The Linux Operating System

The Linux Operating System Tonga Institute of Higher Education Lecture 1: Introduction and Working with Linux

What is Linux? • Linux is an operating system that evolved from a kernel created by Linus Torvalds when he was a student at the University of Helsinki. • To say that Linux is an operating system means that it's meant to be used as an alternative to other operating systems like MS-DOS, the various versions of MS Windows, Mac OS, Solaris and others. Linux is not a program like a word processor and is not a set of programs like an office suite. • It is a different way to run your computer. Instead of letting Microsoft control how you work, you can let Linux give you another option.

A history of Linux • When Linus Torvalds was studying at the University of Helsinki, he was using a version of the UNIX operating system called 'Minix'. • Linus and other users sent requests for modifications and improvements to Minix's creator, Andrew Tanenbaum, but he felt that they weren't necessary. • That's when Linus decided to create his own operating system that would take into account users' comments and suggestions for improvements.

The Start of Free Software • This philosophy of asking for users comments and suggestions and using them to improve computer programs was not new. • Richard Stallman, a professor in America, had been advocating just such an approach to computer programming and use since the early 1970's. • He was a pioneer in the concept of 'free software.' He left his school in 1984 and founded GNU. The goal of GNU was to produce software that was free to use, distribute and modify. • Linus Torvalds' goal 6 years later was basically the same: to produce an operating system that took into account user feedback.

What did Linus actually make? • When Linus first starting working on his new operating system he built the “kernel” first. The focal point of any operating system is its 'kernel'. • Without going into great detail, the kernel is what tells the processor what to do when your program wants to do something. It is the like a policeman directing traffic. If a car wants to get to the other side of the road, it has to ask the policeman first. The policeman will then tell the car that it can go. • The kernel acts in the same way by controlling programs and letting them use the processor. So, without a kernel, an operating system doesn't exist. But also, without programs, a kernel is useless.

The meeting of great minds • In 1991, Richard Stallman and Linus Torvalds found out about each other and realized that they both had what the other wanted. • So, because they were so far apart they used the Internet (which was just starting out and was very small) to exchange ideas and code. • The Internet in reality let Linux be created and also played a big role in its future development, because people all over the world were able to learn about it.

Linux is Introduced • So with a bunch of programs from GNU and the kernel of Linux, Linus released the first version and asked people on the Internet if they wanted to help build an operating system. • Many responded, and at first they were people with extensive computer programming backgrounds. They helped to write drivers for hardware, necessary programs for an operating systems and anything else they decided they needed on the computer. • This was when Linux became known as an operating system for computer professionals only, but today it is quite easy to install and use.

Why is Linux Succeeding? • Linux has proven to be a tremendously stable and versatile operating system, particularly as a network server. • When Linux is deployed as a web server or in corporate networks, its down-time is almost negligible. There have been cases when Linux servers have been running for more than a year without re-booting. • Its cost effectiveness has sold it more than anything else. Linux can be installed on a home PC as well as a network server for a fraction of the cost of other companies' software packages. More reliability and less cost - it's ideal. • This is because it is completely free. You can download the entire operating system and all the programs you want free of charge

So what is Linux really? • Linux is an operating system that is based on the UNIX operating system which has been around for 30 years. • The big difference is that UNIX needed special hardware to run and it cost a lot of money. • Linux's big advantage is that it has been remade to run on any type of computer hardware, including the inexpensive Intel processors. • This opened the door to letting everyone have the power, security and flexibility of a UNIX operating system, on their own network

How do you get Linux? • There are a number of ways to get Linux. • If you have a lot of time, you can download the ISO images (CD images that you can burn onto CDs). Most distributions are 2-3 CDs, which is about 1-2 gigabytes of data. There are websites all around the world dedicated towards letting people download these files • You can also purchase the CDs from a company like RedHat. Although they let people download their software for free, they also will sell the software with support and documentation

What can we use it for? • Linux works well as a server or a workstation. • There are programs that let a Linux machine run web, ftp, mail, SQL, firewall and Novell servers among many others. • It is also easily used for programming, graphics and audio/video processing among many others • Because it's stable, secure, and the code is open source, more and more people are using it on a daily basis for a wide range of applications

Working with Linux • Linux is a true multi-user system, which means that many users can be working with the same computer at the same time. • There are two types of users, the root user and everyone else. • The root is the superuser of the system. This is the user that can do anything he wants. • But root is actually more like the 'janitor' of the Linux system. Root has the keys to everything, he can shut off the lights, shut off the heat, lock you out of the building; he has to clean up the system and in the end make sure everything runs. And the most important thing about being a janitor - he sees everything.

