Clobbered default database in postgreSQL
Your question is very unclear (see comment) but I'm going to make a guess at it anyway.

I think you DROPped the postgres database. You're used to always connecting to PostgreSQL as the postgres superuser using the postgres database, probably via sudo and peer authentication with something like:

sudo -u postgres psql


where you don't specify a database name to connect to. So with no postgres database, you don't know how to connect anymore. You get an error like:

psql: FATAL:  database "postgres" does not exist


If so, you just need to connect to a different database and re-create the postgres database. It only exists as a convenient scratch area - the system doesn't actually care if the postgres database exists or not, and doesn't use it for anything.

Something like:

sudo -u postgres psql template1 -c 'CREATE DATABASE postgres;'


will do the trick.

If you dropped the template1 database as well, you could still recover by connecting to any other database on the server and re-creating template1 from the locked, protected template0 database; see the documentation on template databases.

Key things to understand:


You don't have to connect to the postgres database. It doesn't get used for anything except a default place to connect to when using the postgres user. If you DROP it the system doesn't care.
psql connects by default to the database with the same name as the current user. You can just pick another one with psql databasename.
psql connects by default with the username of the current unix user. You can just pick another one with (eg) psql -U someuser. This will work fine if pg_hba.conf is configured to permit the connection.
While the postgres user is the default superuser, you can create another one, and you don't have to rely on peer authentication to use it either; you can use md5 password auth or whatever you want. So while you're probably used to just using sudo -u postgres psql you can actually set things up in a variety of flexible ways. I frequently create a database superuser for my regular unix user account (CREATE USER myuser WITH SUPERUSER ENCRYPTED PASSWORD 'blah';) when I'm on a scratch/development box, so I'm not messing about with sudo all the time.