The Unix build notes do not show how to install version 4.8 apart from saying
BerkeleyDB is required for the wallet. Ubuntu and Debian have their own libdb-dev and libdb++-dev packages, but these will install BerkeleyDB 5.1 or later. This will break binary wallet compatibility with the distributed executables, which are based on BerkeleyDB 4.8.If you do not care about wallet compatibility, pass --with-incompatible-bdb to configure. Otherwise, you can build from self-compiled depends (see above).
The referenced README.md from the quoted
Now, you can either build from self-compiled depends or install the required dependencies:
does not discuss BerkeleyDB 4.8.
I know there is
./contrib/install_db4.sh in the source for installing BerkeleyDB 4.8 but it abords on my Ubuntu with
curl: (7) Failed to connect to git.savannah.gnu.org port 443: No route to host.