When running a psql command, it fails with the error message below:
[gpadmin@mdw pg_log]$ psql
psql: could not connect to server: Permission denied
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
Because Greenplum postgres process will create a temp file under /tmp/ directory, psql would also need to access /tmp/ while starting.
After setting /tmp/ directory permission to 777, psql should be working fine again.