Introduction and Overview Getting Started

Introduction and Overview Getting Started 1 Chapter-1 Introduction and Overview Getting Started Chapter Objectives Definition of operating system and the services offered by it. Types of operating system. History of UNIX and Linux along with their features. File system architecture details. Types of users and files in UNIX/LINUX. Basic UNIX Commands. Recap. Quiz. 1.1 Definition of Operating System and the services offered by it Operating system (OS) is a set of programs that manages the activities of the computer system and lets the user use the system resources effectively. Most desktop and laptop PCs come pre loaded with Microsoft Windows. Macintosh computers come with Mac OS X. Many corporate servers use the Linux or UNIX operating systems. The operating system is the first thing loaded onto the computer without the operating system; a computer is of no use. An operating system creates the ability to: a. serve a variety of purposes b. interact with users in more complicated ways c. keep up with needs that change overtime d. management of the processor, RAM, I/O e. file and Information Management f. management of execution of applications

2 Linux At the simplest level, an operating system does two things: 1. It manages the hardware and software resources of the system. In a desktop computer, these resources include such things as the processor, disk space, memory and more. 2. It provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware. The first task, managing the hardware and software resources, is very important, as various programs and input methods compete for the attention of the central processing unit and demand memory, storage and input/output bandwidth for their own purposes. The second task, providing a consistent application interface, is especially important if there is to be more than one of a particular type of computer using the operating system, or if the hardware making up the computer is ever open to change. A consistent application program interface allows a software developer to write an application on one computer and have a high level of confidence that it will run on another computer of the same type, even if the amount of memory or the quantity of storage is different on the two machines. There are cases where processes need to communicate with each other to exchange information. It may be between processes running on the same computer or running on the different computers. By providing this service the operating system relieves the user of the worry of passing messages between processes. In case where the messages need to be passed to processes on the other computers through a network it can be done by the user programs. The user program may be customized to the specifics of the hardware through which the message transits and provides the service interface to the operating system. 1.2 Types of Operating System From the previous section, we understood that Operating systems that create a link between end users and the applications form the core of computer systems. It dissociates the programs, the hardware and simplifies resource management. Let us look at the different types of operating systems in this section. Single user and Multi user Operating Systems: In a single user OS type, only a single person has access to all resources and in case of multi user OS, multiple users can access a computer system concurrently. Time sharing system can be classified as multi user systems as they enable a multiple user access to a computer through the sharing of time. Being able to have multiple accounts on a Windows operating system does not make it a multi user system. Rather, only the network administrator is the real user. But for a Unix

Introduction and Overview Getting Started 3 like operating system, it is possible for two users to login at a time and this capability of the OS makes it a multi user operating system. Some examples of multi user operating systems are Linux, Unix, and Windows 2000. Single tasking and Multi tasking Operating Systems: When a single program is allowed to run at a time, the system is grouped under a single tasking system, while in case the operating system allows the execution of multiple tasks at one time, it is classified as a multitasking operating system. Multitasking can be of two types namely, pre emptive or co operative. In pre emptive multitasking, the operating system slices the CPU time and dedicates one slot to each of the process. Unix like operating systems such as Solaris and Linux support pre emptive multitasking. Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. MS Windows prior to Windows 95 used to support cooperative multitasking. UNIX and Windows 2000 are examples of multitasking systems. Real time Operating System: It is a multitasking operating system that aims at executing real time applications. Real time operating systems often use specialized scheduling algorithms so that they can achieve a deterministic nature of behavior. The main object of real time operating systems is their quick and predictable response to events. They either have an event driven or a time sharing design. Time sharing operating systems switch tasks based on the clock interrupts while an event driven system switches between tasks based on their priorities. DSP BIOS is an example for real time Operating system. Distributed Operating System: An operating system that manages a group of independent computers and makes them appear like a single computer is known as distributed operating system. The development of networked computers that could be linked and communicate with each other, gave rise to distributed computing. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system. Embedded System: The operating systems designed for being used in embedded computer systems are known as embedded operating systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE, Minix 3 and Free BSD are some examples of embedded operating systems. 1.3 History of UNIX and LINUX along with their features 1.3.1 Unix In 1969-1970, Kenneth Thompson, Dennis Ritchie, and others at AT&T Bell Labs began developing a small operating system on a little used PDP-7. The

