When upgrading Portal 10.5.1 to 10.6 I get the following error message in the log:
lc_collate values for database "postgres" do not match: old "Swedish_Sweden.1252", new "English_United States.1252"
Failure, exiting
Failed to upgrade the PostgreSQL from 9.3.12 to 9.6.3.
Someone else having the same problem?
I received a similar error when upgrading from 10.5 to 10.6.1. "Failed to upgrade the PostgreSQL from 9.3.12 to 9.6.8."
ESRI Support had me change the permissions on all the Portal folders (for example C:\Program Files\ArcGIS\Portal) and Python folder to "Full Control" for the Portal User prior to installation. I was able to revert to 10.5 using a pre-install snapshot, change the folder permissions, installed 10.6.1 and it worked.
Hope this helps someone.