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NAME

mmdebstrap - multi-mirror Debian chroot creation

SYNOPSIS

mmdebstrap [OPTION...] [SUITE [TARGET [MIRROR...]]]

DESCRIPTION

mmdebstrap creates a Debian chroot of SUITE into TARGET from one or more _MIRROR_s. It is meant as an alternative to the debootstrap tool (see section DEBOOTSTRAP). In contrast to debootstrap it uses apt to resolve dependencies and is thus able to use more than one mirror and resolve more complex dependency relationships. See section OPERATION for an overview of how mmdebstrap works internally.

The SUITE option may either be a valid release code name (eg, sid, bookworm, trixie) or a symbolic name (eg, unstable, testing, stable, oldstable). Any suite name that works with apt on the given mirror will work. The SUITE option is optional if no TARGET and no MIRROR option is provided. If SUITE is missing, then the information of the desired suite has to come from standard input as part of a valid apt sources.list file or be set up via hooks. The value of the SUITE argument will be used to determine which apt index to use for finding out the set of Essential:yes packages and/or the set of packages with the right priority for the selected variant. This functionality can be disabled by choosing the empty string for SUITE. See the section VARIANTS for more information.

The TARGET option may either be the path to a directory, the path to a tarball filename, the path to a squashfs image, the path to an ext2 or ext4 image, a FIFO, a character special device, or -. The TARGET option is optional if no MIRROR option is provided. If TARGET is missing or if TARGET is -, an uncompressed tarball will be sent to standard output. Without the --format option, TARGET will be used to choose the format. See the section FORMATS for more information.

The MIRROR option may either be provided as a URI, in apt one-line format, as a path to a file in apt's one-line or deb822-format, or -. If no MIRROR option is provided, then http://deb.debian.org/debian is used as the default. If SUITE does not refer to "unstable" or "testing", then SUITE-updates and SUITE-security mirrors are automatically added. If a MIRROR option starts with "deb " or "deb-src " then it is used as a one-line format entry for apt's sources.list inside the chroot. If a MIRROR option contains a "://" then it is interpreted as a mirror URI and the apt line inside the chroot is assembled as "deb [arch=A] B C D" where A is the host's native architecture, B is the MIRROR, C is the given SUITE and D is the components given via --components (defaults to "main"). If a MIRROR option happens to be an existing file, then its contents are written into the chroot's sources.list (if the first MIRROR is a file in one-line format) or into the chroot's sources.list.d directory, named with the extension .list or .sources, depending on whether the file is in one-line or deb822 format, respectively. If MIRROR is - then standard input is pasted into the chroot's sources.list. More than one mirror can be specified and are appended to the chroot's sources.list in the given order. If you specify a https or tor MIRROR and you want the chroot to be able to update itself, don't forget to also install the ca-certificates package, the apt-transport-https package for apt versions less than 1.5 and/or the apt-transport-tor package using the --include option, as necessary.

All status output is printed to standard error unless --logfile is used to redirect it to a file or --quiet or --silent is used to suppress any output on standard error. Help and version information will be printed to standard error with the --help and --version options, respectively. Otherwise, an uncompressed tarball might be sent to standard output if TARGET is - or if no TARGET was specified.

OPTIONS

Options are case insensitive. Short options may be bundled. Long options require a double dash and may be abbreviated to uniqueness. Options can be placed anywhere on the command line, even before or mixed with the SUITE, TARGET, and MIRROR arguments. A double dash -- can be used to stop interpreting command line arguments as options to allow SUITE, TARGET and MIRROR arguments that start with a single or double dash. Option order only matters for options that can be passed multiple times as documented below.

  • -h,--help

    Print synopsis and options of this man page and exit.

  • --man

    Show the full man page as generated from Perl POD in a pager. This requires the perldoc program from the perl-doc package. This is the same as running:

      pod2man /usr/bin/mmdebstrap | man -l -

  • --version

    Print the mmdebstrap version and exit.

  • --variant=name

    Choose which package set to install. Valid variant _name_s are extract, custom, essential, apt, required, minbase, buildd, important, debootstrap, -, and standard. The default variant is debootstrap. See the section VARIANTS for more information.

  • --mode=name

    Choose how to perform the chroot operation and create a filesystem with ownership information different from the current user. Valid mode _name_s are auto, sudo, root, unshare, fakeroot, fakechroot and chrootless. The default mode is auto. See the section MODES for more information.

  • --format=name

    Choose the output format. Valid format _name_s are auto, directory, tar, squashfs, ext2, ext4 and null. The default format is auto. See the section FORMATS for more information.

  • --aptopt=option|file

    Pass arbitrary _option_s to apt. Will be permamently added to /etc/apt/apt.conf.d/99mmdebstrap inside the chroot. Use hooks for temporary configuration options. Can be specified multiple times. Each option will be appended to 99mmdebstrap. A semicolon will be added at the end of the option if necessary. If the command line argument is an existing file, the content of the file will be appended to 99mmdebstrap verbatim.

    Example: This is necessary for allowing old timestamps from snapshot.debian.org

      --aptopt='Acquire::Check-Valid-Until "false"'
  --aptopt='Apt::Key::gpgvcommand "/usr/libexec/mmdebstrap/gpgvnoexpkeysig"'

    Example: Settings controlling download of package description translations

      --aptopt='Acquire::Languages { "environment"; "en"; }'
  --aptopt='Acquire::Languages "none"'

    Example: Enable installing Recommends (by default mmdebstrap doesn't)

      --aptopt='Apt::Install-Recommends "true"'

    Example: Configure apt-cacher or apt-cacher-ng as an apt proxy

      --aptopt='Acquire::http { Proxy "http://127.0.0.1:3142"; }'

    Example: For situations in which the apt sandbox user cannot access the chroot

      --aptopt='APT::Sandbox::User "root"'

    Example: Minimizing the number of packages installed from experimental

      --aptopt='APT::Solver "aspcud"'
  --aptopt='APT::Solver::aspcud::Preferences
     "-count(solution,APT-Release:=/a=experimental/),-removed,-changed,-new"'

  • --keyring=file|directory

    Change the default keyring to use by apt during the initial setup. This is similar to setting Dir::Etc::Trusted and Dir::Etc::TrustedParts using --aptopt except that the latter setting will be permanently stored in the chroot while the keyrings passed via --keyring will only be visible to apt as run by mmdebstrap. Do not use --keyring if apt inside the chroot needs to know about your keys after the initial chroot creation by mmdebstrap. This option is mainly intended for users who use mmdebstrap as a deboostrap drop-in replacement. As such, it is probably not what you want to use if you use mmdebstrap with more than a single mirror unless you pass it a directory containing all the keyrings you need.

    By default, the local setting of Dir::Etc::Trusted and Dir::Etc::TrustedParts are used to choose the keyring used by apt as run by mmdebstrap. These two locations are set to /etc/apt/trusted.gpg and /etc/apt/trusted.gpg.d by default. Depending on whether a file or directory is passed to this option, the former and latter default can be changed, respectively. Since apt only supports a single keyring file and directory, respectively, you can not use this option to pass multiple files and/or directories. Using the --keyring argument in the following way is equal to keeping the default:

      --keyring=/etc/apt/trusted.gpg --keyring=/etc/apt/trusted.gpg.d

    If you need to pass multiple keyrings, use the signed-by option when specifying the mirror like this:

      mmdebstrap mysuite out.tar "deb [signed-by=/path/to/key.gpg] http://..."

    Another reason to use signed-by instead of --keyring is if apt inside the chroot needs to know by what key the repository is signed even after the initial chroot creation.