4 Linux operating system was soon christened UNIX, a pun on an earlier operating system project called MULTICS. In 1972-1973, the system was rewritten in the programming language C, an unusual step that was visionary: due to this decision, UNIX was the first widely used operating system that could switch from and outlive its original hardware. Other innovations were added to UNIX as well, in part due to synergies between Bell Labs and the academic community. In 1979, the "seventh edition'' (V7) version of UNIX was released, the oldest of all extant UNIX systems. 1.3.2 Linux In 1991, Linus Torvalds began developing an operating system kernel, which he named "Linux". This kernel could be combined with the FSF material and other components to produce a freely modifiable and very useful operating system. This book will term the kernel itself the "Linux kernel'' and an entire combination as "Linux''. Note that many use the term "GNU/Linux'' instead for this combination. Linux is not derived from UNIX source code, but its interfaces are intentionally like UNIX. Therefore, UNIX lessons learned generally apply to both, including information on security. 1.3.3 Comparison of Unix and Linux UNIX is copyrighted name only big companies are allowed to use the UNIX copyright and name, so IBM AIX, Sun Solaris and HP UX all are UNIX operating systems. Most UNIX systems are commercial in nature. Linux is a UNIX Clone. It is just a kernel. All Linux distributions include GUI system, GNU utilities (e.g., ls, cp, mv, date, bash etc), installation and management tools, GNU c/c++ Compilers, Editors (VI) and various applications (e.g., Open Office, Firefox etc). However, most UNIX operating systems are considered as a complete operating system as everything comes from a single source or vendor. Linux is Free. It can be downloaded from the Internet or redistributed under GNU licenses. There is a best community support for Linux. Most UNIX like operating systems are not free. However, some Linux distributions such as Red hat/novell provides additional Linux support, consultancy, bug fixing, and training for additional fees. Linux is considered as most user friendly UNIX like operating systems. It makes it easy to install sound card, flash players and other desktop goodies. However, Apple OS X is most popular UNIX operating system for desktop usage. Linux comes with open source netfilter/iptables based firewall tool to protect the server and desktop from crackers and hackers. UNIX operating system comes with its own firewall product or need to purchase third party software such as Checkpoint UNIX firewall.

Introduction and Overview Getting Started 5 1.4 File system architecture details Generalized file system provides a simple and unified way to access resources. The basic unit is a file. A file consists of essential data, metadata (data about the data), nonessential metadata, and some information. Unless the file is a directory, the information is given "as is" and not analyzed by the file system. Essential metadata can be edited only by the file system driver and other privileged programs, since, improper editing may make the file unusable. Nonessential metadata contain information useful for indexing systems (the indexing systems are ordinary programs, and not a part of the file system). Nonessential metadata have a nested structure. A directory (also known as a folder) is a file that may contain other files inside the file. Since, the file system is flexible and extensible, different directories may have different physical implementation. Essential metadata may include file size; date created, last modified, last accessed; directory structure; and special storage properties. Metadata of a directory may apply to files inside the directory. A symbolic link is an empty file that points to a file. The link may indicate either an absolute location or a location relative to the location of the link. Unless requested otherwise, a reference to a symbolic link is a reference to the file to which the link points. Files are identified by their path, such as /file_system/folder/file. For example, name 1/name 2 identifies file name 2 inside the file name1. Copying the file copies the contents of the identified file to the identified path. The file may then or during copying be converted to the appropriate structure for files in that location. The contents of the root file system must be adequate to boot, restore, recover, and/or repair the system. a. To boot a system, enough must be present on the root partition to mount other file systems. This includes utilities, configuration, boot loader information, and other essential start up data. /usr, /opt, and /var are designed such that they may be located on other partitions or file systems. b. To enable recovery and/or repair of a system, those utilities needed by an experienced maintainer to diagnose and reconstruct a damaged system must be present on the root file system. c. To restore a system, those utilities needed to restore from system back ups (on floppy, tape, etc.) must be present on the root file system. The following directories, or symbolic links to directories, are required in /. Directory bin boot Description Essential command binaries Static files of the boot loader

