Managing Linux Systems with Webmin: System Administration and Module Development [Paperback]

This chapter explains what Webmin is, why it was written, and what you can expect from this book.

Webmin is a program that simplifies the process of managing a Linux or UNIX system. Traditionally, you have needed to manually edit configuration files and run commands to create accounts, set up web servers, or manage email forwarding. Webmin now lets you perform these tasks through an easy-to-use web interface, and automatically updates all of the required configuration files for you. This makes the job of administering your system much easier.

Some of the things that you can do with Webmin include:

• Exporting files and directories to other systems with the NFS protocol
• Setting up disk quotas to control how much space users can take up with their files
• Installing, viewing, and removing software packages in RPM and other formats
• Changing your system's IP address, DNS settings, and routing configuration
• Setting up a firewall to protect your computer or give hosts on an internal LAN access to the Internet
• Creating and configuring virtual web sites for the Apache Web server
• Managing databases, tables, and fields in a MySQL or PostgreSQL database server

These are just a few of the available functions. Webmin lets you configure almost all of the common services and popular servers on UNIX systems using a simple web interface. It protects you from the syntax errors and other mistakes that are often made when editing configuration files directly, and warns you before potentially dangerous actions.

Because Webmin is accessed though a web browser, you can log in to it from any system that is connected to yours through a network. There is absolutely no difference between running it locally and running it remotely, and it is much easier to use over the network than other graphical configuration programs.

Webmin has what is known as a modular design. This means that each of its functions is contained in a module that can generally be installed or removed independently from the rest of the program. Each module is responsible for managing some service or server, such as UNIX users, the Apache Web server, or software packages.

If you have been manually configuring your system up till now, any existing settings will be recognized by Webmin. It always reads the standard configuration files on your system and updates them directly, instead of using its own separate database. This means that you can freely mix Webmin, manual configuration, and other programs or scripts that work in the same way.

Even though this book is written for Linux users, Webmin can be used on many other flavors of UNIX as well, such as Solaris, FreeBSD, and HP/UX. One of its biggest strengths is its understanding of the differences between all these operating systems and the way it adjusts its user interface and behavior to fit your OS. This means that it can often hide the underlying differences between each UNIX variant and present a similar or identical interface no matter which one you are using.

Webmin on its own is not particularly useful though—it is only a configuration tool, so you must have programs installed for it to configure. For example, the Apache module requires that the actual Apache Web server be installed. Fortunately, all of the services and servers that Webmin manages are either included with most Linux distributions as standard, or can be freely downloaded and installed.

Webmin was written for use by people who have some Linux experience but are not familiar with the intricacies of system administration. Even though it makes the process of creating UNIX users or managing the Squid proxy server easy, you must first have some idea of what a UNIX account is and what Squid does. The average Webmin user is probably someone running it on their Linux system at home or on a company network.

The program assumes that you are familiar with basic TCP/IP networking concepts, such as IP addresses, DNS servers, and hostnames. It also assumes that the user understands the layout of the UNIX filesystem, what users and groups are, and where user files are located. If you use Webmin to manage a server like Apache or Sendmail, you should first have an idea of what they can do and what kind of configuration you want completed.

Webmin itself runs with full UNIX root privileges, which means that it can edit any file and run any command on your system. This means that it is quite possible to delete all of the files on your system or make it un-bootable if you make a mistake when using the program, especially if you are configuring something that you don't understand. Even though Webmin will usually warn you before performing some potentially dangerous action, there is still plenty of scope for causing damage.

Even though it can be used on a system with no connection to the Internet, Webmin does benefit if your Linux system is on a network. It can download new software packages, Perl modules, or even new versions of Webmin for you, if connected. A permanent high-speed connection is best, but even a dial-up connection is good enough for most purposes.

Because Webmin runs with root privileges, you must be able to log in to your system as root to install and start it. This means that it cannot be used on a system on which you have only a normal UNIX account, such as a virtual web server that is shared with other people. You might, however, be able to get your system administrator to install and configure it for you.

If you are already an experienced UNIX system administrator, Webmin may not feel like the tool for you because using it is generally slower than directly editing configuration files and running commands. However, even the experts can benefit from its automatic syntax checking and the actions that it can perform automatically.