    The signed-by option will automatically be added to the final sources.list if the keyring required for the selected SUITE is not yet trusted by apt. Automatically adding the signed-by option in these cases requires gpg to be installed. If gpg and ubuntu-archive-keyring are installed, then you can create a Ubuntu Bionic chroot on Debian like this:

      mmdebstrap bionic ubuntu-bionic.tar

    The resulting chroot will have a source.list with a signed-by option pointing to /usr/share/keyrings/ubuntu-archive-keyring.gpg.

    You do not need to use --keyring or signed-by if you placed the keys that apt needs to know about into /etc/apt/trusted.gpg.d in the --setup-hook (which is before apt update runs), for example by using the copy-in special hook. You also need to copy your keys into the chroot explicitly if the key you passed via signed-by points to a location that is not otherwise populated during chroot creation (for example by installing a keyring package).

  • --dpkgopt=option|file

    Pass arbitrary _option_s to dpkg. Will be permanently added to /etc/dpkg/dpkg.cfg.d/99mmdebstrap inside the chroot. Use hooks for temporary configuration options. Can be specified multiple times. Each option will be appended to 99mmdebstrap. If the command line argument is an existing file, the content of the file will be appended to 99mmdebstrap verbatim.

    Example: Exclude paths to reduce chroot size

      --dpkgopt='path-exclude=/usr/share/man/*'
  --dpkgopt='path-include=/usr/share/man/man[1-9]/*'
  --dpkgopt='path-exclude=/usr/share/locale/*'
  --dpkgopt='path-include=/usr/share/locale/locale.alias'
  --dpkgopt='path-exclude=/usr/share/doc/*'
  --dpkgopt='path-include=/usr/share/doc/*/copyright'
  --dpkgopt='path-include=/usr/share/doc/*/changelog.Debian.*'

  • --include=pkg1[,pkg2,...]

    Comma or whitespace separated list of packages which will be installed in addition to the packages installed by the specified variant. The direct and indirect hard dependencies will also be installed. The behaviour of this option depends on the selected variant. The extract and custom variants install no packages by default, so for these variants, the packages specified by this option will be the only ones that get either extracted or installed by dpkg, respectively. For all other variants, apt is used to install the additional packages. Package names are directly passed to apt and thus, you can use apt features like pkg/suite, pkg=version, pkg-, use a glob or regex for pkg, use apt patterns or pass a path to a .deb package file (see below for notes concerning passing the path to a .deb package file in unshare mode). See apt(8) for the supported syntax.

    The option can be specified multiple times and the packages are concatenated in the order in which they are given on the command line. If later list items are repeated, then they get dropped so that the resulting package list is free of duplicates. So the following are equivalent:

      --include="pkg1/stable pkg2=1.0 pkg3-"
  --include=pkg1/stable,pkg2=1.0,pkg3-,,,
  --incl=pkg1/stable --incl="pkg2=1.0 pkg3-" --incl=pkg2=1.0,pkg3-

    Since the list of packages is separated by comma or whitespace, it is not possible to mix apt patterns or .deb package file paths containing either commas or whitespace with normal package names. If you do, your patterns and paths will be split by comma and whitespace as well and become useless. To pass such a pattern or package file path, put them into their own --include option. If the argument to --include starts with an apt pattern or with a file path, then it will not be split:

      --include="?or(?priority(required), ?priority(important))"
  --include="./path/to/deb with spaces/and,commas/foo.deb"

    Specifically, all arguments to --include that start with a ?, !, ~, (, /, ./ or ../ are not split and treated as single arguments to apt. To add more packages, use multiple --include options. To disable this detection of patterns and paths, start the argument to --include with a comma or whitespace.

    If you pass the path to a .deb package file using --include, mmdebstrap will ensure that the path exists. If the path is a relative path, it will internally by converted to an absolute path. Since apt (outside the chroot) passes paths to dpkg (on the inside) verbatim, you have to make the .deb package available under the same path inside the chroot as well or otherwise dpkg inside the chroot will be unable to access it. This can be achieved using a setup-hook. A hook that automatically makes the contents of file:// mirrors as well as .deb packages given with --include available inside the chroot is provided by mmdebstrap as --hook-dir=/usr/share/mmdebstrap/hooks/file-mirror-automount. This hook takes care of copying all relevant file to their correct locations and cleans up those files at the end. In unshare mode, the .deb package paths have to be accessible by the unshared user as well. This means that the package itself likely must be made world-readable and all directory components on the path to it world-executable.

  • --components=comp1[,comp2,...]

    Comma or whitespace separated list of components like main, contrib, non-free and non-free-firmware which will be used for all URI-only MIRROR arguments. The option can be specified multiple times and the components are concatenated in the order in which they are given on the command line. If later list items are repeated, then they get dropped so that the resulting component list is free of duplicates. So the following are equivalent:

      --components="main contrib non-free non-free-firmware"
  --components=main,contrib,non-free,non-free-firmware
  --comp=main --comp="contrib non-free" --comp="main,non-free-firmware"

  • --architectures=native[,foreign1,...]

    Comma or whitespace separated list of architectures. The first architecture is the native architecture inside the chroot. The remaining architectures will be added to the foreign dpkg architectures. Without this option, the native architecture of the chroot defaults to the native architecture of the system running mmdebstrap. The option can be specified multiple times and values are concatenated. If later list items are repeated, then they get dropped so that the resulting list is free of duplicates. So the following are equivalent:

      --architectures="amd64 armhf mipsel"
  --architectures=amd64,armhf,mipsel
  --arch=amd64 --arch="armhf mipsel" --arch=armhf,mipsel

  • --simulate, --dry-run

    Run apt-get with --simulate. Only the package cache is initialized but no binary packages are downloaded or installed. Use this option to quickly check whether a package selection within a certain suite and variant can in principle be installed as far as their dependencies go. If the output is a tarball, then no output is produced. If the output is a directory, then the directory will be left populated with the skeleton files and directories necessary for apt to run in it. No hooks are executed in with --simulate or --dry-run.

  • --setup-hook=command

    Execute arbitrary _command_s right after initial setup (directory creation, configuration of apt and dpkg, ...) but before any packages are downloaded or installed. At that point, the chroot directory does not contain any executables and thus cannot be chroot-ed into. See section HOOKS for more information.

    Example: add additional apt sources entries on top of the default ones:

      --setup-hook='echo "deb http..." > "$1"/etc/apt/sources.list.d/custom.list'

    Example: Setup chroot for installing a sub-essential busybox-based chroot with --variant=custom --include=dpkg,busybox,libc-bin,base-files,base-passwd,debianutils

      --setup-hook='mkdir -p "$1/bin"'
  --setup-hook='for p in awk cat chmod chown cp diff echo env grep less ln
      mkdir mount rm rmdir sed sh sleep sort touch uname mktemp; do
      ln -s busybox "$1/bin/$p"; done'
  --setup-hook='echo root:x:0:0:root:/root:/bin/sh > "$1/etc/passwd"'
  --setup-hook='printf "root:x:0:\nmail:x:8:\nutmp:x:43:\n" > "$1/etc/group"'

    For a more elegant way for setting up a sub-essential busybox-based chroot, see the --hook-dir option below.

  • --extract-hook=command

    Execute arbitrary _command_s after the Essential:yes packages have been extracted but before installing them. See section HOOKS for more information.

