Install The PostgreSQL on the Ubuntu Server hosted by the Digital Ocean

Today I tried to install the postgresql on the ubuntu server hosted by the digital ocean like[1]. It should be a quite easy task. But I kept getting errors when I typed the command "psql", the error showed up:

psql: could not connect to server: No such file or directory    Is the server running locally and accepting    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

  When I search this error I didn't get any useful link which can solve my problem. 

  I tried uninstalling the postgresql and reinstalling the postgresql, I found there is something wrong during the installation similar with:

sudo /etc/init.d/postgresql startperl: warning: Setting locale failed.perl: warning: Please check that your locale settings:    LANGUAGE = (unset),    LC_ALL = (unset),    LC_MESSAGES = "en_IN.UTF-8",    LANG = "en_US.UTF-8"    are supported and installed on your system.   perl: warning: Falling back to the standard locale ("C"). * No PostgreSQL clusters exist; see "man pg_createcluster"

  Then I found [2], problems solved. 

Reference:

[1] https://www.digitalocean.com/community/articles/how-to-install-and-use-postgresql-on-ubuntu-12-04

[2] http://stackoverflow.com/questions/17399622/postgresql-9-2-installation-on-ubuntu-12-04