Chapter 1. Getting Started - Login, Mail, Internet Access, UNIX Components

CONTENTS

Chapter 1. Getting Started - Login, Mail, Internet Access, UNIX Components

•  Introduction
•  Multi-User UNIX
•  Online Manual Pages
•  Electronic Mail
•  Accessing the Internet
•  UNIX Components

Introduction

I'll cover a wide variety of topics in this chapter that help you get started quickly on your UNIX system. The topics I'll cover include the following:

• Multi-user UNIX

• Uppercase and lowercase letters

• Login process (text and CDE)

• Login name and password

• Entering commands

• Logoff

• Electronic mail

• Internet access

• UNIX components

The topics in this chapter are covered in overview fashion with many examples. You can read a topic in this chapter while you try out the commands on your UNIX system. As I point out in every chapter in this book, differences occur among UNIX variants in almost every area. For instance, the command options on one UNIX variant may be somewhat different on another UNIX variant. Don't get overly concerned about the differences; just be aware of the fact that they exist and work through them as a matter of course. In an upcoming chapter, for instance, I spend some time on Common Desktop Environment (CDE). This is a graphical user interface found on many UNIX variants. It may not be available on your system, or your system administrator may have chosen a different graphical user interface. The same is true for most topics covered in this book. In general, though, most of what takes place at the command prompt is similar among UNIX variants, so you'll be able to take most of the examples in this chapter and use them on your system.

I put "UNIX Components" at the end of this chapter because you'll appreciate this topic much more after you have logged in and performed some basic commands.

Multi-User UNIX

Most UNIX systems are multi-user, meaning that several users may be using a single computer at the same time. You can connect to a UNIX system in a variety of different ways. You may have a character-terminal on which you can enter commands at the command line that does not support any graphical interface. You may have a computer with a graphics display connected directly to the computer. You may have an X-terminal that runs a graphical user interface over a Local Area Network (LAN). It is difficult to discern a directly connected graphics display from an X-terminal because both run the same graphical user interface - usually Common Desktop Environment (CDE). Although there are many options available for interfaces among UNIX variants, you always have access to the command line in UNIX. There is a wide variety of graphical user interfaces and graphical devices available, all of which support terminal windows that give you access to the command line.

Even systems that have only one character-based or graphics-based terminal connected to them are usually multi-user. With only one terminal connected to a system, why would you need to support multiple simultaneous users? To begin, you may have a user working on the directly connected terminal and additional users connected over the local area network. You may also want to have multiple windows open on your graphics terminal performing different tasks as different users.

Single-user systems are usually those dedicated to an individual user for his or her work. These systems provide a full UNIX environment but provide access for only a single user.

Most of the topics covered throughout this book apply to both single-user and multi-user systems.

All UNIX systems are multitasking, meaning that more than one process and application can be running on a system at a time. Later in the book, we look at the many processes running on a UNIX system all at the same time.

Uppercase and Lowercase Letters

UNIX systems distinguish between uppercase and lowercase for both commands and file names. The meaning of a command or the name of a file takes on a different meaning, depending on the way in which uppercase and lowercase letters are used. The following are examples of different file names on a UNIX system:

program  Program  prograM  PROGRAM 

If you wish to compile a file called program with the cc command on a UNIX system, you must issue the following command:

cc program 

If you were to issue one of the following commands, you would not compile the desired program:

CC program  cc Program 

The first example would not run the desired program called cc, because CC, with uppercase characters, is different from cc with lowercase characters. In the second example, the desired compiler called cc would indeed be invoked; however, the file called Program that we have specified is different from the desired file called program.

In addition to using care with uppercase and lowercase on UNIX systems, you also need to be aware of the fact that there are different file types on UNIX systems. Some different types of files found on UNIX systems, as well as how to determine the type of file you are dealing with, are covered in Chapter 2.

Login Process

All users on a UNIX system have a login name set up for them by the system administrator. The system administrator may consult you on the login name you wish to use. You gain access to the system by supplying both your login name and password. I cover this process shortly.

The rules for the login name you choose are determined by your system administrator. Typically, a login name will be two to eight characters in length. There are usually no special characters used in a login name.

There is not typically any security associated with a login name so pick a name easy for you to remember. Your name may also be used by other system users to send you messages and electronic mail, so a name by which other users know you will also be helpful.

