating
625           through the full directory tree of the container. Besides actual
626           file ownership, file ACLs are adjusted as well.
627
628           This option is implied if --private-users=pick is used. This option
629           has no effect if user namespacing is not used.
630
631       -U
632           If the kernel supports the user namespaces feature, equivalent to
633           --private-users=pick --private-users-chown, otherwise equivalent to
634           --private-users=no.
635
636           Note that -U is the default if the systemd-nspawn@.service template
637           unit file is used.
638
639           Note: it is possible to undo the effect of --private-users-chown
640           (or -U) on the file system by redoing the operation with the first
641           UID of 0:
642
643               systemd-nspawn ... --private-users=0 --private-users-chown
644
645   Networking Options
646       --private-network
647           Disconnect networking of the container from the host. This makes
648           all network interfaces unavailable in the container, with the
649           exception of the loopback device and those specified with
650           --network-interface= and configured with --network-veth. If this
651           option is specified, the CAP_NET_ADMIN capability will be added to
652           the set of capabilities the container retains. The latter may be
653           disabled by using --drop-capability=. If this option is not
654           specified (or implied by one of the options listed below), the
655           container will have full access to the host network.
656
657       --network-interface=
658           Assign the specified network interface to the container. This will
659           remove the specified interface from the calling namespace and place
660           it in the container. When the container terminates, it is moved
661           back to the calling namespace. Note that --network-interface=
662           implies --private-network. This option may be used more than once
663           to add multiple network interfaces to the container.
664
665           Note that any network interface specified this way must already
666           exist at the time the container is started. If the container shall
667           be started automatically at boot via a systemd-nspawn@.service unit
668           file instance, it might hence make sense to add a unit file drop-in
669           to the service instance (e.g.
670           /etc/systemd/system/systemd-nspawn@foobar.service.d/50-network.conf)
671           with contents like the following:
672
673               [Unit]
674               Wants=sys-subsystem-net-devices-ens1.device
675               After=sys-subsystem-net-devices-ens1.device
676
677           This will make sure that activation of the container service will
678           be delayed until the "ens1" network interface has shown up. This is
679           required since hardware probing is fully asynchronous, and network
680           interfaces might be discovered only later during the boot process,
681           after the container would normally be started without these
682           explicit dependencies.
683
684       --network-macvlan=
685           Create a "macvlan" interface of the specified Ethernet network
686           interface and add it to the container. A "macvlan" interface is a
687           virtual interface that adds a second MAC address to an existing
688           physical Ethernet link. The interface in the container will be
689           named after the interface on the host, prefixed with "mv-". Note
690           that --network-macvlan= implies --private-network. This option may
691           be used more than once to add multiple network interfaces to the
692           container.
693
694           As with --network-interface=, the underlying Ethernet network
695           interface must already exist at the time the container is started,
696           and thus similar unit file drop-ins as described above might be
697           useful.
698
699       --network-ipvlan=
700           Create an "ipvlan" interface of the specified Ethernet network
701           interface and add it to the container. An "ipvlan" interface is a
702           virtual interface, similar to a "macvlan" interface, which uses the
703           same MAC address as the underlying interface. The interface in the
704           container will be named after the interface on the host, prefixed
705           with "iv-". Note that --network-ipvlan= implies --private-network.
706           This option may be used more than once to add multiple network
707           interfaces to the container.
708
709           As with --network-interface=, the underlying Ethernet network
710           interface must already exist at the time the container is started,
711           and thus similar unit file drop-ins as described above might be
712           useful.
713
714       -n, --network-veth
715           Create a virtual Ethernet link ("veth") between host and container.
716           The host side of the Ethernet link will be available as a network
717           interface named after the container's name (as specified with
718           --machine=), prefixed with "ve-". The container side of the
719           Ethernet link will be named "host0". The --network-veth option
720           implies --private-network.
721
722           Note that systemd-networkd.service(8) includes by default a network
723           file /usr/lib/systemd/network/80-container-ve.network matching the
724           host-side interfaces created this way, which contains settings to
725           enable automatic address provisioning on the created virtual link
726           via DHCP, as well as automatic IP routing onto the host's external
727           network interfaces. It also contains
728           /usr/lib/systemd/network/80-container-host0.network matching the
729           container-side interface created this way, containing settings to
730           enable client side address assignment via DHCP. In case
731           systemd-networkd is running on both the host and inside the
732           container, automatic IP communication from the container to the
733           host is thus available, with further connectivity to the external
734           network.
735
736           Note that --network-veth is the default if the
737           systemd-nspawn@.service template unit file is used.
738
739           Note that on Linux network interface names may have a length of 15
740           characters at maximum, while container names may have a length up
741           to 64 characters. As this option derives the host-side interface
742           name from the container name the name is possibly truncated. Thus,
743           care needs to be taken to ensure that interface names remain unique
744           in this case, or even better container names are generally not
745           chosen longer than 12 characters, to avoid the truncation. If the
746           name is truncated, systemd-nspawn will automatically append a
747           4-digit hash value to the name to reduce the chance of collisions.
