A common problem while installing a module is that one or more of its components have requirements which cannot be fulfilled.
This document describes scenarios in which this can happen and possible
solutions. It assumes that the module in question is successfully built in
official infrastructure and available on the examined system for installation.
You can verify the latter with
dnf module list or
dnf module list <name
of the module>.
Dependency problems while installing a module can happen for a variety of reasons:
One of the packages involved is packaged wrongly, i.e. that the package is available but carries a requirement which can’t be fulfilled, for instance because of typos, versioning issues, requiring a private library that isn’t listed as being satisfied by the package carrying it. Solving this is beyond the scope of this document.
Another available module contains a package which would satisfy the requirement but that module isn’t pulled in as a runtime dependency. In most cases adding that missing dependency should fix the issue.
A package that would satisfy the requirement is built by this or another
available module but is filtered out after building, by being listed in the
data/filter/rpms section of the modulemd file. A likely reason that it is
listed there is that it in turn isn’t installable because one of its
requirements can’t be fulfilled. Depending on the circumstances, there are
different possible approaches:
If a package that would fulfill a dependency isn’t part of any available module, one can add it to an existing module as a component or to create a new module for it (if filtering out the package that causes the dependency isn’t an option). If the component on its own is only useful in conjunction with the software contained in the module that can’t be installed the best place is to put it there. If it has wider uses, a decision needs to be made if another existing module or a newly created one is the best place for it.
If any of the packages which are installed on the system or would be installed with the module conflict with each other because of the contained files, version requirements or the like, these need to be resolved. How that is done is outside the scope of this document.
Fixing component-level dependency issues can generally be done in two ways: Either by providing whatever is missing or by removing the need for it in the first place.
If a package whose dependency can’t be fulfilled isn’t part of the API of the
module or required directly or indirectly by an API package it can be filtered
out by adding it to the
data/filter/rpms list in the modulemd file. This is
an approach that usually requires little work beyond establishing that these
prerequisites are met.
Adding a component to a module (or creating a new one) isn’t a one-step process
because the component may have unfulfilled dependencies of its own (which can
have other dependencies and so forth). Using a lather-rinse-repeat approach is
time-consuming (you’d have to wait for a compose to happen before testing the
changed module is possible) but the information to resolve these issues is
available from the outset, assuming that the dependencies are resolvable within
the set of Fedora packages. Instead of trying to resolve this manually (which
can be time-consuming on its own), one can use tools like
fedmod to generate
the whole dependency chain programmatically.
The first step is to use
fedmod rpm2module <component> which creates a
modulemd file for a module containing the component and its dependencies. If
one wanted to do just that (and nothing failed) besides getting the module
reviewed and made available. Regardless of if the component should go into an
existing module or shouldn’t be filtered out any longer, the information in the
generated modulemd file can be used to augment the module that should carry it
(arguably more work but still less than resolving dependencies manually, one at
Consider this error while attempting to install a module
$ dnf module install 389-ds Fedora - Bikeshed - Developmental packages for the next Fedora release 8.5 MB/s | 3.5 MB 00:00 Last metadata expiration check: 0:00:00 ago on Fri 13 Oct 2017 02:44:48 PM UTC. Error: Problem 1: conflicting requests - nothing provides libtcmalloc.so.4()(64bit) needed by 389-ds-base-libs-126.96.36.199-1.module_506864e9.x86_64 Problem 2: conflicting requests - nothing provides libtcmalloc.so.4()(64bit) needed by 389-ds-base-188.8.131.52-1.module_506864e9.x86_64
In this case one needs to find out which package provides
libtcmalloc.so.4()(64bit), e.g. by running
dnf repoquery --whatprovides
<dependency> on an (as of now at least) not yet modular Fedora system and if
dnf info <package> to find out the source package which can then
be added to a module.
Often, removing dependencies is done by disabling a component feature that is
not needed in a module but would pull in a whole tree of other dependencies.
It would be the right approach more often for components that aren’t part of a
module’s API. This approach is trickier because you then need to introduce a
macro to enable or disable the functionality (and the dependencies in question)
in the spec file of the component, and you need to take care that its use in
data/buildopts/rpms/macros doesn’t introduce side effects in the other
components which are built as part of the module.