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Securing Linux systems and applications; understanding Linux security features.

Linux is a free software operating system kernel similar to Unix kernels. It provides standard Unix-style discretionary access control, with the ability to use mandatory access control. The name “Linux” more often than not means a Unix-like operating system based on the Linux kernel: a Linux distribution. Although Android is based on a Linux kernel, the rest of the system is very different.

The basic resource model is 'everything is a file' with support for the usual Unix filesystem permissions, and some support for more flexible access control lists. The roles are described in terms of users (who are typically either physical users or system services) and groups. The permissions of an application are those of the user executing it. There are more advanced security frameworks for Linux, including AppArmor , grsecurity , SELinux , Smack , Tomoyo .

The basic firewall manipulation tool is iptables. The common methods of privilege elevation are su and sudo.

BackTrack is a Linux distribution tailored for penetration testing .

For functional questions (“How do I use this tool which is not specifically a security tool?”), try asking on our sister site Unix & Linux.