Feuerfest

Another small important detail I learned today about epoch numbers in package names. Or rather: I was forced to understand what I already saw for years but never thought about.

RedHat's package manager yum (and by that extent also dnf and rpm) treat a non-specified epoch number as 0. This confused me today as a specified package couldn't be found. And an dnf info packagename didn't show the Epoch: field. Despite the package name clearly including an epoch version of 0.

Turns out this is document in RedHat Enterprise Linux 9: Advanced Topics - 6.3.1. The Epoch directive and Debian treats and Epoch number of 0 in the exact same way.

RedHat says:

The Epoch directive enables to define weighted dependencies based on version numbers.

If this directive is not listed in the RPM spec file, the Epoch directive is not set at all. This is contrary to common belief that not setting Epoch results in an Epoch of 0. However, the dnf utility treats an unset Epoch as the same as an Epoch of 0 for the purposes of depsolving.

However, listing Epoch in a spec file is usually omitted because in majority of cases introducing an Epoch value skews the expected RPM behavior when comparing versions of packages.

This effectivly means: If the epoch number is listed as None, it is 0. Just like in this example:

user@host:~$ rpm -q --qf "%{EPOCH}:%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH}\n" bind-utils
(none):bind-utils-9.20.21-150700.3.18.1.x86_64

And Debian says pretty much the same in their manual regarding Control files and their fields: 5.6.12 version

epoch
This is a single (generally small) unsigned integer. It may be omitted, in which case zero is assumed.

Epochs can help when the upstream version numbering scheme changes, but they must be used with care. You should not change the epoch, even in experimental, without getting consensus on debian-devel first.

Interesting. I only had to use an Epoch number of 1 for a company internal Debian package once. As someone build a different package with the exact same name (despite the name having nothing to with what his because did) as this person just copy&pasted some build-scripts but apparently didn't change all important values. That was 10+ years ago.

Never stumbled about this particular case with how the 0 is treated.

You never stop learning.