Your password must meet the requirements set forth by the system administrator. The first time you log in you may have no password or only a temporary password that must be changed after you initially log in to the system. Passwords normally have such requirements as a minimum of six characters and a minimum of one special character. Your system administrator may also require passwords to be changed on a regular basis. Your password should be complete nonsense so that no one could even begin to guess it.

Let's now look at an example login process. I begin with a character-based login session.

On your terminal you will receive a login prompt as shown in the following example. You respond to the login prompt with the name and temporary password supplied to you by your system administrator:

*******************************************************************  * This is a private system operated for Your Company              *  * business. Authorization from management is required to use      *  * this system. Use by unauthorized persons is prohibited.         *  *******************************************************************    login: martyp    Password:    Last login: Fri Sep 17 07:12:57 from atlm0547.atl.hp.    TERM set to vt100    martyp $ 

The login was successful. We entered the correct login name and password and were granted access to the system.

You may occasionally enter an invalid user name or password. In the following example we first enter a valid user name and an invalid password. On the next attempt we enter an invalid user name. On the third attempt we enter all the correct information and are granted access to the system.

*******************************************************************  * This is a private system operated for Your Company              *  * business. Authorization from management is required to use      *  * this system. Use by unauthorized persons is prohibited.         *  *******************************************************************  login: martyp  Password:                          <-- first attempt, invalid password  Login incorrect  *******************************************************************  * This is a private system operated for Your Company              *  * business. Authorization from management is required to use      *  * this system. Use by unauthorized persons is prohibited.         *  *******************************************************************  login: m                       <-- second attempt, invalid user name  Password:  Login incorrect  *******************************************************************  * This is a private system operated for Your Company              *  * business. Authorization from management is required to use      *  * this system. Use by unauthorized persons is prohibited.         *  *******************************************************************  login: martyp                      <-- third attempt, valid user name  Password:                                       and password  Last login: Fri Sep 17 07:12:57 from atlm0547.atl.hp.  DISPLAY set to atlm0547:0.0  TERM set to vt100  martyp $ 

Note that after both the first and second failed attempts to log in to the system, we "start over." The system recognizes the invalid user name on the first attempt and the invalid password on the second attempt and in both cases supplies a "Login incorrect" message and starts over. The "Login incorrect" message is intentionally ambiguous, so you don't know whether your user name, password, or both are incorrect; therefore as little information as possible is give to someone attempting unauthorized access to the system.

After the successful login, you are given information about the system, your terminal, and any other information the system administrator thinks would be useful to you. This information surely differs on your system.

After login we want to proceed to issue commands. In this example, the first command we'll issue is to change the temporary password supplied to us by the system administrator. You may find that after your first login you are required to change your password. The passwd command is used to change the password. Let's issue the passwd command and try to change our password to the current password, that is, no change. Then let's try to change the password to passwd. Finally, we'll change the password to a valid password:

martyp $ passwd  passwd:  Changing password for martyp  Enter login password:  New password:                     <-- change to current password  passwd(SYSTEM): Password cannot be circular shift of logonid.  New password:                      <-- change to passwd  passwd(SYSTEM): The first 6 characters of the password  must contain at least two alphabetic characters and at least  one numeric or special character.  New password:                      <-- change to valid password  Re-enter new password:  passwd (SYSTEM): passwd successfully changed for martyp  martyp $ 

When we try to change the password to the current password, which is the same as our user name, we are told that the password can't be a "circular shift of loginid." This means that the login name and the password on this system must differ substantially. When we try to change our password to passwd, we are told that the first six characters must contain at least one numeric or special character to make the new password more difficult to guess. Finally, we conform to the rules for a new password and receive an indication that the change was made. Note again that the system supplies no visible characters when we type the new passwords.

Some features of a good password are:

• A minimum of six characters that should include special characters such as a slash (/), a dot (.), or an asterisk (*).

• No words should be used for a password.

• Don't make the password personal, such as name, address, favorite sports team, etc.

• Don't usesomething easy to type, such as123456, orqwerty.

• Some people say that misspelled words are acceptable, but I don't recommend using them. Spell check programs that match misspelled words to correctly spelled words can be used to guess at words that might be misspelled for a password.

• A password generator that produces unintelligible passwords works the best.

