Ubuntu Manpage: machinectl - Control the systemd machine manager

Provided by: systemd-container_251.4-1ubuntu7_amd64

NAME

       machinectl - Control the systemd machine manager

SYNOPSIS

       machinectl [OPTIONS...] {COMMAND} [NAME...]

DESCRIPTION

machinectl may be used to introspect and control the state of the systemd(1) virtual
machine and container registration manager systemd-machined.service(8).

machinectl may be used to execute operations on machines and images. Machines in this
sense are considered running instances of:

• Virtual Machines (VMs) that virtualize hardware to run full operating system (OS)
instances (including their kernels) in a virtualized environment on top of the host
OS.

• Containers that share the hardware and OS kernel with the host OS, in order to run OS
userspace instances on top the host OS.

• The host system itself.

Machines are identified by names that follow the same rules as UNIX and DNS hostnames. For
details, see below.

Machines are instantiated from disk or file system images that frequently — but not
necessarily — carry the same name as machines running from them. Images in this sense may
be:

• Directory trees containing an OS, including the top-level directories /usr/, /etc/,
and so on.

• btrfs subvolumes containing OS trees, similar to regular directory trees.

• Binary "raw" disk image files containing MBR or GPT partition tables and Linux file
systems.

• Similarly, block devices containing MBR or GPT partition tables and file systems.

• The file system tree of the host OS itself.

COMMANDS

The following commands are understood:

Machine Commands
list
List currently running (online) virtual machines and containers. To enumerate machine
images that can be started, use list-images (see below). Note that this command hides
the special ".host" machine by default. Use the --all switch to show it.

status NAME...
Show runtime status information about one or more virtual machines and containers,
followed by the most recent log data from the journal. This function is intended to
generate human-readable output. If you are looking for computer-parsable output, use
show instead. Note that the log data shown is reported by the virtual machine or
container manager, and frequently contains console output of the machine, but not
necessarily journal contents of the machine itself.

show [NAME...]
Show properties of one or more registered virtual machines or containers or the
manager itself. If no argument is specified, properties of the manager will be shown.
If a NAME is specified, properties of this virtual machine or container are shown. By
default, empty properties are suppressed. Use --all to show those too. To select
specific properties to show, use --property=. This command is intended to be used
whenever computer-parsable output is required, and does not print the control group
tree or journal entries. Use status if you are looking for formatted human-readable
output.

start NAME...
Start a container as a system service, using systemd-nspawn(1). This starts
systemd-nspawn@.service, instantiated for the specified machine name, similar to the
effect of systemctl start on the service name. systemd-nspawn looks for a container
image by the specified name in /var/lib/machines/ (and other search paths, see below)
and runs it. Use list-images (see below) for listing available container images to
start.

Note that systemd-machined.service(8) also interfaces with a variety of other
container and VM managers, systemd-nspawn is just one implementation of it. Most of
the commands available in machinectl may be used on containers or VMs controlled by
other managers, not just systemd-nspawn. Starting VMs and container images on those
managers requires manager-specific tools.

To interactively start a container on the command line with full access to the
container's console, please invoke systemd-nspawn directly. To stop a running
container use machinectl poweroff.

login [NAME]
Open an interactive terminal login session in a container or on the local host. If an
argument is supplied, it refers to the container machine to connect to. If none is
specified, or the container name is specified as the empty string, or the special
machine name ".host" (see below) is specified, the connection is made to the local
host instead. This will create a TTY connection to a specific container or the local
host and asks for the execution of a getty on it. Note that this is only supported for
containers running systemd(1) as init system.

This command will open a full login prompt on the container or the local host, which
then asks for username and password. Use shell (see below) or systemd-run(1) with the
--machine= switch to directly invoke a single command, either interactively or in the
background.

shell [[NAME@]NAME [PATH [ARGUMENTS...]]]
Open an interactive shell session in a container or on the local host. The first
argument refers to the container machine to connect to. If none is specified, or the
machine name is specified as the empty string, or the special machine name ".host"
(see below) is specified, the connection is made to the local host instead. This works
similar to login but immediately invokes a user process. This command runs the
specified executable with the specified arguments, or the default shell for the user
if none is specified, or /bin/sh if no default shell is found. By default, --uid=, or
by prefixing the machine name with a username and an "@" character, a different user
may be selected. Use --setenv= to set environment variables for the executed process.