748           However, the hash algorithm is not collision-free. (See
749           systemd.net-naming-scheme(7) for details on older naming algorithms
750           for this interface). Alternatively, the --network-veth-extra=
751           option may be used, which allows free configuration of the
752           host-side interface name independently of the container name — but
753           might require a bit more additional configuration in case bridging
754           in a fashion similar to --network-bridge= is desired.
755
756       --network-veth-extra=
757           Adds an additional virtual Ethernet link between host and
758           container. Takes a colon-separated pair of host interface name and
759           container interface name. The latter may be omitted in which case
760           the container and host sides will be assigned the same name. This
761           switch is independent of --network-veth, and — in contrast — may be
762           used multiple times, and allows configuration of the network
763           interface names. Note that --network-bridge= has no effect on
764           interfaces created with --network-veth-extra=.
765
766       --network-bridge=
767           Adds the host side of the Ethernet link created with --network-veth
768           to the specified Ethernet bridge interface. Expects a valid network
769           interface name of a bridge device as argument. Note that
770           --network-bridge= implies --network-veth. If this option is used,
771           the host side of the Ethernet link will use the "vb-" prefix
772           instead of "ve-". Regardless of the used naming prefix the same
773           network interface name length limits imposed by Linux apply, along
774           with the complications this creates (for details see above).
775
776           As with --network-interface=, the underlying bridge network
777           interface must already exist at the time the container is started,
778           and thus similar unit file drop-ins as described above might be
779           useful.
780
781       --network-zone=
782           Creates a virtual Ethernet link ("veth") to the container and adds
783           it to an automatically managed Ethernet bridge interface. The
784           bridge interface is named after the passed argument, prefixed with
785           "vz-". The bridge interface is automatically created when the first
786           container configured for its name is started, and is automatically
787           removed when the last container configured for its name exits.
788           Hence, each bridge interface configured this way exists only as
789           long as there's at least one container referencing it running. This
790           option is very similar to --network-bridge=, besides this automatic
791           creation/removal of the bridge device.
792
793           This setting makes it easy to place multiple related containers on
794           a common, virtual Ethernet-based broadcast domain, here called a
795           "zone". Each container may only be part of one zone, but each zone
796           may contain any number of containers. Each zone is referenced by
797           its name. Names may be chosen freely (as long as they form valid
798           network interface names when prefixed with "vz-"), and it is
799           sufficient to pass the same name to the --network-zone= switch of
800           the various concurrently running containers to join them in one
801           zone.
802
803           Note that systemd-networkd.service(8) includes by default a network
804           file /usr/lib/systemd/network/80-container-vz.network matching the
805           bridge interfaces created this way, which contains settings to
806           enable automatic address provisioning on the created virtual
807           network via DHCP, as well as automatic IP routing onto the host's
808           external network interfaces. Using --network-zone= is hence in most
809           cases fully automatic and sufficient to connect multiple local
810           containers in a joined broadcast domain to the host, with further
811           connectivity to the external network.
812
813       --network-namespace-path=
814           Takes the path to a file representing a kernel network namespace
815           that the container shall run in. The specified path should refer to
816           a (possibly bind-mounted) network namespace file, as exposed by the
817           kernel below /proc/$PID/ns/net. This makes the container enter the
818           given network namespace. One of the typical use cases is to give a
819           network namespace under /run/netns created by ip-netns(8), for
820           example, --network-namespace-path=/run/netns/foo. Note that this
821           option cannot be used together with other network-related options,
822           such as --private-network or --network-interface=.
823
824       -p, --port=
825           If private networking is enabled, maps an IP port on the host onto
826           an IP port on the container. Takes a protocol specifier (either
827           "tcp" or "udp"), separated by a colon from a host port number in
828           the range 1 to 65535, separated by a colon from a container port
829           number in the range from 1 to 65535. The protocol specifier and its
830           separating colon may be omitted, in which case "tcp" is assumed.
831           The container port number and its colon may be omitted, in which
832           case the same port as the host port is implied. This option is only
833           supported if private networking is used, such as with
834           --network-veth, --network-zone= --network-bridge=.
835
836   Security Options
837       --capability=
838           List one or more additional capabilities to grant the container.
839           Takes a comma-separated list of capability names, see
840           capabilities(7) for more information. Note that the following
841           capabilities will be granted in any way: CAP_AUDIT_CONTROL,
842           CAP_AUDIT_WRITE, CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
843           CAP_FOWNER, CAP_FSETID, CAP_IPC_OWNER, CAP_KILL, CAP_LEASE,
844           CAP_LINUX_IMMUTABLE, CAP_MKNOD, CAP_NET_BIND_SERVICE,
845           CAP_NET_BROADCAST, CAP_NET_RAW, CAP_SETFCAP, CAP_SETGID,
846           CAP_SETPCAP, CAP_SETUID, CAP_SYS_ADMIN, CAP_SYS_BOOT,
847           CAP_SYS_CHROOT, CAP_SYS_NICE, CAP_SYS_PTRACE, CAP_SYS_RESOURCE,
848           CAP_SYS_TTY_CONFIG. Also CAP_NET_ADMIN is retained if
849           --private-network is specified. If the special value "all" is
850           passed, all capabilities are retained.
