John Goerzen

“ An operating system is the set of basic programs and utilities that make your computer run. At the core of an operating system is the kernel. The kernel is the most fundamental program on the computer: It does all the basic housekeeping and lets you start other programs. Debian uses the Linux kernel, a completely free piece of software started by Linus Torvalds and supported by thousands of programmers worldwide. ”

“ So a hard link is a filename and an inode number. A file is really an inode: a location on disk, file type, permissions mode, etc. A symlink is an inode that contains the name of a hard link. A symlink pairs one filename with a second filename, whereas a hard link pairs a filename with an inode number.
All hard links to the same file have equal status. That is, one is as good as another; if you perform any operation on one, it’s just the same as performing that operation on any of the others. This is because the hard links all refer to the same inode. ”

“ You may wonder why would people spend hours of their own time writing software and carefully packaging it, only to give it all away. The answers are as varied as the people who contribute.
Many believe in sharing information and having the freedom to cooperate with one another, and they feel that free software encourages this. A long tradition that upholds these values, sometimes called the Hacker [7] Ethic, started in the 1950s. The Debian GNU/Linux Project was founded based on these Free Software ethics of freedom, sharing, and cooperation. ”

“ Once you mount a filesystem, there’s no need to pay any attention to physical devices.
However, before you can mount a filesystem or actually create a filesystem on a disk that doesn’t have one yet, it’s necessary to refer to the devices themselves. All devices have names, which are located in the /dev directory. If you type ls /dev now, you’ll see a pretty lengthy list of every possible device you could have on your Debian system. For a summary of some devices, see Table 2.1 on page [*] . A more thorough list can be found on your system in the file /usr/src/linux/Documentation/devices.txt. ”

“ Every file has two owners: a user and a group. The above case is a little confusing because there’s a group called root in addition to the root user. Groups are just collections of users who are collectively permitted access to some part of the system. A good example is a games group. Just to be mean, you might create a group called games on your computer and then set up your system so that only people in a games group are allowed to play games. ”

“ The proc filesystem contains information about the system and running processes. Some of the “files” in /proc are reasonably understandable to humans (try typing cat /proc/meminfo or cat /proc/cpuinfo) ; others are arcane collections of numbers. Often, system utilities use these to gather information and present it to you in a more understandable way.
People frequently panic when they notice one file in particular— /proc/kcore —which is generally huge. This is (more or less) a copy of the contents of your computer’s memory. It’s used to debug the kernel. ”

“ Most people feel that a swap partition is also a necessity, although this isn’t strictly true. “Swap” is scratch space for an operating system, which allows the system to use disk storage as “virtual memory” in addition to physical memory. Putting swap on a separate partition allows Linux to make much more efficient use of it. It is possible to force Linux to use a regular file as swap, but this is not recommended.
The only real drawback to using more partitions is that it is often difficult to know in advance what your needs will be. ”

“ In the space of just a few decades, lives the world over have been changed by computing technology. We, the people behind the Free Software movement, are seeking to continue this trend by truly opening up software to everyone—not just the few people working for the companies that write it—but everyone. ”

“ More and more people are looking for ways to avoid the inflated price of proprietary software. A growing community contributes in appreciation for all the great free software they’ve received from others.
Many in academia create free software to help get the results of their research into wider use. Businesses help maintain free software so they can have a say in how it develops—there’s no quicker way to get a new feature than to implement it yourself or hire a consultant to do so! Business is also interested in greater reliability and the ability to choose between support vendors. ”

“ If you already have an operating system on your system (Windows 95, Windows NT, DOS, etc.) and you want to install Debian GNU/Linux on the same disk, you will probably need to repartition the disk. In general, changing a partition that already has a filesystem on it will destroy any information in that filesystem. Therefore, you should always make backups before doing any repartitioning. Using the analogy of the house, you would probably want to move all the furniture out of the way before moving a wall or you risk destroying your furniture. ”

“ At many sites, only the system administrator has the root password, and only the system administrator can do the things that one must be root to do. If you’re using your own personal computer, you are the system administrator, of course. If you don’t have root privileges, you will have to rely on your system administrator to perform any tasks that require root privileges. ”

“ Today, GNU/Linux plays a dominant role in Internet servers and among ISPs, in academia, among computer hobbyists, and in computer science research. Debian GNU/Linux has brought the power of Free Software to everything from laptops to flights aboard the Space Shuttle. As I write this, companies the world over are experiencing the joy and benefits that are Free Software. ”

“ The installation procedure can wipe out all of the data on a hard disk! The programs used in installation are quite reliable and most have seen years of use; still, a false move can cost you. Even after backing up, be careful and think about your answers and actions. Two minutes of thinking can save hours of unnecessary work.
Debian makes it possible to have both Debian GNU/Linux and another operating system installed on the same system. If you plan to use this option, make sure that you have on hand the original CD-ROM or floppies of the other installed operating systems. ”

“ You risk losing valuable data!
If you are the only user of your computer, you might want to turn the computer off when you’re done with it.
To avoid possibly weakening some hardware components, only turn off the computer when you’re done for the day. Power up and power down are the two greatest contributors to wear and tear on computer components. Turning the computer on and off once a day is probably the best compromise between your electric bill and your computer’s lifespan. ”

“ Daemon originally meant Disks And Extensions MONitor. A daemon is a non-interactive process, that is, it’s run by the system and users never have to worry about it. Daemons provide services like Internet connectivity, printing, or e-mail.
Now press u and give top your username when it asks. The u command asks to see only those processes belonging to you; it allows you to ignore all the daemons and whatever other people are doing. You might notice bash, the name of your shell. You’ll pretty much always be running bash. ”

