A. Administrative Issues
Every Linux system has an administrator---someone who installs the
hardware and software, maintains the system, and generally keeps things
running smoothly. A single-user home Linux system, once installed and
running, needs little administration--but the occasional upgrade or
maintenance task is necessary.
This appendix exists as a reference for those users who will also be
performing the administrative duties on their system. While a complete
administrative guide is out of the scope of this book, the goal of this
appendix is to point the new Linux administrator in the right direction,
giving tips on how to choose the computer you'll use for Linux, install
Debian GNU/Linux on it, and get it ready for use.
Unlike the rest of this book, this chapter contains recipes describing
commands to be run by root, the superuser account. Many of these
commands cannot be run by an ordinary user; instead of the normal
shell prompt used for examples throughout the rest of the book
(`$'), the examples in these recipes use a pound sign (`#'),
which is the default prompt for the root account.
If you're new to Linux administration, you may want to consult the help
resources listed in If You Need More Help.
A.1 Linux and Hardware Compatibility
@sf{WWW}: http://www.thedukeofurl.org/
In days gone by, Linux enthusiasts had to piece together computer
systems from individual components, since the salesmen at computer
stores had never even
heard of Linux or the free software
movement. But no more. Today, many dealers sell complete systems with
Linux pre-installed, including corporations like Dell Computers and
IBM.
(44)
The Duke of URL reviews the latest hardware as it performs with
Linux. His periodic "Linux Buyer's Guide" feature lists current
hardware that works well on a Linux-based system, and it gives sample
configurations (with prices and links to vendors) for putting together a
complete system--from low-end budget system to a blazing,
dual-processor rig.
Since Linux runs on many different computers and supports a wide range
of hardware, and because everyone has different needs, I won't make too
many recommendations as to which specific hardware to buy. (Systems
change too fast for such a list to be useful, anyway.)
Before you make a hardware purchase, though, make sure that it's
compatible with Linux--that bargain video-capture board will be
worthless if it has a proprietary interface that only works with a
certain non-free operating system.
To find out whether your hardware will work under Linux, try the
following:
-
Read the Linux Hardware Compatibility HOWTO (see section Reading System Documentation and Help Files), an up-to-date list of
hardware that is compatible with Linux.
-
Visit the Linux Hardware Database and
Linux Hardware.Net sites, which
provide reviews and information about hardware that works with Linux.
-
Search the Internet--particularly Usenet news and the
linux.com site--for the hardware you
intend to buy. Read any trouble reports people may have written about
getting it to work with Linux, so that you won't be writing the
next report about it.
A.2 Shutting Down the System
To shut down the system properly, use shutdown. It notifies all
users and processes of the impending shutdown, blocks new logins, and
brings the system down cleanly. (Just cutting power to the system
without cleanly stopping processes and unmounting filesystems could
result in the loss or corruption of data.)
To halt the system once the shutdown is complete, use the `-h'
option; to reboot the system after shutdown, use `-r' instead.
The following recipes describe ways of using shutdown to do
useful things.
A.2.1 Shutting Down Immediately
To shut down the system at a certain time, you normally give that time
as an argument; use the special `now' argument to begin the
shutdown process immediately.
-
To immediately shut down and halt the system, type:
-
To immediately shutdown the system, and then reboot, type:
You can follow the `now' argument with a quoted message that will
be displayed on all terminals of all users currently logged in.
-
To immediately shut down and halt the system, and send a warning message
to all users, type:
| | # shutdown -h now "The system is being shut down now!" RET
|
A.2.2 Shutting Down at a Certain Time
To shut down the system at a certain time, give that time (in 24-hour
format) as an argument.
-
To shut down and then reboot the system at 4:23 a.m., type:
-
To shut down and halt the system at 8:00 p.m., type:
To shut down the system in a certain number of minutes, give that number
of minutes prefaced by a plus sign (`+').
-
To shut down and halt the system in five mintues, type:
Follow the time with a quoted message to display it on the terminals of
all logged in users.
-
To shut down and halt the system at midnight, and give a warning message
to all logged-in users, type:
| | # shutdown -h 00:00 "The system is going down for maintenance at
midnight" RET
|
A.2.3 Cancelling a Shutdown
If you have given a shutdown and decide that you don't actually
want to shut the system down, run shutdown again with the
`-c' option. This command stops any shutdowns in progress.
-
To cancel any pending
shutdown, type:
As with a normal system shutdown, you can send out an explanatory
message with the cancel that will be shown to all users.
