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+
+An APT with random-access removable media HOWTO
+by James Cameron, 2005-10-25
+
+
+
+
Synopsis
+
+ Describes how to upgrade non-connected or low-speed linked
+ Debian systems using APT with random-access removable media.
+
+ Package is a set of shell scripts.
+
+
Usage Cases
+
+
+- take a pen drive or other storage in to work or a cafe to download updates,
+
- take it to friend's place to upgrade their systems without having to wait for downloads.
+
+
+The essence of it is to keep a per-target dpkg(8) status file and run
+"apt-get --download-only dist-upgrade" against a prepared directory,
+like this:
+
+
+# extract the status for the target system
+gzip --decompress --stdout var/lib/dpkg/status.${name}.gz > /tmp/status
+
+# simulate a dist-upgrade to fetch the packages
+apt-get \
+ -o Dir="." \
+ -o Dir::Etc::SourceList=${PWD}/etc/apt/sources.list \
+ -o Dir::State::Lists=${PWD}/var/lib/apt/lists/ \
+ -o Dir::State::status=/tmp/status \
+ -o Dir::Cache::Archives=${PWD}/var/cache/apt/archives \
+ -o Dir::Cache::srcpkgcache=/tmp/srcpkgcache.bin \
+ -o Dir::Cache::pkgcache=/tmp/pkgcache.bin \
+ -o Debug::NoLocking=true \
+ --download-only --yes dist-upgrade
+
+
+
+More detail below.
+
+
Resources
+
+
+
+Using Darcs
+
+Darcs is a distributed revision control system by David Roundy
+designed to replace centralised CVS. apt-walkabout is provided via
+darcs to encourage contributions.
+
+
+
+
+| install darcs : |
+apt-get install darcs |
+ |
+
+
+
+| checkout initial copy : |
+darcs get http://quozl.linux.org.au/darcs/apt-walkabout
(this creates a directory apt-walkabout in your current directory) |
+
+
+
+| propose a change : |
+darcs record
darcs send
(this sends a mail to me with your changes) |
+
+
+
+| update : |
+darcs pull
(this updates your directory with changes made by me and others) |
+
+
+
+
+
+
+ChangeLog for 0.9-5 released 2005-08-20
+
+
+ - Makefile (distclean): add to remove warning during make
+ package.
+
+
- src/update-via-ssh: remove remote tree after completion.
+
+
- src/update: do the update, don't just --print-uris.
+
+
- src/apply: removed overwrite of host's sources and
+ package list.
+
+
- src/clean-by-exclusion: clean up the displayed messages,
+ including a summary of the size of what is to be removed.
+
+
- src/clean-by-exclusion, src/each: ignore hidden status
+ files by restricting depth of search in var/lib/dpkg.
+
+
+
+APT Normality
+
+ On a normal system APT is used to maintain a list of package
+ sources (/etc/apt/sources.list), a set of downloaded package
+ lists (/var/lib/apt/lists), and a cache of downloaded package
+ archives (/var/cache/apt/archives).
+
+
+
+ The update phase downloads the package lists from the
+ internet. The dist-upgrade phase downloads the packages and
+ installs them.
+
+
+
+
apt-walkabout
+
+ With apt-walkabout, we operate on removable media instead of
+ using the root filesystem. A status file for each target
+ system is kept, and a package list and archives cache is
+ maintained.
+
+
+
+ The package lists are downloaded from the internet, the
+ upgrade is simulated to fetch the packages using the
+ per-target status file, and when the media is mounted on the
+ target system the changes can be applied.
+
+
+
+ A fetch can be run for each remote target system being
+ administered; all the packages required are downloaded to the
+ removable media.
+
+ Timing comparison, side by side, old method, vs apt-walkabout:
+
+
+| normal |
+
+
+- visit the target, (or ssh to it),
+
- download packages using target's internet connection,
+
- go home.
+
|
|---|
+
+| interim |
+
+- download some packages, or most of them, e.g. my apt cache, cut to a CD or take a laptop,
+
- visit them,
+
- install packages, download missing, have a drink while stressing over it,
+
- go home.