“ As we mentioned earlier in section 1.1, the design of Debian GNU/Linux comes from the Unix operating system. Unlike common desktop operating systems such as DOS, Windows, and MacOS, GNU/Linux is usually found on large servers and multiuser systems.
This means that Debian has features those other operating systems lack. It allows a large number of people to use the same computer at once, as long as each user has his or her own terminal. [2] To permit many users to work at once, Debian must allow many programs and applications to run simultaneously. ”

“ The second reason is generally more important in a business setting, but it really depends on your use of the machine. Suppose something runs out of control and starts eating disk space. If the process causing the problem happens to have root privileges (the system keeps a percentage of the disk away from users) , you could suddenly find yourself out of disk space. This is not good since the operating system needs to use real files (besides swap space) for many things. It may not even be a problem of local origin. For example, unsolicited e-mail (“spam”) can easily fill a partition. ”

“ Backups are important under any operating system. Debian GNU/Linux provides several different utilities that you might want to use. Additionally, while many of these utilities were aimed at tape backups originally, you’ll find that they are now being used for other things. For instance, tar is being used for distributing programs over the Internet. Some of the utilities that you’ll find include the following:
◼ Taper is a menu-driven, easy-to-learn backup program that can back up to a variety of media. Its limitation is that it doesn’t handle large (4GB or larger) backups. ”

“ Every process has at least three connections to the outside world. The standard input is one source of the process’s data; the standard output is one place the process sends data; and the standard error is a place the process can send error messages. (These are often abbreviated stdin, stdout, and stderr.)
The words “source” and “place” are intentionally vague. These standard input and output locations can be changed by the user; they could be the screen, the keyboard, a file, even a network connection. ”

“ Linux is loaded by a program called LILO, or LInux LOader. LILO can also load other operating systems and ask you which system you’d like to load.
The first thing that happens when you turn on an Intel PC is that the BIOS executes. BIOS stands for Basic Input Output System. It’s a program permanently stored in the computer on read-only chips. It performs some minimal tests and then looks for a floppy disk in the first disk drive. If it finds one, it looks for a “boot sector” on that disk and starts executing code from it, if there is any. ”

“ This is a fundamental way to keep your system secure. If you are running a multi-user system or a server, it is important to make sure that permissions are correct. A good rule of thumb is to set files to have the minimum permissions necessary for use.
If you are running a network server, there are some other things to be aware of as well. First, you ought to uninstall or turn off any network services you’re not using. A good place to start is the file /etc/inetd.conf; you can probably disable some of these. For most network services, it’s also possible to control who has access to them ”

“ The first is for safety. If something happens to corrupt the filesystem, generally only one partition is affected. Thus, you only have to replace (from the backups you’ve been carefully keeping) a portion of your system. At the very least, you should consider creating what is commonly called a “root partition.” This contains the most essential components of the system. If any other partitions get corrupted, you can still boot into GNU/Linux to fix the system. This can save you the trouble of having to reinstall the system from scratch. ”

“ A terminal is just a keyboard and a screen that are connected to the computer through the network, over a modem, or directly. You keyboard and monitor form a terminal that is directly attached to the computer: This special terminal is often called the console.
Much of the power (and complexity) of GNU/Linux systems stems from these two features. For example, the system must have a way to keep users from accidentally deleting each other’s files. ”

“ The kernel will not allow normal users to change important system files. This means that things stay the way they’re supposed to, safe from accidents, viruses, and even malicious pranks. Unlike other operating systems, Debian is safe from these threats. You won’t need an anti-virus program.
However, sometimes you need to change important system files; for example, you might want to install new software or configure your network connection. To do so, you have to have greater powers than a normal user; you must become the root user (also called the superuser) . ”

“ Unix-like systems are multiuser, and so you have your own electronic identity as a user on the system. Type finger yourusername to look at some of the information about you that’s publically available. To change the name and shell listed there, you can use the commands chfn and chsh. Only the superuser can change your login (username) and directory. You’ll notice that it says “No plan.” A “plan” is just some information you can make available to others. To create a plan, you put whatever information you want people to see in a file called .plan. ”

“ But you can go from a text VC to the X virtual console using only Alt. If you never leave X, you won’t have to worry about this; X automatically switches you to its virtual console when it starts up.
Once you get used to them, virtual consoles will probably become an indispensable tool for getting many things done at once. (The X Window system serves much the same purpose, providing multiple windows rather than multiple consoles.) You can run a different program on each VC or log on as root on one VC and as yourself on another. Or everyone in the family can use his or her own VC ”

“ To this end, you have a username or login. If you installed Debian yourself, you should have been asked to give such a name during installation. If you are logging on to a system administered by someone else, you’ll have to ask him for an account on the system and a corresponding username.
You also have a password, so no one else can pretend to be you. If you don’t have a password, anyone can log on to your computer from the Internet and do bad things. ”

“ It’s a bad thing to just press the power switch when you’re done using the computer. It is also bad to reboot the machine (with the Reset button) without first taking proper precautions. The Linux kernel, in order to improve performance, has a disk cache. This means it temporarily stores information meant for permanent storage in RAM. Because memory is thousands of times faster than a disk, this makes many file operations move more quickly. Periodically, the information Linux has in memory is actually written to the disk. ”

“ This sets Linux to be the bootable partition—the one that will be loaded from the hard disk.
Note that multiple operating system booting on a single machine is still something of a black art. This book does not even attempt to document the various boot managers, which vary by architecture and even by sub-architecture. You should see your boot manager’s documentation for more information. Remember: When working with the boot manager, you can never be too careful. ”