We'll cover many commands throughout the chapters in this book. The passwd command is important to know for your initial login, because you may be required to change your password immediately.

If you gain access to your system through a graphical user interface login screen, you enter your user name and password just as you would at the command line. You can retype your user name and password if you make errors, just as you would at the command line. After successful login, you have a graphical environment in which to work. Figure 1-1 shows a Common Desktop Environment with many windows open.

Figure 1-1. Common Desktop Environment after Successful Login

You can see in Figure 1-1 that there are many activities taking place in the graphical environment. Chapter 4, devoted to the Common Desktop Environment, covers many of the components in Figure 1-1 in detail.

Online Manual Pages

A set of on-line manual pages is supplied with nearly every UNIX variant. The "man" pages, as they are known, are usually complete, current, and an excellent all-around reference. Most other operating systems provide online help that is a small subset of the complete help that is available in the operating system manuals. The "man" pages, on the other hand, are very useful and most UNIX users first go to the "man" pages when any questions arise related to a command. If you don't know the command you need but know a command that is related to the function you wish to perform, you can view the "man" page for the command you know and see the other related commands it references.

To view the "man" page for a command, you simply issue man and the name of the command you wish to use, as shown in the following example from a Solaris system:

martyp $ man passwd  Reformatting page.  Wait... done  User Commands                                        passwd(1)  NAME       passwd - change login password and password attributes  SYNOPSIS       passwd  [-r  | files  | -r nis  | -r nisplus ]  [name]       passwd  [ -r files  ]  [ -egh ]  [name]       passwd  [ -r files  ] -s  [ -a ]       passwd  [ -r files  ] -s  [name]       passwd  [ -r files  ]  [-d  | -l ]  [ -f ]  [  -n min  ]   [      -w warn]  [ -x max] name       passwd -r nis  [ -egh ]  [name]       passwd -r nisplus  [ -egh ]  [ -D domainname]  [name]       passwd -r nisplus -s  [ -a ]       passwd -r nisplus  [ -D domainname] -s  [name]      passwd -r nisplus  [ -l ]  [ -f ]  [ -n min]  [  -w warn  ]       [ -x max]  [ -D domainname] name  DESCRIPTION      The passwd command changes the password or lists password      attributes associated with the user's login name. Addition     ally, privileged users may use passwd to install or change      passwords and attributes associated with any login name.      When used to change a password, passwd prompts everyone for      their  old password, if any. It then prompts for the new      password twice. When the old password is entered, passwd      checks to see if it has "aged" sufficiently. If "aging" is      insufficient, passwd terminates; see pwconv(1M), nist     bladm(1), and shadow(4) for additional information.      When NIS or NIS+ is in effect on a system, passwd changes      the NIS or NIS+ database. The NIS or NIS+ password may be      different from the password on the local machine. If NIS or      NIS+ is running, use passwd -r to change password informa     tion on the local machine.      The pwconv command creates and updates /etc/shadow with      information from /etc/passwd. pwconv relies on a special      value of 'x' in the password field of  /etc/passwd. This      value of 'x' indicates that the password for the user is      already in /etc/shadow and should not be modified.  User Commands                                         passwd(1)      If aging is sufficient, a check is made to ensure that  the      new password meets construction requirements. When the new      password is entered a second time, the two copies of the new      password are compared. If the two copies are not identical,      the cycle of prompting for the new password is repeated for,      at most, two more times.      Passwords must be constructed to meet the following require- --More--(17%) 

This partial listing, as indicated by the "17%" at the end of the example, shows the "man" page for the passwd command we used earlier in this chapter. You can issue the man command for topics other than commands. You can also get information on system calls, library routines, and other information. You can even get information on the man command itself, as shown in the following example from the same system:

