SQL*Plus displays the version of Oracle to which you connected and the versions of available tools such as PL/SQL. The command prompt indicates that SQL*Plus is ready to accept your commands. If ...

NOLOG Establishes no initial connection to Oracle. Before issuing any SQL commands, you must issue a CONNECT command to establish a valid logon. Use /NOLOG when you want to have a SQL*Plus command ...

and this configuration appears to be compatible both with Oracle's sqlplus command-line utility and with database links that are used for distributed transactions between multiple database instances.