"Peer authentication" means that it‘s comparing your database username against your Linux username. It should work if you‘re logged in as postgres. You probably don‘t want to hit that md5 rule in pg_hba, as the postgres database user generally doesn‘t have a password. –

The Problem you have is, that if u dont define the Host, your system will decide.

explicit add "-h localhost", this will fix it

pg_dump: [archiver (db)] connection to database “dbase” failed: FATAL: Peer authentication failed for user “postgres”