UNIX Tutorial One

1.1 Changing Your Password

passwd

A password is given to you by your instructor or by the system administrator. Your account is for your use only. Do not share your login password with others.

Your password is probably something very random and difficult to remember. Writing it on an index card and taping it to you laptop keeps it handy, but that also (mostly) defeats the purpose of your password. You will want to change it to something you can remember more easily. However, you should not change it to a dictionary word, or some simple combination, e.g., "bluefish" or "doghouse". Password guessing software such as "John the Ripper", "Satan", or "Cain and Abel" can easily discover such simple passwords. Remember, gottlieb is connected (via ssh) to the big bad Internet. Anyone from anywhere in the world can probably find your e-mail address, and thereby guess your login name. From that guess, password hacking software does the rest. Please do not use weak passwords.

To change your password, type

% passwd

You will be prompted to enter your current password. After successfully entering your current password, you will prompted to enter a new password. Finally, you will be prompted to enter the new password a second time to verify it. The new password takes effect immediately.

1.2 Listing files and directories

ls (list)

When you first login, your current working directory is your home directory. Your home directory has the same name as your user-name, for example, ee91ab, and it is where your personal files and subdirectories are saved.

To find out what is in your home directory, type

% ls

The ls command lists the contents of your current working directory.

There may be no files visible in your home directory, in which case, the UNIX prompt will be returned. Alternatively, there may already be some files inserted by the System Administrator when your account was created.

ls does not, in fact, cause all the files in your home directory to be listed, but only those ones whose name does not begin with a dot (.) Files beginning with a dot (.) are known as hidden files and usually contain important program configuration information. They are hidden because you should not change them unless you are very familiar with UNIX!!!

To list all files in your home directory including those whose names begin with a dot, type

% ls -a

ls is an example of a command which can take options: -a is an example of an option. The options change the behavior of the command. It is a long standing Unix convention that options start with a minus sign. For this reason, it is strongly recommended to never create a file whose name begins with a minus sign; any command which attemps to act on that file will interpret characters following the minus sign as (possibly invalid) options.

There are online manual pages that tell you which options a particular command can take, and how each option modifies the behaviour of the command. (See later in this tutorial)

Another option for the ls command is -l. The '-l' option specifies the long form listing and is discussed in Tutoral 5.

1.3 Making Directories

mkdir (make directory)

We will now make a subdirectory in your home directory to hold the files you will be creating and using in the course of this tutorial. To make a subdirectory called unixstuff in your current working directory type

% mkdir unixstuff

To see the directory you have just created, type

% ls

1.4 Changing to a different directory 

cd (change directory)

The command cd directory means change the current working directory to 'directory'. The current working directory may be thought of as the directory you are in, i.e. your current position in the file-system tree.

To change to the directory you have just made, type

% cd unixstuff

Type ls to see the contents (which should be empty)

Exercise 1a

Make another directory inside the unixstuff directory called backups

1.5 The directories . and ..

Still in the unixstuff directory, type

% ls -a

As you can see, in the unixstuff directory (and in all other directories), there are two special directories called (.) and (..)

In UNIX, (.) means the current directory, so typing

% cd .

NOTE: there is a space between cd and the dot

means stay where you are (the unixstuff directory).

This may not seem very useful at first, but using (.) as the name of the current directory will save a lot of typing, as we shall see later in the tutorial.

 

(..) means the parent of the current directory, so typing

% cd ..

will take you one directory up the hierarchy (back to your home directory). Try it now.

Note: typing cd with no argument always returns you to your home directory. This is very useful if you are lost in the file system.

1.6 Pathnames

pwd (print working directory)

Pathnames enable you to work out where you are in relation to the whole file-system. For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type

% pwd

The full pathname will look something like this -

/home/csc221/jonewh13

which means that jonewh13 (William Jones' home directory) is in the directory csc221 (the class directory). The class directory csc221 is located in the /home directory.

 

Exercise 1b

Use the commands ls, pwd and cd to explore the file system.

(Remember, if you get lost, type cd by itself to return to your home-directory)

1.7 More about home directories and pathnames

Understanding pathnames

First type cd to get back to your home-directory, then type

% ls unixstuff

to list the conents of your unixstuff directory.

 

Now type

% ls backups

You will get a message like this -

backups: No such file or directory

The reason is, backups is not in your current working directory. To use a command on a file (or directory) not in the current working directory (the directory you are currently in), you must either cd to the correct directory, or specify its full pathname. To list the contents of your backups directory, you must type

% ls unixstuff/backups

 

~ (your home directory)

Home directories can also be referred to by the tilde ~ character. It can be used to specify paths starting at your home directory. So typing

% ls ~/unixstuff

will list the contents of your unixstuff directory, no matter where you currently are in the file system.

What do you think

% ls ~

would list?

What do you think

% ls ~/..

would list?

Summary

passwd allows you to change your password
ls list files and directories
ls -a list all files and directories
ls -l give the long form listing of files and directories
mkdir make a directory
cd directory change to named directory
cd change to home-directory
cd ~ change to home-directory
cd .. change to parent directory
pwd display the path of the current directory

Continue with the Tutorial

M.Stonebank@surrey.ac.uk, © 9th October 2000