To enable privileges required to create external tables that access files on HDFS:

1. Grant the following privileges on gphdfs to the owner of the external table.
   • Grant SELECT privileges to enable creating readable external tables on HDFS.
   • Grant INSERT privileges to enable creating writable external tables on HDFS.

     Use the GRANT command to grant read privileges (SELECT) and, if needed, write privileges (INSERT) on HDFS to the Greenplum system user (gpadmin).

     GRANT INSERT ON PROTOCOL gphdfs TO gpadmin; 

2. Greenplum Database uses OS credentials to connect to HDFS. Grant read privileges and, if needed, write privileges to HDFS to the Greenplum administrative user (gpadmin OS user).