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"?

postgresql.service - PostgreSQL RDBMS
Loaded: loaded (/lib/systemd/system/postgresql.service; enabled)
Active: active (exited) since tue 2016-05-24 09:24:13 CEST; 3s ago
Process: 5658 ExecStart=/bin/true (code=exited, status=0/SUCCESS)
Main PID: 5658 (code=exited, status=0/SUCCESS)

sudo service postgresql start (or restart or stop)

DETAIL:  Permissions should be u=rwx (0700).
FATAL:  data directory "/var/lib/postgresql/9.4/main" has group or world access

sudo chown -R postgres:postgres /var/lib/postgresql/9.4/
sudo chmod -R u=rwX,go= /var/lib/postgresql/9.4/

psql -U username -h localhost

root@cloud:~# psql -u postgres -h localhost


/usr/lib/postgresql/9.6/bin/psql: invalid option -- 'u'
Try "psql --help" for more information.
root@kencloud:~# psql -U postgres -h localhost
psql: could not connect to server: Connection refused
    Is the server running on host "localhost" (127.0.0.1) and accepting
    TCP/IP connections on port 5432?