Using sendmail

Using the m4 Macro Processor

The m4 macro processor is used to generate the sendmail.cf configuration file, which comes with the sendmail package in Red Hat Linux. The main macro file, sendmail.mc, is included with the sendmail package, but that file needs other m4 macro files that are in the sendmail-cf package. To be able to process the sendmail.mc file, you have to install the sendmail-cf package, as explained in the previous section. This section introduces you to the m4 macro processor.

A macro is a symbolic name for some action or a long string of characters. A macro processor such as m4 usually reads its input file and copies it to the output, processing the macros along the way. The processing of a macro generally involves performing some action and generating some output. Because a macro generates a lot more text in the output than merely the macro's name, the processing of macros is referred to as macro expansion.

Secret

Note that m4 is stream based (like the sed editor, described in Chapter 8). That means it copies the input characters to the output, while expanding any macros. The m4 macro processor does not have any concept of lines, so it copies newline characters to the output. That's why you see the word dnl in most m4 macro files; dnl is an m4 macro that stands for delete through newline. The dnl macro deletes all characters starting at the dnl up to and including the next newline character. The newline characters in the output don't cause any harm; they merely create unnecessary blank lines. The sendmail macro package uses dnl to avoid such blank lines in the output configuration file. Because dnl basically means delete everything up to the end of the line, m4 macro files also use dnl as the prefix for comment lines.

To see a very simple use of m4, consider the following m4 macro file that defines two macros-hello and bye-and uses them in a form letter:

dnl ###################################################
dnl #  File: ex.m4
dnl #  A simple example of m4 macros
dnl ###################################################
define(`hello', `Dear Sir/Madam')dnl
define(`bye',
`Sincerely,


Customer Service')dnl
dnl Now type the letter and use the macros
hello,

This is to inform you that we received your recent inquiry.
We will respond to your question soon.

bye

Type this text using your favorite text editor, and save it in a file named ex.m4. You can name a macro file anything you like, but it is customary to use the .m4 extension for m4 macro files.

Before you process the macro file by using m4, note the following key points the preceding example illustrates:

• Use the dnl macro to start all the comment lines (for example, the first four lines in the example).

• End each macro definition with the dnl macro. Otherwise, when m4 processes the macro file, it produces a blank line for each macro definition.

• Use the built-in m4 command define to define a new macro. The macro name and the value are both enclosed between a pair of left and right quotes (`...'). Note that you cannot use the plain single quote to enclose the macro name and definition.

Now process the macro file ex.m4 by using m4 as follows:

m4 ex.m4
Dear Sir/Madam,

This is to inform you that we received your recent inquiry.
We will respond to your question soon.

Sincerely,


Customer Service 

As you can see, m4 prints the form letter on standard output, expanding the macros hello and bye into their defined values. If you want to save the form letter in a file called letter, use the shell's output redirection feature, like this:

m4 ex.m4 > letter

What if you want to use the word hello or bye in the letter without expanding them? You can do so by enclosing these macros in a pair of left- and right-quotes (`...'). You have to do this for other predefined m4 macros, such as define. To use define as a plain word, not as a macro to expand, write `define'.

sendmail.mc file

The simple example in the preceding section should give you an idea of how m4 macros are defined and used to create configuration files such as the sendmail.cf file. Essentially, many complex macros are written and stored in files in the /usr/share/sendmail-cf directory. A top-level macro file, sendmail.mc, described later in this section, brings in these macro files with the include macro (used to copy a file into the input stream).

By defining its own set of high-level macros in files located in the /usr/share/sendmail-cf directory, sendmail essentially creates its own macro language. The sendmail macro files use the .mc extension. The primary sendmail macro file you should configure is sendmail.mc, located in the /etc/mail directory.

Unlike the /etc/mail/sendmail.cf file, the /etc/mail/sendmail.mc file is short and should be easier to work with. Here is the full listing of the /etc/mail/sendmail.mc file that comes with Red Hat Linux:

divert(-1)dnl
dnl #
dnl # This is the sendmail macro config file for m4. If you make changes to
dnl # /etc/mail/sendmail.mc, you will need to regenerate the
dnl # /etc/mail/sendmail.cf file by confirming that the sendmail-cf package is
dnl # installed and then performing a
dnl #
dnl #     make -C /etc/mail
dnl #
include(`/usr/share/sendmail-cf/m4/cf.m4')dnl
VERSIONID(`setup for Red Hat Linux')dnl
OSTYPE(`linux')dnl
dnl #
dnl # Uncomment and edit the following line if your outgoing mail needs to
dnl # be sent out through an external mail server:
dnl #
dnl define(`SMART_HOST',`smtp.your.provider')
dnl #
define(`confDEF_USER_ID',``8:12'')dnl
dnl define(`confAUTO_REBUILD')dnl
define(`confTO_CONNECT', `1m')dnl
define(`confTRY_NULL_MX_LIST',true)dnl
define(`confDONT_PROBE_INTERFACES',true)dnl
define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
define(`ALIAS_FILE', `/etc/aliases')dnl
dnl define(`STATUS_FILE', `/etc/mail/statistics')dnl
define(`UUCP_MAILER_MAX', `2000000')dnl
define(`confUSERDB_SPEC', `/etc/mail/userdb.db')dnl
define(`confPRIVACY_FLAGS', `authwarnings,novrfy,noexpn,restrictqrun')dnl
define(`confAUTH_OPTIONS', `A')dnl
dnl #
dnl # The following allows relaying if the user authenticates, and disallows
dnl # plaintext authentication (PLAIN/LOGIN) on non-TLS links
dnl #
dnl define(`confAUTH_OPTIONS', `A p')dnl
dnl #
dnl # PLAIN is the preferred plaintext authentication method and used by
dnl # Mozilla Mail and Evolution, though Outlook Express and other MUAs do
dnl # use LOGIN. Other mechanisms should be used if the connection is not
dnl # guaranteed secure.
dnl #
dnl TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
dnl define(`confAUTH_MECHANISMS', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLA
IN')dnl
dnl #
dnl # Rudimentary information on creating certificates for sendmail TLS:
dnl #     make -C /usr/share/ssl/certs usage
dnl #
dnl define(`confCACERT_PATH',`/usr/share/ssl/certs')
dnl define(`confCACERT',`/usr/share/ssl/certs/ca-bundle.crt')
dnl define(`confSERVER_CERT',`/usr/share/ssl/certs/sendmail.pem')
dnl define(`confSERVER_KEY',`/usr/share/ssl/certs/sendmail.pem')
dnl #
dnl # This allows sendmail to use a keyfile that is shared with OpenLDAP's
dnl # slapd, which requires the file to be readable by group ldap
dnl #
dnl define(`confDONT_BLAME_SENDMAIL',`groupreadablekeyfile')dnl
dnl #
dnl define(`confTO_QUEUEWARN', `4h')dnl
dnl define(`confTO_QUEUERETURN', `5d')dnl
dnl define(`confQUEUE_LA', `12')dnl
dnl define(`confREFUSE_LA', `18')dnl
define(`confTO_IDENT', `0')dnl
dnl FEATURE(delay_checks)dnl
FEATURE(`no_default_msa',`dnl')dnl
FEATURE(`smrsh',`/usr/sbin/smrsh')dnl
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
FEATURE(`virtusertable',`hash -o /etc/mail/virtusertable.db')dnl
FEATURE(redirect)dnl
FEATURE(always_add_domain)dnl
FEATURE(use_cw_file)dnl
FEATURE(use_ct_file)dnl
dnl #
dnl # The -t option will retry delivery if e.g. the user runs over his quota.
dnl #
FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
FEATURE(`access_db',`hash -T<TMPF> -o /etc/mail/access.db')dnl
FEATURE(`blacklist_recipients')dnl
EXPOSED_USER(`root')dnl
dnl #
dnl # The following causes sendmail to only listen on the IPv4 loopback address
dnl # 127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl #
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
dnl #
dnl # The following causes sendmail to additionally listen to port 587 for
dnl # mail from MUAs that authenticate. Roaming users who can't reach their
dnl # preferred sendmail daemon due to port 25 being blocked or redirected find
dnl # this useful.
dnl #
dnl DAEMON_OPTIONS(`Port=submission, Name=MSA, M=Ea')dnl
dnl #
dnl # The following causes sendmail to additionally listen to port 465, but
dnl # starting immediately in TLS mode upon connecting. Port 25 or 587 followed
dnl # by STARTTLS is preferred, but roaming clients using Outlook Express can't
dnl # do STARTTLS on ports other than 25. Mozilla Mail can ONLY use STARTTLS
dnl # and doesn't support the deprecated smtps; Evolution <1.1.1 uses smtps
dnl # when SSL is enabled-- STARTTLS support is available in version 1.1.1.
dnl #
dnl # For this to work your OpenSSL certificates must be configured.
dnl #
dnl DAEMON_OPTIONS(`Port=smtps, Name=TLSMTA, M=s')dnl
dnl #
dnl # The following causes sendmail to additionally listen on the IPv6 loopback
dnl # device. Remove the loopback address restriction listen to the network.
dnl #
dnl # NOTE: binding both IPv4 and IPv6 daemon to the same port requires
dnl #       a kernel patch
dnl #
dnl DAEMON_OPTIONS(`port=smtp,Addr=::1, Name=MTA-v6, Family=inet6')dnl
dnl #
dnl # We strongly recommend not accepting unresolvable domains if you want to
dnl # protect yourself from spam. However, the laptop and users on computers
dnl # that do not have 24x7 DNS do need this.
dnl #
FEATURE(`accept_unresolvable_domains')dnl
dnl #
dnl FEATURE(`relay_based_on_MX')dnl
dnl #
dnl # Also accept email sent to "localhost.localdomain" as local email.
dnl #
LOCAL_DOMAIN(`localhost.localdomain')dnl
dnl #
dnl # The following example makes mail from this host and any additional
dnl # specified domains appear to be sent from mydomain.com
dnl #
dnl MASQUERADE_AS(`mydomain.com')dnl
dnl #
dnl # masquerade not just the headers, but the envelope as well
dnl #
dnl FEATURE(masquerade_envelope)dnl
dnl #
dnl # masquerade not just @mydomainalias.com, but @*.mydomainalias.com as well
dnl #
dnl FEATURE(masquerade_entire_domain)dnl
dnl #
dnl MASQUERADE_DOMAIN(localhost)dnl
dnl MASQUERADE_DOMAIN(localhost.localdomain)dnl
dnl MASQUERADE_DOMAIN(mydomainalias.com)dnl
dnl MASQUERADE_DOMAIN(mydomain.lan)dnl
MAILER(smtp)dnl
MAILER(procmail)dnl

