Ubuntu.my.id

What does the colon (:) and dash (-) in an Ubuntu dpkg version number mean?

Posted on Jun 30, 2023

Question

I'm trying to get the version number of an already installed package, in order to build a dependencies list for a dpkg.

If I type "dpkg -l | grep libqtcore4" into my terminal I get the following result:

ii  libqtgui4       4:4.7.4-0ubuntu8      Qt 4 GUI module
ii  libqtgui4:i386  4:4.7.4-0ubuntu8      Qt 4 GUI module

My question is; what on earth does the colon (:) mean in the version number, and what does the -0ubuntu mean on the end?

Answer

The number before the : is the epoch. This overrides the version for ordering purposes, e.g. 3:3.1 is considered newer than 2:3.2. It's used when a packager needs to downgrade a package in the repos for one of various reasons.

The number (value, really) after the - is the release. It differentiates between different releases of a package that have the same version. It's used for e.g. security patches to an existing version of the software.