Unix operating system Bamuengine.com Bamuengine.com

What is operating system: An operating system (OS) is software that manages the resources of a computer Like most managers, the OS aims to manage its resources in a safe and efficient way Examples of computer resources are: CPU, RAM, disk memory, printers, displays, keyboard, mouse, etc The OS also isolates users and application programmers from the underlying computer Bamuengine.com

Common features of O.S: Process management. Interrupts Memory management File system Device drivers Networking (TCP/IP) Security Bamuengine.com

History of UNIX: In the late 1960’s i.e.nearly 1969-Summer Unix was developed at AT&T’s Bell’s lab where a joint project to develop an ambitious multi-using,multi-tasking O.S. for mainframe computers known as MULTICS(Multiplexed Information and Computing System).MULTICS failed ,but it inspired Ken Thompson a researcher at Bell’s lab to have a write for simpler operating system himself. Ken Thompson then teamed up with Dennis Ritchie ,the author of first C compiler in 1973.They wrote UNIX kernel in C-which was a big step for system portability….. Recently,UNIX standards were nearly as numerous as its variants Bamuengine.com

History of unix: Bamuengine.com

Characteristics of unix: 1.Memoryalloction : It keeps tracks of primary memory i.e which part of it is in use or not and by whom , as well as it allocates memory when a program requests. 2.Processer management :It allocate the C.P.U for a process or deallocates if not required….. 3.DeviceManagement:Keep tracks of all devices It decides for how much time and to whom should be given the priority. 4.FileManagement:It allocates and deallocates the resources.it also decides to whom should the resources be give… 5.Security:By means of password and some other techniques,preventing unauthorized access to program and data. Bamuengine.com

Features of UNIX O.S: 1.Portable: Unix can be installed on many hardware platforms.its widespread use can be traced to develop it using C language… 2.Multi-user: The UNIX users allow multiple users to concurrently share hardware and software. 3.Multi-tasking:Unix allows a user to run more than one program at a time. In fact more than one program are running at the background while user is working on the foreground. 4.Networking: While UNIX was developed to an interactive, multiuser, multitasking system,networking is incorporated in the heart of the operating system. Bamuengine.com

5.Organized file system : UNIX has a very organized file and directory system that allows users to organize and maintain files.. 6.Device independence:UNIXtreats input,output devices as ordaniryfiles.The destination of file input and outputis easily controlled through UNIX design feature called redirection. 7.Utilities:UNIX provides a rich library of utilities that can increase user’s productivity Bamuengine.com

Difference between unix and windows: Unix o.s Windows o.s 1.It is an open source.   2.It has very high security system. 3.It is a command based O.S. 4.The file system is arranged in hierichial manner. 5.unix is not user friendly. 1.It is a close source.   2.It has low security system. 3.It is a not command based O.S. 4.The file system is arranged in a parallel manner 5 . It is user friendly Bamuengine.com

Architecture of Unix O.S : An system architecture is the conceptual model that define the structure, behaviour and more view of the system. Unix is a layered operating system . It consist of following parts: 1.Hardware 2.Kernel. 3.Shell. 4.User and utilities Bamuengine.com

Two main parts of UNIX OS is: 1.Kernel 2.Shell Bamuengine.com

Kernel: The kernel is a program that costitute the central core of a computer operating system It has complete control over everything that occurs in the system. The kernel is the core of the computer of the operating system. It is loaded in memory when the system is booted and communicate directly with the hardware. Bamuengine.com

kernels Micro kernel Hybrid kernel Exo kernel Monotithic kernel Bamuengine.com

Unix System Kernel Three major tasks of kernel: Process Management Device Management File Management Three additional Services for Kernel: Virtual Memory Networking Network File Systems Experimental Kernel Features: Multiprocessor support Lightweight process (thread) support Bamuengine.com

Block Diagram of System Kernel User Programs Libraries User Level Kernel Level System Call Interface File Subsystem Inter-process communication Process control subsystem Scheduler Device drivers Memory management hardware control hardware Bamuengine.com Hardware Level

The Shell: The shell acts as an interface(command interpreter) between user and kernel. It is the interpreter that translates the command that are typed into the terminal. The series of commands are called shell script. Bamuengine.com

Shells Bourne shell (sh) Bourne again shell Korn shell C shell (csh) (ksh) Bourne again shell (bash) Bourne shell (sh) Bamuengine.com

The layers of a UNIX system. UNIX Interfaces The layers of a UNIX system. User Interface Bamuengine.com

