The distribution source list is used to locate archives of the debian distribution. It is designed to support any number of active sources and to support a mix of source media. The file lists one source per line, with the fastest source listed first. The format of each line is:
type uri args
The first item, type, indicates the format for the remainder of the line. It is designed to indicate the structure of the distribution the line is talking about. Currently the only defined value is deb which indicates a standard debian archive with a dists dir.
The deb type is to be a typical two level debian distributions, dist/distribution/component. Typically distribution is one of stable, unstable or frozen while component is one of main, contrib, non-free or non-us. The format for the deb line is as follows:
deb uri distribution compontent [component ...]
uri for the deb type must specify the base of the debian distribution. APT will automatically generate the proper longer URIs to get the information it needs. distribution can specify an exact path, in this case the components must be omitted and distribution must end in a slash.
Since only one distribution can be specified per deb line it may be necessary to list a number of deb lines for the same URI. APT will sort the URI list after it has generated a complete set to allow connection reuse. It is important to order things in the sourcelist from most prefered to least prefered (fastest to slowest).
URIs in the source list support a large number of access schemes.
cdrom:Debian 1.3/debian
http://www.debian.org/archive
ftp://ftp.debian.org/debian
file:/var/debian
smb://ftp.kernel.org/pub/mirrors/debian
All permanent information aquired from any of the sources is stored in the lists directory. Thus, there must be a way to relate the filename in the lists directory to a line in the sourcelist. To simplify things this is done by quoting the URI and treating _'s as quoteable characters and converting / to _. The URI spec says this is done by converting a sensitive character into %xx where xx is the hexadecimal representation from the ascii character set. Examples:
http://www.debian.org/archive/dists/stable/binary-i386/Packages /var/state/apt/lists/www.debian.org_archive_dists_stable_binary-i386_Packages cdrom:Debian 1.3/debian/Packages /var/state/apt/info/Debian%201.3_debian_Packages
The other alternative that was considered was to use a deep directory structure but this poses two problems, it makes it very difficult to prune directories back when sources are no longer used and complicates the handling of the partial directory. This gives a very simple way to deal with all of the situations that can arise. Also note that the same rules described in the Archive Directory section regarding the partial sub dir apply here as well.
The extra status file serves the same purpose as the normal dpkg status file (/var/lib/dpkg/status) except that it stores information unique to apt. This includes the autoflag, target distribution and version and any other uniqe features that come up over time. It duplicates nothing from the normal dpkg status file. Please see other APT documentation for a discussion of the exact internal behavior of these fields. The Package field is placed directly before the new fields to indicate which package they apply to. The new fields are as follows:
Please see cache.sgml for a complete description of what this file is. The cache file is updated whenever the contents of the lists directory changes. If the cache is erased, corrupted or of a non-matching version it will be automatically rebuilt by all of the tools that need it. srcpkgcache.bin contains a cache of all of the package files in the source list. This allows regeneration of the cache when the status files change to use a prebuilt version for greater speed.
The archives directory is where all downloaded .deb archives go. When the file transfer is initiated the deb is placed in partial. Once the file is fully downloaded and its MD5 hash and size are verifitied it is moved from partial into archives/. Any files found in archives/ can be assumed to be verified.
No dirctory structure is transfered from the receiving site and all .deb file names conform to debian conventions. No short (msdos) filename should be placed in archives. If the need arises .debs should be unpacked, scanned and renamed to their correct internal names. This is mostly to prevent file name conflicts but other programs may depend on this if convenient. A conforming .deb is one of the form, name_version_arch.deb. Our archive scripts do not handle epochs, but they are necessary and should be re-inserted. If necessary _'s and :'s in the fields should be quoted using the % convention. It must be possible to extract all 3 fields by examining the file name. Downloaded .debs must be found in one of the package lists with an exact name + version match..
The Methods directory is more fully described in the APT Methods interface document.
The mirror list is stored on the primary debian web server (www.debian.org) and contains a machine readable list of all known debian mirrors. It's format and style mirror the Package file.
Some form of network measurement will have to be used to gauge performance of each of the mirrors. This will be discussed later, initial versions will use the first found URI.
This file plays and important role in how APT presents the archive to the user. Its main purpose is to present a descriptive name for the source of each version of each package. It also is used to detect when new versions of debian are released. It augments the package file it is associated with by providing meta information about the entire archive which the Packages file describes.
The full name of the distribution for presentation to the user is formed as 'label version archive', with a possible extended name being 'label version archive component'.
The file is formed as the package file (RFC-822) with the following tags defined:
The location of the Release file in the archive is very important, it must be located in the same location as the packages file so that it can be located in all situations. The following is an example for the current stable release, 1.3.1r6
Archive: stable Compontent: main Version: 1.3.1r6 Origin: Debian Label: Debian Architecture: i386This is an example of experimental,
Archive: experimental Version: 0 Origin: Debian Label: Debian Architecture: mixed NotAutomatic: YesAnd unstable,
Archive: unstable Compontent: main Version: 2.1 Origin: Debian Label: Debian Architecture: i386