TestOut Linux Pro Practice Test

The command needed to start a network interface after making configuration changes is "ifup iface." This command is specifically designed to bring a network interface up based on the configuration defined in the network files, such as `/etc/network/interfaces` on Debian-based systems or similar locations in other distributions.

Using "ifup" will not only activate the interface but also apply any settings related to IP addressing, routing, and other parameters that you've configured. This ensures that any changes made to the configuration file are put into effect and the interface is operational.

In contrast, other commands like "ip link set iface up" may also activate the interface, but they do not necessarily apply the configuration set in dedicated network configuration files. "ip start iface" is not a valid command in standard Linux environments. Similarly, "restart iface" does not exist as a command in most distributions; it might be a concept in service management but lacks the specificity required for network configuration. Thus, "ifup" stands out as the correct and comprehensive choice.