Note that machinectl shell does not propagate the exit code/status of the invoked
shell process. Use systemd-run instead if that information is required (see below).

When using the shell command without arguments, (thus invoking the executed shell or
command on the local host), it is in many ways similar to a su(1) session, but, unlike
su, completely isolates the new session from the originating session, so that it
shares no process or session properties, and is in a clean and well-defined state. It
will be tracked in a new utmp, login, audit, security and keyring session, and will
not inherit any environment variables or resource limits, among other properties.

Note that systemd-run(1) with its --machine= switch may be used in place of the
machinectl shell command, and allows non-interactive operation, more detailed and
low-level configuration of the invoked unit, as well as access to runtime and exit
code/status information of the invoked shell process. In particular, use systemd-run's
--wait switch to propagate exit status information of the invoked process. Use
systemd-run's --pty switch for acquiring an interactive shell, similar to machinectl
shell. In general, systemd-run is preferable for scripting purposes. However, note
that systemd-run might require higher privileges than machinectl shell.

enable NAME..., disable NAME...
Enable or disable a container as a system service to start at system boot, using
systemd-nspawn(1). This enables or disables systemd-nspawn@.service, instantiated for
the specified machine name, similar to the effect of systemctl enable or systemctl
disable on the service name.

poweroff NAME...
Power off one or more containers. This will trigger a reboot by sending SIGRTMIN+4 to
the container's init process, which causes systemd-compatible init systems to shut
down cleanly. Use stop as alias for poweroff. This operation does not work on
containers that do not run a systemd(1)-compatible init system, such as sysvinit. Use
terminate (see below) to immediately terminate a container or VM, without cleanly
shutting it down.

reboot NAME...
Reboot one or more containers. This will trigger a reboot by sending SIGINT to the
container's init process, which is roughly equivalent to pressing Ctrl+Alt+Del on a
non-containerized system, and is compatible with containers running any system
manager.

terminate NAME...
Immediately terminates a virtual machine or container, without cleanly shutting it
down. This kills all processes of the virtual machine or container and deallocates all
resources attached to that instance. Use poweroff to issue a clean shutdown request.

kill NAME...
Send a signal to one or more processes of the virtual machine or container. This means
processes as seen by the host, not the processes inside the virtual machine or
container. Use --kill-who= to select which process to kill. Use --signal= to select
the signal to send.

bind NAME PATH [PATH]
Bind mounts a file or directory from the host into the specified container. The first
path argument is the source file or directory on the host, the second path argument is
the destination file or directory in the container. When the latter is omitted, the
destination path in the container is the same as the source path on the host. When
combined with the --read-only switch, a ready-only bind mount is created. When
combined with the --mkdir switch, the destination path is first created before the
mount is applied. Note that this option is currently only supported for systemd-
nspawn(1) containers, and only if user namespacing (--private-users) is not used. This
command supports bind mounting directories, regular files, device nodes, AF_UNIX
socket nodes, as well as FIFOs.

copy-to NAME PATH [PATH]
Copies files or directories from the host system into a running container. Takes a
container name, followed by the source path on the host and the destination path in
the container. If the destination path is omitted, the same as the source path is
used.

If host and container share the same user and group namespace, file ownership by
numeric user ID and group ID is preserved for the copy, otherwise all files and
directories in the copy will be owned by the root user and group (UID/GID 0).

copy-from NAME PATH [PATH]
Copies files or directories from a container into the host system. Takes a container
name, followed by the source path in the container and the destination path on the
host. If the destination path is omitted, the same as the source path is used.

