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linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

means that it's suggesting a GID of 100. This is the default choice.



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<A NAME="Heading20<FONT COLOR="#000077"><B>TIP:</B> </FONT>In this <TT>adduser</TT>

	script and many other Linux programs, default choices are presented in square brackets.

	Simply press the Enter key to accept the default, or type the new value if you don't

	want to accept the default value. Sometimes (as you will see a little further on

	in the <TT>adduser</TT> utility) you are given two choices--usually <TT>y</TT> for

	yes and <TT>n</TT> for no--separated by a <TT>/</TT> or <TT>|</TT> character. The

	item in uppercase is the default choice, which you can use by pressing Enter. The

	other choice must be typed explicitly. In the following examples, yes is always the

	default choice: <TT>[Y/n]</TT>, <TT>[Y|n]</TT>, <TT>[Yn]</TT>. 

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<P>The default Group ID of 100 is fine for this new user, so simply press Enter.

In most cases you will not want to change the suggested Group ID.</P>

<PRE><FONT COLOR="#0066FF">GID [100]:

Group 'users', GID 100

First unused uid is 501

UID [501]:

</FONT></PRE>

<P>The <TT>adduser</TT> utility did not echo your Group ID choice to the screen.

This can be a little disconcerting if you're not used to it, especially if you look

back and try to figure out what you've done! Most Linux commands don't echo what

you have done, though, so this is a good time to get used to it.</P>

<P>The <TT>adduser</TT> utility now asks for a UID or User ID. Linux suggests a default

value of 501. Again, the default is fine in this case, so just press Enter.



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<A NAME="Heading21<FONT COLOR="#000077"><B>NOTE: </B></FONT>The User ID is

	used by Linux whenever it is referring to something you have done. The operating

	system is designed to use a number rather than the full login name because it takes

	up less room and is easier to manipulate. The User ID is important, and each login

	on the system has its own unique number. By convention, UIDs of 500 or less are special

	system UIDs; <TT>root</TT>'s UID is 0. Regular users get UIDs starting at 501. 

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<P>The <TT>adduser</TT> utility then shows two more prompts asking for the user's

home directory and the shell:</P>

<PRE><FONT COLOR="#0066FF">Home Directory [/home/fido]:

Shell [/bin/bash]:

</FONT></PRE>

<P>Choose the default values for <TT>Home Directory</TT> and <TT>Shell</TT>. I'll

explain more about directories in Chapter 8 and look at different shells in Chapters

10, &quot;<TT>bash</TT>,&quot; 11, &quot;<TT>pdksh</TT>,&quot; and 12, &quot;<TT>tcsh</TT>.&quot;

The default values are suitable for most user IDs.</P>

<P>As a last step, the <TT>adduser</TT> program asks for a password for the new user.

At the prompt, enter a suitable password. If you press Enter without typing anything

else, the password is set to the same string as the login. This is not recommended,

because it is easy to guess. Even a simple password is better.</P>

<PRE><FONT COLOR="#0066FF">Password [fido]:



Information for new user [fido]:

Home directory: [/home/fido] Shell: [/bin/bash]

uid: [501] gid: [100]

Is this correct? [y/N]:

</FONT></PRE>

<P>The <TT>adduser</TT> program now verifies that you are happy with all the information

you have entered. If you are, type <TT>y</TT> for yes, and press Enter. The default

value (shown by the capital letter) is <TT>N</TT> for no. If you choose the default,

you are telling the script that the information displayed is not correct, and you

have to start the whole process over again.</P>

<P>When you answer <TT>y</TT> to the question <TT>Is this correct?</TT>, the <TT>adduser</TT>

program creates the new user's directory and adds the user information to the system

configuration files. You see the following information appear on the screen as the

<TT>adduser</TT> utility does its work. When the utility has finished, you see the

Linux shell prompt again:</P>

<PRE><FONT COLOR="#0066FF">Adding login [fido] and making directory [/home/fido]



Adding the files from the /etc/skel directory:

./.less -&gt; /home/fido/./.less

./.lessrc -&gt; /home/fido/./.lessrc

darkstar:~#

</FONT></PRE>

<P>We will look at how to remove unwanted users from your <TT>/etc/passwd</TT> file

in Chapter 41, &quot;Users.&quot;

<H3 ALIGN="CENTER"><A NAME="Heading22<FONT COLOR="#000077">Logging Out</FONT></H3>

<P>Now that you have created a new user, you can use it in the next couple of chapters

to explore Linux. To finish with your session as <TT>root</TT>, log out of the system

by typing <TT>logout</TT>:</P>

<PRE><FONT COLOR="#0066FF">

darkstar:~# logout

Welcome to Linux 2.0.0.

darkstar login:

</FONT></PRE>

<P>You see the login prompt displayed again. At this point, you can log back in as

<TT>root</TT>, or as the new user you have just created.</P>

<P>Some systems enable you to log out with the Ctrl-D sequence. If the shell you

are using supports Ctrl-D as a logout command, the login prompt reappears. Otherwise,

you may see a message such as this:</P>

<PRE><FONT COLOR="#0066FF">Use &quot;logout&quot; to leave the shell.

