Linux comes with a host based firewall called Netfilter. The netfilter is a set of hooks inside the Linux kernel that allows kernel modules to register callback functions with the network stack. A registered callback function is then called back for every packet that traverses the respective hook within the network stack. This Linux based firewall is controlled by the program called iptables to handles filtering for IPv4, and ip6tables handles filtering for IPv6. I strongly recommend that you first read our quick tutorial that explains how to configure a host-based firewall called Netfilter (iptables) under CentOS / RHEL / Fedora / Redhat Enterprise Linux. If you are using Ubuntu/Debian Linux, see how to setup UFW for more info. This post lists most simple iptables solutions required by a new Linux user to secure his or her Linux operating system from intruders.
This is an interesting visualization techniques for software analysis. From the article:
Despite being a very important part of any operating system, file systems tend to get little attention. Linux has three editions for Linux Device Drivers, another three for Understanding the Linux Kernel and two for Linux Kernel Development. The first is a detail analysis of one particular Linux Kernel tree and the second is a shorter one done over a large number of file systems from Linux Kernel 2.6.0 to 2.6.29. After that there is a small section that shows some aspects of the BSD family. After conclusions there is an appendix consisting of three things: the first one explains how the file systems for Linux were compiled, the second one shows timelines for the releases of Linux Kernel, FreeBSD, NetBSD and OpenBSD; the last is a detailed map of the external symbols of the kernel modules analyzed in the second section.