-
To cancel any pending
shutdown and send an explanatory message to
all logged in users, type:
| | # shutdown -c "Sorry, I hit the wrong key!" RET
|
This command cancels any pending system shutdown and displays the
message, `Sorry, I hit the wrong key!' on all the terminals of
anyone logged in.
A.3 Installing Software
All Linux distributions come with a multitude of software programs (also
called "binaries"). But sooner or later, you will want to install more
programs, or you will want to upgrade your existing software when newer
versions are available. The following sections talk about installing
the Debian GNU/Linux distribution itself, installing and upgrading
software when from Debian packages, and how to install stand-alone shell
scripts.
A.3.1 Getting and Installing Debian
@sf{WWW}: http://www.cheapbytes.com/
@sf{WWW}: http://www.debian.org/
@sf{WWW}: http://www.debian.org/releases/stable/
You can get a copy of Debian GNU/Linux on CD-ROM from local or online
vendors, or you can download the installation files from the Internet
(recommended only if you have a fast Internet connection, of course).
If you choose to buy a copy of Debian in a local computer store, be sure
you get the most recent version. If a store only carries an older
version, the software might not work with your brand-new hardware!
(Visit the Debian Web site to find the
number of the latest version.)
If you'd rather buy a copy online, Cheap*Bytes sells affordable Debian GNU/Linux CD-ROMs. The Debian
Project maintains a full list of vendors at
http://www.debian.org/distrib/vendors/.
The precise details of installation are out of the scope of this book,
but the Debian
installation guide comes on the CD-ROM. It contains step-by-step
instructions and the latest release notes.
A.3.2 Installing a Debian Package
Debian makes the software programs available in `.deb'
packages, files that contain everything necessary for the
installation of a given software program.
There are different methods of installing packages on a Debian system:
via dselect, where you select packages from a menu; dpkg,
a command-line tool for installing packages; and apt-get, part of
Debian's new "Advanced Package Tool" system.
To install a package when you know the package name, mount your Debian
distribution (for example, if you install Debian via CD-ROM, put the
first Debian CD-ROM disc in your CD-ROM drive). Then run apt-get
with the `install' command option, and give the name of the package
to install as an argument. Should there be additional packages that must
be installed first (called dependencies), or should the package
conflict with others already installed, an action will be presented to
fix this, and you will be prompted to confirm or abort the operation.
-
To install the `miscfiles' package, type:
| | # apt-get install miscfiles RET
|
If you already have the `.deb' file, use dpkg to install
it. Use the `-i' option and give the name of the file as an
option. Any conflicts or dependencies will have to be resolved by you
before the package is installed. If a problem is detected, dpkg
will report it and exit without installing the package.
-
To install the package in the `miscfiles-1.1.7.deb' file, type:
| | # dpkg -i miscfiles-1.1.7.deb RET
|
Finally, to peruse available packages and choose them from a menu, use
dselect, the Debian package selection tool. A word of caution:
its menu interface is different from most programs you have probably
encountered, and its usage is unfortunately an acquired skill. Even the
man page makes note of this: "The
dselect package
selection interface is confusing or even alarming to the new user."
NOTE: If you're new to Debian, I recommend consulting
Dselect Documentation for Beginners.
A.3.3 Upgrading a Debian Package
People are constantly contributing to the free software movement. This
means that new software programs are constantly being added to Linux
distributions, and current software programs are continually being
improved--new features to match new hardware, faster program execution,
security updates, and so forth. A Linux system, therefore, needs to be
kept up to date in order to reap the benefits of the latest free
software.
To upgrade a single package, use apt-get with the `install'
argument, and follow that with the name of the package to upgrade.
-
To upgrade the `sview' package, type:
| | # apt-get install sview RET
|
This command will upgrade the `sview' package to the most current
version available, if greater than the version already installed on your
system. If additional packages must be upgraded first in order for this
new package upgrade to function properly, this command will fetch and
upgrade those packages, too. Before downloading any packages,
apt-get will show the list of packages that will be installed,
replaced, or otherwise changed, and wait for confirmation first.
To bring your entire Debian system up to date, use the apt-get tool
with the following command arguments. First, use the `update'
argument to update your system's list of available software
packages. Then run apt-get again, using either the `upgrade'
argument to upgrade all of the installed packages to their most recently
available versions, or use the `dist-upgrade' argument when a new
version of the Debian system is announced, to upgrade to that new
version.
-
To upgrade all of the software on your system to their most recent
versions, type:
| | # apt-get update RET
...processing messages...
# apt-get upgrade RET
...processing messages...