</FONT></PRE>

<P>If you have used other UNIX systems before, you may be used to using Ctrl-D to

log out. The default shell used by Linux does not support Ctrl-D unless the keymappings

are changed to allow it.

<H3 ALIGN="CENTER"><A NAME="Heading23<FONT COLOR="#000077">Trying Out Your

New Login</FONT></H3>

<P>Now we can try out our new login. We can also look at some of the interesting

features and capabilities of Linux.</P>

<P>At the login prompt, type the login name you have just created. If you were conscientious

and assigned a nonzero-length password to your new login, enter the password when

prompted.</P>

<P>You should now see the following:</P>

<PRE><FONT COLOR="#0066FF">darkstar login: fido

Password:

Last login: Sun Dec 11 19:14:22 on tty1

Linux 2.0.0.



Quiet!  I hear a hacker....

</FONT></PRE>

<PRE><FONT COLOR="#0066FF">darkstar:~$

</FONT></PRE>

<P>Note that your prompt looks different from the <TT>root</TT> prompt. The <TT>$</TT>

prompt indicates that you are a regular user running under the <TT>bash</TT> shell

(which was the default choice presented by the <TT>adduser</TT> program). Also, there

is no <TT>You have mail</TT> message.



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<A NAME="Heading24<FONT COLOR="#000077"><B>NOTE: </B></FONT>Linux can be configured

	to automatically mail a message to all new users. This can be a greeting, or can

	give system information and etiquette. 

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<P>To see an example of the difference between the <TT>root</TT> login and a regular

user login, type <TT>adduser</TT> at the shell prompt and press Enter.</P>

<PRE><FONT COLOR="#0066FF">darkstar:~$ adduser

bash: adduser: command not found

</FONT></PRE>

<P>The message you get looks somewhat cryptic. However, it has a typical Linux error

message structure, so it's worth taking a little effort to understand it.

<H4 ALIGN="CENTER"><A NAME="Heading25<FONT COLOR="#000077">Linux Error Messages</FONT></H4>

<P>First of all, the program that's giving you the message is your shell, <TT>bash</TT>.

It therefore announces itself with <TT>bash:</TT>, somewhat like the character in

a play script. Next is the shell's &quot;monologue.&quot; Being the &quot;strong

and silent&quot; type of character, <TT>bash</TT>'s monologue is very terse and to

the point. It declares the object that is causing it problems (<TT>adduser</TT>),

and the problem with this object: the command (<TT>adduser</TT>) can't be found.</P>

<P>If the error message were expanded into real English, it would go something like

this: &quot;Hi, I'm <TT>bash</TT>. You know that <TT>adduser</TT> command you gave

me? I looked everywhere for <TT>adduser</TT> but I couldn't find it, so I couldn't

perform whatever actions <TT>adduser</TT> would have specified.&quot; With time,

you will get quite good at understanding Linux error message grammar.

<H4 ALIGN="CENTER"><A NAME="Heading26<FONT COLOR="#000077">Search Paths</FONT></H4>

<P>Why can <TT>root</TT> find <TT>adduser</TT>, but an ordinary user cannot? Linux

has many directories, and each directory can hold many files (one of which can be

the elusive <TT>adduser</TT>). In theory, Linux could go search through the file

system until it found <TT>adduser</TT>. But if <TT>root</TT> accidentally mistyped

<TT>adduser</TT> as <TT>aduser</TT>, Linux would have to rummage through every nook

and cranny before finally giving up. This could take 10 or more seconds, and cause

needless wear and tear on your hard drive.</P>

<P>Therefore, Linux has search paths for finding commands (discussed in Chapter 8).

Usually, only a small part of the entire Linux file system is on the search path,

which literally is the path along which Linux searches. Because <TT>root</TT> makes

use of many system administration programs such as <TT>adduser</TT>, the directories

that hold these programs are in <TT>root</TT>'s search path. Ordinary users do not

have system administration directories in their search path.</P>

<P>However, if you explicitly tell Linux where a file is located, it does not need

to look through its search path. As it happens, <TT>adduser</TT> is found in the

<TT>/sbin</TT> directory. Try running <TT>/sbin/adduser</TT>.</P>

<PRE><FONT COLOR="#0066FF">darkstar:~$ /sbin/adduser

</FONT></PRE>

<PRE><FONT COLOR="#0066FF">bash: /sbin/adduser: Permission denied

</FONT></PRE>

<P>This time, <TT>bash</TT> could find <TT>adduser</TT> (because you told it exactly

where to look), but discovered that an ordinary user does not have permission to

run <TT>adduser</TT>. As you can see, Linux limits the actions of logins to their

privilege level.

