An alternative to debootstrap which uses apt internally and is thus able to use more than one mirror and resolve more complex dependencies.
Use like debootstrap:
sudo mmdebstrap unstable ./unstable-chroot
Without superuser privileges:
mmdebstrap unstable unstable-chroot.tar
With complex apt options:
cat /etc/apt/sources.list | mmdebstrap > unstable-chroot.tar
For the full documentation use:
pod2man ./mmdebstrap | man -l -
The sales pitch in comparison to debootstrap
- more than one mirror possible
- security and updates mirror included for Debian stable chroots
- 3-6 times faster
- chroot with apt in 11 seconds
- gzipped tarball with apt is 27M small
- bit-by-bit reproducible output
- unprivileged operation using Linux user namespaces, fakechroot or proot
- can operate on filesystems mounted with nodev
- foreign architecture chroots with qemu-user
- variant installing only Essential:yes packages and dependencies
- temporary chroots by redirecting to /dev/null
The author believes that a chroot of a Debian stable release should include the latest packages including security fixes by default. This has been a wontfix with debootstrap since 2009 (See #543819 and #762222). Since mmdebstrap uses apt internally, support for multiple mirrors comes for free and stable or oldstable chroots will include security and updates mirrors.
A side-effect of using apt is being 3-6 times faster than debootstrap. The timings were carried out on a laptop with an Intel Core i5-5200U.
|minbase||14.18 s||51.47 s|
|buildd||20.55 s||59.38 s|
|-||18.98 s||127.18 s|
Apt considers itself an
Essential: yes package. This feature allows one to
create a chroot containing just the
Essential: yes packages and apt (and
their hard dependencies) in just 11 seconds.
If desired, a most minimal chroot with just the
Essential: yes packages and
their hard dependencies can be created with a gzipped tarball size of just 34M.
By using dpkg's
--path-exclude option to exclude documentation, even smaller
gzipped tarballs of 21M in size are possible. If apt is included, the result is
a gzipped tarball of only 27M.
These small sizes are also achieved because apt caches and other cruft is
stripped from the chroot. This also makes the result bit-by-bit
reproducible if the
$SOURCE_DATE_EPOCH environment variable is set.
The author believes, that it should not be necessary to have superuser privileges to create a file (the chroot tarball) in one's home directory. Thus, mmdebstrap provides multiple options to create a chroot tarball with the right permissions without superuser privileges. Depending on what is available, it uses either Linux user namespaces, fakechroot or proot. Debootstrap supports fakechroot but will not create a tarball with the right permissions by itself. Support for Linux user namespaces and proot is missing (see bugs #829134 and #698347, respectively).
When creating a chroot tarball with debootstrap, the temporary chroot directory cannot be on a filesystem that has been mounted with nodev. In unprivileged mode, mknod is never used, which means that /tmp can be used as a temporary directory location even if if it's mounted with nodev as a security measure.
If the chroot architecture cannot be executed by the current machine, qemu-user is used to allow one to create a foreign architecture chroot.
Limitations in comparison to debootstrap
Debootstrap supports creating a Debian chroot on non-Debian systems but mmdebstrap requires apt and is thus limited to Debian and derivatives.
There is no
The following options, don't exist:
coverage.sh runs mmdebstrap in all kind of scenarios to execute
all code paths of the script. It verifies its output in each scenario and
displays the results gathered with Devel::Cover. It also compares the output of
mmdebstrap with debootstrap in several scenarios. To run the testsuite, run:
./make_mirror.sh CMD=./mmdebstrap ./coverage.sh
To also generate perl Devel::Cover data, omit the
CMD environment variable.
But that will also take a lot longer.
The make_mirror.sh script will be a no-op if nothing changed in Debian unstable. You don't need to run make_mirror.sh before every invocation of coverage.sh. When you make changes to make_mirror.sh and want to regenerate the cache, run:
touch -d yesterday shared/cache/debian/dists/unstable/Release
mmdebstrap has bugs. Report them here: https://gitlab.mister-muffin.de/josch/mmdebstrap/issues
- Johannes Schauer (main author)
- Helmut Grohne
- Benjamin Drung