PostgreSQL is a powerful, open source relational database management system.

The correct command to enter the PostgreSQL interactive shell is psql_client cpm postgres. This command allows the administrator to view and manipulate the database of the Check Point Management (CPM) module, which stores the configuration and policy data. The psql_client command is a Check Point wrapper for the psql command, which is the native PostgreSQL interactive shell. The psql_client command takes two arguments: the first one is the name of the database module, and the second one is the name of the database user. In this case, the database module is cpm and the database user is postgres.

The other commands are incorrect because:

A. mysql_client cpm postgres is not a valid command. The mysql_client command is used to access the MySQL database, which is not used by Check Point. The Check Point database is based on PostgreSQL, not MySQL.

B. mysql -u root is not a valid command. The mysql command is used to access the MySQL database, which is not used by Check Point. The Check Point database is based on PostgreSQL, not MySQL. Moreover, the -u option specifies the MySQL user name, which is not relevant for Check Point.

D. psql_client postgres cpm is not a valid command. The psql_client command takes the database module name as the first argument, and the database user name as the second argument. In this case, the database module name is cpm and the database user name is postgres. The order of the arguments is reversed in this command.