BASIC ARCHITECTURE OF UNIX OPERATING SYSTEM.
UNIX operating system is like a layered one we first find H/W block next the heart of an operating system i.e, KERNEL, then SHELL ,and then users hence with this architecture there is something new called shell which we don’t find in any other operating system because of which there wont be any bugs in the system the detail structure can be thought in the class with pictorial presentation.
Hardware is nothing but the system components which can be seen with human eye or can be touched like monitor,keyboard,hard disk etc..,
The kernel is the heart of the operating system. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.
The shell is the utility that processes your requests. When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. C Shell, Bourne Shell and Korn Shell are the most famous shells which are available with most of the Unix variants.
Shell maintains two directories. They are :
/sbin : It contains all super user executable commands.
/bin : It contains all normal user executable commands
COMMANDS AND UTILITIES :-
There are various commands and utilities which you can make use of in your day to day activities. cp, mv, catand grep, etc. are few examples of commands and utilities. There are over 250 standard commands plus numerous others provided through 3rd party software. All the commands come along with various options.
USER : –
User can be classified in two types :
1.Root user (or) Super user(#)
ROOT USER (or) SUPER USER(#) :
He is a administrator for Operating system who has full control over operating system and the prompt for the super user will be “# “ once he login to the command prompt.
Ex: Creating Users, Creating Mount points, Installing packages etc..,
NORMAL USER ($) :
He is a user who has limited access towards operating system and the login prompt for the normal user will be “$”.
Ex: Creation of files and directories etc….,
About sudo :
sudo stands for “superuser do”, or “switch user do”) allows a user with proper permissions to execute a command as another user, such as the superuser.
sudo allows a permitted user to execute a command as another user, according to specifications in the /etc/sudoers file. The real and effective uid and gid of the issuing user are then set to match those of the target user account as specified in the passwdfile.
By default, sudo requires that users authenticate themselves with a password. By default, this is the user’s password, not the root password itself.
Once a user has been authenticated, a timestamp is recorded and the user may use sudo without a password for a short period of time (5 minutes, unless configured differently in sudoers). This timestamp can be renewed if the user issues sudo with the -v flag.
If a user not listed in sudoers tries to run a command using sudo, it is considered an unsuccessful attempt to breach system security and mail is sent to the proper authorities, as defined at configure time or in the sudoers file. The default authority to be notified of unsuccessful sudo attempts is root. Note that the mail will not be sent if an unauthorized user tries to run sudo with the -l or -v flags; this allows users to determine for themselves whether or not they are allowed to use sudo.
sudo can log both successful and unsuccessful attempts (as well as errors) to syslog, a unique log file, or both. By default, sudo will log to syslog but this can be changed at configure time or in the sudoers file.
FILE SYSTEM :
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.
/ (root directory) : It is top most directory in Unix operating system which maintains all the sub-directories and it is also named as root directory.
/sbin : It is a directory which contains all the super user executable commands.
/bin : It is a directory which contains all normal user executable commands.
/etc : It is a directory which contains all system configuration files.
/usr : It is a directory which contains manual pages of operating system.
/var : It is a directory which contains mails, error messages and log messages.
/dev : It is a directory which contains all the logical names of physical devices.
/opt : It is a directory which used to maintain all the third party software’s.
/tmp : It Holds temporary files used between system boots.
/proc : Contains all processes marked as a file by process number or other information that is dynamic to 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.
/boot : Contains files for booting the system.
/lib : Contains shared library files and sometimes other kernel-related files.
/kernel : Contains kernel files.
/disk1 : It is a directory which is used to store any application related data.
/disk2 : It is a directory which is used to store any application related data.
Thank You …..