    Example: Install busybox symlinks

      --extract-hook='chroot "$1" /bin/busybox --install -s'

  • --essential-hook=command

    Execute arbitrary _command_s after the Essential:yes packages have been installed but before installing the remaining packages. The hook is not executed for the extract and custom variants. See section HOOKS for more information.

    Example: Enable unattended upgrades

      --essential-hook='echo unattended-upgrades
      unattended-upgrades/enable_auto_updates boolean true
      | chroot "$1" debconf-set-selections'

    Example: Select Europe/Berlin as the timezone

      --essential-hook='echo tzdata tzdata/Areas select Europe
      | chroot "$1" debconf-set-selections'
  --essential-hook='echo tzdata tzdata/Zones/Europe select Berlin
      | chroot "$1" debconf-set-selections'

  • --customize-hook=command

    Execute arbitrary _command_s after the chroot is set up and all packages got installed but before final cleanup actions are carried out. See section HOOKS for more information.

    Example: Add a user without a password

      --customize-hook='chroot "$1" useradd --home-dir /home/user
      --create-home user'
  --customize-hook='chroot "$1" passwd --delete user'

    Example: set up /etc/hostname and /etc/hosts

      --customize-hook='echo host > "$1/etc/hostname"'
  --customize-hook='echo "127.0.0.1 localhost host" > "$1/etc/hosts"'

    Example: to mimic debootstrap behaviour, mmdebstrap copies from the host. Remove them in a --customize-hook to make the chroot reproducible across multiple hosts:

      --customize-hook='rm "$1"/etc/resolv.conf'
  --customize-hook='rm "$1"/etc/hostname'

  • --hook-directory=directory

    Execute scripts in directory with filenames starting with setup, extract, essential or customize, at the respective stages during an mmdebstrap run. The files must be marked executable. Their extension is ignored. Subdirectories are not traversed. This option is a short-hand for specifying the remaining four hook options individually for each file in the directory. If there are more than one script for a stage, then they are added alphabetically. This is useful in cases, where a user wants to run the same hooks frequently. For example, given a directory ./hooks with two scripts setup01-foo.sh and setup02-bar.sh, this call:

      mmdebstrap --customize=./scriptA --hook-dir=./hooks --setup=./scriptB

    is equivalent to this call:

      mmdebstrap --customize=./scriptA --setup=./hooks/setup01-foo.sh \
      --setup=./hooks/setup02-bar.sh --setup=./scriptB

    The option can be specified multiple times and scripts are added to the respective hooks in the order the options are given on the command line. Thus, if the scripts in two directories depend upon each other, the scripts must be placed into a common directory and be named such that they get added in the correct order.

    Example 1: Run mmdebstrap with eatmydata

      --hook-dir=/usr/share/mmdebstrap/hooks/eatmydata

    Example 2: Setup chroot for installing a sub-essential busybox-based chroot

      --hook-dir=/usr/share/mmdebstrap/hooks/busybox

    Example 3: Automatically mount all directories referenced by file:// mirrors into the chroot

      --hook-dir=/usr/share/mmdebstrap/hooks/file-mirror-automount

  • --skip=stage[,stage,...]

    mmdebstrap tries hard to implement sensible defaults and will try to stop you before shooting yourself in the foot. This option is for when you are sure you know what you are doing and allows one to skip certain actions and safety checks. See section OPERATION for a list of possible arguments and their context. The option can be specified multiple times or you can separate multiple values by comma or whitespace.

  • -q,--quiet, -s,--silent

    Do not write anything to standard error. If used together with --verbose or --debug, only the last option will take effect.

  • -v,--verbose

    Instead of progress bars, write the dpkg and apt output directly to standard error. If used together with --quiet or --debug, only the last option will take effect.

  • -d,--debug

    In addition to the output produced by --verbose, write detailed debugging information to standard error. Errors will print a backtrace. If used together with --quiet or --verbose, only the last option will take effect.

  • --logfile=filename

    Instead of writing status information to standard error, write it into the file given by filename.

MODES

Creating a Debian chroot requires not only permissions for running chroot but also the ability to create files owned by the superuser. The selected mode decides which way this is achieved.

  • auto

    This mode automatically selects a fitting mode. If the effective user id is the one of the superuser, then the sudo mode is chosen. Otherwise, the unshare mode is picked if /etc/subuid and /etc/subgid are set up correctly. Should that not be the case and if the fakechroot binary exists, the fakechroot mode is chosen.

  • sudo, root

    This mode directly executes chroot and is the same mode of operation as is used by debootstrap. It is the only mode that can directly create a directory chroot with the right permissions. If the chroot directory is not accessible by the _apt user, then apt sandboxing will be automatically disabled. This mode needs to be able to mount and thus requires CAP_SYS_ADMIN.

  • unshare

    When used as a normal (not root) user, this mode uses Linux user namespaces to allow unprivileged use of chroot and creation of files that appear to be owned by the superuser inside the unshared namespace. A tarball created in this mode will be bit-by-bit identical to a tarball created with the root mode. With this mode, the only binaries that will run as the root user will be newuidmap(1) and newgidmap(1) via their setuid bit. Running those successfully requires /etc/subuid and /etc/subgid to have an entry for your username. This entry was usually created by adduser(8) already.

    The unshared user will not automatically have access to the same files as you do. This is intentional and an additional security against unintended changes to your files that could theoretically result from running mmdebstrap and package maintainer scripts. To copy files in and out of the chroot, either use globally readable or writable directories or use special hooks like copy-in and copy-out.

    Besides the user namespace, the mount, pid (process ids), uts (hostname) and ipc namespaces will be unshared as well. See the man pages of namespaces(7) and unshare(2) as well as the manual pages they are linking to.

    A directory chroot created with this mode will end up with wrong ownership information (seen from outside the unshared user namespace). For correct ownership information, the directory must be accessed from a user namespace with the right subuid/subgid offset, like so:

      $ lxc-usernsexec -- lxc-unshare -s 'MOUNT|PID|UTSNAME|IPC' -- \
  > /usr/sbin/chroot ./debian-rootfs /bin/bash

    Or without LXC:

      $ mmdebstrap --unshare-helper /usr/sbin/chroot ./debian-rootfs /bin/bash

    Or without mmdebstrap:

      $ unshare --map-auto --map-user=65536 --map-group=65536 --keep-caps -- \
  > /usr/sbin/chroot ./debian-rootfs /bin/bash

    The above uses --map-auto to map the block of user/group ids for the effective user/group to a block starting at user/group ID 0. We also want to map the current effective user/group ID into the subuid/subgid range using --map-user and --map-group, respectively. But if that uid/gid overlaps with the respective range, a "hole" will be removed from the mapping by the unshare(1) utility and the remaining uid/gid values will get shifted. Thus, we map the current effective user/group ID to the highest possible uid/gid, putting them at the end. Since that means that the user/group will be "nobody" and not "root" inside the namespace, --keep-caps propagate permitted capabilities into the ambient set and thus give the user CAP_DAC_OVERRIDE and other capabilities that it would've had. The following does NOT work:

      $ unshare --map-root-user --map-auto ...            # or equavalient:
  $ unshare --map-user=0 --map-group=0 --map-users=auto --map-groups=auto ...

