Fundamentals of Linux
Linux is an operating system that was initially created as a hobby by a young student, Linus Torvalds, at the University of Helsinki in Finland. Linus had an interest in Minix, a small UNIX system, and decided to develop a system that exceeded the Minix standards. He began his work in 1991 when he released version 0.02 and worked steadily until 1994 when version 1.0 of the Linux Kernel was released. The kernel, at the heart of all Linux systems, is developed and released under the GNU General Public License and its source code is freely available to everyone. It is this kernel that forms the base around which a Linux operating system is developed. There are now literally hundreds of companies and organizations and an equal number of individuals that have released their own versions of operating systems based on the Linux kernel. More information on the kernel can be found at our sister site, LinuxHQ and at the official Linux Kernel Archives. The current full-featured version is 2.6 (released December 2003) and development continues. [http://www.linux.org/info/index.html]
- Passwords
- Early versions of UNIX kept encrypted passwords in /etc/passwd file
- Most versions now keep passwords in shadow file (only accessible to root)
- UNIX uses one-way hash algorithm (Crypt)
- Some newer versions using MD5
- Encrypted password is 11 characters with a 2-character salt
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- Unix Commands
- Access Control is managed through file permissions (rwx for owner, group, and everyone)
- inetd - Internet standard services daemon; /etc/inetd.conf is the main configuration file that lists all of the services and which are active
- netstat - program which provides information about the network on which the host is running
- su and suid - su (super-user) is the root or administrative account; A program with suid permissions runs as root without the user have root privileges (ex. /usr/bin/passwd)
- sudo allows you to run applications as root if you know the root password
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