851
852           If the special value of "help" is passed, the program will print
853           known capability names and exit.
854
855           This option sets the bounding set of capabilities which also limits
856           the ambient capabilities as given with the --ambient-capability=.
857
858       --drop-capability=
859           Specify one or more additional capabilities to drop for the
860           container. This allows running the container with fewer
861           capabilities than the default (see above).
862
863           If the special value of "help" is passed, the program will print
864           known capability names and exit.
865
866           This option sets the bounding set of capabilities which also limits
867           the ambient capabilities as given with the --ambient-capability=.
868
869       --ambient-capability=
870           Specify one or more additional capabilities to pass in the
871           inheritable and ambient set to the program started within the
872           container. The value "all" is not supported for this setting.
873
874           All capabilities specified here must be in the set allowed with the
875           --capability= and --drop-capability= options. Otherwise, an error
876           message will be shown.
877
878           This option cannot be combined with the boot mode of the container
879           (as requested via --boot).
880
881           If the special value of "help" is passed, the program will print
882           known capability names and exit.
883
884       --no-new-privileges=
885           Takes a boolean argument. Specifies the value of the
886           PR_SET_NO_NEW_PRIVS flag for the container payload. Defaults to
887           off. When turned on the payload code of the container cannot
888           acquire new privileges, i.e. the "setuid" file bit as well as file
889           system capabilities will not have an effect anymore. See prctl(2)
890           for details about this flag.
891
892       --system-call-filter=
893           Alter the system call filter applied to containers. Takes a
894           space-separated list of system call names or group names (the
895           latter prefixed with "@", as listed by the syscall-filter command
896           of systemd-analyze(1)). Passed system calls will be permitted. The
897           list may optionally be prefixed by "~", in which case all listed
898           system calls are prohibited. If this command line option is used
899           multiple times the configured lists are combined. If both a
900           positive and a negative list (that is one system call list without
901           and one with the "~" prefix) are configured, the negative list
902           takes precedence over the positive list. Note that systemd-nspawn
903           always implements a system call allow list (as opposed to a deny
904           list!), and this command line option hence adds or removes entries
905           from the default allow list, depending on the "~" prefix. Note that
906           the applied system call filter is also altered implicitly if
907           additional capabilities are passed using the --capabilities=.
908
909       -Z, --selinux-context=
910           Sets the SELinux security context to be used to label processes in
911           the container.
912
913       -L, --selinux-apifs-context=
914           Sets the SELinux security context to be used to label files in the
915           virtual API file systems in the container.
916
917   Resource Options
918       --rlimit=
919           Sets the specified POSIX resource limit for the container payload.
920           Expects an assignment of the form "LIMIT=SOFT:HARD" or
921           "LIMIT=VALUE", where LIMIT should refer to a resource limit type,
922           such as RLIMIT_NOFILE or RLIMIT_NICE. The SOFT and HARD fields
923           should refer to the numeric soft and hard resource limit values. If
924           the second form is used, VALUE may specify a value that is used
925           both as soft and hard limit. In place of a numeric value the
926           special string "infinity" may be used to turn off resource limiting
927           for the specific type of resource. This command line option may be
928           used multiple times to control limits on multiple limit types. If
929           used multiple times for the same limit type, the last use wins. For
930           details about resource limits see setrlimit(2). By default resource
931           limits for the container's init process (PID 1) are set to the same
932           values the Linux kernel originally passed to the host init system.
933           Note that some resource limits are enforced on resources counted
934           per user, in particular RLIMIT_NPROC. This means that unless user
935           namespacing is deployed (i.e.  --private-users= is used, see
936           above), any limits set will be applied to the resource usage of the
937           same user on all local containers as well as the host. This means
938           particular care needs to be taken with these limits as they might
939           be triggered by possibly less trusted code. Example:
940           "--rlimit=RLIMIT_NOFILE=8192:16384".
941
942       --oom-score-adjust=
943           Changes the OOM ("Out Of Memory") score adjustment value for the
944           container payload. This controls /proc/self/oom_score_adj which
945           influences the preference with which this container is terminated
946           when memory becomes scarce. For details see proc(5). Takes an
947           integer in the range -1000...1000.
948
949       --cpu-affinity=
950           Controls the CPU affinity of the container payload. Takes a comma
951           separated list of CPU numbers or number ranges (the latter's start
952           and end value separated by dashes). See sched_setaffinity(2) for
953           details.
954
955       --personality=
956           Control the architecture ("personality") reported by uname(2) in
957           the container. Currently, only "x86" and "x86-64" are supported.