As the comments (the lines that begin with dnl) in the beginning of the file explain, you can generate the /etc/mail/sendmail.cf file by running the sendmail.mc file through the m4 macro processor with the following command (you have to log in as root):

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

The comments also tell you that you need the sendmail-cf package to process this file.

From the previous section's description of m4 macros, you can see that the sendmail.mc file uses define to create new macros. You can also see the liberal use of dnl to avoid inserting too many blank lines into the output.

The other uppercase words such as OSTYPE, FEATURE, and MAILER are sendmail macros. These are defined in the .m4 files located in the subdirectories of the /usr/share/ sendmail-cf directory and are incorporated into the sendmail.mc file with the following include macro:

include(`/usr/share/sendmail-cf/m4/cf.m4')

The /usr/share/sendmail-cf/m4/cf.m4 file, in turn, includes the cfhead.m4 file, which includes other m4 files, and so on. The net effect is that, as the m4 macro processor processes the sendmail.mc file, the macro processor incorporates many m4 files from various subdirectories of /usr/share/sendmail-cf.

Note the following key points about the /etc/mail/sendmail.mc file:

• The VERSIONID(`linux setup for Red Hat Linux') macro inserts the version information enclosed in quotes into the output.

• OSTYPE(`linux') specifies Linux as the operating system. You have to specify this early to ensure proper configuration. It is customary to place this macro right after the VERSIONID macro.

• MAILER(smtp) describes the mailer. According to the /usr/share/sendmail-cf/README file, MAILER, declarations should always be placed at the end of the sendmail.mc file, and MAILER(`smtp') should always precede MAILER (`procmail'). The mailer smtp refers to the SMTP mailer.

• FEATURE macros request various special features. For example, FEATURE (`blacklist_recipients') turns on the capability to block incoming mail for certain user names, hosts, or addresses. The specification for what mail to allow or refuse is placed in the access database (/etc/mail/access.db file). You also need the FEATURE(`access_db') macro to turn on the access database.

• MASQUERADE_AS(`mydomain.com') causes sendmail to label outgoing mail as having come from the host mydomain.com (replace this with your domain name). The idea is for a large organization to set up a single sendmail server that handles the mail for many subdomains and makes everything appear to come from a single domain (for example, mail from many departments in a University would appear to come from the University's main domain name).