Root • Since root can do anything he wants, he also has to be careful about what he does. One wrong move, one file deleted that should not be, and the whole system might crash and not be able to start again. • Generally, you should only use root when you really need to. If there is some system administration task that needs to be done, you will have to use root, but then you should switch back. • This is to protect your computer from yourself

The other users • You'll be working as one of those other users most of the time. • Other users can have whatever user name they want, as long as there is no spaces or strange characters. • So now that you have a user name what can you do? • If you're not at the physical computer, you'll have to log in using a remote client program. • Once you have logged in, then you will see a command line interface (CLI) in front of you

Telnet and SSH • To log into a Linux computer, you'll need a remote connection program. • For a long time the only option was telnet, but people soon realized that telnet was very insecure because it sent all it's data over the network unencrypted and anyone could see it. That means anyone can see your password • SSH is the secure version of telnet. It encrypts all data before it is sent so no one can look at it. Most Linux computers don't even allow people to use telnet anymore.

Using a remote client program • So now that we want to use the program we need to give the program the name of the “host” we want to log into. • The host is the name of the computer on the network. If you know the computer's IP address, you can also use that. • Telnet Example > telnet website.com Trying 72.138.35.44... Connected to website.com. Escape character is '^]'. Red Hat Linux release 8.0 (Psyche) Kernel 2.4.18-14 on an i686 login:

After the login – the shell • When you're running Linux and start to type things on that black screen, you are using a shell. • This command line interface is really just a program that sends what you type to the operating system kernel to tell it what to do. All operating systems will use some type of shell to get commands from the keyboard to the computer.

What to do in the shell • So the way that you use Linux is by typing commands into the shell. • Commands are just programs that you run and help you see information or will perform a task. • We're going to look at the most important commands, the ones that you will use all the time firstly. • The first one we should look at is 'cd'. MS-DOS users will be familiar with this. cd will get you in and out of directories. • Example: cd / • This will get you into the 'root' or main directory. It is the first directory in the Linux system.

The 'ls' command • Now that you have changed directories, you'll want to see what's in them. • The ls command will list everything in a directory. • Example: ls • You can also see what's in other directories by passing 'ls' an argument. That means you will type the name of the program, then a space, then you will type an argument. For ls, it will be the name of a directory • Example: ls /bin Example: ls /home/user • Example: ls /etc Example: ls .. • Notice that you can also change into a directory and then list what is inside of it.

Some Shortcuts on Linux • There are a few things to make life easier for people who need to type all day. • If you press the up arrow, it will show you the last command you typed into the shell. If you keep pressing up, it will show you the entire history • If you just want to see the entire history, try typing history into the shell. You'll get a list of commands you typed. • Another handy tool is if you are typing the name of a directory or file, you can type part of it and then press the tab key and Linux will fill in the rest

Using options with commands • An option is an argument that's passed to a program that will make the program run a little differently. • For example, typing: ls -l will give you more detailed information about the contents of a directory. • Try this: First let's go to the “/usr” directory by typing • cd /usr then type: ls -l • You will see more information, like dates, some numbers, letter combinations, it'll say 'root' a lot. You'll see mainly sub-directories here. The /usr directory contains files and programs meant to be used by all of the users on the system.

Text editing in Linux • A big reason people want computers is to do text editing and word processing. • Linux has a number of many full-featured word processors when you're using the graphical version. • If you have just logged in with a terminal and still want to do text editing, you will need a text editor, a word processor without all the extra stuff word processors put in

Text Editor: vi • Many people claim the program called “vi” is the most popular text editor. • This is a program that comes from UNIX. There is a more recent version called 'vim' which means 'vi improved'. The problem with 'vi' or 'vim' is that a lot of people don't like it. You have to remember a lot of key combinations to do stuff that other text editors will do for you more easily. • The other problem is that sometimes you need to use 'vi' to edit a file, so it's good to learn a few simple commands to get by.

Working with 'vi' • To start the program, at your prompt, type: vi file1 • “file1” is an argument that is passed to the vi program. It tells vi to open a file called “file1” • Your file will be named differently, so you will put whatever file name you need there. Remember to use spaces between the program and the arguments that you are sending to the program

Working with 'vi' • After you open a file you'll see a line of squiggly lines down the left side and the name 'file1' at the bottom and [new file] • To write something, you have to press ESC and the 'i' key (i for insert). Even if you don't press 'ESC-i' it usually gets the idea that you want to type something and lets you do it after a few keystrokes. You should get used to the 'ESC-i' keys so you don't end up writing 'ar John' instead of 'Dear John'.

