справочник команд DNF (DNF Command Reference)
Синхронизация метаданных (Metadata synchronization)
Correct operation of DNF depends on having access to up-to-date
data from all enabled repositories but contacting remote mirrors
on every operation considerably slows it down and costs bandwidth
for both the client and the repository provider. The
metadata_expire (see dnf.conf(5)) repository configuration option
is used by DNF to determine whether a particular local copy of
repository data is due to be re-synced. It is crucial that the
repository providers set the option well, namely to a value where
it is guaranteed that if particular metadata was available in
time T on the server, then all packages it references will still
be available for download from the server in time T +
metadata_expire.
To further reduce the bandwidth load, some of the commands where
having up-to-date metadata is not critical (e.g. the list
command) do not look at whether a repository is expired and
whenever any version of it is locally available to the user's
account, it will be used. For non-root use, see also the
--cacheonly switch. Note that in all situations the user can
force synchronization of all enabled repositories with the
--refresh switch.