martyp $ man man  Reformatting page.  Wait... done  User Commands                                              man(1)  NAME       man - find and display reference manual pages  SYNOPSIS       man  [ - ]  [ -adFlrt ]  [ -M path]  [  -T macro-package  ]       [ -s section] name...       man  [ -M path] -k keyword...       man  [ -M path] -f file...  DESCRIPTION    The man command displays information from the reference    manuals. It displays complete manual pages that you select    by name, or one-line summaries selected either by keyword    (-k), or by the name of an associated file (-f). If no     manual page is located, man prints an error message.  Source Format    Reference Manual pages are marked up with either nroff(1)    or sgml(5) (Standard Generalized Markup Language) tags.    The man command recognizes the type of markup and processes    the file accordingly. The various source files are kept in     separate directories depending on the type of markup.  Location of Manual Pages    The online Reference Manual page directories are convention   ally located in /usr/share/man. The nroff sources are     located in the /usr/share/man/man* directories. The     SGML sources are located in the /usr/share/man/sman* direc   tories. Each directory corresponds to a section of the    manual. Since these directories are optionally installed,     they may not reside on your host; you may have to mount     /usr/share/man from a host on which they do reside.    If there are preformatted, up-to-date versions in the    corresponding cat * or fmt * directories, man simply    displays or prints those versions. If the preformatted ver   sion of interest is out of date or missing, man reformats    it prior to display and will store the preformatted version     if cat * or fmt * is writable. The windex database is  --More--(13%) 

This example shows only 13% of the "man" page for the man command. Notice under "SYNOPSIS" that you can specify the section number of the "man" page you wish to view. The "man" pages are grouped into a number of categories. Usually, around eight groupings, or sections, exist for most UNIX variants. Some topics appear in more than one of the sections. You can specify the section number for a command if you know it. In the following example, we search for information on the passwd command and see that it appears in more than one section. We can view the "man" page for the command in section 1 and then the "man" page in section 4, as shown in the following example:

 

 

martyp $ pwd  /usr/man  martyp $ find . -name passwd*  ./sman1/passwd.1  ./sman4/passwd.4  martyp $ man -s 1 passwd  Reformatting page.  Wait... done  User Commands                                        passwd(1)  NAME       passwd - change login password and password attributes  SYNOPSIS       passwd  [-r  | files  | -r nis  | -r nisplus ]  [name]       passwd  [ -r files  ]  [ -egh ]  [name]       passwd  [ -r files  ] -s  [ -a ]       passwd  [ -r files  ] -s  [name]       passwd  [ -r files  ]  [-d  | -l ]  [ -f ]  [  -n min]   [      -w warn]  [ -x max] name       passwd -r nis  [ -egh ]  [name]       passwd -r nisplus  [ -egh ]  [ -D domainname]  [name]  --More--(3%)  martyp $ man -s 4 passwd  Reformatting page.  Wait... done  File Formats                                         passwd(4)  NAME       passwd - password file  SYNOPSIS       /etc/passwd  DESCRIPTION       /etc/passwd is a local source of information about users'       accounts. The password file can be used in conjunction with  other password sources, including the NIS maps  passwd.byname and passwd.bygid and the NIS+ table passwd .  Programs use the getpwnam(3C) routines to access this infor mation.       Each passwd entry is a single line of the form:       username:password:uid:gid:gcos-field:home-dir:login-shell       where  --More--(13%) 

We haven't yet covered some of the commands used in this example; however, all you need to know is that a passwd.1 and a passwd.4 were found under the "man" pages.

The "man" page for passwd from section 1 is the same as the one used in an earlier example. The "man" page for passwd from section 4 is for the /etc/passwd file. These are two different "man" pages, one for the passwd command and one for the /etc/passwd file. It is not uncommon to have multiple "man" pages for the same keyword. By default, the first section in which an occurrence of a "man" page appears is used if no section number is specified.

Some UNIX variants, such as Linux, use a capital "S" for specifying the section number. In our example, we used a lowercase "s." As I will point out throughout the book, there are many differences among UNIX variants in the ways in which commands are used, the outputs of commands, and in some cases the commands themselves. Please keep in mind that you may encounter such differences in your work, so don't hesitate to use the "man" pages on your system as a reference.

