They are a type of low level software that is used to manage computer hardware resources and provides common services for computer programs. Application programs usually require an operating system to function.
This is what controls peripherals which include keyboards and mice etc. An example of this is windows controlling monitors by changing the resolution; mouse setting the click speed.
Udev depends on the sysfs file system which was introduced in the 2.5 kernel. It is sysfs which makes devices visible in user space. When a device is added or removed, kernel events are produced which will notify Udev in user space.
The external binary /sbin/hotplug was used in earlier releases to inform Udev about device state change. That has been replaced and Udev can now directly listen to those events through Netlink.
Security-Enhanced Linux (
SELinux) is a Linux kernel security module that provides the mechanism for supporting access
control security policies, including United States Department of Defense-style mandatory access controls (MAC).
SELinux is a set of kernel modifications and user-space tools that can be added to various Linux distributions. Its architecture strives to separate enforcement of security decisions from the security policy itself and streamlines the volume of software charged with security policy enforcement. The key concepts underlying SELinux can be traced to several earlier projects by the United States National Security Agency.