    Using the format of lxc-usernsexec(1), these options will result in the following mapping:

      0:$UID:1 + 1:$SUBUIDBASE:65535

    So a hole is punched in the automatically mapped range at the very beginning to make space for the user id of the current user as root inside the namespace and the remaining uids are shifted. With --map-user=65536 the mapping is as follows and places the current user at the end of the range, preventing any shifting:

      0:$SUBUIDBASE:65536 + 65536:$UID:1

    Lastly, if you don't mind using superuser privileges and have systemd-nspawn available and you know your subuid/subgid offset (100000 in this example):

      $ sudo systemd-nspawn --private-users=100000 \
  > --directory=./debian-rootfs /bin/bash

    A directory created in unshare mode cannot be removed the normal way. Instead, use something like this:

      $ unshare --map-root-user --map-auto rm -rf ./debian-rootfs

    The above unshare(1) command will map user and group ids into different ranges compared to the mapping used by mmdebstrap (effectively shifting them one up) but it will provide the required capabilities for the removal operation.

    If this mode is used as the root user, the user namespace is not unshared (but the mount namespace and other still are) and created directories will have correct ownership information. This is also useful in cases where the root user wants the benefits of an unshared mount namespace to prevent accidentally messing up the system.

  • fakeroot, fakechroot

    This mode will exec mmdebstrap again under fakechroot fakeroot. A directory chroot created with this mode will end up with wrong permissions. If you need a directory then run mmdebstrap under fakechroot fakeroot -s fakeroot.env and use fakeroot.env later when entering the chroot with fakechroot fakeroot -i fakeroot.env chroot .... This mode will not work if maintainer scripts are unable to handle LD_PRELOAD correctly like the package initramfs-tools until version 0.132. This mode will also not work with a different libc inside the chroot than on the outside. See the section LIMITATIONS in fakechroot(1).

  • chrootless

    Uses the dpkg option --force-script-chrootless to install packages into TARGET without dpkg and apt inside TARGET but using apt and dpkg from the machine running mmdebstrap. Maintainer scripts are run without chrooting into TARGET and rely on their dependencies being installed on the machine running mmdebstrap. Only very few packages support this mode. Namely, as of 2022, not all essential packages support it. See https://wiki.debian.org/Teams/Dpkg/Spec/InstallBootstrap or the dpkg-root-support usertag of debian-dpkg@lists.debian.org in the Debian bug tracking system. WARNING: if this option is used carelessly with packages that do not support DPKG_ROOT, this mode can result in undesired changes to the system running mmdebstrap because maintainer-scripts will be run without chroot(1). Make sure to run this mode without superuser privileges and/or inside a throw-away chroot environment like so:

      mmdebstrap --variant=apt --include=mmdebstrap \
      --customize-hook='chroot "$1" mmdebstrap --mode=chrootless
                        --variant=apt unstable chrootless.tar' \
      --customize-hook='copy-out chrootless.tar .' unstable /dev/null

VARIANTS

All package sets also include the direct and indirect hard dependencies (but not recommends) of the selected package sets. The variants minbase, buildd and -, resemble the package sets that debootstrap would install with the same --variant argument. The release with a name matching the SUITE argument as well as the native architecture will be used to determine the Essential:yes and priority values. To select packages with matching priority from any suite, specify the empty string for SUITE. The default variant is debootstrap.

  • extract

    Installs nothing by default (not even Essential:yes packages). Packages given by the --include option are extracted but will not be installed.

  • custom

    Installs nothing by default (not even Essential:yes packages). Packages given by the --include option will be installed. If another mode than chrootless was selected and dpkg was not part of the included package set, then this variant will fail because it cannot configure the packages.

  • essential

    Essential:yes packages. If SUITE is a non-empty string, then only packages from the archive with suite or codename matching SUITE will be considered for selection of Essential:yes packages.

  • apt

    The essential set plus apt. It is roughly equivalent to running mmdebstrap with

      --variant=essential --include="apt"

  • buildd

    The essential set plus apt and build-essential. It is roughly equivalent to running mmdebstrap with

      --variant=essential --include="apt,build-essential"

  • required, minbase

    The essential set plus all packages with Priority:required. It is roughly equivalent to running mmdebstrap with

      --variant=essential --include="?priority(required)"

  • important, debootstrap, -

    The required set plus all packages with Priority:important. This is the default of debootstrap. It is roughly equivalent to running mmdebstrap with

      --variant=essential --include="~prequired|~pimportant"

  • standard

    The important set plus all packages with Priority:standard. It is roughly equivalent to running mmdebstrap with

      --variant=essential --include="~prequired|~pimportant|~pstandard"

FORMATS

The output format of mmdebstrap is specified using the --format option. Without that option the default format is auto. The following formats exist:

  • auto

    When selecting this format (the default), the actual format will be inferred from the TARGET positional argument. If TARGET was not specified, then the tar format will be chosen. If TARGET happens to be /dev/null or if standard output is /dev/null, then the null format will be chosen. If TARGET is an existing directory, and does not equal to -, then the directory format will be chosen. If TARGET ends with .tar or with one of the filename extensions listed in the section COMPRESSION, or if TARGET equals -, or if TARGET is a named pipe (fifo) or if TARGET is a character special file, then the tar format will be chosen. If TARGET ends with .squashfs or .sqfs, then the squashfs format will be chosen. If TARGET ends with .ext2 then the ext2 format will be chosen. If TARGET ends with .ext4 then the ext4 format will be chosen. If none of these conditions apply, the directory format will be chosen.

  • directory, dir

    A chroot directory will be created in TARGET. If the directory already exists, it must either be empty or only contain an empty lost+found directory. The special TARGET - does not work with this format because a directory cannot be written to standard output. If you need your directory be named -, then just explicitly pass the relative path to it like ./-. If a directory is chosen as output in any other mode than sudo, then its contents will have wrong ownership information and special device files will be missing. Refer to the section MODES for more information.

  • tar

    A temporary chroot directory will be created in $TMPDIR or /tmp if $TMPDIR is not set. A tarball of that directory will be stored in TARGET or sent to standard output if TARGET was omitted or if TARGET equals -. If TARGET ends with one of the filename extensions listed in the section COMPRESSION, then a compressed tarball will be created. The tarball will be in POSIX 1003.1-2001 (pax) format and will contain extended attributes. To preserve the extended attributes, you have to pass --xattrs --xattrs-include='*' to tar when extracting the tarball.

  • squashfs, sqfs

    A temporary chroot directory will be created in $TMPDIR or /tmp if $TMPDIR is not set. A tarball of that directory will be piped to the tar2sqfs utility, which will create an xz compressed squashfs image with a blocksize of 1048576 bytes in TARGET. The special TARGET - does not work with this format because tar2sqfs can only write to a regular file. If you need your squashfs image be named -, then just explicitly pass the relative path to it like ./-. The tar2sqfs tool only supports a limited set of extended attribute prefixes. Therefore, extended attributes are disabled in the resulting image. If you need them, create a tarball first and remove the extended attributes from its pax headers. Refer to the EXAMPLES section for how to achieve this.

  • ext2

    A temporary chroot directory will be created in $TMPDIR or /tmp if $TMPDIR is not set. A tarball of that directory will be piped to the genext2fs utility, which will create an ext2 image that will be approximately 90% full in TARGET. The special TARGET - does not work with this format because genext2fs can only write to a regular file. If you need your ext2 image be named -, then just explicitly pass the relative path to it like ./-. To convert the result to an ext3 image, use tune2fs -O has_journal TARGET and to convert it to ext4, use tune2fs -O extents,uninit_bg,dir_index,has_journal TARGET.

    CAUTION: the ext2 format does not support timestamps beyond 2038 January 19, does not support sub-second precision timestamps and does not support extended attributes. Its inode size of 128 prevents adding these features with tune2fs later on.