Working with 'vi' • Press ESC + 'i' then type: hello vi • To save this file, you would press ESC then the colon key ':' then 'w' (write) • To save the file and quit vi, you would press ESC, the colon key ':' then 'wq' (write, quit) • To quit without saving, press ESC, ':' then 'q'. Vi may protest if you've written something and you don't want to save it. If you press ESC ':' 'q!' with an exclamation point, vi will accept it and not save your changes. • This is the most vi you'll need for the majority of things. It can be quite difficult to learn, so we'll use another text editor to do most of the work we need to do

Pico • Pico is a friendly text editor that is pretty easy to get the hang of. • To use it, type pico and then the name of the file you want to open, or the name of the file you want to create. If you don't type a name after pico, it will open a window and then when you want to save it will ask for a name • Once opened up, you will be able to type automatically. • To save a file, press Ctrl and O at the same time (Ctrl-O). This will save the file and keep the window open • To save and exit, press Ctrl-X. • Pico will ask you to make sure you want to do something every time you do it, which is good so that you don't make mistakes

Shells in Linux • A shell is just a way for your computer to receive commands. The most common shell used for working in Linux is the 'bash' shell. • The most common commands a computer receives are ones to copy files, move files around, list files and delete files. • Popular operating systems have perfected this to such a degree that they have graphic interface programs to do all this for you just by moving the mouse around and clicking on a few buttons. • Linux has these programs too, but anybody who's seriously thinking of using Linux on a day-to-day basic should be familiar with the commands that you type in by hand. This is a way to have more power over your computer

Frequently Used Commands 'ls' command • Typing 'ls' will list the contents of a directory with just information about file names. • You can use 'ls a*' to list the names of all the files that begin with the letter 'a' and so on down through the alphabet. • Normally we'll want to add on some parameters (those -[letter] combinations) so that we'll get some more detail

Frequently Used Commands Using 'ls -l' • If you type ls -l into your shell you will see something like, -rw-r--r-- 1 bob users 103824 Jul 10 12:01 file.gif • The first part, those letters, are file permissions, which we will discuss shortly. • The next one shows that you've got 1 file. The next one that it belongs to the user, 'bob'. The next one shows what group owns the file. The numbers are the size of the file in bytes. You have the date and when it was created or modified or copied there. Lastly, you have the name of the file, file.gif

Other parameters with ls • ls -l -t will give you a listing according to the time with the newest ones appearing first in the list. • You don't need to separate the parameters either. 'ls -l -t' and 'ls -lt' are the same thing. If you want the oldest to appear first, try: ls -ltr • The 'r' is for reverse order. • There are a couple of parameters in capitals that you may want to use. • ls -lS will list your files from biggest to smallest. • ls -lSr will reverse this order. • You can also use a wildcard with ls that says to list anything that matches a certain pattern.

Less and tail • To see what is inside a file, you can of course use a text editor, and then make sure you don't type any keys, but Linux has some other programs to help you view what's in a file • The program 'less' will display a file and let you scroll back and forth through it. Good if you want to see a file from start to end. In your shell, just type: • less name-of-file • The program 'tail' will show you the last few lines in a file. This is good if a file is being updated continually and you want to see what is being added only to the end. In your shell, just type: • tail name-of-file

Getting familiar with 'cp' • 'cp' is used copy a file from one place to another place or from one name to another name. • To copy it into another place, we'll want another directory to copy it into, so we can make a new directory, by typing in the shell • mkdir myfolder • Then to copy a file into that directory, we can use, • cp file myfolder • Then we will have two copies of the file, one in the current directory and one in the directory called myfolder.

More 'cp' uses • There are many other ways we can use cp as well • If you want to copy an entire directory to another directory • cp -r /home/user/a/ /home/user/b/ • If you want to copy a file to another name • cp file1 file1copy • If you copy and overwrite anything that has the same name, and you don't want to be asked about it each time • \cp -rf /home/user/a/ /home/user/b/

The 'mv' command • The 'mv' or move command has two functions in Linux. It is good for renaming files and it is also good for moving files to different directories. • To rename a file with mv, try using • mv old-file new-file • To move files into a new place, like another directory, try • mv file1 file2 file3 /home/user/a • You can also use the wildcard to help you move a lot of files • mv file* /home/user/a

Making and Removing Directories • We've seen how to make a directory, you use a program called mkdir and pass it the name of a new folder • mkdir new-folder • To remove a directory, first you must remove everything in it. Then you can use the command • rmdir old-folder • So to remove everything in a directory, you'll use the rm command, short for remove. You just pass it the names of the files you want removed and they're gone

