Can not run PostgreSQL after drop table I've deleted database from PostgreSQL and after this I can do nothing. 
Here what i receive with createuser

$ createuser -D new_user
createuser: could not connect to database postgres: FATAL:  role "postgres" does not exist


And this when try to run psql

$ psql
psql: FATAL:  role "postgres" does not exist


I've tried above with root, postgres, custom users. Still same output

Also I searched for pg_hba.conf like this
 find / -name 'pg_hba.conf'
and got this

/var/lib/postgres-xc/DN2/pg_hba.conf
/var/lib/postgres-xc/DN1/pg_hba.conf
/var/lib/postgres-xc/CN/pg_hba.conf
/etc/postgres-xc/coordinator/CN/pg_hba.conf
/etc/postgres-xc/datanode/DN2/pg_hba.conf
/etc/postgres-xc/datanode/DN1/pg_hba.conf
/etc/postgresql/9.3/main/pg_hba.conf


I've changed connection method to trustfor localhost and IPv4 in /etc/postgresql/9.3/main/pg_hba.conf. 

What should I do get rid of this error?

Does connection method in other files above should be edited too?
Main problem was that I could not run psql command under no user.
Output I received was:

psql: FATAL:  role "any role" does not exist


any role means that I tried to run psql under each user on my system(root,postgresql,my_user)

After all I haven't figured out what the problem was, I decided to reinstall PostgreSQL. 

And this process turned out rather hard to.

So if you have problems with deleting and reinstalling PostgreSQL, read on.

Here what I had to do.

echo "deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main" &gt; /etc/apt/sources.list.d/pgdg.list

wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -


sudo apt-get update

now we get error about missing postgresql-common
to fix it we need to install above package
lets determine its version

sudo apt-cache policy postgresql-common


and install it

sudo apt-get install postgresql-common=151.pgdg12.4+1


we can get error that postgresql-client-common not installed
so we need to do the same
determine it version

sudo apt-cache policy postgresql-client-common


and install

sudo apt-get install postgresql-client-common=151.pgdg12.4+1


after this we can install postgresql like this

sudo apt-get install postgresql-9.3 postgresql-contrib-9.3