  • ext4

    A temporary chroot directory will be created in $TMPDIR or /tmp if $TMPDIR is not set. A tarball of that directory will be piped to the mke2fs utility, which will create an ext4 image that will be approximately 90% full in TARGET. The special TARGET - does not work with this format because mke2fs can only write to a regular file. If you need your ext4 image be named -, then just explicitly pass the relative path to it like ./-. If SOURCE_DATE_EPOCH is set, the filesystem UUID and hash_seed will be set to a UUID derived from SOURCE_DATE_EPOCH to create reproducible images.

  • null

    A temporary chroot directory will be created in $TMPDIR or /tmp if $TMPDIR is not set. After the bootstrap is complete, the temporary chroot will be deleted without being part of the output. This is most useful when the desired artifact is generated inside the chroot and it is transferred using special hooks such as sync-out. It is also useful in situations where only the exit code or stdout or stderr of a process run in a hook is of interest.

HOOKS

This section describes properties of the hook options --setup-hook, --extract-hook, --essential-hook and --customize-hook which are common to all four of them. Any information specific to each hook is documented under the specific hook options in the section OPTIONS.

The options can be specified multiple times and the commands are executed in the order in which they are given on the command line. There are four different types of hook option arguments. If the argument passed to the hook option starts with copy-in, copy-out, tar-in, tar-out, upload or download followed by a space, then the hook is interpreted as a special hook. Otherwise, if command is an existing executable file from $PATH or if command does not contain any shell metacharacters, then command is directly exec-ed with the path to the chroot directory passed as the first argument. Otherwise, command is executed under sh and the chroot directory can be accessed via $1. Background (daemon) processes spawned in a hook are not guaranteed to persist beyond the hook that created them.

Most environment variables set by mmdebstrap (like DEBIAN_FRONTEND, LC_ALL and PATH) are preserved. Most notably, APT_CONFIG is being unset. If you need the path to APT_CONFIG as written by mmdebstrap it can be found in the MMDEBSTRAP_APT_CONFIG environment variable. All environment variables set by the user are preserved, except for TMPDIR which is cleared. See section TMPDIR. Furthermore, MMDEBSTRAP_MODE will store the mode set by --mode, MMDEBSTRAP_FORMAT stores the format chosen by --format, MMDEBSTRAP_HOOK stores which hook is currently run (setup, extract, essential, customize), MMDEBSTRAP_ARGV0 stores the name of the binary with which mmdebstrap was executed and MMDEBSTRAP_VERBOSITY stores the numerical verbosity level (0 for no output, 1 for normal, 2 for verbose and 3 for debug output). The MMDEBSTRAP_INCLUDE variable stores the list of packages, apt patterns or file paths given by the --include option, separated by a comma and with commas and percent signs in the option values urlencoded. If SUITE name was supplied, it's stored in MMDEBSTRAP_SUITE.

In special hooks, the paths inside the chroot are relative to the root directory of the chroot. The path on the outside is relative to current directory of the original mmdebstrap invocation. The path inside the chroot must already exist. Paths outside the chroot are created as necessary.

In fakechroot mode, tar, or sh and cat have to be run inside the chroot or otherwise, symlinks will be wrongly resolved and/or permissions will be off. This means that the special hooks might fail in fakechroot mode for the setup hook or for the extract and custom variants if no tar or sh and cat is available inside the chroot.

  • copy-out pathinside [pathinside ...] pathoutside

    Recursively copies one or more files and directories recursively from pathinside inside the chroot to pathoutside outside of the chroot.

  • copy-in pathoutside [pathoutside ...] pathinside

    Recursively copies one or more files and directories into the chroot into, placing them into pathinside inside of the chroot.

  • sync-out pathinside pathoutside

    Recursively copy everything inside pathinside inside the chroot into pathoutside. In contrast to copy-out, this command synchronizes the content of pathinside with the content of pathoutside without deleting anything from pathoutside but overwriting content as necessary. Use this command over copy-out if you don't want to create a new directory outside the chroot but only update the content of an existing directory.

  • sync-in pathoutside pathinside

    Recursively copy everything inside pathoutside into pathinside inside the chroot. In contrast to copy-in, this command synchronizes the content of pathoutside with the content of pathinside without deleting anything from pathinside but overwriting content as necessary. Use this command over copy-in if you don't want to create a new directory inside the chroot but only update the content of an existing directory.

  • tar-in outside.tar pathinside

    Unpacks a tarball outside.tar from outside the chroot into a certain location pathinside inside the chroot. In unshare mode, device nodes cannot be created. To ignore device nodes in tarballs, use --skip=tar-in/mknod.

  • tar-out pathinside outside.tar

    Packs the path pathinside from inside the chroot into a tarball, placing it into a certain location outside.tar outside the chroot. To emulate behaviour of cp and to provide control over the path which gets put into the tarball, a chdir() is performed to the dirname() of pathinside and then the basename() of pathinside is packaged as a tarball. For example, if pathinside is /boot/. then first a chdir() into /boot will be performed before packing up the contents of . inside /boot.

  • download fileinside fileoutside

    Copy the file given by fileinside from inside the chroot to outside the chroot as fileoutside. In contrast to copy-out, this command only handles files and not directories. To copy a directory recursively out of the chroot, use copy-out or tar-out. Its advantage is, that by being able to specify the full path on the outside, including the filename, the file on the outside can have a different name from the file on the inside. In contrast to copy-out and tar-out, this command follows symlinks.

  • upload fileoutside fileinside

    Copy the file given by fileoutside from outside the chroot to inside the chroot as fileinside. In contrast to copy-in, this command only handles files and not directories. To copy a directory recursively into the chroot, use copy-in or tar-in. Its advantage is, that by being able to specify the full path on the inside, including the filename, the file on the inside can have a different name from the file on the outside. In contrast to copy-in and tar-in, permission and ownership information will not be retained.

OPERATION

This section gives an overview of the different steps to create a chroot. At its core, what mmdebstrap does can be put into a 14 line shell script:

mkdir -p "$2/etc/apt" "$2/var/cache" "$2/var/lib"
cat << END > "$2/apt.conf"
Apt::Architecture "$(dpkg --print-architecture)";
Apt::Architectures "$(dpkg --print-architecture)";
Dir "$(cd "$2" && pwd)";
Dir::Etc::Trusted "$(eval "$(apt-config shell v Dir::Etc::Trusted/f)"; printf "$v")";
Dir::Etc::TrustedParts "$(eval "$(apt-config shell v Dir::Etc::TrustedParts/d)"; printf "$v")";
END
echo "deb http://deb.debian.org/debian/ $1 main" > "$2/etc/apt/sources.list"
APT_CONFIG="$2/apt.conf" apt-get update
APT_CONFIG="$2/apt.conf" apt-get --yes --download-only install '?essential'
for f in "$2"/var/cache/apt/archives/*.deb; do dpkg-deb --extract "$f" "$2"; done
chroot "$2" sh -c "dpkg --install --force-depends /var/cache/apt/archives/*.deb"

The additional complexity of mmdebstrap is to support operation without superuser privileges, bit-by-bit reproducible output, hooks and foreign architecture support.

The remainder of this section explains what mmdebstrap does step-by-step.

