Linux is an open-source implementation of the long-lived UNIX operating system and the Ubuntu Hardy (8.04) version is the particular distribution of Linux installed on most of the workstations in the Department of Computing from summer 2008. Many of the workstations also run Microsoft's Windows Vista operating system and you can select either of these when starting up the machine; systems which run both will start up in Linux unless you specifically select Windows Vista.

Type in your login name, which you will have received in your starter pack, then press the enter/return key. Now type in your password and press the return key again. For security reasons, the password isn't displayed on the screen as you type it.

When you have given the banner program your login name and password, the screen will clear and after a few seconds your desktop will appear.

Using X-Windows

The window manager

A program called the window manager controls what you see on the screen; there are a number of different ones you can select from - this guide uses one called KDE as an example.

Using the mouse

You will notice that moving the mouse affects the position of a cursor in the window. The mouse provides your primary interaction with the graphics user interface. It controls most of the functions of the window system and you will use the mouse to point to and select desired options. When you slide the mouse on its mat, the mouse cursor on the display tracks the movement. When you press or hold the mouse buttons, the system responds with appropriate actions. The mouse has three buttons, known as left, middle and right (with the cable pointing away from your wrist).

Raising and minimising windows

Sooner or later you will have many overlapping windows on your screen. You can raise an obscured window to the front of the display to see its contents by clicking the left mouse button when the cursor is over the window.

After some time, your screen will normally contain several windows, and you may find it convenient to temporarily move some windows out of the way. You can do this by changing the window into an icon, which is a small symbol that represents a window but takes little space. You can iconify the window by clicking in the leftmost of the three small boxes at the left hand corner of the title bar. It is known as the minimise button. The contents of the window aren't visible when it is shown as an icon. The icon appears in the bar along the top of the screen and you can change the icon back into its full window representation by clicking on this. You can also use the pager (the squares numbered "One" to "Four" on the task bar) to view different areas of the desktop.

Moving a window

Position the mouse cursor in the bar at the top of the window, called the title bar, then press and hold the left mouse button. Drag the window to the new location. Release the mouse button when you are satisfied with the position of the window.

Resizing a window

To enlarge or shrink a window, place the mouse cursor over the small box at the extreme left hand side of the title bar of your window and click the left mouse button. A menu will appear which offers various window operations including resizing. Move the mouse until the cursor is over resize, click the left button and move the mouse to stretch or shrink the window. Click the left button again when the window is the size you want.

Logging out

When you are ready to finish your session, click the K button on the taskbar and choose the Logoutoption. After you have confirmed your decision to logout all windows will close, the screen will clear, and a few seconds later the login banner will re-appear, ready for the next user.

Conventions used in this Guide

Instructions which you give to the Linux operating system are known as commands. In this guide, all examples of command usage are indented; command names and other words which form part of the command appear exactly as they are to be typed. For example, describing how the xemacs editor can be invoked, the example will appear as either:

xemacs File1

Note that words representing generalised arguments to commands (eg. filename) appear in italics. Sometimes examples are given which show the screen output of a command -- in other words, what you might expect to see if you were to type a certain command at a terminal. These examples are represented thus:

vector17% ls -a
.cshrc File1
.login File2
vector17%

Literal keys on the keyboard are enclosed within angled brackets as, for example:

<RETURN>

meaning press the key marked RETURN (note that on some keyboards this key is simply marked ¿).

Similarly, sequences such as:

Ctrl-c

mean you should press the key marked Ctrl and the key c at the same time.

The examples we give usually refer to computers supported by the Computing Support Group (CSG) and may therefore not be available on laptops or home machines or non-maintained desktops.

Online help

man lpr

will give you information on the standard printing command.

If you are not sure of the exact name of the command that you want information on, you can try a keyword search by giving the k flag to man. Eg:

man -k editor

Changing your password

vector17% kpasswd dcw@IC.AC.UK
Old password for user: (type in your current College password -- it will not appear
on the screen)
New Password for user: (type in your new password -- it will not appear
on the screen)
Verifying, please re-enter New Password for user: (type in your new
password again)
Password changed.
vector17%

A print job can be sent to a printer by using this command:

Each printer in the department has a blue label on it indicating its name.

See also: manual page on lpr.

Email

Files and networks and home directories

The diagram shows the classic Linux directory structure:

Root is always addressed as "/" and the division between each directory is also a "/". So the pathname to reach File1 in the directory fred is:

	/homes/fred/File1

In most cases, your home directory will not be physically stored on a file system attached to the computer you are connecting to. In other words, the file system is being mounted across the network onto the computer to which you are connected. NFS (Network File System) makes sure that the filesystem containing your home directory is mounted and accessible by you at all times during your session. Similarly, other file systems are mounted across the network so that compilers, applications and data can be shared among all the users of the network.

File Management

Listing files

To list the contents of the current directory (the directory you are currently "in"), simply type:

	ls

• ls -a
  causes ls to list all the files and subdirectories including dot files such as .login and .cshrc. The file called '.' refers to the current directory. The file called '..' refers to the directory above the current directory -- the parent directory.

• ls -l
  causes ls to display eight columns of information about each file. These columns give information such as access permissions, size of the file, date, time when last modified, name of the owner etc. It will not list 'dot' files, ie. system files named beginning with a dot.

• ls -d
  causes ls to display the names of the directories without displaying their contents.

Seeing files

Various commands are available for reading the contents of a file.

