On Linux systems, there is no default password set.

To set the default password:

1. Run the psql command from the postgres user account:

   sudo -u postgres psql postgres
   

2. Set the password:

   \password postgres
   

3. Enter a password.

4. 1. Close psql.

      \q
      

    

   Source: https://docs.boundlessgeo.com/suite/1.1.1/dataadmin/pgGettingStarted/firstconnect.html