changed password for postgres login in pgAdmin, now can't connect to server
I think there are two unrelated problems here:

1) failure to connect on Unix domain socket

This part of ps output:


  /opt/PostgreSQL/9.3/bin/postgres -D /home/dev/postgres_data


indicates that you're not running postgresql as packaged for Ubuntu. Ubuntu doesn't install its binaries inside /opt (it doesn't even create /opt) and your data directory /home/dev/postgres_data is non-standard too.

The usual suspect is a postgres server installed with the EntrepriseDB installer instead.

/var/run/postgresql is the default unix_socket_directory of Ubuntu's postgres, not Entreprisedb's or any other. Using the psql command-line tool shipping with Ubuntu against a non-Ubuntu leads to this error you mentioned:


  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"?


This mismatch is frequent on Mac OS X because there are quite a few incompatible PostgreSQL installers for it and Apple ships with a client-side postgresql that's not configured for any of them.

Short of getting rid of EntrepriseDB's postgres and installing Ubuntu's (good idea for the future but overkill for just that problem), you need to locate your unix_socket_directory, typically by consulting your postgresql.conf, which should be inside the data directory: /home/dev/postgres_data according to ps.

Then give it as the -h argument to psql, this will be tried instead of /var/run/postgresql. Per the manual page:

 -h hostname, --host=hostname
           Specifies the host name of the machine on which the server is
           running. If the value begins with a slash, it is used as the
           directory for the Unix-domain socket.


2) bad postgres password

If you successfully changed a db password with pgAdmin but can't use it, it may be that you're experiencing a known pgAdmin bug.

See PostgreSQL user can not connect to server after changing password