• MASQUERADE_DOMAIN(subdomain.mydomain.com) instructs sendmail to send mail from an address such as user@subdomain.mydomain.com as having originated from the same user name at the domain specified by the MASQUERADE_AS macro.

  Insider Insight

  The sendmail macros such as FEATURE and MAILER are described in the /usr/ share/sendmail-cf/README file. Consult that file to learn more about the sendmail macros before you make changes to the sendmail.mc file.

Learning the sendmail.cf File Syntax

The sendmail.cf file's syntax is designed to be easy to parse by the sendmail program because sendmail reads this file whenever it starts. Human readability was not a primary consideration when the file's syntax was designed. Still, with a little explanation, you can understand the meaning of the control lines in sendmail.cf.

Secret

Each sendmail control line begins with a single-letter operator that defines the meaning of the rest of the line. A line that begins with a space or a tab is considered a continuation of the previous line. Blank lines and lines beginning with a pound sign (#) are comments.

Often, there is no space between the single-letter operator and the arguments that follow the operator. This makes the lines even harder to understand. For example, sendmail.cf uses the concept of a class-essentially a collection of phrases. You can define a class named P and add the phrase REDIRECT to that class with the following control line:

CPREDIRECT

Because everything is jumbled together, it's hard to decipher. On the other hand, to define a class named Accept and set it to the values OK and RELAY, write the following:

C{Accept}OK RELAY

This may be slightly easier to understand because the delimiters (such as the class name, Accept) are enclosed in curly braces.

Other more recent control lines are even easier to understand. For example, the line

O HelpFile=/etc/mail/helpfile

defines the option HelpFile as the filename /etc/mail/helpfile. That file contains help information sendmail uses when it receives a HELP command.

Table 15-1 summarizes the one-letter control operators used in sendmail.cf. Each entry also shows an example of that operator. This table should help you understand some of the lines in sendmail.cf.

Preparing the User Database

The user database helps sendmail deliver incoming mail when there is no centralized mail server. For example, suppose mail addressed to jdoe@someplace.net should really be sent to jd@home.someplace.net. This involves identifying a user's maildrop-the location where a user receives mail-to sendmail. You can accomplish this task by creating the user database.

sendmail expects the user database in a binary file /etc/mail/userdb.db in the Berkeley database format. Follow these steps to create the binary user database file:

1. Edit the text file /etc/mail/userdb and add lines for each user for whom you need to identify a maildrop location. The lines look like this:

   loginname:mailname      emailname@someplace.net
   emailname:maildrop     loginname@home

2. Convert the text file /etc/mail/userdb into a Berkeley database file that sendmail can use by running the makemap with the following command:

   makemap btree /etc/mail/userdb < /etc/mail/userdb

   This creates the database file /etc/mail/userdb.db from the text file /etc/mail/userdb.

   Caution

   You must remember to run makemap every time you change /etc/mail/userdb, otherwise sendmail will not be using your latest user database when sending mail.

Preparing the Mailer Table

The mailer table database specifies how to route email messages destined for specific domains. You specify these mail routings in a text file /etc/mail/mailertable. For

example, suppose all mail meant for the mydomain.net should be sent to the host mailhost.mydomain.net. You can specify this with the following entry in /etc/mail/ mailertable:

.mydomain.net        smtp:mailhost.mydomain.net

The left-hand side of each line is a domain name. The right-hand side is of the form mailer:host, where mailer is a mail transfer agent and host is the hostname to be provided to that mailer.

After editing the text file /etc/mail/mailertable, you have to convert it into a binary database by running makemap with the following command:

makemap hash /etc/mail/mailertable < /etc/mail/mailertable

Preparing the Access Database

The access database causes sendmail to accept or refuse mail from specified domains and also control the behavior of sendmail in various situations. The database is a list of names (user names, hostnames, or network addresses) and codes that specify the action sendmail performs.

Secret

You can use the access database to stop spam (unsolicited email). You prepare the access database by editing the text file /etc/mail/access. Like other sendmail databases, each line in that file has two fields. On each line, the left-hand side is an email address, a domain name, or an IP address (IPv6 addresses have to be prefixed with Ipv6:). The right-hand side is typically a code that specifies what sendmail should do.