<H3 ALIGN="CENTER"><A NAME="Heading27<FONT COLOR="#000077">Virtual Terminals</FONT></H3>

<P>Linux, as mentioned earlier, is a multiuser, multitasking system. This means that

more than one login can access the system at the same time, and that each login can

be doing one or more different things all at the same time. A serious multiuser system

will have several terminals (consisting of a keyboard and a display screen) wired

or networked to the main computer unit.</P>

<P>Although you probably don't have any terminals attached to your system, you still

can log in several times under the same or different login names, using your single

keyboard and screen! This magic is performed by using virtual terminals.</P>

<P>Press Alt-F2. When you do so, everything on your screen should disappear, to be

replaced by the following:</P>

<PRE><FONT COLOR="#0066FF">Welcome to Linux 2.0.0.



darkstar login:

</FONT></PRE>

<P>Log in as your &quot;regular&quot; login (not <TT>root</TT>). When the shell prompt

is displayed, type <TT>who</TT> at the prompt and press Enter. You should see the

following:</P>

<PRE><FONT COLOR="#0066FF">darkstar:~$ who

fido     tty2     Dec 14 01:42

fido     tty1     Dec 14 01:40

</FONT></PRE>

<P>When you run the Linux command <TT>who</TT>, your screen displays the names of

all logins currently logged into the system, and where they are logged in from. (Your

login name will appear, of course, instead of <TT>fido</TT> in the preceding example.)</P>

<P>By convention, <TT>tty1</TT> is the main console screen. It is the &quot;normal&quot;

one that appears after Linux has started up, so you don't have to do anything special

to get it. If you have switched to any other virtual consoles, you can return to

<TT>tty1</TT> by pressing Alt-F1.</P>

<P>How many virtual screens are active on your system? Try going through all the

Alt-Fn keys. Alternatively, you can scroll through the virtual screens by using the

Alt-right arrow combination to move up through the screens, or Alt-left arrow to

move down.</P>

<P>Quite often you find yourself doing something, perhaps in a long and complicated

program, and realize that you should have done something else first. Flip to another

virtual terminal and do whatever it is.</P>

<P>Another handy use of virtual terminals is when, through experimentation or otherwise,

your screen locks up or starts typing in strange symbols. From a different virtual

terminal, you can try to fix things, or restart the system if necessary.</P>

<P>Linux also comes with a very powerful multitasking windowing environment called

X. Installing and running X Window systems is described in Chapter 21, &quot;Installing

XFree86.&quot;

<H3 ALIGN="CENTER"><A NAME="Heading28<FONT COLOR="#000077">Commands and Programs</FONT></H3>

<P>&quot;Run the <TT>who</TT> command&quot; and &quot;Run <TT>who</TT>&quot; are

much more common ways of saying &quot;Type <TT>who</TT> at the prompt and press Enter.&quot;

We will use the shorter expressions wherever their meaning is clear. Sometimes people

familiar with Linux drop the word &quot;run,&quot; so that one user might tell another,

&quot;I tried <TT>who</TT> but didn't see anything unusual.&quot; It's understood

by the context that when they &quot;tried <TT>who</TT>,&quot; they actually ran it.</P>

<P>Something else you will notice if you are reading carefully is that there seem

to be both Linux programs and Linux commands. A command is what you type at the shell

prompt. For this reason, the combination of the shell prompt and what you type after

it is often called a command line. When you press the Enter key, Linux takes the

command you've entered and tries to perform it. The Linux system has built-in responses

to some commands; for other commands it finds the appropriately named program on

your hard disk and executes that program.</P>

<P>In the strictest sense, then, the command is what you type, and the program is

what performs your command. However, very simple programs with straightforward results,

such as <TT>who</TT>, are often referred to as commands, although there is actually

a <TT>who</TT> program on your hard disk. More complicated programs, usually interactive

such as <TT>adduser</TT>, or open-ended such as a text editor, are called programs.

So you might hear one experienced user tell another, &quot;The <TT>adduser</TT> program

worked fine. I tried the <TT>who</TT> command 15 minutes later and the new user had

logged in already.&quot;

<H3 ALIGN="CENTER"><A NAME="Heading29<FONT COLOR="#000077">Summary</FONT></H3>

<P>In this chapter, we assigned a password to the <TT>root</TT> login and created

a new user ID to be used in the next few chapters. We tried out Linux multitasking,

and we learned some useful Linux terminology tips that will serve us well in the

future (we will try to avoid seeing too many error messages, though). At this point,

you can either ensure that you have logged out of all virtual terminals, or move

on to the following chapters.</P>



<P>In the next two chapters, we will become more familiar with using Linux. In Chapter

7, &quot;Basic Commands,&quot; we try out a variety of Linux commands as we exercise

our Linux muscles. In Chapter 8, we learn more about how Linux stores its programs

and data, and explore some of the interesting terrain on your hard drive.









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