Rather than issuing the find command to see what "man" pages cover the passwd command, we could have used the man command with the "-k" option. This "-k" option combined with a keyword, such as password in our example, searches all the "man" page descriptions for passwd. One-line summaries are produced whereever passwd is found. The following example shows what is produced for such a keyword search:

# man -k passwd  d_passwd          d_passwd (4)- dial-up password file  getpw             getpw (3c)- get passwd entry from UID  nispasswd          nispasswd (1)- change NIS+ password information  nispasswdd         rpc.nispasswdd (1m) - NIS+ password update daemon  passwd             passwd (1)- change login password and password attributes  passwd             passwd (4)- password file  pwconv             pwconv (1m)- installs and updates /etc/shadow                     with information from /etc/passwd  rpc.nispasswdd     rpc.nispasswdd (1m) - NIS+ password update daemon  rpc.yppasswdd      rpc.yppasswdd (1m) - server for modifying NIS password file  yppasswd           yppasswd (1)- change your network password in the NIS database  yppasswdd          rpc.yppasswdd (1m) - server for modifying NIS password file 

 

This command produces a long list of "man" pages from a database, including sections 1 and 4 for passwd that our find command produced. In order to use the "-k" option, a "man" page database must have been produced by your system administrator by issuing the catman command.

I am obviously a big advocate of using "man" pages, because I included many "man" pages at the end of chapters throughout the book. Anytime you see the "man" page icon, there is a "man" page for the command in the chapter number referenced in the icon. Although the "man" page for your UNIX variant may be different from the one appearing in the book, the commands on most UNIX variants are similar, and the "man" pages act as an excellent reference.

Electronic Mail

All UNIX variants come with electronic mail programs. You can use one of the electronic mail programs on your system to send and receive electronic mail from other users on the system. You can also communicate with users on other systems and across the Internet if your system administrator has set up this capability. In this chapter, we'll cover the basics of sending and receiving electronic mail. I cover this very early in the book because you may receive a message after your first login indicating that you have received mail messages and you'll want to read them. You may receive a welcome message or a request to change your password immediately after your first login.

The most basic electronic mail program, and one that exists on every UNIX variant on which I have worked, is mail. This is a very easy program to use that requires very little explanation. In the following example, I invoke the mail program, issue "?" to print a list of mail commands, read a message from Tom, reply to his message, and save the original message:

* Welcome to sys1  Last unsuccessful login: Mon Mar 8 09:32:13  Last login: Mon Sep 27 07:21:01    *********************************************************************    * This is a private system operated for use by our company only.    *    *********************************************************************  * Welcome to sys1  You have mail.  TERM set to vt100  sys1:/home/martyp  martyp $ mail  Mail [5.2 UCB]  Type ? for help.  "/var/spool/mail/martyp": 1 message 1 new  >N 1 tomf             Mon Sep 27 07:23 11/392  "12:00 Phone Call"  ? ?  Control Commands:     q                       Quit - apply mailbox commands entered this session.     x                       Quit - restore mailbox to original state.     ! <cmd>                 Start a shell, run <cmd>, and return to mailbox.     cd [<dir>]              Change directory to <dir> or $HOME.  Display Commands:     t [<msg_list>]          Display messages in <msg_list> or current message.     n                       Display next message.     f [<msg_list>]          Display headings of messages.     h [<num>]               Display headings of group containing message <num>.  Message Handling:     e [<num>]               Edit message <num> (default editor is ex).     d [<msg_list>]          Delete messages in <msg_list> or current message.     u [<msg_list>]          Recall deleted messages.     s [<msg_list>] <file>   Append messages (with headings) to <file>.     w [<msg_list>] <file>   Append messages (text only) to <file>.     pre [<msg_list>]        Keep messages in system mailbox.  Creating New Mail:     m <addrlist>            Create/send new message to addresses in <addrlist>.     r [<msg_list>]          Send reply to senders and recipients of messages.     R [<msg_list>]          Send reply only to senders of messages.     a                       Display list of aliases and their addresses.  =============================== Mailbox Commands ==============================  ? t  Message  1:  From tomf Mon Sep 27 07:23:30  Date: Mon, 27 Sep 1999 07:23:30 -0700  From: <tomf>  To: martyp  Subject: 12:00 Phone Call  Please call me at 12:00 CA time to discuss trip.  Tom  ? R  To: tomf  Subject: Re:  12:00 Phone Call  I'll call you then.  Marty  Cc:  ? s  "/home/martyp/mbox" [Appended] 11/392  ? q  sys1:/home/martyp  martyp $ 

This mail session is typical. We first used mail to invoke the electronic mail program. We are informed that there is one message from tomf with the subject 12:00 Phone Call. We then use ? to get a list of mail commands. I selected this particular system for the mail examples because of the clear help messages that are produced with ?. We then use t to display the message we received, R to reply to tomf the sender of the message, s to save and delete the message, and finally quit with q. A file called mbox has been produced that contains all of the saved messages.

