Greetings,
An F25 -> F26 upgrade includes a move from Postgresql 9.5.x to 9.6.x, and PostGIS 2.2.x to 2.3.x.
You need to do some extensive preliminary work as well as post-upgrade.
This page may help for those with non-GIS databases: http://tso.bzb.us/2017/07/postgresql-upgrade-fedora-26.html
... but since I have three PostGIS databases, it doesn't work.
Previously, this happened in the F23->F24 upgrade; I posted my hacks that got me through the upgrade to this thread: https://lists.fedoraproject.org/archives/list/users@lists.fedoraproject.org/...
They got me through the F25->F26 upgrade.
fyi,
Max Pyziur pyz@brama.com