18-08-2012, 04:39 PM
LINUX SYSTEM AND NETWORK ADMINISTRATION
Linux-Operating-System.ppt (Size: 300.5 KB / Downloads: 44)
UNIX
Unix is a multi-user, multi-tasking operating system.
You can have many users logged into a system simultaneously, each running many programs.
It's the kernel's job to keep each process and user separate and to regulate access to system hardware, including cpu, memory, disk and other I/O devices.
History of UNIX
First Version was created in Bell Labs in 1969.
Some of the Bell Labs programmers who had worked on this project, Ken Thompson, Dennis Ritchie, Rudd Canaday, and Doug McIlroy designed and implemented the first version of the Unix File System on a PDP-7 along with a few utilities. It was given the name UNIX by Brian Kernighan.
00:00:00 Hours, Jan 1, 1970 is time zero for UNIX. It is also called as epoch.
What is LINUX
Linux is a free Unix-type operating system originally created by Linus Torvalds with the assistance of developers around the world.
It originated in 1991 as a personal project of Linus Torvalds, a Finnish graduate student.
The Kernel version 1.0 was released in 1994 and today the most recent stable version is 2.6.9
Developed under the GNU General Public License , the source code for Linux is freely available to everyone.
File System
The Unix file system looks like an inverted tree structure.
You start with the root directory, denoted by /, at the top and work down through sub-directories underneath it.
Each node is either a file or a directory of files, where the latter can contain other files and directories.
You specify a file or directory by its path name, either the full, or absolute, path name or the one relative to a location.
The full path name starts with the root, /, and follows the branches of the file system, each separated by /, until you reach the desired file,
Directories, Files and Inodes
Every directory and file is listed in its parent directory.
In the case of the root directory, that parent is itself.
A directory is a file that contains a table listing the files contained within it, giving file names to the inode numbers in the list.
The information about all the files and directories is maintained in INODE TABLE
An Inode (Index Nodes) is an entry in the table containing information about a file (metadata) including file permissions, UID, GID, size, time stamp, pointers to files data blocks on the disk etc.
Users, Groups and Access Permissions
In UNIX/LINUX, there is a concept of user and an associated group
The system determines whether or not a user or group can access a file or program based on the permissions assigned to them.
Apart from all the users, there is a special user called Super User or the root which has permission to access any file and directory