You can see from this example how easily you can handle the messages in your mailbox. It may be, however, that you wish to view summary information of the messages you have saved and deleted. The file mbox in my home directory was created to store messages that were saved and then deleted. We can view summary information of these messages using the option "-f " and mbox as an input file, as shown in the following example:

martyp $ mail -f mbox  Mail [5.2 UCB]  Type ? for help.  "mbox": 4 messages    1 tomf          Sun Sep 26 18:14 11/343  "Training"   >2 donnak        Mon Sep 27 07:23 12/402  "Performance"    3 carollync     Mon Sep 27 07:27 12/380  "Software Update"    4 tomf          Mon Sep 27 07:38 11/357  "12:00 Phone Call" 

You can see in this example that there were four messages saved in mbox that we can work with simply by specifying the number of the file (1-4). The current message is indicated by the right arrow >. Information is available on the date and time of delivery of the message, the size of the message in lines and characters, and the subject of the message. Saving and deleting files with s ensures that a copy of the file is maintained so that you can later access it.

A slightly more advanced electronic mail program is on some systems, called mailx. When run, mailx produces a list of messages for you rather than displaying them one at a time as mail does. The mailx list of messages is similar to the list we just saw with deleted and saved messages using mail -f mbox. With mailx, you get the status of whether or not you have read the messages. You get a single character preceding each message indicating that the message is N for new, O for old messages that have been read, and U for unread messages. On some systems, such as the Red Hat Linux system used for many of the examples in this book, you get the list of messages when you run mail just as you would when you run mailx on other systems. The following example shows what you would see when you run mailx:

martyp $ mailx  Mail [5.2 UCB]  Type ? for help.  "/var/spool/mail/martyp": 2 messages 1 new 2 unread   U  1 tomf            Mon Sep 29 08:40 13/394  "Networking"  >N  2 donnak        Mon Sep 29 08:49 10/342  "Interoperability"  ? 

The first message is U for unread. The second message is N for new. The right arrow is next to the new message.

You are not restricted to saving messages to the default file mbox. You can organize your messages by saving them to different files. The following example shows saving a message to the file trip:

martyp $ mailx  Mail [5.2 UCB] [AIX 4.1]  Type ? for help.  "/var/spool/mail/martyp": 2 messages 2 unread  >U  1 tomf              Mon Sep 27 08:49  11/352  "NY trip"   U  2 donnak           Wed Sep 29 04:44  11/354  "login change"  ?  Message 1:  From tomf Mon Sep 27 08:49:09  Date: Mon, 27 Sep 08:49:08 -0700  From: <tomf>  To: martyp  Subject: NY trip  I am going to change the date of the NY trip.  ? s trip  "trip" [New file] 11/352  ? q  Held 1 message in /var/spool/mail/martyp  martyp $ 

After we invoked mailx, a "Return" caused thefirst messageto be read.

The file trip was created when this message was saved with s trip, and now we can store all related messages in the file trip.

Messages saved to a file can be printed with the lp command. We'll talk about lp later in the book in the system administration chapter; however, at this time it is sufficient to know that files can be printed to the default printer by issuing the command lp filename. To print the file trip, we would issue the command lp trip.

Sending electronic mail is just as easy as reading it. The simplest way to send a message is to type mailx or mail and the username of the person to whom you wish to send the message. We'll do just this in the message below to tomf:

martyp $ mail tomf  Subject: Pickup  I'll be at the airport in NY to give you a ride.  Marty  Cc:  martyp $ 

A ^D (control D) was used to end the mail message. This message will be in the mailbox of tomf. You can send messages using Internet naming if your system has enabled this functionality. The following example shows sending the same message to tomf to his Internet electronic mail address:

martyp $ mail [e-mail]  Subject: Pickup  I'll be at the airport in NY to give you a ride.  Marty  Cc:  martyp $ 

The ability to send messages to other systems and to Internet addresses requires that your system administrator set up this functionality.

If you have a graphical user interface on your system, you probably have a tool that helps you manage mail. Although the tool runs in your graphical environment, it is probably using one of the mail programs we covered earlier. Figure 1-2 shows accessing mail in the Common Desktop Environment.