  • check

    Upon startup, several checks are carried out, like:

    • whether required utilities (apt, dpkg, tar) are installed
    • which mode to use and whether prerequisites are met
    • do not allow chrootless mode as root (without fakeroot) unless inside a chroot. This check can be disabled using --skip=check/chrootless
    • whether the requested architecture can be executed (requires arch-test) using qemu binfmt_misc support. This requires arch-test and can be disabled using --skip=check/qemu
    • how the apt sources can be assembled from SUITE, MIRROR and --components and/or from standard input as deb822 or one-line format and whether the required GPG keys exist.
    • which output format to pick depending on the --format argument or name of TARGET or its type.
    • whether the output directory is empty. This check can be disabled using --skip=check/empty
    • whether adding a signed-by to apt/sources.list is necessary. This requires gpg and can be disabled using --skip=check/signed-by

  • setup

    The following tasks are carried out unless --skip=setup is used:

    • create required directories
    • write out the temporary apt config file
    • populates /etc/apt/apt.conf.d/99mmdebstrap and /etc/dpkg/dpkg.cfg.d/99mmdebstrap with config options from --aptopt and --dpkgopt, respectively
    • write out /etc/apt/sources.list
    • copy over /etc/resolv.conf and /etc/hostname
    • populate /dev if mknod is possible

  • setup-hook

    Run --setup-hook options and all setup* scripts in --hook-dir.

  • update

    Runs apt-get update using the temporary apt configuration file created in the setup step. This can be disabled using --skip=update.

  • download

    In the extract and custom variants, apt-get install is used to download all the packages requested via the --include option. In the remaining variants, apt patterns are used to find the Essential:yes packages from the native architecture. If SUITE is a non-empty string, then only packages from the archive with suite or codename matching SUITE will be considered for selection of Essential:yes packages.

  • mount

    Mount relevant device nodes, /proc and /sys into the chroot and unmount them afterwards. This can be disabled using --skip=chroot/mount or specifically by --skip=chroot/mount/dev, --skip=chroot/mount/proc and --skip=chroot/mount/sys, respectively. mmdebstrap will disable running services by temporarily moving /usr/sbin/policy-rc.d and /usr/sbin/start-stop-daemon if they exist. This can be disabled with --skip=chroot/policy-rc.d and --skip=chroot/start-stop-daemon, respectively.

  • extract

    Extract the downloaded packages into the rootfs.

  • prepare

    In fakechroot mode, environment variables LD_LIBRARY_PATH will be set up correctly. For foreign fakechroot environments, LD_LIBRARY_PATH and QEMU_LD_PREFIX are set up accordingly. This step is not carried out in extract mode and neither for the chrootless variant.

  • extract-hook

    Run --extract-hook options and all extract* scripts in --hook-dir.

  • essential

    Uses dpkg --install to properly install all packages that have been extracted before. Removes all packages downloaded in the download step, except those which were present in /var/cache/apt/archives/ before (if any). This can be disabled using --skip=essential/unlink. This step is not carried out in extract mode.

  • essential-hook

    Run --essential-hook options and all essential* scripts in --hook-dir. This step is not carried out in extract mode.

  • install

    Install the apt package into the chroot, if necessary and then run apt from inside the chroot to install all remaining packages. This step is not carried out in extract mode.

  • customize-hook

    Run --customize-hook options and all customize* scripts in --hook-dir. This step is not carried out in extract mode.

  • unmount

    Unmount everything that was mounted during the mount stage and restores /usr/sbin/policy-rc.d and /usr/sbin/start-stop-daemon if necessary.

  • zombie-reaping

    Wait for (reap) still running processes (background processes or zombie processes), unless --skip=zombie-reaping is used.

  • cleanup

    Performs cleanup tasks, unless --skip=cleanup is used:

    • Removes the package lists (unless --skip=cleanup/apt/lists) and apt cache (unless --skip=cleanup/apt/cache). Both removals can be disabled by using --skip=cleanup/apt.
    • Remove all files that were put into the chroot for setup purposes, like /etc/apt/apt.conf.d/00mmdebstrap and the temporary apt config. This can be disabled using --skip=cleanup/mmdebstrap.
    • Remove files that make the result unreproducible and write the empty string to /etc/machine-id if it exists. This can be disabled using --skip=cleanup/reproducible. Note that this will not remove files that make the result unreproducible on machines with differing /etc/resolv.conf or /etc/hostname. Use a --customize-hook to make those two files reproducible across multiple hosts. See section SOURCE_DATE_EPOCH for more information. The following files will be removed:
      • /var/log/dpkg.log
      • /var/log/apt/history.log
      • /var/log/apt/term.log
      • /var/log/alternatives.log
      • /var/cache/ldconfig/aux-cache
      • /var/log/apt/eipp.log.xz
      • /var/lib/dbus/machine-id
    • Remove everything in /run inside the chroot. This can be disabled using --skip=cleanup/run.
    • Remove everything in /tmp inside the chroot. This can be disabled using --skip=cleanup/tmp.

  • output

    For formats other than directory, pack up the temporary chroot directory into a tarball, ext2 image, ext4 image or squashfs image and delete the temporary chroot directory.

    If --skip=output/dev is added, the resulting chroot will not contain the device nodes, directories and symlinks that debootstrap creates but just an empty /dev as created by base-files.

    If --skip=output/mknod is added, the resulting chroot will not contain device nodes (neither block nor character special devices). This is useful if the chroot tarball is to be exatracted in environments where mknod does not function like in unshared user namespaces.

EXAMPLES

Use like debootstrap:

$ sudo mmdebstrap unstable ./unstable-chroot

Without superuser privileges:

$ mmdebstrap unstable unstable-chroot.tar

With no command line arguments at all. The chroot content is entirely defined by a sources.list file on standard input.

$ mmdebstrap < /etc/apt/sources.list > unstable-chroot.tar

Since the tarball is output on stdout, members of it can be excluded using tar on-the-fly. For example the /dev directory can be removed from the final tarbal in cases where it is to be extracted by a non-root user who cannot create device nodes:

$ mmdebstrap unstable | tar --delete ./dev > unstable-chroot.tar

Create a tarball for use with sbuild --chroot-mode=unshare:

$ mmdebstrap --variant=buildd unstable ~/.cache/sbuild/unstable-amd64.tar

Create a buildd tarball for EOL distro:

$ mmdebstrap --include=apt --variant=buildd --aptopt \
    'Apt::Key::gpgvcommand "/usr/libexec/mmdebstrap/gpgvnoexpkeysig"' \
    --aptopt='Acquire::Check-Valid-Until "false"' \
    --keyring=/usr/share/keyrings/debian-archive-removed-keys.gpg \
    --hook-dir=/usr/share/mmdebstrap/hooks/maybe-jessie-or-older \
    jessie ~/.cache/sbuild/jessie-arm64.tar \
    http://archive.debian.org/debian

Instead of a tarball, a squashfs image can be created:

$ mmdebstrap unstable unstable-chroot.squashfs

By default, mmdebstrap runs tar2sqfs with --no-skip --exportable \--compressor xz --block-size 1048576. To choose a different set of options, and to filter out all extended attributes not supported by tar2sqfs, pipe the output of mmdebstrap into tar2sqfs manually like so:

$ mmdebstrap unstable \
    | mmtarfilter --pax-exclude='*' \
        --pax-include='SCHILY.xattr.user.*' \
        --pax-include='SCHILY.xattr.trusted.*' \
        --pax-include='SCHILY.xattr.security.*' \
    | tar2sqfs --quiet --no-skip --force --exportable --compressor xz \
        --block-size 1048576 unstable-chroot.squashfs

By default, debootstrapping a stable distribution will add mirrors for security and updates to the sources.list.