Image Commands
list-images
Show a list of locally installed container and VM images. This enumerates all raw disk
images and container directories and subvolumes in /var/lib/machines/ (and other
search paths, see below). Use start (see above) to run a container off one of the
listed images. Note that, by default, containers whose name begins with a dot (".")
are not shown. To show these too, specify --all. Note that a special image ".host"
always implicitly exists and refers to the image the host itself is booted from.

image-status [NAME...]
Show terse status information about one or more container or VM images. This function
is intended to generate human-readable output. Use show-image (see below) to generate
computer-parsable output instead.

show-image [NAME...]
Show properties of one or more registered virtual machine or container images, or the
manager itself. If no argument is specified, properties of the manager will be shown.
If a NAME is specified, properties of this virtual machine or container image are
shown. By default, empty properties are suppressed. Use --all to show those too. To
select specific properties to show, use --property=. This command is intended to be
used whenever computer-parsable output is required. Use image-status if you are
looking for formatted human-readable output.

clone NAME NAME
Clones a container or VM image. The arguments specify the name of the image to clone
and the name of the newly cloned image. Note that plain directory container images are
cloned into btrfs subvolume images with this command, if the underlying file system
supports this. Note that cloning a container or VM image is optimized for file systems
that support copy-on-write, and might not be efficient on others, due to file system
limitations.

Note that this command leaves hostname, machine ID and all other settings that could
identify the instance unmodified. The original image and the cloned copy will hence
share these credentials, and it might be necessary to manually change them in the
copy.

If combined with the --read-only switch a read-only cloned image is created.

rename NAME NAME
Renames a container or VM image. The arguments specify the name of the image to rename
and the new name of the image.

read-only NAME [BOOL]
Marks or (unmarks) a container or VM image read-only. Takes a VM or container image
name, followed by a boolean as arguments. If the boolean is omitted, positive is
implied, i.e. the image is marked read-only.

remove NAME...
Removes one or more container or VM images. The special image ".host", which refers to
the host's own directory tree, may not be removed.

set-limit [NAME] BYTES
Sets the maximum size in bytes that a specific container or VM image, or all images,
may grow up to on disk (disk quota). Takes either one or two parameters. The first,
optional parameter refers to a container or VM image name. If specified, the size
limit of the specified image is changed. If omitted, the overall size limit of the sum
of all images stored locally is changed. The final argument specifies the size limit
in bytes, possibly suffixed by the usual K, M, G, T units. If the size limit shall be
disabled, specify "-" as size.

Note that per-container size limits are only supported on btrfs file systems.

clean
Remove hidden VM or container images (or all). This command removes all hidden machine
images from /var/lib/machines/, i.e. those whose name begins with a dot. Use
machinectl list-images --all to see a list of all machine images, including the hidden
ones.

When combined with the --all switch removes all images, not just hidden ones. This
command effectively empties /var/lib/machines/.

Note that commands such as machinectl pull-tar or machinectl pull-raw usually create
hidden, read-only, unmodified machine images from the downloaded image first, before
cloning a writable working copy of it, in order to avoid duplicate downloads in case
of images that are reused multiple times. Use machinectl clean to remove old, hidden
images created this way.

Image Transfer Commands
pull-tar URL [NAME]
Downloads a .tar container image from the specified URL, and makes it available under
the specified local machine name. The URL must be of type "http://" or "https://", and
must refer to a .tar, .tar.gz, .tar.xz or .tar.bz2 archive file. If the local machine
name is omitted, it is automatically derived from the last component of the URL, with
its suffix removed.

The image is verified before it is made available, unless --verify=no is specified.
Verification is done either via an inline signed file with the name of the image and
the suffix .sha256 or via separate SHA256SUMS and SHA256SUMS.gpg files. The signature
files need to be made available on the same web server, under the same URL as the .tar
file. With --verify=checksum, only the SHA256 checksum for the file is verified, based
on the .sha256 suffixed file or the SHA256SUMS file. With --verify=signature, the sha
checksum file is first verified with the inline signature in the .sha256 file or the
detached GPG signature file SHA256SUMS.gpg. The public key for this verification step
needs to be available in /usr/lib/systemd/import-pubring.gpg or
/etc/systemd/import-pubring.gpg.