Figure 1-2. Accessing Mail in Common Desktop Environment

The pull-down menus across the top of Figure 1-2 give you selections that perform the same function as the commands covered earlier for saving, forwarding, deleting, and so on.

Accessing the Internet

The Internet has been used extensively on UNIX systems since its inception. The first Web browser to be widely used was an X Window System application called Mosaic developed at the University of Illinois. Many Web browsers are available today that run on UNIX systems including Mosaic, Netscape Communicator, and several others. We'll focus on Netscape Communicator in this section because it is the most widely used on UNIX systems. Many Netscape Communicator packages are available, some with different options from others, and Netscape Navigator, which is a basic Web browser. So keep in mind that you may have not have a Netscape browser or you may have a different Netscape browser from what I cover in this section, but the same principles apply to most browsers.

Your system administrator has probably already set up a browser on your UNIX system. Many UNIX distributions, such as the Linux Red Hat used in many of the examples throughout the book, provide a browser as part of the operating system distribution. The browser and the Internet are invaluable tools when using UNIX systems. You can find the latest information about your UNIX operating system at the Web site of the company providing it. Figure 1-3 shows the Netscape Communicator window displaying the home page of Red Hat.

Figure 1-3. Using aBrowser to Access a HomePage

From this home page, you can search for any topic related to the Red Hat Linux operating system. We connect to a home page by specifying a Uniform Resource Locator (URL) in the Location box of the browser. In this case we have specified www.redhat.com, which is the Red Hat URL. The URLs of the companies supplying the four most often cited UNIX variants used in this book are shown in Table 1-1 in alphabetical order. There is a much more extensive list of URLs in the Preface.

Table 1-1. UNIX Variant Company URLs Used in This Book

URL	Result
www.hp.com	Hewlett-Packard Company
www.ibm.com	International Business Machines Corp.
www.redhat.com	Red Hat, Inc.
www.sun.com	Sun Microsystems, Inc.

From these home pages, you can work your way through the Web site to find the information you need. "Work" is the operative word here. You may be fortunate and use the Search mechanism on the home page you are viewing to find just what you need quickly on a Web site. On the other hand, you may spend a lot of time hunting around a Web site for just what you're after and end up on many related Web sites to get your desired information.

Notice in Figure 1-3 that www.redhat.com is preceded by http://. This is the protocol portion of the URL. http:// is a protocol used to specify a Web page. Many such protocols exist. Table 1-2 lists some of the more commonly used protocols.

Table 1-2. Commonly Used Protocol Specifiers

URL	Result
file:< pathname>	Load a local file into browser as specified by <pathname>.
ftp://	File Transfer Protocol (ftp) will be used.
gopher://	A host offering Gopher services will be used.
http://	A desired web page to access will be used.
https://	A desired secure web page to access will be used.
news://	A network news server will be used.

These are the most commonly used protocols used in conjunction with a browser.

The next several figures show some of the basic customization you can perform to the browser. These are intended to give you a feel for the type of customization you can perform with most browsers.

Although you may already have your browser loaded for you, there may still be some configuration necessary to get it fully operational or some customization you wish to perform. Figure 1-4, on the left-hand side, shows several areas of customization we can perform in Netscape Communicator with Fonts selected in this example:

Figure 1-4. Specifying Browser Fonts

In this example, we have selected Fonts under Appearance to get the information shown in Figure 1-4. Among the options we have for customization is to specify the size of the fonts we wish to use in this application. There is also a Colors selection under Appearance in which we would have a similar set of options to adjust the colors in this application.

The next category of options we can modify is under Navigator, as shown in Figure 1-5.

Figure 1-5. Browser Applications

Under Navigator, we have three potential areas of customization. We are viewing the Applications window. This window lists the applications and the "helper" that will be associated with the application.

The next category is Mail and Newsgroups, shown in Figure 1-6.

Figure 1-6. Browser Disk Space

In Figure 1-6, we are specifying the amount of disk space that can be consumed by messages. Because mail and newsgroups can both result in a lot of large messages being sent to your system, you want to have control over the size of messages you will receive and what messages will be purged based on their age.

The next category is Roaming User, which is related to your setup when Netscape is used on a roaming basis. You are given options for what aspect(s) of your profile will be transferred, as shown in Figure 1-7.