$ mmdebstrap stable stable-chroot.tar

If you don't want this behaviour, you can override it by manually specifying a mirror in various different ways:

$ mmdebstrap stable stable-chroot.tar http://deb.debian.org/debian
$ mmdebstrap stable stable-chroot.tar "deb http://deb.debian.org/debian stable main"
$ mmdebstrap stable stable-chroot.tar /path/to/sources.list
$ mmdebstrap stable stable-chroot.tar - < /path/to/sources.list

Drop locales (but not the symlink to the locale name alias database), translated manual packages (but not the untranslated ones), and documentation (but not copyright and Debian changelog).

$ mmdebstrap --variant=essential \
    --dpkgopt='path-exclude=/usr/share/man/*' \
    --dpkgopt='path-include=/usr/share/man/man[1-9]/*' \
    --dpkgopt='path-exclude=/usr/share/locale/*' \
    --dpkgopt='path-include=/usr/share/locale/locale.alias' \
    --dpkgopt='path-exclude=/usr/share/doc/*' \
    --dpkgopt='path-include=/usr/share/doc/*/copyright' \
    --dpkgopt='path-include=/usr/share/doc/*/changelog.Debian.*' \
    unstable debian-unstable.tar

Create a bootable USB Stick that boots into a full Debian desktop:

$ mmdebstrap --aptopt='Apt::Install-Recommends "true"' --customize-hook \
    'chroot "$1" adduser --comment user --disabled-password user' \
    --customize-hook='echo 'user:live' | chroot "$1" chpasswd' \
    --customize-hook='echo host > "$1/etc/hostname"' \
    --customize-hook='echo "127.0.0.1 localhost host" > "$1/etc/hosts"' \
    --include=linux-image-amd64,task-desktop unstable debian-unstable.tar
$ cat << END > extlinux.conf
> default linux
> timeout 0
>
> label linux
> kernel /vmlinuz
> append initrd=/initrd.img root=LABEL=rootfs
END
# You can use $(sudo blockdev --getsize64 /dev/sdXXX) to get the right
# image size for the target medium in bytes
$ guestfish -N debian-unstable.img=disk:8G -- \
    part-disk /dev/sda mbr : \
    part-set-bootable /dev/sda 1 true : \
    mkfs ext4 /dev/sda1 : \
    set-label /dev/sda1 rootfs : \
    mount /dev/sda1 / : \
    tar-in debian-unstable.tar / xattrs:true : \
    upload /usr/lib/EXTLINUX/mbr.bin /boot/mbr.bin : \
    copy-file-to-device /boot/mbr.bin /dev/sda size:440 : \
    extlinux / : copy-in extlinux.conf / : sync : umount / : shutdown
$ qemu-system-x86_64 -m 1G -enable-kvm debian-unstable.img
$ sudo dd if=debian-unstable.img of=/dev/sdXXX status=progress

On architectures without extlinux you can also boot using grub2:

$ mmdebstrap --include=linux-image-amd64,grub2,systemd-sysv unstable fs.tar
$ guestfish -N debian-unstable.img=disk:2G -- \
    part-disk /dev/sda mbr : \
    part-set-bootable /dev/sda 1 true : \
    mkfs ext4 /dev/sda1 : \
    set-label /dev/sda1 rootfs : \
    mount /dev/sda1 / : \
    tar-in fs.tar / xattrs:true : \
    command "grub-install /dev/sda" : \
    command update-grub : \
    sync : umount / : shutdown
$ qemu-system-x86_64 -m 1G -enable-kvm debian-unstable.img

Build libdvdcss2.deb without installing installing anything or changing apt sources on the current system:

$ mmdebstrap --variant=apt --components=main,contrib --include=libdvd-pkg \
    --customize-hook='chroot $1 /usr/lib/libdvd-pkg/b-i_libdvdcss.sh' \
    | tar --extract --verbose --strip-components=4 \
        --wildcards './usr/src/libdvd-pkg/libdvdcss2_*_*.deb'
$ ls libdvdcss2_*_*.deb

Use as replacement for autopkgtest-build-qemu and vmdb2 for all architectures supporting EFI booting (amd64, arm64, armhf, i386, riscv64), use a convenience wrapper around mmdebstrap:

$ mmdebstrap-autopkgtest-build-qemu unstable ./autopkgtest.img

Use as replacement for autopkgtest-build-qemu and vmdb2 on architectures supporting extlinux (amd64 and i386):

$ mmdebstrap --variant=important --include=linux-image-amd64 \
    --customize-hook='chroot "$1" passwd --delete root' \
    --customize-hook='chroot "$1" useradd --home-dir /home/user --create-home user' \
    --customize-hook='chroot "$1" passwd --delete user' \
    --customize-hook='echo host > "$1/etc/hostname"' \
    --customize-hook='echo "127.0.0.1 localhost host" > "$1/etc/hosts"' \
    --customize-hook=/usr/share/autopkgtest/setup-commands/setup-testbed \
    unstable debian-unstable.tar
$ cat << END > extlinux.conf
> default linux
> timeout 0
>
> label linux
> kernel /vmlinuz
> append initrd=/initrd.img root=/dev/vda1 rw console=ttyS0
END
$ guestfish -N debian-unstable.img=disk:8G -- \
    part-disk /dev/sda mbr : \
    part-set-bootable /dev/sda 1 true : \
    mkfs ext4 /dev/sda1 : mount /dev/sda1 / : \
    tar-in debian-unstable.tar / xattrs:true : \
    upload /usr/lib/EXTLINUX/mbr.bin /boot/mbr.bin : \
    copy-file-to-device /boot/mbr.bin /dev/sda size:440 : \
    extlinux / : copy-in extlinux.conf / : sync : umount / : shutdown
$ qemu-img convert -O qcow2 debian-unstable.img debian-unstable.qcow2

As a debootstrap wrapper to run it without superuser privileges but using Linux user namespaces instead. This fixes Debian bug #829134.

$ mmdebstrap --variant=custom --mode=unshare \
    --setup-hook='debootstrap unstable "$1"' \
    - debian-debootstrap.tar

Build a non-Debian chroot like Ubuntu bionic:

$ mmdebstrap --aptopt='Dir::Etc::Trusted
   "/usr/share/keyrings/ubuntu-keyring-2012-archive.gpg"' bionic bionic.tar

If, for some reason, you cannot use a caching proxy like apt-cacher or apt-cacher-ng, you can use the sync-in and sync-out special hooks to synchronize a directory outside the chroot with /var/cache/apt/archives inside the chroot.

$ mmdebstrap --variant=apt --skip=essential/unlink \
    --setup-hook='mkdir -p ./cache "$1"/var/cache/apt/archives/' \
    --setup-hook='sync-in ./cache /var/cache/apt/archives/' \
    --customize-hook='sync-out /var/cache/apt/archives ./cache' \
    unstable /dev/null

Instead of copying potentially large amounts of data with sync-in you can also use a bind-mount in combination with a file:// mirror to make packages from the outside available inside the chroot:

$ mmdebstrap --variant=apt --skip=essential/unlink \
    --setup-hook='mkdir "$1/tmp/mirror"' \
    --setup-hook='mount -o ro,bind /tmp/mirror "$1/tmp/mirror"' \
    --customize-hook='sync-out /var/cache/apt/archives ./cache' \
    --customize-hook='umount "$1/tmp/mirror"; rmdir "$1/tmp/mirror";' \
    unstable /dev/null file:///tmp/mirror http://deb.debian.org/debian

To automatically mount all directories referenced by file:// mirrors into the chroot you can use a hook:

$ mmdebstrap --variant=apt \
    --hook-dir=/usr/share/mmdebstrap/hooks/file-mirror-automount \
    unstable /dev/null file:///tmp/mirror1 file:///tmp/mirror2

Create a system that can be used with docker:

