Which file contains mappings between ports and the names of applications associated with them?

The file that contains mappings between ports and the names of applications associated with them is /etc/services. This file is a standard configuration file on Unix-like operating systems that provides a list of known service names and their corresponding port numbers and protocols. This information is used by the operating system and network applications to map common network service names to the specific ports they use for communication.

Understanding this mapping is vital for network security and troubleshooting, as it allows system administrators to know which applications are associated with specific ports, facilitating proper firewall configurations and network monitoring. For instance, if a system administrator wants to restrict access to a certain application, knowing the port number it operates on—typically found in the /etc/services file—enables them to configure firewall rules accurately.

The other options refer to files that do not contain this specific mapping. /var/log/services is not a standard file used for service mappings; it could imply a log file but is not recognized for storing service-to-port associations. /etc/protocols is focused on defining the protocols used in networking, such as defining names corresponding to network protocol numbers, while /var/run/services typically deals with temporary runtime data and does not include a definitive list of service mappings.