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Does it make sense that apt-cache depends/rdepends are not always inverse to each other?

For instance, I have a host where apt-cache rdepends liblognorm1 lists these reverse dependencies: rsyslog liblognorm-dev, but apt-cache depends rsyslog does not include liblognorm1 (only liblognorm5) in its dependencies.

Is this a feature or a bug?

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Its a feature, and a necessary one, and your example is already a very good example.

A libraries older version might be depended on by an older version of a program. That programs current version will not depend on that older version of the library though. It may depend on a newer version of the library, or may have dropped/replaced that dependency.

The same program name can appear in the depends/rdepends output, but it can be referring to different versions. Use apt-cache showpkg, its output is a bit more clear about which version you are looking at and which other other packages are required or broken in which versions.

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  • The host had liblognorm1, liblognorm5, rsyslog (but not liblognorm-dev) installed. So I have concluded that it was safe to purge liblognorm1. – rookie099 Apr 4 '18 at 11:13
  • Agreed, except in the case of liblognorm1 it was marked as manual and so apt-get autoremove did not pick it up. This seems to be the default setting on a plain-vanilla Debian Jessie installation. – rookie099 Apr 4 '18 at 12:07

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