It is also possible to give different people different levels of access to Webmin, so that an experienced administrator can use it to safely delegate responsibility to less-skilled subordinates. For example, you might want someone to be only able to manage the BIND DNS server and nothing else, while giving yourself full access to the system and all of Webmin's functions.

Webmin, the program, was designed and created by me, Jamie Cameron—the author of this book. I started it back in 1997 and released the first version (0.1) in October of that year. Since that time, its user interface, features, and appearance have changed dramatically, and almost all of the code has been re-written. The basic concept of a web-based administration tool, however, has been the same since that very first release.

I started writing it when I was the administrator for a system running a DNS server and was spending a lot of time updating the server's configuration files to add new host records requested by users. Giving them the root password was not an option—they did not have the experience to properly edit the zone files and re-start the server. The solution was a simple web interface that would display existing DNS records and allow them to be edited, created, and deleted. Users could then safely be given access to this interface to make the changes that they needed.

DNS management was just the start though. Once I saw the possibilities for simplifying the configuration of a UNIX system though a web interface, I started adding other features to the program and putting them into modules. Next came modules for UNIX users, Samba, mounting filesystems, NFS, and Cron jobs. I thought up the name Webmin, made it available for anyone to download, and announced it on a few mailing lists. The initial feedback was good, so I kept on writing.

Over the years, the program has gone through three different user interfaces, grown to 83 modules, added support for non-English languages, provided advanced access control, included lots more operating systems, and offered many other features. The Linux distribution companies Caldera and MSC.Linux have supported the project financially, and many users have made contributions of code patches, modules, translations, and suggestions. In addition to the standard modules, over 100 have been written by other people and are available to be added to Webmin on your system once you have installed the program.

This book explains how to install Webmin, how to use almost all of its modules, and how to write your own. The book focuses on the standard modules that come with the Webmin package, not those written by other people. Not all of the 83 standard modules are covered, however, as some are not very useful to the average administrator.

Although this book is written primarily for Linux users, the program behaves almost identically on other operating systems. Each chapter also lists any differences between Linux and other UNIX variants in their "Other Operating Systems" sections. This means that it is still very useful if you are running Webmin on FreeBSD, Solaris, MacOS X, or some other variety of UNIX.

Each chapter in the book covers the use of Webmin for managing a particular service or server, such as NFS exports, Sendmail, or the ProFTPD FTP server. Most chapters only discuss a single module, but some cover two or three that have similar or related purposes. Each chapter is pretty much self-contained, so there is no need to read through the entire book in sequence if you just want to find out how to configure one server. Chapters, and possibly, however, should be read first as they explain how to install Webmin, how to secure it, and how to limit what other users can do with a module, respectively.

Each chapter is broken up into sections, and most sections explain how to perform a specific task. A section will generally contain an introduction to the task explaining why you might want to do it, followed by a list of steps to follow in the Webmin user interface to carry it out. At the beginning of each chapter are sections that introduce the server being configured and the concepts behind it, and list the underlying configuration files that get modified when you use the module covered in that chapter.

Chapters to cover the development of your own Webmin modules and themes, and therefore have a different style. The average user does not need to read them, but if you have an idea for a module that is not currently available, they provide all the information that you need to implement it.

This book should be read by anyone wanting to use Webmin to manage their Linux or UNIX systems. It was written for readers with a basic knowledge of UNIX commands and concepts—people who have installed Linux and have used it for a while.

Each chapter starts with an introduction to the service being configured so that readers have some idea of what the DNS protocol is for or how a firewall works. Even so, a complete novice should not try to set up a server until he understands how it works and what he wants it to do. The best way to learn is to use the service on some other system as a user. For example, if you have used a proxy server before on some other network, then you will have the background knowledge needed to use this book to set up the Squid proxy on your own system.

The development chapters, on the other hand, are written for someone who already understands how to write Perl scripts and CGI programs on a UNIX system. This means that they are more complex than the rest of the book, and assume some knowledge of programming and manual system administration. They can be skipped, however, if you just want to learn how to use Webmin rather than how to extend it.

This book could not have been written without the support of Jill Harry and the others at Prentice Hall, Robert Kern for suggesting the idea, my wife Foong Ching for her constant support, and all the members of the Webmin mailing list for their ideas and suggestions over the years.