958           This is useful when running a 32-bit container on a 64-bit host. If
959           this setting is not used, the personality reported in the container
960           is the same as the one reported on the host.
961
962   Integration Options
963       --resolv-conf=
964           Configures how /etc/resolv.conf inside of the container shall be
965           handled (i.e. DNS configuration synchronization from host to
966           container). Takes one of "off", "copy-host", "copy-static",
967           "copy-uplink", "copy-stub", "replace-host", "replace-static",
968           "replace-uplink", "replace-stub", "bind-host", "bind-static",
969           "bind-uplink", "bind-stub", "delete" or "auto".
970
971           If set to "off" the /etc/resolv.conf file in the container is left
972           as it is included in the image, and neither modified nor bind
973           mounted over.
974
975           If set to "copy-host", the /etc/resolv.conf file from the host is
976           copied into the container, unless the file exists already and is
977           not a regular file (e.g. a symlink). Similar, if "replace-host" is
978           used the file is copied, replacing any existing inode, including
979           symlinks. Similar, if "bind-host" is used, the file is bind mounted
980           from the host into the container.
981
982           If set to "copy-static", "replace-static" or "bind-static" the
983           static resolv.conf file supplied with systemd-resolved.service(8)
984           (specifically: /usr/lib/systemd/resolv.conf) is copied or bind
985           mounted into the container.
986
987           If set to "copy-uplink", "replace-uplink" or "bind-uplink" the
988           uplink resolv.conf file managed by systemd-resolved.service
989           (specifically: /run/systemd/resolve/resolv.conf) is copied or bind
990           mounted into the container.
991
992           If set to "copy-stub", "replace-stub" or "bind-stub" the stub
993           resolv.conf file managed by systemd-resolved.service (specifically:
994           /run/systemd/resolve/stub-resolv.conf) is copied or bind mounted
995           into the container.
996
997           If set to "delete" the /etc/resolv.conf file in the container is
998           deleted if it exists.
999
1000           Finally, if set to "auto" the file is left as it is if private
1001           networking is turned on (see --private-network). Otherwise, if
1002           systemd-resolved.service is running its stub resolv.conf file is
1003           used, and if not the host's /etc/resolv.conf file. In the latter
1004           cases the file is copied if the image is writable, and bind mounted
1005           otherwise.
1006
1007           It's recommended to use "copy-..."  or "replace-..."  if the
1008           container shall be able to make changes to the DNS configuration on
1009           its own, deviating from the host's settings. Otherwise "bind" is
1010           preferable, as it means direct changes to /etc/resolv.conf in the
1011           container are not allowed, as it is a read-only bind mount (but
1012           note that if the container has enough privileges, it might simply
1013           go ahead and unmount the bind mount anyway). Note that both if the
1014           file is bind mounted and if it is copied no further propagation of
1015           configuration is generally done after the one-time early
1016           initialization (this is because the file is usually updated through
1017           copying and renaming). Defaults to "auto".
1018
1019       --timezone=
1020           Configures how /etc/localtime inside of the container (i.e. local
1021           timezone synchronization from host to container) shall be handled.
1022           Takes one of "off", "copy", "bind", "symlink", "delete" or "auto".
1023           If set to "off" the /etc/localtime file in the container is left as
1024           it is included in the image, and neither modified nor bind mounted
1025           over. If set to "copy" the /etc/localtime file of the host is
1026           copied into the container. Similarly, if "bind" is used, the file
1027           is bind mounted from the host into the container. If set to
1028           "symlink", a symlink is created pointing from /etc/localtime in the
1029           container to the timezone file in the container that matches the
1030           timezone setting on the host. If set to "delete", the file in the
1031           container is deleted, should it exist. If set to "auto" and the
1032           /etc/localtime file of the host is a symlink, then "symlink" mode
1033           is used, and "copy" otherwise, except if the image is read-only in
1034           which case "bind" is used instead. Defaults to "auto".
1035
1036       --link-journal=
1037           Control whether the container's journal shall be made visible to
1038           the host system. If enabled, allows viewing the container's journal
1039           files from the host (but not vice versa). Takes one of "no",
1040           "host", "try-host", "guest", "try-guest", "auto". If "no", the
1041           journal is not linked. If "host", the journal files are stored on
1042           the host file system (beneath /var/log/journal/machine-id) and the
1043           subdirectory is bind-mounted into the container at the same
1044           location. If "guest", the journal files are stored on the guest
1045           file system (beneath /var/log/journal/machine-id) and the
1046           subdirectory is symlinked into the host at the same location.
1047           "try-host" and "try-guest" do the same but do not fail if the host
1048           does not have persistent journaling enabled. If "auto" (the
1049           default), and the right subdirectory of /var/log/journal exists, it
1050           will be bind mounted into the container. If the subdirectory does
1051           not exist, no linking is performed. Effectively, booting a
1052           container once with "guest" or "host" will link the journal
1053           persistently if further on the default of "auto" is used.
