The Apache "HostnameLookups" property allows Apache enter the actual hostname (vs. just the IP address) address into its logs. You should NOT change it from the default value of "No." Enabling HostnameLookups can seriously degrade your servers' performance and increase your risk of DenialOfService attacks.
Should it become necessary to resolve an IP address to a DNS name, the utility "logresolve" (located in the /usr/sbin directory) can be used to obtain this information.
To use logresolve:
1. Launch the logresolve utility.
2. Enter the IP address in question into the terminal window.
3. Press the return key.
4. The DNS name of that IP address displays in the terminal window.