APT with random-access removable media HOWTO
by James Cameron, 2006-08-23

Synopsis

	Describes how to upgrade non-connected or low-speed linked
	Debian systems using APT with random-access removable media.

Pictures & Diagrams

	See *.png

Types of removable media

	- write-once sequential-access (CD-R) [not supported]
	- write-many sequential-access (CD-RW) [not 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,

	- 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, Adopt

	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, Update

	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 update 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,
	  [see the poll script for a combination update and fetch]
	- 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, Clean by exclusion

	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 clean-by-exclusion script,
	- umount filesystem,
	- remove media.