1054
1055           Note that --link-journal=try-guest is the default if the
1056           systemd-nspawn@.service template unit file is used.
1057
1058       -j
1059           Equivalent to --link-journal=try-guest.
1060
1061   Mount Options
1062       --bind=, --bind-ro=
1063           Bind mount a file or directory from the host into the container.
1064           Takes one of: a path argument — in which case the specified path
1065           will be mounted from the host to the same path in the container, or
1066           a colon-separated pair of paths — in which case the first specified
1067           path is the source in the host, and the second path is the
1068           destination in the container, or a colon-separated triple of source
1069           path, destination path and mount options. The source path may
1070           optionally be prefixed with a "+" character. If so, the source path
1071           is taken relative to the image's root directory. This permits
1072           setting up bind mounts within the container image. The source path
1073           may be specified as empty string, in which case a temporary
1074           directory below the host's /var/tmp/ directory is used. It is
1075           automatically removed when the container is shut down. Mount
1076           options are comma-separated and currently, only rbind and norbind
1077           are allowed, controlling whether to create a recursive or a regular
1078           bind mount. Defaults to "rbind". Backslash escapes are interpreted,
1079           so "\:" may be used to embed colons in either path. This option may
1080           be specified multiple times for creating multiple independent bind
1081           mount points. The --bind-ro= option creates read-only bind mounts.
1082
1083           Note that when this option is used in combination with
1084           --private-users, the resulting mount points will be owned by the
1085           nobody user. That's because the mount and its files and directories
1086           continue to be owned by the relevant host users and groups, which
1087           do not exist in the container, and thus show up under the wildcard
1088           UID 65534 (nobody). If such bind mounts are created, it is
1089           recommended to make them read-only, using --bind-ro=.
1090
1091       --inaccessible=
1092           Make the specified path inaccessible in the container. This
1093           over-mounts the specified path (which must exist in the container)
1094           with a file node of the same type that is empty and has the most
1095           restrictive access mode supported. This is an effective way to mask
1096           files, directories and other file system objects from the container
1097           payload. This option may be used more than once in case all
1098           specified paths are masked.
1099
1100       --tmpfs=
1101           Mount a tmpfs file system into the container. Takes a single
1102           absolute path argument that specifies where to mount the tmpfs
1103           instance to (in which case the directory access mode will be chosen
1104           as 0755, owned by root/root), or optionally a colon-separated pair
1105           of path and mount option string that is used for mounting (in which
1106           case the kernel default for access mode and owner will be chosen,
1107           unless otherwise specified). Backslash escapes are interpreted in
1108           the path, so "\:" may be used to embed colons in the path.
1109
1110           Note that this option cannot be used to replace the root file
1111           system of the container with a temporary file system. However, the
1112           --volatile= option described below provides similar functionality,
1113           with a focus on implementing stateless operating system images.
1114
1115       --overlay=, --overlay-ro=
1116           Combine multiple directory trees into one overlay file system and
1117           mount it into the container. Takes a list of colon-separated paths
1118           to the directory trees to combine and the destination mount point.
1119
1120           Backslash escapes are interpreted in the paths, so "\:" may be used
1121           to embed colons in the paths.
1122
1123           If three or more paths are specified, then the last specified path
1124           is the destination mount point in the container, all paths
1125           specified before refer to directory trees on the host and are
1126           combined in the specified order into one overlay file system. The
1127           left-most path is hence the lowest directory tree, the
1128           second-to-last path the highest directory tree in the stacking
1129           order. If --overlay-ro= is used instead of --overlay=, a read-only
1130           overlay file system is created. If a writable overlay file system
1131           is created, all changes made to it are written to the highest
1132           directory tree in the stacking order, i.e. the second-to-last
1133           specified.
1134
1135           If only two paths are specified, then the second specified path is
1136           used both as the top-level directory tree in the stacking order as
1137           seen from the host, as well as the mount point for the overlay file
1138           system in the container. At least two paths have to be specified.
1139
1140           The source paths may optionally be prefixed with "+" character. If
1141           so they are taken relative to the image's root directory. The
1142           uppermost source path may also be specified as an empty string, in
1143           which case a temporary directory below the host's /var/tmp/ is
1144           used. The directory is removed automatically when the container is
1145           shut down. This behaviour is useful in order to make read-only
1146           container directories writable while the container is running. For
1147           example, use "--overlay=+/var::/var" in order to automatically
1148           overlay a writable temporary directory on a read-only /var/
1149           directory.
1150
1151           For details about overlay file systems, see overlayfs.txt[5]. Note
1152           that the semantics of overlay file systems are substantially
1153           different from normal file systems, in particular regarding
1154           reported device and inode information. Device and inode information
1155           may change for a file while it is being written to, and processes
1156           might see out-of-date versions of files at times. Note that this
1157           switch automatically derives the "workdir=" mount option for the
1158           overlay file system from the top-level directory tree, making it a
1159           sibling of it. It is hence essential that the top-level directory
1160           tree is not a mount point itself (since the working directory must
1161           be on the same file system as the top-most directory tree). Also
1162           note that the "lowerdir=" mount option receives the paths to stack
1163           in the opposite order of this switch.
