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What Linux Does
On any operating system,
a core set of tasks is performed. On multi-user
or server systems such as Linux, these tasks include adding and configuring
printers, adding and administering users, and adding new hardware to the system.
Each of these tasks could take up an entire chapter in this book. In fact, I do
cover all of these, and many others, in a fair bit of detail later on.
I think it's important to briefly cover all of the basic tasks that an
administrator needs to perform in one place. There are a couple of reasons for
this. First, many administrators of Linux systems are not only novice
administrators, they are novice users. They get into the position as they are
the only ones in the company or department with computer experience. (They've
worked with DOS
before.) Second, by introducing the varied aspects of system
administration here, I hope to lay the foundation for later chapters. If you are not familar
with this issue, you may have trouble later.
Keep in mind that depending on what packages are installed, any Linux
distribution can do a lot more. Here we will be discussing just the basic
administrative functions.
The average user may not want to get into the details that the later
chapters provide. So here I give an overview of the more important components.
Hopefully, this will give you a better understanding of what goes into an
operating system as well as just how complex the job is that your system
administrator does.
The first job of a system administrator
is to add users to the system.
Access is gained to the system only through user accounts. Although it may be
all that a normal user is aware of, these accounts consist of substantially more
than just a name and password. Each user must also be assigned one of the
shells, a home directory,
and a set of privileges to access system resources.
Although the system administrator
could create a single user account
for all users to use to log in, it ends up creating more problems than it solves. Each
user has his/her own password and home directory.
If there were a single user,
everyone's files would be stored in the same place and everyone would have access
to everyone else's data. This may be fine in certain circumstances, but not in
most.
Users are normally added to the system through the adduser command. Here,
when adding a user, you can input that user's default shell,
his/her home directory as well as his/her access privileges.
Another very common function is the addition and configuration of system
printers. This includes determining what physical connection the printer has to
the system, what characteristics the printer has (to choose the appropriate
model printer) as well as making the printer available for printing.
Generically, all the files and programs that are used to access and manage
printers are called the print spool, although not all of them are in the spool
directory.
Adding a printer is accomplished like in many UNIX
dialects: you do it
manually with the primary configuration file, /etc/printcap file. The printcap
man-page lists all the capabilities that your version of Linux supports. You
must also add the appropriate directory and enable printing on the port. We'll
get into more detail about it as we move on.
What happens when you want to remove a file and inadvertently end up
removing the wrong one (or maybe more than one)? If you are like me with my
first computer, you're in big trouble. The files are gone, never to show up
again. I learned the hard way about the need to do backups. If you have a good
system administrator,
he/she has probably already learned the lesson and makes
regular backups of your system.
There are several ways of making backups and several different utilities for
doing them. Which program to use and how often to make backups completely
depends on the circumstances. The system administrator
needs to take into account things like how much data needs to be backed up, how often the data are
changed, how much can be lost, and even how much will fit on the backup
media.
There are tasks that an administrator
may need to perform at regular
intervals, such as backups, cleaning up temporary directories, or calling up
remote sites to check for incoming mail. The system administrator
could have a
checklist of these things and a timer that goes off once a day or every hour to
remind him/her of these chores, which he/she then executes manually.
Fortunately, performing regular tasks can be automated. One basic utility in
every UNIX
version is cron. Cron (the "o" is short) is a program that
sits in the background and waits for specific times. When these times are
reached, it starts pre-defined programs to accomplish various, arbitrarily
defined tasks. These tasks can be set to run at intervals ranging from once a
minute to once a year, depending on the needs of the system administrator.
Cron "jobs" (as they are called) are grouped together into files,
called cron tables, or crontabs for short. There are several
that are created by default on your system and many users and even system
administrators can go quite a long time before they notice them. These monitor
certain aspects of system activity, clean up temporary files, and even check to
see if you have UUCP
jobs that need to be sent.
What about a program that you only want to run one time at a specific time
and then never again? Linux provides a mechanism: at. Like cron, at will run a
job at a specific time, but once it has completed, the job is never run again.
A third command that relates to cron and at, the batch command, differs from
the other two in that batch runs the job you submit whenever it has time; that
is, when the system load permits.
Linux supports the idea of virtual consoles (VCs), like SCO. With this, the
system console (the keyboard and monitor attached to the computer itself) can
work like multiple terminals. By default, the system is configured with at least
four VCs that you switch between by pressing the ALT key and one of the function
keys F1-F6.
Normally, you will only find the first six VCs active. Also, if you are
using the X
Windowing System, it normally starts up on VC 7. To switch from
the X-Windows screen to one of the virtual consoles, you need to press
CTRL-ALT plus the appropriate function key.
Keeping the data on your system safe is another important task for the system
administrator. Linux provides a couple of useful tools for this: tar and cpio.
Each has its own advantages and disadvantages. Check out the details on the
respective man-page.
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