The container image will be downloaded and stored in a read-only subvolume in
/var/lib/machines/ that is named after the specified URL and its HTTP etag. A writable
snapshot is then taken from this subvolume, and named after the specified local name.
This behavior ensures that creating multiple container instances of the same URL is
efficient, as multiple downloads are not necessary. In order to create only the
read-only image, and avoid creating its writable snapshot, specify "-" as local
machine name.

Note that the read-only subvolume is prefixed with .tar-, and is thus not shown by
list-images, unless --all is passed.

Note that pressing C-c during execution of this command will not abort the download.
Use cancel-transfer, described below.

pull-raw URL [NAME]
Downloads a .raw container or VM disk image from the specified URL, and makes it
available under the specified local machine name. The URL must be of type "http://" or
"https://". The container image must either be a .qcow2 or raw disk image, optionally
compressed as .gz, .xz, or .bz2. If the local machine name is omitted, it is
automatically derived from the last component of the URL, with its suffix removed.

Image verification is identical for raw and tar images (see above).

If the downloaded image is in .qcow2 format it is converted into a raw image file
before it is made available.

Downloaded images of this type will be placed as read-only .raw file in
/var/lib/machines/. A local, writable (reflinked) copy is then made under the
specified local machine name. To omit creation of the local, writable copy pass "-" as
local machine name.

Similar to the behavior of pull-tar, the read-only image is prefixed with .raw-, and
thus not shown by list-images, unless --all is passed.

Note that pressing C-c during execution of this command will not abort the download.
Use cancel-transfer, described below.

import-tar FILE [NAME], import-raw FILE [NAME]
Imports a TAR or RAW container or VM image, and places it under the specified name in
/var/lib/machines/. When import-tar is used, the file specified as the first argument
should be a tar archive, possibly compressed with xz, gzip or bzip2. It will then be
unpacked into its own subvolume in /var/lib/machines/. When import-raw is used, the
file should be a qcow2 or raw disk image, possibly compressed with xz, gzip or bzip2.
If the second argument (the resulting image name) is not specified, it is
automatically derived from the file name. If the filename is passed as "-", the image
is read from standard input, in which case the second argument is mandatory.

Optionally, the --read-only switch may be used to create a read-only container or VM
image. No cryptographic validation is done when importing the images.

Much like image downloads, ongoing imports may be listed with list-transfers and
aborted with cancel-transfer.

import-fs DIRECTORY [NAME]
Imports a container image stored in a local directory into /var/lib/machines/,
operates similar to import-tar or import-raw, but the first argument is the source
directory. If supported, this command will create btrfs snapshot or subvolume for the
new image.

export-tar NAME [FILE], export-raw NAME [FILE]
Exports a TAR or RAW container or VM image and stores it in the specified file. The
first parameter should be a VM or container image name. The second parameter should be
a file path the TAR or RAW image is written to. If the path ends in ".gz", the file is
compressed with gzip, if it ends in ".xz", with xz, and if it ends in ".bz2", with
bzip2. If the path ends in neither, the file is left uncompressed. If the second
argument is missing, the image is written to standard output. The compression may also
be explicitly selected with the --format= switch. This is in particular useful if the
second parameter is left unspecified.

Much like image downloads and imports, ongoing exports may be listed with
list-transfers and aborted with cancel-transfer.

Note that, currently, only directory and subvolume images may be exported as TAR
images, and only raw disk images as RAW images.

list-transfers
Shows a list of container or VM image downloads, imports and exports that are
currently in progress.

cancel-transfer ID...
Aborts a download, import or export of the container or VM image with the specified
ID. To list ongoing transfers and their IDs, use list-transfers.

OPTIONS

The following options are understood:

-p, --property=
When showing machine or image properties, limit the output to certain properties as
specified by the argument. If not specified, all set properties are shown. The
argument should be a property name, such as "Name". If specified more than once, all
properties with the specified names are shown.

-a, --all
When showing machine or image properties, show all properties regardless of whether
they are set or not.

When listing VM or container images, do not suppress images beginning in a dot
character (".").

When cleaning VM or container images, remove all images, not just hidden ones.

--value
When printing properties with show, only print the value, and skip the property name
and "=".

-l, --full
Do not ellipsize process tree entries or table. This implies --max-addresses=full.