Figure 1-7. Roaming User Items

Figure 1-7 shows some of the items that will be transferred if you are using a roaming access server. No matter where you are using Netscape, you would like to have such a setup as your User Preferences be consistent, and this category gives you options for your roaming setup.

The next category is Composing, which gives you options related to Web documents you publish, as shown in Figure 1-8.

Figure 1-8. Selections Related to Publishing

We are viewing Publish under Composing in Figure 1-8, which provides options about Web-related publishing you may perform, such as the location of documents.

The final category is Advanced, which contains information about Cache and Proxies, as shown in Figure 1-9.

Figure 1-9. Selecting Proxies

In the interest of protecting computer systems from intrusion, most companies have set up a firewall for the purpose of restricting access to systems. This restriction means that getting both in and out of many company networks is difficult. The proxy server is a means by which you can get access to the Internet. We have selected Proxies in Figure 1-9, which produces the dialog box shown in Figure 1-10.

Figure 1-10. Specifying Proxy-Related Information

In Figure 1-10, we have set up the addresses and port numbers of the proxy servers for two types of Internet access. This setup may have already been performed for you by your system administrator. If not, you will want to confer with them prior to making such configuration changes if you don't know this information.

The other category under Advanced is Cache, as shown in Figure 1-11.

Figure 1-11. Cache Customization

The browser-related cache is used to increase the speed of your Internet work by saving copies of frequently used information locally so that you don't have to continually go out over the network to reload the information. You can specify the size of cache and location for the cached data to be saved in this window.

You will determine the type of customization you want to perform soon after using your browser. Most browsers give you the option to perform the type of customization we have covered in this section.

UNIX Components

I have waited until the end of this chapter to cover the components of a UNIX system, because after login, issuing some commands, and possibly accessing the Internet, you surely have a feel for the way in which you interact with a UNIX system. Now is an appropriate time to cover the high-level components of which a UNIX system is comprised.

Figure 1-12 is a high-level depiction of a UNIX system:

Figure 1-12. High-Level UNIX System Structure

Before describing this figure, I'll first mention that everyone has a somewhat different way of viewing the components of UNIX. This figure contains the most important components from a user perspective.

At the heart of this diagram is the hardware. UNIX, in its many forms, now runs on many different types of hardware. I won't cover much in the way of hardware in this book, because so many options are related to the hardware on which UNIX runs.

The next circle from the center of this diagram is the kernel. The kernel performs many functions including: management of devices, memory, and processes; scheduling and execution of all commands; and containment of drivers that control system hardware. The kernel is an aspect of the system that system administrators spend a lot of time maintaining. When a new device is configured, a device driver may have to be added to the kernel in order to support the new device. There is also substantial tuning that can be performed to the kernel in order to optimize system performance for the application(s) running on the UNIX system. Users have only indirect interaction with the kernel through the commands you issue that work their way to the kernel.

The next circle is the shell. The shell takes commands from you and starts the process of executing the commands. This is about as far into the UNIX diagram as a typical user goes. In addition to passing commands to more inner layers of the system, the shell allows you to run commands in the background and run shell programs. We'll cover three of the most commonly used shells in later chapters and also cover the basics of shell programming. Most of the material in the book is based on work performed by you at the command line, which is part of the shell.

The next circle is the Common Desktop Environment (CDE) or other graphical user interface. Chapter 4 is devoted to CDE in this book, and many examples use CDE and another graphical interface called Gnome that runs on the Linux system. You usually don't see the graphical user interface as a separate circle in such UNIX diagrams, because most of the work done in a graphical user interface works its way down to a shell command. Since most UNIX users use a graphical user interface, I think this warrants its own circle.

The final circle is the user. Through all of the layers shown in this figure, you accomplish your work on a UNIX system.

Because most of the examples in the book take place at the command line, and the remainder in a graphical user interface, you don't really need to concern yourself with inner UNIX circles as a user. Because your system administrator, database administrator, and others maintaining the system spend a substantial amount of their time dealing with these innermost components, Figure 1-13 is helpful in that it gives you an appreciation for the areas with which your associates are focused. Your shell, mail system, user interface, browser interface, and other components are customized and maintained by you, so these topics will be covered in upcoming chapters, as well as interacting with the UNIX file system and the UNIX commands you'll be issuing.

CONTENTS