$ mmdebstrap unstable | sudo docker import - debian
[...]
$ sudo docker run -it --rm debian whoami
root
$ sudo docker rmi debian

Create and boot a qemu virtual machine for an arbitrary architecture using the debvm-create wrapper script around mmdebstrap:

$ debvm-create -r stable -- --architecture=riscv64
$ debvm-run

Create a system that can be used with podman:

$ mmdebstrap unstable | podman import - debian
[...]
$ podman run --network=none -it --rm debian whoami
root
$ podman rmi debian

As a docker/podman replacement:

$ mmdebstrap unstable chroot.tar
[...]
$ mmdebstrap --variant=custom --skip=update,tar-in/mknod \
    --setup-hook='tar-in chroot.tar /' \
    --customize-hook='chroot "$1" whoami' unstable /dev/null
[...]
root
$ rm chroot.tar

You can re-use a chroot tarball created with mmdebstrap for further refinement. Say you want to create a minimal chroot and a chroot with more packages installed, then instead of downloading and installing the essential packages twice you can instead build on top of the already present minimal chroot:

$ mmdebstrap --variant=apt unstable chroot.tar
$ mmdebstrap --variant=custom --skip=update,setup,cleanup,tar-in/mknod \
    --setup-hook='tar-in chroot.tar /' \
    --customize-hook='chroot "$1" apt-get install --yes pkg1 pkg2' \
    '' chroot-full.tar

ENVIRONMENT VARIABLES

  • SOURCE_DATE_EPOCH

    By setting SOURCE_DATE_EPOCH the result will be reproducible across multiple runs with the same options and mirror content. Note that for debootstrap compatibility, mmdebstrap will copy the host's /etc/resolv.conf and /etc/hostname into the chroot. This means that the mmdebstrap output will differ if it is run on machines with differing /etc/resolv.conf and /etc/hostname contents. To make the result reproducible across different hosts, you need to manually either delete both files from the output:

      $ mmdebstrap --customize-hook='rm "$1"/etc/resolv.conf' \
               --customize-hook='rm "$1"/etc/hostname' ...

    or fill them with reproducible content:

      $ mmdebstrap --customize-hook='echo nameserver X > "$1"/etc/resolv.conf' \
               --customize-hook='echo host > "$1"/etc/hostname' ...

  • TMPDIR

    When creating a tarball, a temporary directory is populated with the rootfs before the tarball is packed. The location of that temporary directory will be in /tmp or the location pointed to by TMPDIR if that environment variable is set. Setting TMPDIR to a different directory than /tmp is useful if you have /tmp on a tmpfs that is too small for your rootfs.

    If you set TMPDIR in unshare mode, then the unshared user must be able to access the directory. This means that the directory itself must be world-writable and all its ancestors must be at least world-executable.

    Since TMPDIR is only valid outside the chroot, the variable is being unset when running hook scripts. If you need a valid temporary directory in a hook, consider using /tmp inside your target directory.

DEBOOTSTRAP

This section lists some differences to debootstrap.

  • More than one mirror possible
  • Default mirrors for stable releases include updates and security mirror
  • Multiple ways to operate as non-root: fakechroot and unshare
  • twice as fast
  • Can create a chroot with only Essential:yes packages and their deps
  • Reproducible output by default if $SOURCE_DATE_EPOCH is set
  • Can create output on filesystems with nodev set
  • apt cache and lists are cleaned at the end
  • foreign architecture chroots using qemu-user

Limitations in comparison to debootstrap:

  • Only runs on systems with apt installed (Debian and derivatives)

  • No SCRIPT argument (use hooks instead)

  • Some debootstrap options don't exist, namely:

    --second-stage, --exclude, --resolve-deps, --force-check-gpg, --merged-usr, --no-merged-usr and --cache-dir.

MERGED-/USR

mmdebstrap will create a merged-/usr chroot or not depending on whether packages setting up merged-/usr (i.e. the usrmerge package) are installed or not. In Debian, the essential package init-system-helpers depends on the usrmerge package, starting with Debian 12 (Bookworm).

Before Debian 12 (Bookworm), to force mmdebstrap to create a chroot with merged-/usr using symlinks, either explicitly install the usrmerge package:

--include=usrmerge

or setup merged-/usr using the debootstrap-method which takes care of the architecture specific symlinks and installs the usr-is-merged package.

--hook-dir=/usr/share/mmdebstrap/hooks/merged-usr

To force mmdebstrap to create a chroot without merged-/usr even after the Debian 12 (Bookworm) release, you can use the following hook:

--hook-dir=/usr/share/mmdebstrap/hooks/no-merged-usr

This will write "this system will not be supported in the future" into /etc/unsupported-skip-usrmerge-conversion inside the chroot and install the usr-is-merged package to avoid the installation of the usrmerge package and its dependencies.

If you are using mmdebstrap in a setup where you do not know upfront whether the chroot you are creating should be merged-/usr or not and you want to avoid installation of the usrmerge package and it's dependencies, you can use:

--hook-dir=/usr/share/mmdebstrap/hooks/maybe-merged-usr

That hook will use the availability of the usr-is-merged package to decide whether to call the merged-usr hook or not.

COMPRESSION

mmdebstrap will choose a suitable compressor for the output tarball depending on the filename extension. The following mapping from filename extension to compressor applies:

extension compressor
--------------------
.tar      none
.gz       gzip
.tgz      gzip
.taz      gzip
.Z        compress
.taZ      compress
.bz2      bzip2
.tbz      bzip2
.tbz2     bzip2
.tz2      bzip2
.lz       lzip
.lzma     lzma
.tlz      lzma
.lzo      lzop
.lz4      lz4
.xz       xz
.txz      xz
.zst      zstd

To change compression specific options, either use the respecitve environment variables like XZ_OPT or send mmdebstrap output to your compressor of choice with a pipe.

WRAPPERS

debvm

debvm helps create and run virtual machines for various Debian releases and architectures. The tool debvm-create can be used to create a virtual machine image and the tool debvm-run can be used to run such a machine image. Their purpose primarily is testing software using qemu as a containment technology. These are relatively thin wrappers around mmdebstrap and qemu.

bdebstrap

bdebstrap is a YAML config based multi-mirror Debian chroot creation tool. bdebstrap is an alternative to debootstrap and a wrapper around mmdebstrap to support YAML based configuration files. It inherits all benefits from mmdebstrap. The support for configuration allows storing all customization in a YAML file instead of having to use a very long one-liner call to mmdebstrap. It also layering multiple customizations on top of each other, e.g. to support flavors of an image.

BUGS

https://gitlab.mister-muffin.de/josch/mmdebstrap/issues

https://bugs.debian.org/src:mmdebstrap

As of version 1.20.9, dpkg does not provide facilities preventing it from reading the dpkg configuration of the machine running mmdebstrap. Therefore, until this dpkg limitation is fixed, a default dpkg configuration is recommended on machines running mmdebstrap. If you are using mmdebstrap as the non-root user, then as a workaround you could run chmod 600 /etc/dpkg/dpkg.cfg.d/* so that the config files are only accessible by the root user. See Debian bug #808203.

With apt versions before 2.1.16, setting [trusted=yes] or Acquire::AllowInsecureRepositories "1" to allow signed archives without a known public key or unsigned archives will fail because of a gpg warning in the apt output. Since apt does not communicate its status via any other means than human readable strings, and because mmdebstrap wants to treat transient network errors as errors, mmdebstrap treats any warning from "apt-get update" as an error.

SEE ALSO

debootstrap(8), debvm(1), bdebstrap(1)