--kill-who=
When used with kill, choose which processes to kill. Must be one of leader, or all to
select whether to kill only the leader process of the machine or all processes of the
machine. If omitted, defaults to all.

-s, --signal=
When used with kill, choose which signal to send to selected processes. Must be one of
the well-known signal specifiers such as SIGTERM, SIGINT or SIGSTOP. If omitted,
defaults to SIGTERM.

The special value "help" will list the known values and the program will exit
immediately, and the special value "list" will list known values along with the
numerical signal numbers and the program will exit immediately.

--uid=
When used with the shell command, chooses the user ID to open the interactive shell
session as. If the argument to the shell command also specifies a user name, this
option is ignored. If the name is not specified in either way, "root" will be used by
default. Note that this switch is not supported for the login command (see below).

-E NAME[=VALUE], --setenv=NAME[=VALUE]
When used with the shell command, sets an environment variable for the executed shell.
This option may be used more than once to set multiple variables. When "=" and VALUE
are omitted, the value of the variable with the same name in the program environment
will be used.

Note that this option is not supported for the login command.

--mkdir
When used with bind, creates the destination file or directory before applying the
bind mount. Note that even though the name of this option suggests that it is suitable
only for directories, this option also creates the destination file node to mount over
if the object to mount is not a directory, but a regular file, device node, socket or
FIFO.

--read-only
When used with bind, creates a read-only bind mount.

When used with clone, import-raw or import-tar a read-only container or VM image is
created.

-n, --lines=
When used with status, controls the number of journal lines to show, counting from the
most recent ones. Takes a positive integer argument. Defaults to 10.

-o, --output=
When used with status, controls the formatting of the journal entries that are shown.
For the available choices, see journalctl(1). Defaults to "short".

--verify=
When downloading a container or VM image, specify whether the image shall be verified
before it is made available. Takes one of "no", "checksum" and "signature". If "no",
no verification is done. If "checksum" is specified, the download is checked for
integrity after the transfer is complete, but no signatures are verified. If
"signature" is specified, the checksum is verified and the image's signature is
checked against a local keyring of trustable vendors. It is strongly recommended to
set this option to "signature" if the server and protocol support this. Defaults to
"signature".

--force
When downloading a container or VM image, and a local copy by the specified local
machine name already exists, delete it first and replace it by the newly downloaded
image.

--format=
When used with the export-tar or export-raw commands, specifies the compression format
to use for the resulting file. Takes one of "uncompressed", "xz", "gzip", "bzip2". By
default, the format is determined automatically from the image file name passed.

--max-addresses=
When used with the list-machines command, limits the number of ip addresses output for
every machine. Defaults to 1. All addresses can be requested with "all" as argument to
--max-addresses=. If the argument to --max-addresses= is less than the actual number
of addresses, "..."follows the last address.

-q, --quiet
Suppresses additional informational output while running.

-H, --host=
Execute the operation remotely. Specify a hostname, or a username and hostname
separated by "@", to connect to. The hostname may optionally be suffixed by a port ssh
is listening on, separated by ":", and then a container name, separated by "/", which
connects directly to a specific container on the specified host. This will use SSH to
talk to the remote machine manager instance. Container names may be enumerated with
machinectl -H HOST. Put IPv6 addresses in brackets.

-M, --machine=
Connect to systemd-machined.service(8) running in a local container, to perform the
specified operation within the container.

--no-pager
Do not pipe output into a pager.

--no-legend
Do not print the legend, i.e. column headers and the footer with hints.

--no-ask-password
Do not query the user for authentication for privileged operations.

-h, --help
Print a short help text and exit.

--version
Print a short version string and exit.

MACHINE AND IMAGE NAMES

The machinectl tool operates on machines and images whose names must be chosen following
strict rules. Machine names must be suitable for use as hostnames following a conservative
subset of DNS and UNIX/Linux semantics. Specifically, they must consist of one or more
non-empty label strings, separated by dots. No leading or trailing dots are allowed. No
sequences of multiple dots are allowed. The label strings may only consist of alphanumeric
characters as well as the dash and underscore. The maximum length of a machine name is 64
characters.