Here is an example of a /etc/mail/access file:

spammer@somewhere.net           DISCARD
spam.com                        REJECT
mybuddy.com                     RELAY
192.168.15                      REJECT
IPv6:2002:c0a8:02c5             REJECT
some.unresolvable.domain.net    OK
junkmail.com                    ERROR:550 "Junk mail not allowed"

The codes on the right-hand side tell sendmail what to do for each case. For example, all messages from spammer@somewhere.net are discarded without any error message. On the other hand, when the action is REJECT, sendmail rejects the email with a general message. You can even use the access database to accept messages even when some errors occur. In this example, the OK keyword causes sendmail to accept messages from some.unresolvable.domain.net even though DNS could not translate that domain name to an IP address.

After editing the text file /etc/mail/access, you must convert it to a binary database with the following command:

makemap hash /etc/mail/access < /etc/mail/access

Storing the Address List in a Separate File

Although defining an alias with all the addresses works, the drawback is that you must edit the /etc/aliases file whenever you want to add a new name to the list. You need to log in as root to edit the /etc/aliases file (or ask the system administrator to edit the file for you). A better solution is to store the address list in a separate file in your home directory and make sendmail read that file with the :include: directive in the alias definition.

For example, Emily might put the address list for the webmasters alias in the /home/emily/mlist/webms file (assuming that /home/emily is the login directory of user emily). Then the /etc/aliases file would reference the address list as follows:

webmasters: :include:/home/emily/mlist/webms

In the /home/emily/mlist/webms file, each address appears on a separate line:

emily (Emily B. -- list owner)
webmaster@appdev (Webmaster, Application Development Group)
webmaster@mktg (Webmaster, Marketing Department)

As you can see, you can put helpful comments in parentheses.

Every time sendmail sends a message to the webmasters alias, it reads the /home/emily/mlist/webms file. Thus, you can add a new user by simply editing this file.

If you use an address file, make sure that only the owner can modify it. Use the command chmod 644 filename to set the permission properly.

Ensuring That Replies Go to the List

When you set up a mailing list, you want any replies to go to everyone in the list so that discussions can take place among the group. However, when you use a sendmail alias to define a mailing list, the reply goes to the person who has sent the message instead of to the entire list. You can correct this problem by making the alias start a new sendmail process and by changing the sender's address through the -f option of sendmail.

Here's how you define the webmasters list by using this approach:

webmasters: "|/usr/lib/sendmail -fwebmasters -oi dist-webmasters"
dist-webmasters: :include:/home/emily/mlist/webms