1164
1165           Note that this option cannot be used to replace the root file
1166           system of the container with an overlay file system. However, the
1167           --volatile= option described above provides similar functionality,
1168           with a focus on implementing stateless operating system images.
1169
1170   Input/Output Options
1171       --console=MODE
1172           Configures how to set up standard input, output and error output
1173           for the container payload, as well as the /dev/console device for
1174           the container. Takes one of interactive, read-only, passive, pipe
1175           or autopipe. If interactive, a pseudo-TTY is allocated and made
1176           available as /dev/console in the container. It is then
1177           bi-directionally connected to the standard input and output passed
1178           to systemd-nspawn.  read-only is similar but only the output of the
1179           container is propagated and no input from the caller is read. If
1180           passive, a pseudo TTY is allocated, but it is not connected
1181           anywhere. In pipe mode no pseudo TTY is allocated, but the standard
1182           input, output and error output file descriptors passed to
1183           systemd-nspawn are passed on — as they are — to the container
1184           payload, see the following paragraph. Finally, autopipe mode
1185           operates like interactive when systemd-nspawn is invoked on a
1186           terminal, and like pipe otherwise. Defaults to interactive if
1187           systemd-nspawn is invoked from a terminal, and read-only otherwise.
1188
1189           In pipe mode, /dev/console will not exist in the container. This
1190           means that the container payload generally cannot be a full init
1191           system as init systems tend to require /dev/console to be
1192           available. On the other hand, in this mode container invocations
1193           can be used within shell pipelines. This is because intermediary
1194           pseudo TTYs do not permit independent bidirectional propagation of
1195           the end-of-file (EOF) condition, which is necessary for shell
1196           pipelines to work correctly.  Note that the pipe mode should be
1197           used carefully, as passing arbitrary file descriptors to less
1198           trusted container payloads might open up unwanted interfaces for
1199           access by the container payload. For example, if a passed file
1200           descriptor refers to a TTY of some form, APIs such as TIOCSTI may
1201           be used to synthesize input that might be used for escaping the
1202           container. Hence pipe mode should only be used if the payload is
1203           sufficiently trusted or when the standard input/output/error output
1204           file descriptors are known safe, for example pipes.
1205
1206       --pipe, -P
1207           Equivalent to --console=pipe.
1208
1209   Credentials
1210       --load-credential=ID:PATH, --set-credential=ID:VALUE
1211           Pass a credential to the container. These two options correspond to
1212           the LoadCredential= and SetCredential= settings in unit files. See
1213           systemd.exec(5) for details about these concepts, as well as the
1214           syntax of the option's arguments.
1215
1216           Note: when systemd-nspawn runs as systemd system service it can
1217           propagate the credentials it received via
1218           LoadCredential=/SetCredential= to the container payload. A systemd
1219           service manager running as PID 1 in the container can further
1220           propagate them to the services it itself starts. It is thus
1221           possible to easily propagate credentials from a parent service
1222           manager to a container manager service and from there into its
1223           payload. This can even be done recursively.
1224
1225           In order to embed binary data into the credential data for
1226           --set-credential= use C-style escaping (i.e.  "\n" to embed a
1227           newline, or "\x00" to embed a NUL byte. Note that the invoking
1228           shell might already apply unescaping once, hence this might require
1229           double escaping!).
1230
1231   Other
1232       --no-pager
1233           Do not pipe output into a pager.
1234
1235       -h, --help
1236           Print a short help text and exit.
1237
1238       --version
1239           Print a short version string and exit.
1240

ENVIRONMENT

1242       $SYSTEMD_LOG_LEVEL
1243           The maximum log level of emitted messages (messages with a higher
1244           log level, i.e. less important ones, will be suppressed). Either
1245           one of (in order of decreasing importance) emerg, alert, crit, err,
1246           warning, notice, info, debug, or an integer in the range 0...7. See
1247           syslog(3) for more information.
1248
1249       $SYSTEMD_LOG_COLOR
1250           A boolean. If true, messages written to the tty will be colored
1251           according to priority.
1252
1253           This setting is only useful when messages are written directly to
1254           the terminal, because journalctl(1) and other tools that display
1255           logs will color messages based on the log level on their own.
1256
1257       $SYSTEMD_LOG_TIME
1258           A boolean. If true, log messages will be prefixed with a timestamp.
1259
1260           This setting is only useful when messages are written directly to
1261           the terminal or a file, because journalctl(1) and other tools that
1262           display logs will attach timestamps based on the entry metadata on
1263           their own.
1264
1265       $SYSTEMD_LOG_LOCATION
1266           A boolean. If true, messages will be prefixed with a filename and
1267           line number in the source code where the message originates.
