A Quick dive into Unix & Linux
What is UNIX?
UNIX is an OS developed by Ken Thompson at AT&T Bell Labs,USA. It is Writted in C language. It is a Multi-user, multi tasking OS.
As UNIX was written in C Language it could be ported into different hardware architectures. The UNIX kernel acts as an interpreter between HW & applications
Unix can mainly be bounded by the four concepts:-
Kernel − The kernel is the heart of the operating system. Its main job is to interact with the hardware and perform the tasks like memory management, task scheduling and file management.
Shell − The shell is the utility that processes users requests.
When a command is entered at the terminal, the shell interprets the command and calls the program. The shell uses standard syntax for all commands.
Some famous shells available with UNIX are C Shell, Bourne Shell and Korn Shell.
Commands and Utilities − To interact with the OS the user can make us of commands like cp, mv, cat and grep, etc. There are over 250 standard commands plus numerous others provided through 3rd party software. All the commands come along with various options.
Files and Directories − All the data of Unix is organized into files. All files are then organized into directories. These directories are further organized into a tree-like structure called the filesystem.
UNIX file ststem
/ :This is the root directory which should contain only the directories needed at the top level of the file structure
/bin: This is where the executable files are located. These files are available to all users. These are the binaries which contains the utilities like dir, ls ,cp etc.
/dev: These are device drivers are available
/etc: Supervisor directory commands, configuration files, disk configuration files, valid user lists, groups, ethernet, hosts, where to send critical messages
/lib: Contains shared library files and sometimes other kernel-related files
/boot: Contains files for booting the system
/home: Contains the home directory for users and other accounts
/mnt: Used to mount other temporary file systems, such as cdrom and floppy for the CD-ROM drive and floppy diskette drive, respectively
/proc: Contains all processes marked as a file by process number or other information that is dynamic to the system
/tmp: Holds temporary files used between system boots
/usr: Used for miscellaneous purposes, and can be used by many users. Includes administrative commands, shared files, library files, and others
/var: Typically contains variable-length files such as log and print files and any other type of file that may contain a variable amount of data
/sbin: Contains binary (executable) files, usually for system administration. For example, fdisk and ifconfig utlities
/kernel: Contains kernel files
/root: This is, the system administrator. This account’s home directory is usually on the initial filesystem, and hence not in /home (which may be a mount point for another filesystem) in case specific maintenance needs to be performed, during which other filesystems are not available. Such a case could occur, for example, if a hard disk drive suffers physical failures and cannot be properly mounted.
Have you always worried about your passwords?
UNIX supports something called as “Password ageing” meaning the the password gets expired quite frequently.
UNIX is highly secured platform and some of its features for protection are:
1. It provides Usernames & Passwords to individual users
2. At file level there are differnt permissions for read, write and execute permissions. Aslso each of these files can define the level of access for different users.
3. UNIX supports file encryption. Thus every file is encoded in to a format which if any person succeeds in opening also he will see garbage data. The file needs to be decrypyted to view the contents.