6 Linux dev etc lib media mnt opt sbin srv tmp usr var Device files Host specific system configuration Essential shared libraries and kernel modules Mount point for removable media Mount point for mounting a file system temporarily Add on application software packages Essential system binaries Data for services provided by this system Temporary files Secondary hierarchy Variable data Each directory listed above is specified in detail in separate subsections below. /usr and /var each have a complete section in this document due to the complexity of those directories. 1.5 Types of users and files in UNIX/LINUX Linux supports numerous file system types a. Ext2: This is like UNIX file system. It has the concepts of blocks, inodes and directories. b. Ext3: It is ext2 file system enhanced with journaling capabilities. Journaling allows fast file system recovery. Supports POSIX ACL (Access Control Lists). c. Isofs (iso9660): Used by CDROM file system. d. Sysfs: It is a ram based file system initially based on ramfs. It is used to exporting kernel objects so that end user can use it easily. e. Procfs: The proc file system acts as an interface to internal data structures in the kernel. It can be used to obtain information about the system and to change certain kernel parameters at runtime using sysctl command. For example, you can find out cpuinfo with following command: # cat /proc/cpuinfo f. Or you can enable or disable routing/forwarding of IP packets between interfaces with following command: # cat /proc/sys/net/ipv4/ip_forward # echo "1" > /proc/sys/net/ipv4/ip_forward # echo "0" > /proc/sys/net/ipv4/ip_forward g. NFS: Network file system allows many users or systems to share the same files by using a client/server methodology. NFS allows sharing all of the above file system.

Introduction and Overview Getting Started 7 h. Linux also supports Microsoft NTFS, vfat and many other file systems. See Linux kernel source tree Documentation/file system directory for list of all supported file system. i. You can find out what type of file systems currently mounted with mount command: $ mount OR $ cat /proc/mounts A UNIX file system is a collection of files and directories stored. Each file system is stored in a separate whole disk partition. The following are a few of the file system: a. / - Special file system that incorporates the files under several directories including /dev, /sbin, /tmp etc b. /usr - Stores application programs c. /var - Stores log files, mails and other data d. /tmp - Stores temporary files 1.6 Basic UNIX commands a. ls --- lists your files ls - l --- lists your files in 'long format', which contains lots of useful information. ls - a --- lists all files, including the ones whose filenames begin in a dot. b. more filename --- shows the first part of a file, as much as will fit on one screen. c. emacs filename --- is an editor that lets you create and edit a file. d. mv filename1 filename2 --- moves a file e. cp filename1 filename2 --- copies a file f. rm filename --- removes a file. g. diff filename1 filename2 --- compares files, and shows where they differ h. wc filename --- tells you how many lines, words and characters there are in a file i. chmod options filename --- change the read, write and execute permissions on files. j. File Compression i. gzip filename --- compresses files, so that they take up much less space. ii. gunzip filename --- uncompresses files compressed by gzip. iii. gzcat filename --- to look at a gzipped file without actually having to gunzip it.