1268
1269           Note that the log location is often attached as metadata to journal
1270           entries anyway. Including it directly in the message text can
1271           nevertheless be convenient when debugging programs.
1272
1273       $SYSTEMD_LOG_TID
1274           A boolean. If true, messages will be prefixed with the current
1275           numerical thread ID (TID).
1276
1277           Note that the this information is attached as metadata to journal
1278           entries anyway. Including it directly in the message text can
1279           nevertheless be convenient when debugging programs.
1280
1281       $SYSTEMD_LOG_TARGET
1282           The destination for log messages. One of console (log to the
1283           attached tty), console-prefixed (log to the attached tty but with
1284           prefixes encoding the log level and "facility", see syslog(3), kmsg
1285           (log to the kernel circular log buffer), journal (log to the
1286           journal), journal-or-kmsg (log to the journal if available, and to
1287           kmsg otherwise), auto (determine the appropriate log target
1288           automatically, the default), null (disable log output).
1289
1290       $SYSTEMD_PAGER
1291           Pager to use when --no-pager is not given; overrides $PAGER. If
1292           neither $SYSTEMD_PAGER nor $PAGER are set, a set of well-known
1293           pager implementations are tried in turn, including less(1) and
1294           more(1), until one is found. If no pager implementation is
1295           discovered no pager is invoked. Setting this environment variable
1296           to an empty string or the value "cat" is equivalent to passing
1297           --no-pager.
1298
1299       $SYSTEMD_LESS
1300           Override the options passed to less (by default "FRSXMK").
1301
1302           Users might want to change two options in particular:
1303
1304           K
1305               This option instructs the pager to exit immediately when Ctrl+C
1306               is pressed. To allow less to handle Ctrl+C itself to switch
1307               back to the pager command prompt, unset this option.
1308
1309               If the value of $SYSTEMD_LESS does not include "K", and the
1310               pager that is invoked is less, Ctrl+C will be ignored by the
1311               executable, and needs to be handled by the pager.
1312
1313           X
1314               This option instructs the pager to not send termcap
1315               initialization and deinitialization strings to the terminal. It
1316               is set by default to allow command output to remain visible in
1317               the terminal even after the pager exits. Nevertheless, this
1318               prevents some pager functionality from working, in particular
1319               paged output cannot be scrolled with the mouse.
1320
1321           See less(1) for more discussion.
1322
1323       $SYSTEMD_LESSCHARSET
1324           Override the charset passed to less (by default "utf-8", if the
1325           invoking terminal is determined to be UTF-8 compatible).
1326
1327       $SYSTEMD_PAGERSECURE
1328           Takes a boolean argument. When true, the "secure" mode of the pager
1329           is enabled; if false, disabled. If $SYSTEMD_PAGERSECURE is not set
1330           at all, secure mode is enabled if the effective UID is not the same
1331           as the owner of the login session, see geteuid(2) and
1332           sd_pid_get_owner_uid(3). In secure mode, LESSSECURE=1 will be set
1333           when invoking the pager, and the pager shall disable commands that
1334           open or create new files or start new subprocesses. When
1335           $SYSTEMD_PAGERSECURE is not set at all, pagers which are not known
1336           to implement secure mode will not be used. (Currently only less(1)
1337           implements secure mode.)
1338
1339           Note: when commands are invoked with elevated privileges, for
1340           example under sudo(8) or pkexec(1), care must be taken to ensure
1341           that unintended interactive features are not enabled. "Secure" mode
1342           for the pager may be enabled automatically as describe above.
1343           Setting SYSTEMD_PAGERSECURE=0 or not removing it from the inherited
1344           environment allows the user to invoke arbitrary commands. Note that
1345           if the $SYSTEMD_PAGER or $PAGER variables are to be honoured,
1346           $SYSTEMD_PAGERSECURE must be set too. It might be reasonable to
1347           completely disable the pager using --no-pager instead.
1348
1349       $SYSTEMD_COLORS
1350           Takes a boolean argument. When true, systemd and related utilities
1351           will use colors in their output, otherwise the output will be
1352           monochrome. Additionally, the variable can take one of the
1353           following special values: "16", "256" to restrict the use of colors
1354           to the base 16 or 256 ANSI colors, respectively. This can be
1355           specified to override the automatic decision based on $TERM and
1356           what the console is connected to.
1357
1358       $SYSTEMD_URLIFY
1359           The value must be a boolean. Controls whether clickable links
1360           should be generated in the output for terminal emulators supporting
1361           this. This can be specified to override the decision that systemd
1362           makes based on $TERM and other conditions.
