postgresql socket connection error

there r too many questions about my problem. but none of them are not just like mine. so i needed to ask it again. when i try to execute some command on postgresql i take this error :

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 is running. here is the ps auwwx|grep postg output :

postgres  2857  0.0  0.0   6056  1668 pts/4    S    01:13   0:00 su postgres
postgres  2866  0.0  0.0   5804  1888 pts/4    S    01:13   0:00 bash
postgres 15543  0.0  0.1  44580  6256 pts/4    S    01:41   0:00 /opt/PostgreSQL/9.1/bin/postgres -D /opt/PostgreSQL/9.1/data
postgres 15544  0.0  0.0  14616   808 ?        Ss   01:41   0:00 postgres: logger process                                    
postgres 15546  0.0  0.0  44564  1172 ?        Ss   01:41   0:00 postgres: writer process                                    
postgres 15547  0.0  0.0  44564  1164 ?        Ss   01:41   0:00 postgres: wal writer process                                
postgres 15548  0.0  0.0  45124  2148 ?        Ss   01:41   0:00 postgres: autovacuum launcher process                       
postgres 15549  0.0  0.0  14908  1240 ?        Ss   01:41   0:00 postgres: stats collector process                           
alix     17375  0.1  0.0   5684  1952 pts/4    S+   02:00   0:00 nano postgresql.conf
alix     17445  0.0  0.0   4628   840 pts/0    S+   02:01   0:00 grep --color=auto postg

and here is my postgresql.conf file :

# - Connection Settings -

#listen_addresses = 'localhost'         # what IP address(es) to listen on;
                                        # comma-separated list of addresses;
                                        # defaults to 'localhost', '*' = all
                                        # (change requires restart)
port = 5432                             # (change requires restart)
max_connections = 100                   # (change requires restart)
# Note:  Increasing max_connections costs ~400 bytes of shared memory per
# connection slot, plus lock space (see max_locks_per_transaction).
#superuser_reserved_connections = 3     # (change requires restart)
unix_socket_directory = '/var/run/postgresql'           # (change requires restart)
#unix_socket_group = ''                 # (change requires restart)
#unix_socket_permissions = 0777         # begin with 0 to use octal notation
                                        # (change requires restart)

my ls -lA /var/run/postgresql output :

total 0

my pg_hba.conf :

local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
#local   replication     postgres                                peer
#host    replication     postgres        127.0.0.1/32            md5
#host    replication     postgres        ::1/128                 md5

i reinstalled many many times postgresql. purged it removed it.purged it like postgresql* and reinstalled it. but its still same.. i dont know what to do. i am done.

thank you.