103 lines
3.8 KiB
Markdown
103 lines
3.8 KiB
Markdown
mmdebstrap
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==========
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An alternative to debootstrap which uses apt internally and is thus able to use
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more than one mirror and resolve more complex dependencies.
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Usage
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-----
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Use like debootstrap:
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sudo mmdebstrap unstable ./unstable-chroot
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Without superuser privileges:
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mmdebstrap unstable unstable-chroot.tar
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With complex apt options:
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cat /etc/apt/sources.list | mmdebstrap > unstable-chroot.tar
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The sales pitch in comparison to debootstrap
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--------------------------------------------
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Summary:
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- more than one mirror possible
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- security and updates mirror included for Debian stable chroots
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- 2-3 times faster
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- chroot with apt in 11 seconds
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- gzipped tarball with apt is 27M small
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- bit-by-bit reproducible output
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- unprivileged operation using Linux user namespaces, fakechroot or proot
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- can operate on filesystems mounted with nodev
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- foreign architecture chroots with qemu-user
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The author believes that a chroot of a Debian stable release should include the
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latest packages including security fixes by default. This has been a wontfix
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with debootstrap since 2009 (See #543819 and #762222). Since mmdebstrap uses
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apt internally, support for multiple mirrors comes for free and stable or
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oldstable **chroots will include security and updates mirrors**.
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A side-effect of using apt is being **2-3 times faster** than debootstrap. The
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timings were carried out on a laptop with an Intel Core i5-5200U.
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| variant | mmdebstrap | debootstrap |
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| ------- | ---------- | ------------ |
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| minbase | 25.25 s | 51.47 s |
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| buildd | 30.99 s | 59.38 s |
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| - | 29.85 s | 127.18 s |
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Apt considers itself an `Essential: yes` package. This feature allows one to
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create a chroot containing just the `Essential: yes` packages and apt (and
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their hard dependencies) in **just 11 seconds**.
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If desired, a most minimal chroot with just the `Essential: yes` packages and
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their hard dependencies can be created with a gzipped tarball size of just 34M.
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By using dpkg's `--path-exclude` option to exclude documentation, even smaller
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gzipped tarballs of 21M in size are possible. If apt is included, the result is
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a **gzipped tarball of only 27M**.
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These small sizes are also achieved because apt caches and other cruft is
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stripped from the chroot. This also makes the result **bit-by-bit
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reproducible** if the `$SOURCE_DATE_EPOCH` environment variable is set.
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The author believes, that it should not be necessary to have superuser
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privileges to create a file (the chroot tarball) in one's home directory. If
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mmdebstrap is run by an unprivileged user, either Linux user namespaces,
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fakechroot or proot are used to create a chroot tarball. Debootstrap supports
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fakechroot but will not create a tarball with the right permissions by itself.
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Support for Linux user namespaces and proot is missing (see bugs #829134 and
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#698347, respectively).
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When creating a chroot tarball with debootstrap, the temporary chroot directory
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cannot be on a filesystem that has been mounted with nodev. In unprivileged
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mode, mknod is never used, which means that /tmp can be used as a temporary
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directory location even if if it's mounted with nodev as a security measure.
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If the chroot architecture cannot be executed by the current machine, qemu-user
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is used to allow one to create a foreign architecture chroot.
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Limitations in comparison to debootstrap
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----------------------------------------
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Debootstrap supports creating a Debian chroot on non-Debian systems but
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mmdebstrap requires apt.
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There is no `SCRIPT` argument.
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There is no `--second-stage` option.
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Tests
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=====
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The script `test.sh` compares the output of mmdebstrap with debootstrap in
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several scenarios. Since debootstrap needs superuser privileges, `test.sh`
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needs `sudo` to run.
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Bugs
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====
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mmdebstrap has bugs. Report them here:
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https://gitlab.mister-muffin.de/josch/mmdebstrap/issues
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