1363

EXAMPLES

1365       Example 1. Download a Fedora image and start a shell in it
1366
1367           # machinectl pull-raw --verify=no \
1368                 https://download.fedoraproject.org/pub/fedora/linux/releases/33/Cloud/x86_64/images/Fedora-Cloud-Base-33-1.2.x86_64.raw.xz \
1369                 Fedora-Cloud-Base-33-1.2.x86-64
1370           # systemd-nspawn -M Fedora-Cloud-Base-33-1.2.x86-64
1371
1372       This downloads an image using machinectl(1) and opens a shell in it.
1373
1374       Example 2. Build and boot a minimal Fedora distribution in a container
1375
1376           # dnf -y --releasever=33 --installroot=/var/lib/machines/f33 \
1377                 --disablerepo='*' --enablerepo=fedora --enablerepo=updates install \
1378                 systemd passwd dnf fedora-release vim-minimal glibc-minimal-langpack
1379           # systemd-nspawn -bD /var/lib/machines/f33
1380
1381       This installs a minimal Fedora distribution into the directory
1382       /var/lib/machines/f33 and then boots that OS in a namespace container.
1383       Because the installation is located underneath the standard
1384       /var/lib/machines/ directory, it is also possible to start the machine
1385       using systemd-nspawn -M f33.
1386
1387       Example 3. Spawn a shell in a container of a minimal Debian unstable
1388       distribution
1389
1390           # debootstrap unstable ~/debian-tree/
1391           # systemd-nspawn -D ~/debian-tree/
1392
1393       This installs a minimal Debian unstable distribution into the directory
1394       ~/debian-tree/ and then spawns a shell from this image in a namespace
1395       container.
1396
1397       debootstrap supports Debian[7], Ubuntu[8], and Tanglu[9] out of the
1398       box, so the same command can be used to install any of those. For other
1399       distributions from the Debian family, a mirror has to be specified, see
1400       debootstrap(8).
1401
1402       Example 4. Boot a minimal Arch Linux distribution in a container
1403
1404           # pacstrap -c ~/arch-tree/ base
1405           # systemd-nspawn -bD ~/arch-tree/
1406
1407       This installs a minimal Arch Linux distribution into the directory
1408       ~/arch-tree/ and then boots an OS in a namespace container in it.
1409
1410       Example 5. Install the OpenSUSE Tumbleweed rolling distribution
1411
1412           # zypper --root=/var/lib/machines/tumbleweed ar -c \
1413                 https://download.opensuse.org/tumbleweed/repo/oss tumbleweed
1414           # zypper --root=/var/lib/machines/tumbleweed refresh
1415           # zypper --root=/var/lib/machines/tumbleweed install --no-recommends \
1416                 systemd shadow zypper openSUSE-release vim
1417           # systemd-nspawn -M tumbleweed passwd root
1418           # systemd-nspawn -M tumbleweed -b
1419
1420       Example 6. Boot into an ephemeral snapshot of the host system
1421
1422           # systemd-nspawn -D / -xb
1423
1424       This runs a copy of the host system in a snapshot which is removed
1425       immediately when the container exits. All file system changes made
1426       during runtime will be lost on shutdown, hence.
1427
1428       Example 7. Run a container with SELinux sandbox security contexts
1429
1430           # chcon system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 -R /srv/container
1431           # systemd-nspawn -L system_u:object_r:svirt_sandbox_file_t:s0:c0,c1 \
1432                 -Z system_u:system_r:svirt_lxc_net_t:s0:c0,c1 -D /srv/container /bin/sh
1433
1434       Example 8. Run a container with an OSTree deployment
1435
1436           # systemd-nspawn -b -i ~/image.raw \
1437                 --pivot-root=/ostree/deploy/$OS/deploy/$CHECKSUM:/sysroot \
1438                 --bind=+/sysroot/ostree/deploy/$OS/var:/var
1439

EXIT STATUS

1441       The exit code of the program executed in the container is returned.
1442

SEE ALSO

1444       systemd(1), systemd.nspawn(5), chroot(1), dnf(8), debootstrap(8),
1445       pacman(8), zypper(8), systemd.slice(5), machinectl(1), btrfs(8)
1446

NOTES

1448        1. Container Interface
1449           https://systemd.io/CONTAINER_INTERFACE
1450
1451        2. Discoverable Partitions Specification
1452           https://systemd.io/DISCOVERABLE_PARTITIONS
1453
1454        3. OCI Runtime Specification
1455           https://github.com/opencontainers/runtime-spec/blob/master/spec.md
1456
1457        4. OSTree
1458           https://ostree.readthedocs.io/en/latest/
1459
1460        5. overlayfs.txt
1461           https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt
1462
1463        6. Fedora
1464           https://getfedora.org
1465
1466        7. Debian
1467           https://www.debian.org
1468
1469        8. Ubuntu
1470           https://www.ubuntu.com
1471
1472        9. Tanglu
1473           https://www.tanglu.org
1474
1475       10. Arch Linux
1476           https://www.archlinux.org
1477
1478       11. OpenSUSE Tumbleweed
1479           https://software.opensuse.org/distributions/tumbleweed
1480
1481
1482
1483systemd 248                                                  SYSTEMD-NSPAWN(1)
Impressum