Internal and External commands 1.Internal commands: When we type a command the shell won’t look in its path to locate it.Rather,it will execute it from it’s own set of built-in commands That are not stored as separate files.These built in commands are known as internal commands e.g. $ type echo echo is a shell built in command 2.External commands: A program or file having an independent existence in the /bin directory(or /use/bin),it is branded as an external command.Most of the commands in UNIX are external in nature… e.g: $ [ankita@localhost] ls (then press enter) Bamuengine.com

verb [options] [arguments] Command structure : Unix commands takes the following general form: verb [options] [arguments] where verb it is the command name that can be take a set of optional options and one or more optional arguments. Eg: ll -l note Bamuengine.com

The command use file name as argument . Options are also arguments, but given a special name because they are predetermined. An options is normally preceded by a minus sign (-). The command use file name as argument . The commands with its option and argument is known as command line. Exceptions: Some commands in UNIX like pwd do not take any options and arguments . who may or may not be specified with argument ls can be have combinations of both i.e. without argument (ls), with only options (ls –l), with only file name(ls f1), or using combinations Of both (ls –l f1). Bamuengine.com

Flexibility of command usage: UNIX provides flexiblility in using the commands. Combining commands: UNIX allows you to specify more than one command in the single command line . Each command is separted from other by a semicolon (;). Eg: wc sample.txt; ls –l sample.txt Here “ ; “ is known as metacharacter. Bamuengine.com

Entering a command before previous commands has finished: Subsequently commands entered at the keyboard are stored in a buffer ( a temporary storage in memory) that is maintained by the kernel for all keyboard input. The next command will be passed on to the shell for interpretation after the previous command has completed its execution. Bamuengine.com

Concept of mountpoint: Files in unix system are organized into a single Tree structure . It is however possible to have several partitions using a mechanism called mounting which makes it possible to connect a partition to connect a partition to directory in the main tree structure . So the fact of mounting a partition in the directory /mnt/partition makes all the files in the partition accessible from this directory, called the “mount point”. Bamuengine.com

File system: “On a UNIX system, everything is a file, if something is not a file, it is a process.” Some exceptions: Directories : files that are lists of other files. Special files and Device files: All device and peripherals are represented by files. To read or write a device you have to perform these operation on its assosiated file. Most special are in /dev. Links : a system to make a file or directory visible in multiple parts of the system’s file tree. Bamuengine.com

(Domain) socket: a special file type , similar toTCP/IP sockets , providing inter-process networking protected by the file systems’s access control. Named piped: act more or less like sockets and form a way for processes to communicate with each other ,without using network sockets semantics. Bamuengine.com

Ordinary file: This is the most common file type. An ordinary File can be either a text file or a binary file. Text file: it contain only printable character and you can view and edit them. Every line of the text file is terminated with the newline character. Binary file: It contain both printable and nonprintable character that cover the entire ASCII range. Sound and video files are also binary file Bamuengine.com

Directory file: A directory contain no data ,but keeps details of the files and subdirectories that it contains. A directory file contain one entry for every file and subdirectory that it houses. Each entry has two component namely , the filename and a unique identification number of the file or directory(called the inode number). Bamuengine.com

Device files: All the operations on the devices are performed by reading or writing the file representing the devices. Device filename are found in a single directory structure , /dev. A device file is not really a stream of character. It is the attributes of the file that entirely govern the operation of the device. The kernel identifies a device from its attributes and uses them to operate the device. Bamuengine.com

File system of unix: Bamuengine.com

/bin : Essential low-level system utilities / The "root" directory /bin : Essential low-level system utilities /usr/bin : Higher-level system utilities and application programs /sbin : Superuser system utilities (for performing system administration tasks) /lib : Program libraries (collections of system calls that can be included in programs by a compiler)for low-level system utilities /usr/lib : Program libraries for higher-level user programs /tmp : Temporary file storage space (can be used by any user) /home : User home directories containing personal file space for each user. Each directory is named after the login of the user. /etc : UNIX system configuration and information files /dev : Hardware devices /proc : A pseudo-filesystem which is used as an interface to the kernel. Includes a subdirectory for each active program (or process). Bamuengine.com

File handling and directory handling commands: Unix have the same utilities for dealing with files and directories - only some of the names have been changed: · ls is the UNIX version of dir (list files in directory) Syntax: ls -l shows long (detailed) listing. Syntax: ls -last shows long listing - newest first. · cp: copy file Syntax: cp file1 file2 Bamuengine.com

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rm :Replaces the DOS delete command. Syntax: rm filename · mv it will rename filename Syntax: mv file1 file2 · mkdir creates a new directory. Syntax: mkdir dirname · rmdir : deletes a directory. Syntax: rmdir dirname ** all files and subdirectories must be removed first! Bamuengine.com

Inode : Mode Owner info Size Timestamp Direct block Indirect block Double indirect Triple indirect Inode: a structure that store all file attributes except the file name . Maintained in a special area of the disk and copy is loaded into memory when a file is open. Inode number: a number identifying an anode for a file Which is unique in a single system. Displayed with ls -i Bamuengine.com

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