psql: fatal role "root" does not exist

Question

I have gone through many SO question answer my problem was not solved..

This is the method I tried:

user@user-Latitude-XT3:~$ sudo su postgres
No passwd entry for user 'postgres'
user@user-Latitude-XT3:~$ 

and many others.

I keep on getting fatal error user does not exist

any working solution?

please Note before marking duplicate, tried all similar but wasn't solved yet.

Answer 1

This is how I normally login to postgres:

sudo -i
sudo -i -u postgres
psql

Answer 2

Here how i fixed,

1. vi /etc/postgresql/9.3/main/pg_hba.conf

2. local all postgres peer

   here change peer to trust

3. restart, sudo service postgresql restart

4. now try, psql -U postgres