Unable to connect PostgreSQL in CentOS 6.9

hi, I am unable to connect Postgresql

[tattva@tattva ~]$ su
Password:
[root@tattva tattva]# psql -Upostgres
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”?
[root@tattva tattva]#