debian packages version convention

Solution 1:

The Debian Policy Manual has this to say about the version field, which answers some parts of your question:

Format

The format is: [epoch:]upstream_version[-debian_revision]

The three components here are:

epoch

This is a single (generally small) unsigned integer. It may be omitted, in which case zero is assumed. If it is omitted then the upstream_version may not contain any colons. It is provided to allow mistakes in the version numbers of older versions of a package, and also a package's previous version numbering schemes, to be left behind.

upstream_version

This is the main part of the version number. It is usually the version number of the original ("upstream") package from which the .deb file has been made, if this is applicable. Usually this will be in the same format as that specified by the upstream author(s); however, it may need to be reformatted to fit into the package management system's format and comparison scheme.

The comparison behavior of the package management system with respect to the upstream_version is described below. The upstream_version portion of the version number is mandatory.

The upstream_version may contain only alphanumerics[36] and the characters "." (full stop), "+" (plus), "-" (hyphen), ":" (colon), "~" (tilde) and should start with a digit. If there is no debian_revision then hyphens are not allowed; if there is no epoch then colons are not allowed.

debian_revision

This part of the version number specifies the version of the Debian package based on the upstream version. It may contain only alphanumerics and the characters "." (full stop), "+" (plus), "~" (tilde) and is compared in the same way as the upstream_version is.

It is optional; if it isn't present then the upstream_version may not contain a hyphen. This format represents the case where a piece of software was written specifically to be a Debian package, where the Debian package source must always be identical to the pristine source and therefore no revision indication is required.

It is conventional to restart the debian_revision at 1 each time the upstream_version is increased.

The package management system will break the version number apart at the last hyphen in the string (if there is one) to determine the upstream_version and debian_revision. The absence of a debian_revision is equivalent to a debian_revision of 0.

Comparison

When comparing two version numbers, first the epoch of each are compared, then the upstream_version if epoch is equal, and then debian_revision if upstream_version is also equal. epoch is compared numerically. The upstream_version and debian_revision parts are compared by the package management system using the following algorithm:

The strings are compared from left to right.

First the initial part of each string consisting entirely of non-digit characters is determined. These two parts (one of which may be empty) are compared lexically. If a difference is found it is returned. The lexical comparison is a comparison of ASCII values modified so that all the letters sort earlier than all the non-letters and so that a tilde sorts before anything, even the end of a part. For example, the following parts are in sorted order from earliest to latest: ~~, ~~a, ~, the empty part, a.

Then the initial part of the remainder of each string which consists entirely of digit characters is determined. The numerical values of these two parts are compared, and any difference found is returned as the result of the comparison. For these purposes an empty string (which can only occur at the end of one or both version strings being compared) counts as zero.

These two steps (comparing and removing initial non-digit strings and initial digit strings) are repeated until a difference is found or both strings are exhausted.

Note that the purpose of epochs is to allow us to leave behind mistakes in version numbering, and to cope with situations where the version numbering scheme changes. It is not intended to cope with version numbers containing strings of letters which the package management system cannot interpret (such as ALPHA or pre-), or with silly orderings.

ubuntu will indicate that the package has been built specifically for Ubuntu. The alpha and build strings don't seem to have any particular meaning, but dfsg refers to a package that has been modified for compliance with the Debian Free Software Guidelines.

Solution 2:

XubuntuY part of the version e.g. 1ubuntu1

• X is the Debian package version. Most Ubuntu packages are based on Debian packages, which is an "upstream" distro.

  If 0, this means that there is no Debian package: it only exists in Ubuntu.

  X resets when the real upstream version is updated, e.g. Binutils 2.25 to Binutils 2.26.

  Debian versions exist because Debian may make patches to the packages so that is will work better in the Debian system or for security releases.

  Debian developers are of course keen on merging patches back to avoid forking.

  Every time a new set patches is made, this number increases.

• ubuntuY is optional.

  If not present, it means that the Debian package was used directly.

  Otherwise, it means that this is the Yth Ubuntu patch applied on top of a Debian patch, much like Debian applies on top of the real upstream.

  Y resets when X increases.

If you get the source of a package with:

apt-get source gdb

you will see the patches applied by Ubuntu and Debian at:

debian/patches/

Even more interesting, you can clone with bzr and see a list of all the Ubuntu versions with what changed between them:

bzr branch ubuntu:gdb
cd gdb
bzr log | less

See also: https://askubuntu.com/questions/620533/what-is-the-meaning-of-the-xubuntuy-string-in-ubuntu-package-names

What the Epoch actually represents

https://askubuntu.com/questions/441879/why-do-some-packages-have-extra-numbers-on-the-front-of-their-version-string