8 Linux k. printing : i. lpr filename --- print. ii. lpq --- check out the printer queue. iii. lprm jobnumber --- remove something from the printer queue. Points to remember An operating system is a resource manager that is useful to handle all the available resources effectively and efficiently. The following are the available types of operating systems: Single user and Multi user operating systems Single tasking and Multi tasking operating systems Real time operating system and Distributed operating system Linux and UNIX are almost the same, except that Unix is commercial in nature. 1.7 Quiz 1. What is the need for an operating system? 2. What are the types of operating system available? 3. How does RTOS differ from other operating systems? 4. Which one is a free ware UNIX or Linux? 5. Define a file system. 6. What does dev correspond to? 7. How to change the read, write and execute permissions on files? Answers 1. It is acting as a resource manager. It enhances the utilization of available resources and it makes the user more comfortable. 2. There are single user, multi user, single- tasking, multi tasking, real time OS and distributed OS are available in the market. 3. RTOS is an operating system that works for real time system, i.e. logical correctness of the operation within a deterministic deadline is mandatory in that kind of systems. 4. Linux. 5. A UNIX file system is a collection of files and directories stored. 6. Dev refers to device files. 7. Chmod is the simplest way to change the file permissions. Chmod with number followed for user, group and others will get the permissions changed. o o o

Linux/Unix Commands An In-depth Analysis 9 Chapter-2 Linux/Unix Commands An In-depth Analysis Chapter Objectives Understanding Shell. Discuss directory commands. Discuss all file related commands. An analysis of rest of the Linux commands. Recap. Quiz. 2.1 What is Shell? Fortunately or unfortunately computers can only understand Binary (0 s and 1 s) and humans can only understand the English or equivalent high level language. In olden days instructions to the computer were fed in the form of binary only. But it was highly difficult for anyone (though being expert) to interpret and understand. In order to ward off this difficulty every operating system has got an inbuilt interpreter! The shell accepts instruction or command fed by user in English and will translate the same to binary language which computer can understand without any problem. After accepting the input it will process the same and get the output in English that user can easily understand. So, to be short and sweet, Shell is a language translator. Reader will be introduced to Shell of Linux and the commands that are most commonly used. A diagrammatic representation (Fig. 2.1) would make the above paragraph more meaningful and reader can understand it better. User Input (Commands) Shell English to Binary Conversion Yes, Boss! Ican understanding your request Fig. 2.1 Shell A Diagrammatic representation.

10 Linux And Shell is the area where user can play around with the commands and script that has to be run. It can be called as an environment where user can type and get response. Table 2.1 summarizes the available types of shell in the market and along with a brief description of each. Table 2.1: Available shells in the market with a brief description S.No. Name of Shell Description 1. Bourne Shell (bsh) This is the original Unix shell written by Steve Bourne of Bell Labs. This Shell is not as advanced as other latest shells. 2. C Shell (csh) This Shell was written at University of California, Berkeley. It provides C like language support for writing scripts. So, it is called as C Shell. 3. TC Shell (tcsh) This Shell is very advanced and all the features of the C shell together with emacs style editing of the command line is presented in this Shell. It is available for public domain. 4. Korn Shell (ksh) David Korn of Bell labs has written the Shell. This is made available in all Unix systems. Combined features of C and TC shells along with the features of Bourne shell are made available in ksh. This is very advanced and highly efficient shell. This is very interactive in nature as well. 5. Bourne Again Shell (BASH) This shell is written by free software foundation. GNU initiative helped in framing this out totally. Bash is meant totally for the usage of academic community and most of the Linux/ Unix users are using this shell. Bash provides the features of all the previously mentioned shells. It is in short a hybrid shell which combined the features of all shells. 2.2 LINUX / UNIX commands From here on the reader is exposed to the basic Linux commands. It would be very easy to understand if reader has a Linux PC. To get free Linux CD please visit www.shipit.ubuntu.com. One can get free CD from the site by filling the information requested or can download the OS image available from the site. If user has any other Linux OS flavours like Redhat or Fedora it can also be used to try the following commands. Get username and password from system administrator. Start the PC. It will prompt for typing name and password. Type them, Linux world will welcome!