The RPM package manager has a special idea of which files in a package are
configuration files. These files are treated specially during package upgrades:
when a package upgrade changes configuration files for the package, the existing
configuration files are not necessarily overwritten with the upstream changes.
The idea here is that you may have made local changes to these files, or perhaps
you didn't change anything but you want the package to keep working as it did
before, and therefore don't want configuration files changed. In this situation
the package manager will either create a .rpmsave copy of the existing
configuration file and then replace the file with the upstream version, or it
will keep the existing configuration file as-is and save the upstream version
with the .rpmnew suffix.
For example, suppose we have a package named foo and it has a configuration
file named /etc/foo.conf. When foo is first installed the file
/etc/foo.conf will contain the default config from the package. If the package
changes the definition of /etc/foo.conf, an upgrade to foo will either save
the existing config to /etc/foo.conf.rpmsave and overwrite /etc/foo.conf
with the new upstream version, or it will preserve /etc/foo.conf as-is and
save the new upstream version of the file as /etc/foo.conf.rpmnew. Whether you
get a .rpmsave or a .rpmnew file depends on some obscure spec
macros, but in my
experience I get .rpmnew files much more often than I get .rpmsave files.
You should periodically be checking for these .rpmnew and .rpmsave files to
ensure that your system is still running with the intended configuration. In
most cases the package configuration changes are relatively minor, and it may
not be important whether or not you apply the configuration updates. However,
sometimes the configuration changes are important, and in some cases your system
can stop working if you ignore the changes for long enough. For example, some
projects deprecate configuration directives over time, and if you go long enough
without applying config changes your old config file may stop working one day.
Dealing with this is easy if you know about the useful (but not very well known)
tool rpmconf, which is built just for this purpose. It has a few options, but
I normally just use rpmconf -a, which finds all .rpmsave and .rpmnew files
and prompts you about what to do about the changes. For each config file it will
give you options to either install the new upstream version, keep your existing
config file (ignoring the upstream changes), see a diff, skip the change, or
drop into a shell for further examination. I find that rpmconf usually prompts
me about config files I haven't changed, so if it prompts me about a file I'm
unfamiliar with or know I didn't change I just accept the new upstream version.
In principle config files can change after any package update, but in practice
on Fedora they're most common when upgrading from one Fedora release to another.
I usually run rpmconf -a after using dnf system-upgrade to upgrade Fedora
releases.