Denial-of-service (DoS) attacks are considered the least elegant form of hacking. The world of DoS, especially as related to Unix systems, is extremely broad. Denial-of-service conditions can be achieved by anything from smashing the computer system with a sledgehammer to sending sophisticated, custom TCP/IP packets in order to disable network connectivity.
Pedants in computer security sometimes define DoS attacks as the "prevention or delay of authorized access to IT resources." However, many things can affect computers and networked systems; thus, a wide array of attacks is covered under denial-of-service.
This section covers local DoS attacks, relevant network attacks, and some distributed denial-of-service (DDos) attacks. While physically destroying computing resources constitutes a denial-of-service, we will not be covering those attacks since they do not require a computer. However, it is important to remember that cutting a wire is still the most reliable way to stop network connectivity, and incinerating a hard drive is the most reliable way to erase information. Physical security, while not covered here, is of paramount importance in network defense.
Standalone host DoS attacks can work through crashing
applications or operating systems or through exhausting memory, disk,
or CPU resources. They can be loosely categorized into resource
exhausting (such as
cat /dev/zero >
/tmp/file) and resource destruction (such as