A special machine with the name ".host" refers to the running host system itself. This is
useful for execution operations or inspecting the host system as well. Note that
machinectl list will not show this special machine unless the --all switch is specified.

Requirements on image names are less strict, however, they must be valid UTF-8, must be
suitable as file names (hence not be the single or double dot, and not include a slash),
and may not contain control characters. Since many operations search for an image by the
name of a requested machine, it is recommended to name images in the same strict fashion
as machines.

A special image with the name ".host" refers to the image of the running host system. It
hence conceptually maps to the special ".host" machine name described above. Note that
machinectl list-images will not show this special image either, unless --all is specified.

FILES AND DIRECTORIES

       Machine images are preferably stored in /var/lib/machines/, but are also searched for in
       /usr/local/lib/machines/ and /usr/lib/machines/. For compatibility reasons, the directory
       /var/lib/container/ is searched, too. Note that images stored below /usr/ are always
       considered read-only. It is possible to symlink machines images from other directories
       into /var/lib/machines/ to make them available for control with machinectl.

       Note that some image operations are only supported, efficient or atomic on btrfs file
       systems.

       Disk images are understood by systemd-nspawn(1) and machinectl in three formats:

       •   A simple directory tree, containing the files and directories of the container to
           boot.

       •   Subvolumes (on btrfs file systems), which are similar to the simple directories,
           described above. However, they have additional benefits, such as efficient cloning and
           quota reporting.

       •   "Raw" disk images, i.e. binary images of disks with a GPT or MBR partition table.
           Images of this type are regular files with the suffix ".raw".

       See systemd-nspawn(1) for more information on image formats, in particular its
       --directory= and --image= options.

EXAMPLES

Example 1. Download an Ubuntu image and open a shell in it

# machinectl pull-tar https://cloud-images.ubuntu.com/trusty/current/trusty-server-cloudimg-amd64-root.tar.gz
# systemd-nspawn -M trusty-server-cloudimg-amd64-root

This downloads and verifies the specified .tar image, and then uses systemd-nspawn(1) to
open a shell in it.

Example 2. Download a Fedora image, set a root password in it, start it as a service

# machinectl pull-raw --verify=no \
https://download.fedoraproject.org/pub/fedora/linux/releases/36/Cloud/x86_64/images/Fedora-Cloud-Base-36-1.5.x86_64.raw.xz \
Fedora-Cloud-Base-36-1.5.x86-64
# systemd-nspawn -M Fedora-Cloud-Base-36-1.5.x86-64
# passwd
# exit
# machinectl start Fedora-Cloud-Base-36-1.5.x86-64
# machinectl login Fedora-Cloud-Base-36-1.5.x86-64

This downloads the specified .raw image with verification disabled. Then, a shell is
opened in it and a root password is set. Afterwards the shell is left, and the machine
started as system service. With the last command a login prompt into the container is
requested.

Example 3. Exports a container image as tar file

# machinectl export-tar fedora myfedora.tar.xz

Exports the container "fedora" as an xz-compressed tar file myfedora.tar.xz into the
current directory.

Example 4. Create a new shell session

# machinectl shell --uid=lennart

This creates a new shell session on the local host for the user ID "lennart", in a
su(1)-like fashion.

EXIT STATUS

       On success, 0 is returned, a non-zero failure code otherwise.

ENVIRONMENT

$SYSTEMD_LOG_LEVEL
The maximum log level of emitted messages (messages with a higher log level, i.e. less
important ones, will be suppressed). Either one of (in order of decreasing importance)
emerg, alert, crit, err, warning, notice, info, debug, or an integer in the range
0...7. See syslog(3) for more information.

$SYSTEMD_LOG_COLOR
A boolean. If true, messages written to the tty will be colored according to priority.

This setting is only useful when messages are written directly to the terminal,
because journalctl(1) and other tools that display logs will color messages based on
the log level on their own.

$SYSTEMD_LOG_TIME
A boolean. If true, console log messages will be prefixed with a timestamp.

This setting is only useful when messages are written directly to the terminal or a
file, because journalctl(1) and other tools that display logs will attach timestamps
based on the entry metadata on their own.

