Debian Administration

A simple introduction to Debian package tags

One of the new features being introduced into Debian's unstable distribution currently is a "tag" implementation. This allows small pieces of meta-data to be associated with each package in the archive, this data can be useful for searching, and finding new packages.

The historical way that the Debian archive has been managed has been to split it up into sections. There are a small number of sections available and each package belongs to one, and only one, section.

For example a game would go into the Games section, and a Perl library would go in the Perl section. You can see each of the sections, and a brief description here on the Debian website.

Whilst the sections allow a simple and efficient way of categorising software the system suffers from two main flaws:

• The sections are too coarse; not very fine-grained.
• A package can only belong to one section.

As a result of this various people have proposed expanding the number of available sections at different times. Another more flexible and open-ended solution has also been proposed several time; adding "tags" to packages to allow them to be described and categorised more fairly.

The tags system is now live in Debian's unstable distribution (codenamed Sid) and should make it into the Etch release.

I first noticed this by accident when viewing the description of a package with apt-cache. If you view, for example, the description of the tidy package you will see the tag information at the bottom:

skx@mystery:~$ apt-cache show tidy
Package: tidy
Priority: optional
Section: web
Installed-Size: 40
Maintainer: Jason Thomas 
Architecture: i386
Version: 20050415-1
Depends: libc6 (>= 2.3.2.ds1-21), libtidy0
Suggests: tidy-doc
Filename: pool/main/t/tidy/tidy_20050415-1_i386.deb
Size: 17020
MD5sum: 983571c271b64f93b01903f56479a70d
Description: HTML syntax checker and reformatter
 Corrects markup in a way compliant with the latest standards, and
 optimal for the popular browsers.  It has a comprehensive knowledge
 of the attributes defined in the HTML 4.0 recommendation from W3C,
 and understands the US ASCII, ISO Latin-1, UTF-8 and the ISO 2022
 family of 7-bit encodings.  In the output:
 .
  * HTML entity names for characters are used when appropriate.
  * Missing attribute quotes are added, and mismatched quotes found.
  * Tags lacking a terminating '>' are spotted.
  * Proprietary elements are recognized and reported as such.
  * The page is reformatted, from a choice of indentation styles.
 .
 Tidy is a product of the World Wide Web Consortium.
Tag: interface::commandline, use::checking, role::sw-utility, format::html, devel

As you can see the last line of the output includes various tags - giving some details about how it is used "interface::commandline", etc.

This information isn't contained in the Debian package itself, but instead it is contained inside the Packages file.

When you run "apt-get update", or "aptitude update" you connect to a number of repositories and download files which contain details about all the packages held on that repository, including their size, their description, etc, this information can be used to search for a package. Now this file also includes tag information.

The package lists are stored in the directory /var/lib/apt/lists, and are simple text files - You can examine them yourself if you wish to see the various "Tag:" entries.

If you wish you can now search for packages using the tags instead of any keywords which might be located inside the package description.

To do that you will need to install two new tools:

• debtags - Commandline interface to libdebtags functions and Debtags administration tool
• debtags-edit - GUI application to search and tag packages

Installing both packages can be accomplished via apt-get:

apt-get install debtags debtags-edit

(Or "aptitude install debtags debtags-edit" - if you prefer aptitude.)

Once the debtags package has been installed you can conduct queries against the tags. Such as finding packages related to others.

For example you might be interested in seeing which package is related to bash:

skx@mystery:~$ debtags related bash
bash3 - The GNU Bourne Again SHell (Version 3)

You can also search for packages which are related to IMAP mail:

skx@mystery:~$ debtags grep mail::imap
mutt: application, interface::text-mode, made-of::lang-c, mail::imap, mail::pop, protocol::imap, protocol::ipv6, protocol::pop, role::sw-client, uitoolkit::ncurses, works-with::mail
nail: interface::commandline, interface::shell, mail::imap, mail::list, mail::pop, mail::smtp, protocol::imap, protocol::pop, protocol::smtp, role::sw-client, special::completely-tagged, use::transmission, works-with::mail
cyrus21-imapd: interface::daemon, mail::filters, mail::imap, network::service, protocol::imap, protocol::ipv6, role::sw-server, works-with::mail
imapproxy: interface::daemon, mail::imap, protocol::imap, use::proxying
squirrelmail: interface::web, made-of::lang-php, mail::imap, protocol::imap, works-with::mail
getmail4: mail::imap, mail::pop, protocol::imap, protocol::pop, protocol::ssl

How did I know that mail::imap was the tag used for describing mail and IMAP ? That was the result of a "tagsearch":

skx@mystery:~$ debtags tagsearch mail
mail::TODO - Need an extra tag
mail::filters - Filters
mail::imap - Mail access via IMAP
mail::list - Mailing Lists
mail::notification - Notification
mail::pop - Mail access via POP3
mail::smtp - Mail transfer via SMTP
media::mail - Email
protocol::pop - Mail access via POP3
protocol::smtp - SMTP Simple Mail Transport Protocol
works-with::mail - Email

There are several other options, perhaps the best way to learn more is to read the manpage by running "man debtags".

For much more detailed information please consult:

• The debtags homepage
• The debtags FAQ

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