This definition of

BackCover Red Hat Linux 9 Professional Secrets Introduction Conventions Used in This Book About the Companion CD-ROMs Reach Out Acknowledgments Part I: Setting Up Red Hat Linux Chapter 1: An Overview of Red Hat Linux What Is Red Hat Linux? Linux as a UNIX Platform Linux Desktop Linux Networking Linux System Administration Windows and Linux Software Development in Linux Linux as an Internet On-Ramp Summary Chapter 2: Red Hat Linux Installation Understanding the Red Hat Linux Installation Process Preparing Your PC for Linux Installation Booting the Red Hat Linux Installer Installing from the Red Hat Linux CD-ROM Troubleshooting the Installation Using Boot Commands during Installation Learning Other Installation Methods Using kickstart Installation Installing Red Hat Linux on a Laptop Summary Chapter 3: 3X Window System Setup Understanding Video Cards and Monitors Understanding the X Window System Setting up X on Red Hat Linux Running X Summary Chapter 4: Printer Setup Configuring CUPS Print Queues Learning the Printing Commands Understanding the CUPS Printing System Summary Chapter 5: Sound Setup Sound Cards Supported by Red Hat Linux Configuring the Sound Card Learning Sound Device Names Testing the Sound Card Playing Audio CD-ROMs Troubleshooting Sound Cards Summary Chapter 6: Network Setup Networking Basics TCP/IP and the Internet TCP/IP Services and Client/Server Architecture TCP/IP Setup in Linux TCP/IP Network Diagnostics Summary Part II: Exploring Red Hat Linux Chapter 7: Red Hat Linux Basics Starting Red Hat Linux for the First Time Looking up Online Documentation Understanding the Linux File System Using the Nautilus Shell Navigating the File System with Linux Commands Learning the Bash Shell Summary Chapter 8: GNU Utilities An Overview of GNU Software Shell Utilities File Utilities and the find Command Text Utilities Binary Utilities Other Utilities Stream Editor - sed Summary Chapter 9: GUI Desktops Setting up a Graphical Login Using GNOME Using KDE Summary Chapter 10: Red Hat Linux Applications and Utilities Applications on the Companion CD-ROMs Editors Office Tools Graphics and Images Summary Chapter 11: Text Processing Text Editing with ed and vi Working with GNU Emacs Writing Man Pages with groff Preparing Documentation with DocBook Summary Chapter 12: Basic System Administration Revisiting Linux System Administration Becoming root Managing User Accounts Exploring the Start Here Window Managing the File System Using mtools Summary Part III: Internetworking with Red Hat Linux Chapter 13: Internet Connection Setup Deciding How to Connect to the Internet Setting Up IEEE 802.11b Wireless Ethernet Networks Learning the Basics of Dial-Up Networking Using IP Masquerading to Share an Internet Connection Setting Up a PPP Server Summary Chapter 14: Web Server Discovering the World Wide Web Surfing the Net Setting Up the Apache Web Server Using Java Servlets with Apache Creating a Secure Server with SSL Summary Chapter 15: Mail Server Installing Mail Software Understanding Electronic Mail Using sendmail Summary Chapter 16: News Server Using Simple News Strategies Installing News Software Understanding Newsgroups Configuring and Starting the INN Server Setting Up Local Newsgroups Summary Chapter 17: FTP Server Installing FTP Software Understanding FTP Configuring the FTP Server Setting up Secure Anonymous FTP Summary Chapter 18: DNS and NIS Using the Domain Name System (DNS) Using Network Information Service (NIS) Summary Chapter 19: Samba and NFS Sharing Files with NFS Setting Up a Windows Server Using Samba Summary Part IV: Managing Red Hat Linux Chapter 20: Advanced System Administration Understanding How Red Hat Linux Boots Scheduling Jobs in Red Hat Linux Backing Up and Restoring Files Managing Devices Monitoring System Performance Summary Chapter 21: Software Installation and Update Working with the Red Hat Package Manager Building Software Packages from Source Files Installing SRPMS Upgrading Red Hat Linux with the Update Agent Upgrading and Customizing the Linux Kernel Summary Chapter 22: System and Network Security Establishing a Security Framework Securing Red Hat Linux Securing the Host Securing the Network Performing Security Audits Keeping up with Security News and Updates Summary Part V: Programming Red Hat Linux Chapter 23: Software Development in Linux Software Development Tools in Linux The GNU Debugger Implications of GNU Licenses Version Control Linux Programming Topics Summary Chapter 24: Shell and Perl Scripting Looking at Some Shell Scripts Learning the Basics of Shell Scripting in Bash Perl as a Scripting Language Summary Chapter 25: Tcl/Tk Scripting Introducing Tcl Introducing Tk Summary Chapter 26: Java Programming Getting Ready for Java Programming Writing Your First Java Program Learning Java Writing GUI Applications in Java Writing Java Servlets Becoming Proficient in Java Summary Part VI: Appendixes Appendix A: Linux Commands apropos bg cal cat cd chattr chgrp chmod chown chsh compress cp cpio cut date dd df diff du expand fdformat fdisk fg file find fold free fsck grep groups gunzip gzip halt id info kill ldd less ln locate lpr ls lsof man mkdir mkfs mknod mkswap more mount mv nice nl passwd paste patch printenv ps pstree pwd reboot rm rmdir sed shutdown sort split su swapoff swapon sync tac tail tar top touch tr tty type umount unalias uname uncompress uniq wc whatis whereis which zcat, zless, zmore Appendix B: Disk Drives Disk Drive Concepts Floppy Disks in Linux Hard Disk Operations in Linux SCSI Disk Controllers and Linux Appendix C: CD-ROM Drives Supported CD-ROM Drives CD-ROM Troubleshooting Appendix D: Ethernet Cards Supported Ethernet Cards Ethernet Driver Modules Ethernet Autoprobing Multiple Ethernet Cards Appendix E: Modems and Terminals Modems Linux and Modems Setting up Linux for Dial-In Terminals and Multiport Serial Boards Appendix F: PC Cards PCMCIA Card Services for Linux Appendix G: Linux Resources Newsgroups FTP Archive Sites Magazines Appendix H: About the CD-ROMs System Requirements CD-ROM Installation Instructions What's on the CD-ROMs Source Code Coupon Troubleshooting List of Figures List of Tables List of Code Examples List of Sidebars