change the value of "unix_socket_directories" , must used "-h /xx/xx" to use the Unix domain socket

Hi all,
I change the value of "unix_socket_directories" in postgresql.conf , then restart the database, but it cannot connect the database used like this
"psql -d postgres -p 5432" , it must given the parameter " -h /xx/xx" to use the Unix domain socket。
how to fix this issue ?

the test steps as below :
[wln(at)localhost postgres9.3]$ cat data/postgresql.conf | grep unix_socket_directories
unix_socket_directories = '/tmp/wln' # comma-separated list of directories

[wln(at)localhost postgres9.3]$ psql -d postgres -p 5432
psql: could not connect to server: No such file or directory.
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
[wln(at)localhost postgres9.3]$ psql -d postgres -p 5432 -h /tmp/wln
psql (9.3beta2)
Type "help" for help.

postgres=# \q
[wln(at)localhost postgres9.3]$

Thanks,
waln