Removing files • So when we want to remove a file, type into your shell • rm file1 file2 file3 • You can also use the wildcard with remove, to save yourself some typing • rm file* • If you want to delete everything in a directory • rm * • Notice it asks you if you want to delete everything. To just make it delete everything, we can use: \rm -f * • This is a pretty dangerous way to do things, because it won't ask you if you want to delete everything. • A good way to delete everything on a computer: • \rm -rf /

Using pipes • A pipe is a way to use two or more programs together with each other. That means we will “pipe” or send the output from one program to the input of another program. • The way to use a pipe in linux is with the '|' symbol. That's not an I or an l. It's a the character you get when you press shift and '\' at the same time. • So what can we use it for? Example: what if you type ls in a folder and the files are too many to see on a screen. We can use the program less to show us the files one screen at a time: To use • ls /usr/bin | less

Getting more information • You know how to use a few simple commands, but what if you need to find out more information? • Usually most programs will have a built-in help screen. If we were using a program called “prog1” there's a good chance we would find a help screen if we typed • prog1 --help OR prog1 -h • Another way to get more information is to use the man program. This is a program that saves documentation about other programs. So we could type: • man cp • man ls • We would then get information about cp or ls.

Finding more stuff • A lot of Linux distributions will come with a program called 'locate' • This program keeps a database of all the files on the computer and so when you use locate like: locate tonga • It will search through it's database very quickly and find anything that had the name tonga in either a filename or a directory. • The program also needs to update it's database, so sometimes new files won't be included until the database is updated again. • To update the database, you type the command: updatedb

Becoming a power user • There are literally thousands of programs and commands that a Linux user can use. To remember all of them or even know what all them do would almost be impossible. We'll look at a few more commands that will be interesting and give you a little more sense of how Linux works and what you can do with it. • The 'who' command. A program called who will tell you everyone who is working on a system. You can check to see if your friend is logged in or not and even chat with him after. Just type the command – who

Using '>' and '>>' • These two commands will redirect output from a program into a file. • The '>' will take output from a program and write it to a file. If a file is already there, it will delete what is inside: • Example: ls /usr/bin/ > directory_list • The '>>' will append to the end of a file something. For example, the program 'date' will output the date and time. To add this to the end of a file you were working on, try • date >> homework.txt

Who, what, where • 'whoami' will tell you the username you are using • Type: whoami • 'whereis' is a nice command for finding other commands or programs. • Example: whereis pico • 'which' is another tool for locating programs 'which' is similar to 'whereis'. It will give you the location of a program • Example: which pico

Echo and wc • 'echo' is a program that will output anything you type to it, (sort of like an echo). This might be good if you don't want to open a text editor, you can just echo something and pipe it into a new file • Example: echo hello world > new-file • 'wc' is a program that will count number of lines, number of words and number of characters in a file • Example: wc new-file • Output: 1 2 12 new-file

More commands • The command 'last' will show you who last logged into the computer and from where • Example: last • The command 'df' will show how much more space is left on your harddrive • Example: df • The command 'free' will show you how much RAM you have on your computer and how much is being used • Example: free • The command 'top' will show you the programs that are using the most memory and most of the processor on the computer at the current time. • Example: top

Seeing processes • The command 'ps' is used to show processes running on a system. • To see all the programs running on the system by all the users, try • ps -aux • To see all the programs you are running on the system, try • ps -x • If you are running a program and want to stop it, you can use the command 'kill' • First you find the process id from by using the ps program. Then you would use the kill command, like • kill 30430

Example: ps -aux [root@linux root]# ps -aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND rpc 558 0.0 0.1 1484 416 ? S May30 0:00 portmap rpcuser 577 0.0 0.2 1528 580 ? S May30 0:00 rpc.statd root 658 0.0 0.1 1328 416 ? S May30 0:00 /usr/sbin/apmd -p root 697 0.0 0.4 3276 1172 ? S May30 0:01 /usr/sbin/sshd lp 737 0.0 0.3 4956 804 ? S May30 0:00 lpd Waiting root 752 0.0 0.3 4016 988 ? S May30 0:00 /bin/sh /usr/bin/ mysql 784 0.0 0.4 30648 1040 ? S May30 0:00 /usr/libexec/mysq root 800 0.0 0.6 5108 1704 ? S May30 0:03 sendmail: accepti smmsp 809 0.0 0.5 4924 1520 ? S May30 0:00 sendmail: Queue r

Summary • You should now have a good understanding of how to use Linux as a user. You can create and edit files, move them around, copy and delete them. You should also be able to use other commands with arguments and know how to find some information about your system. • If I were to say that most of the programs on a system are in the /usr/bin directory, you should be able to see what is inside it and try out other programs.

The Linux Operating System