$SYSTEMD_LOG_LOCATION
A boolean. If true, messages will be prefixed with a filename and line number in the
source code where the message originates.

Note that the log location is often attached as metadata to journal entries anyway.
Including it directly in the message text can nevertheless be convenient when
debugging programs.

$SYSTEMD_LOG_TID
A boolean. If true, messages will be prefixed with the current numerical thread ID
(TID).

Note that the this information is attached as metadata to journal entries anyway.
Including it directly in the message text can nevertheless be convenient when
debugging programs.

$SYSTEMD_LOG_TARGET
The destination for log messages. One of console (log to the attached tty),
console-prefixed (log to the attached tty but with prefixes encoding the log level and
"facility", see syslog(3), kmsg (log to the kernel circular log buffer), journal (log
to the journal), journal-or-kmsg (log to the journal if available, and to kmsg
otherwise), auto (determine the appropriate log target automatically, the default),
null (disable log output).

$SYSTEMD_PAGER
Pager to use when --no-pager is not given; overrides $PAGER. If neither $SYSTEMD_PAGER
nor $PAGER are set, a set of well-known pager implementations are tried in turn,
including less(1) and more(1), until one is found. If no pager implementation is
discovered no pager is invoked. Setting this environment variable to an empty string
or the value "cat" is equivalent to passing --no-pager.

Note: if $SYSTEMD_PAGERSECURE is not set, $SYSTEMD_PAGER (as well as $PAGER) will be
silently ignored.

$SYSTEMD_LESS
Override the options passed to less (by default "FRSXMK").

Users might want to change two options in particular:

K
This option instructs the pager to exit immediately when Ctrl+C is pressed. To
allow less to handle Ctrl+C itself to switch back to the pager command prompt,
unset this option.

If the value of $SYSTEMD_LESS does not include "K", and the pager that is invoked
is less, Ctrl+C will be ignored by the executable, and needs to be handled by the
pager.

X
This option instructs the pager to not send termcap initialization and
deinitialization strings to the terminal. It is set by default to allow command
output to remain visible in the terminal even after the pager exits. Nevertheless,
this prevents some pager functionality from working, in particular paged output
cannot be scrolled with the mouse.

See less(1) for more discussion.

$SYSTEMD_LESSCHARSET
Override the charset passed to less (by default "utf-8", if the invoking terminal is
determined to be UTF-8 compatible).

$SYSTEMD_PAGERSECURE
Takes a boolean argument. When true, the "secure" mode of the pager is enabled; if
false, disabled. If $SYSTEMD_PAGERSECURE is not set at all, secure mode is enabled if
the effective UID is not the same as the owner of the login session, see geteuid(2)
and sd_pid_get_owner_uid(3). In secure mode, LESSSECURE=1 will be set when invoking
the pager, and the pager shall disable commands that open or create new files or start
new subprocesses. When $SYSTEMD_PAGERSECURE is not set at all, pagers which are not
known to implement secure mode will not be used. (Currently only less(1) implements
secure mode.)

Note: when commands are invoked with elevated privileges, for example under sudo(8) or
pkexec(1), care must be taken to ensure that unintended interactive features are not
enabled. "Secure" mode for the pager may be enabled automatically as describe above.
Setting SYSTEMD_PAGERSECURE=0 or not removing it from the inherited environment allows
the user to invoke arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER
variables are to be honoured, $SYSTEMD_PAGERSECURE must be set too. It might be
reasonable to completely disable the pager using --no-pager instead.

$SYSTEMD_COLORS
Takes a boolean argument. When true, systemd and related utilities will use colors in
their output, otherwise the output will be monochrome. Additionally, the variable can
take one of the following special values: "16", "256" to restrict the use of colors to
the base 16 or 256 ANSI colors, respectively. This can be specified to override the
automatic decision based on $TERM and what the console is connected to.

$SYSTEMD_URLIFY
The value must be a boolean. Controls whether clickable links should be generated in
the output for terminal emulators supporting this. This can be specified to override
the decision that systemd makes based on $TERM and other conditions.