+
|
|---|
+
+| walkabout |
+
+- download all packages required,
+
- visit them,
+
- install packages, no download required,
+
- have a drink without stress,
+
- go home.
+
|
|---|
+
+
+Types of removable media
+
+ - write-once sequential-access (CD-R) [partially supported]
+
- write-many sequential-access (CD-RW) [partially supported]
+
- write-many random-access (USB storage) [supported]
+
+
+Types of random-access removable media
+
+ - floppy disk (too small these days)
+
- zip drive (too rare these days)
+
- USB pen drive (/dev/uba)
+
- USB hard disc drive
+
- IDE removable drive
+
+
+Relevant features of APT
+
+ - uses dpkg's /var/lib/dpkg/status to choose upgrade packages
+
- keeps package lists in /var/lib/apt/lists
+
- keeps package archives in /var/cache/apt/archives
+
- can be told to use any of these on removable media
+
+
+Assumptions
+
+ - removable media is mounted exec and writable
+
- all but package installation can be non-root
+
+
+Basic Procedure
+
+ - obtain the status file from the target system, e.g. by
+ e-mail, ssh, or as part of a prior visit,
+
+
- maintain a package list on the removable media, updating it
+ in the same way "apt-get update" works, but using the
+ "apt-dupdate" script which only grabs deltas,
+
+
- when well connected, download the packages required onto the
+ removable media,
+
+
- travel to the target system, run the apply script.
+
+
+Phase 0, Structure
+
+Aim: to build filesystem structure on removable media.
+Why: to enable the following procedures to work.
+
+ - insert media in target system,
+
- mount filesystem,
+
- unpack the .tar.gz,
+
- run the tree script,
+
- umount filesystem,
+
- remove media.
+
+Phase 1, Adoption
+
+ Aim: obtain the list of package versions installed.
+ Why: so that the fetch phase knows what to get.
+
+ - insert media in target system,
+
- mount filesystem,
+
- run the adopt script, supplying the system name,
+
- umount filesystem,
+
- remove media.
+
+Phase 2, Delta
+
+ Aim: to update the package list on the media.
+ Why: so that the fetch phase knows what to get.
+ Why: so that the target system can be updated with the new list.
+
+ - insert media in either system,
+
- mount filesystem,
+
- ensure internet connection is live,
+
- run the delta script,
+
- umount filesystem,
+
- remove media.
+
+Phase 3, Fetch
+
+ Aim: to download the packages required by a target system.
+ Why: so that the packages can be carried on the media.
+
+ - insert media in either system,
+
- mount filesystem,
+
- ensure internet connection is live,
+
- run the fetch script, once for each target system,
+ [TODO: describe each which runs through each known system]
+
- umount filesystem,
+
- remove media.
+
+Phase 4, Apply
+
+ Aim: to update the target system's package list.
+ Aim: to upgrade the target system packages from the media.
+
+ - insert media in target system,
+
- mount filesystem,
+
- run the apply script,
+
- umount filesystem,
+
- remove media.
+
+Phase 5, Purge
+
+ Aim: to maintain free space on the media.
+ Why: to prevent a fetch from failing due to lack of space.
+
+ - insert media in either system,
+
- mount filesystem,
+
- run the purge script, and optionally the cleanup scripts,
+
- umount filesystem,
+
- remove media.
+
+Procedure Summary
+
+- adopt, gather system state from target ... get a copy of the
+ target system's status file, and for interest, their
+ sources.list file, can also be via email. [while on target
+ system]
+
+
- delta, update package lists ... runs apt-dupdate on the pen
+ drive from internet. [while on either system]
+
+
- fetch, downloads packages required ... using the package lists
+ on the host (not the pen drive, so that my apt-proxy is used),
+ using the target system's status file on the pen drive, into
+ the pen drive archives. [while on either system]
+
+
- apply, upgrades the target ... copies package lists from pen
+ drive to target system, runs a dist-upgrade with --no-download
+ --fix-missing using the pen drive archives. [while on target
+ system]
+
+
- purge, maintains the pen drive cache ... does an "apt-get
+ autoclean" to remove any packages no longer downloadable.
+ [while on either system]
+
+
}