The cat command is used to look at the contents of a file. You can see the contents of any file by typing:

	cat filename

The more command can be used to display a file, one screenful at a time. It is similar to cat, but pauses each time it fills the screen. You can invoke more by typing:

	more filename

Here is a list of some of the most useful commands: b to scroll backward

q to quit

h to get a summary of all the available commands under more

The command less is more than more. It is similar to more except that it offers the commands listed above, plus extra options including: g to go to line N

Moving files

The cp command is used to copy files. It copies one or more files, including text and executable program files. For example, to make a backup of File1, type:

cp File1 File1.bak

where File1.bak is the name of the backup copy of the file. cp can be used to copy files between directories as well. The mv command moves files and directories around within the filesystem. A move differs from a copy operation in that the original name of the file disappears -- the file is effectively renamed. So mv can also then be used for renaming a file or a directory.

Removing files

To delete a file you use the rm command. This command deletes Files from a directory. For example, if you wanted to delete a file called File1 then you can do so by typing:

rm File1

To delete a file, you must have execute and write access permission to the parent directory of the file, but you do not need read or write access permission to the file itself. NB: unlike some other operating systems, once you remove a file in Linux you cannot recover it so be very careful with the rm command.

There are a number of options available which you can look up in the manual pages.

Permissions

Every file or directory that is created on the system has an owner, who is usually the person who created that file or directory in the first place. The owner of a file or directory can then assign various protections, allowing or prohibiting access to that directory or file. There are three classes of users for every file and directory:

• User (the person who initially created it).
• Group (several users combined into a user group).
• Other (all other users of the system).

• Read (a user who has read permission for a file can look at the contents of the file).
• Write (a user who has write permission for a file can change the contents of that file).
• Execute (a user who has execute permission for a file can use it as a command).

The mode of a file or directory can be changed with the chmod command.

For example, if you wanted to set the write permission to a file, you need to type:

chmod +w filename

Similarly, to set the group execute permission on a file:

You can remove permissions from a file's mode by using - instead of +.

Important (Startup) Files in your home directory

Most users will have in their home directory files called .cshrc and .login (by convention, filenames starting with a dot are either administrative or startup files for shells, applications and compilers). The .login file will, among other things, assign appropriate values to important variables such as PATH (which directories to search for commands) and TERM (what kind of terminal you are using).

CHANGING THE DEFAULT SETUP IS NOT RECOMMENDED. For an easy life, leave these startup files alone. They have been carefully constructed to provide a standard environment which works. If you make changes, things may work for a while until something on the system is upgraded or moved. On CSG maintained systems you will in any case not be able to edit most startup files directly since they are simply links (symbolic links) to standard system files. The exception to this is the .cshrc file.

The .cshrc file

The .cshrc initialises the environment for the shell you run (the C-Shell) and is an exception because it is useful, for example, for users to be able to set their own aliases. For new users the .cshrc file contains only one command:

source /usr/local/etc/default.cshrc

This instructs Linux to execute the standard system-wide cshrc file located in the directory /usr/local/etc (you may wish to look at the comments at the beginning of this default file - just type: more /usr/local/etc/default.cshrc). Don't alter this line; you can however add instructions after it. Examples of the kind of additions you might wish to make to your .cshrc file can be found in the section The Shell in the "More information on Linux" part of this guide.

Disk space management

Quotas

Disk space for file storage is not infinite and as a result disk quotas and limits are set for each group of users on the system.

quota -v

will check your quota and current disk usage. If you have exceeded the quota, you will have seven days to remove sufficient files to reduce your usage below the quota. If you exceed the limit, you will be unable to create more files and could lose e-mail. You may also have difficulty logging in - particularly under X-Windows since X creates a number of temporary files.

Compressing your files

The gzip command will compress data. It reduces the size of the named file using adaptive Lempel-Ziv coding. Compressed files can be restored to their original form using the gunzip command. To compress a file, simply type:

gzip filename

The compressed file will automatically be saved under the same filename with a suffix .gz attached to it. A compressed file can be viewed (without the need to uncompress) with:

zcat File1.gz

It is considered good practice to compress files which you do not regularly access.

Temporary file space

/vol/bitbucket is an area of disk where you can create extra workspace for your files without affecting your disk quota. It is therefore an ideal place to store your temporary files. However, a word of caution the files stored under /vol/bitbucket are erased regularly so it is advisable not to store important files in this area. Also note that any files kept here are not confidential - they can be read by anyone.

Core files

From time to time you might find a file called core in your filespace. This is a memory dump and they can be quite big. There are a number of reasons why they arise from simply killing a process to hitting an illegal instruction. Unless you are using them to debug programs, you should delete them and free up some of your disk quota.

Kerberos Authentication

Kerberos is a security system implemented on all CSG supported Linux computer systems. It provides a high level of security since passwords are not stored in any place or in any form that is accessible by persons who may wish to crack them.

Useful Commands

Simple file commands

ls	List the files and directories in the working (current) directory
cat File1 File2	Display the contents of the file File1 concatenated with the contents of the file File2
mv File1 File3	Change the name of (move) file File1 to File3
cp File1 File3	Make a copy of File1 and call it File3
rm File4	Erase (remove) the file File4
less File1	Display the contents of File1 a page at a time, q to stop displaying
lpr File1	Print the contents of File1 on the default printer

Directory commands

pwd	Print the name of the working directory
cd Exercise1	Change the working directory to Exercise1
mkdir Exercise2	Make a new directory and call it Exercise2
rmdir temp	Delete the (empty) directory temp

Finding out (about other users)

finger	Say who is logged in
finger -l tom@doc	Get full details on all DoC users with string "tom" in their name or login
who	Say (briefly) who is logged in

Finding out (general)

man finger	gives you a detailed description of the command finger
man -k library	tries to find any reference to library in the manual

Miscellaneous commands

passwd	Change your password
ssh sync10	Login to remote host sync10
logout	Disconnect from the computer

Part Two: more information on Linux and UNIX

© CSG / Oct 2008