The domain search variable is used to specify a list of domains that are appended to a hostname when resolving it. If the servername is not fully qualified, the resolver will try each domain in the list until it finds a match or fails. By configuring the domain search variable, the technician can avoid typing the full domain name every time they want to ping a server. Verified References: [How to configure DNS suffixes on Linux systems]

Explanation
A checksum is a value that is calculated from a data set to verify its integrity and authenticity. A checksum can be used to compare a downloaded installation package with the original source to ensure that the package has not been corrupted or tampered with during the download or transmission process. If the checksums match, then the package is safe to install. If the checksums do not match, then the package may be infected with malware or contain errors that could cause installation problems. Therefore, validating the checksum for the downloaded installation package is a necessary step before launching the installation again12
1: CompTIA Server+ Certification Exam Objectives 2: How to Verify File Integrity Using Checksums on Linux