#
|
-
To upgrade your Debian system to the most recent release, type:
| | # apt-get update RET
...processing messages...
# apt-get dist-upgrade RET
...processing messages...
#
|
A.3.4 Installing a Shell Script
A shell script is a file that contains commands written in a shell
command language (see section The Shell). You run (or "execute")
a script as you would any other command (see section Running a Command). First, make sure that the script file is executable; if it
isn't, you won't be able to execute it (see section Making a File Executable).
Generally, the administrator installs new shell scripts in the
`/usr/local/bin' directory. If you are on a multi-user system and
you are the only user liable to run a particular script, you can put it
in a special directory in your home directory tree--the `~/bin'
directory is the standard recommendation here--and then add that
directory to your path (see section Adding to Your Path).
Not all executable script files are shell scripts. The first line
of a script contains the full path name of the shell or other program
that is to interpret and execute the script; sometimes, the path may
differ on your system from the one the script was written on, and so you
may have to change this line.
For example, a script may start with the following line:
This line means that the script is written in the perl language;
the text after the `#!' is the full path name of the perl
program, which in this case is `/usr/local/bin/perl'.
If you try to execute this script and the system reports an error
finding the file, you'll have to change that first line to correspond to
the location of the perl binary on your system. The which
tool will output this location.
-
To find out where
perl is installed on your system, type:
If that command returns `/usr/bin/perl' or some path name other
than /usr/local/bin/perl, you'll have to change the location in
the first line of the script to the path name given:
NOTE: If the output of the which command returns
nothing, that means that the perl program is not installed on
your system at all; in that case, you should install the perl
software.
A.4 Administrating Users
This section describes some of the things the system administrator will
have to do in administrating the system's users.
All of these commands must be run by the superuser, using the
root account--these commands edit system files.
A.4.1 Making a User Account
To make a new user account, use adduser. It takes as an argument
the username to use for the new account. It will prompt for default
setup information, including the user's full name and an initial
password to use.
-
To create a new user with a username of
bucky, type:
NOTE: By default, the name of the user's home directory will be
the same as the username. So, for example, the user bucky will
have a home directory of `/home/bucky'.
A.4.2 Letting Users Access Hardware Peripherals
Certain hardware peripherals, like CD-ROM drives and soundcards,
normally require superuser privileges in order to access them. These
devices also have groups of their own, so a regular user can also
access them by having membership to their groups (see section Groups and How to Work in Them).
The groups that regular users might want to be part of include
floppy (the floppy disk drive), audio (the soundcard), and
dialout and dip (modem dial-out privileges).
Use addgroup to add a user to the group associated with a
hardware device. Give as arguments the username to add and the name of
the group to add to.
-
To add the user
doug to the audio group, type:
| | # addgroup doug audio RET
|
A.4.3 Letting Users Mount Drives
The `/etc/fstab' file specifies the details about the filesystems
in use on a system, including those that may be mounted by floppy or
CD-ROM drive. In order to let users mount disks on these drives, make
sure that there is a line in `/etc/fstab' for both the floppy and
CD-ROM drives, each containing the `user' flag:
| | /dev/fd0 /floppy auto defaults,noauto,user 0 0
/dev/cdrom /cdrom auto defaults,noauto,user 0 0
|
A.5 Displaying Information about the System
The following recipes describe ways of displaying information about the
system you are running.
A.5.1 How Long Has the System Been Up?
To find out how long the system has been running, use the uptime
tool. When you run it as a command, it outputs the current time, how
long the system has been running, how many users are logged on, and what
the system "load averages" have been for the past one, five, and
fifteen minutes.
-
To find out how long the system has been up, type:
| | $ uptime RET
3:34pm up 4:31, 4 users, load average: 0.01, 0.05, 0.07
$
|
To get a list of the times and dates when the system was recently
rebooted, give `reboot' as an argument to last (see section Listing the Last Times a User Logged In).
-
To output a list of times when the system was rebooted, type:
NOTE: An operating system capable of running constantly for a
long time without crashes or freeze-ups is a good one, and so having a
high uptime value is a matter of pride for many Linux users. It
is not uncommon to hear of systems that have been running for months and
sometimes even years non-stop--one Linux administrator reported
on the Internet about one of his work systems, which had been running
continuously without reboot for three years!
A.5.2 What Version of Linux Am I Running?
Use the GNU uname tool to see what version of Linux you are
running. By default, it outputs the name of the operating system; the
`-r' option outputs the operating system release number.
-
To output the name of the operating system, type:
-
To output the release number of the operating system, type:
You can also use uname to output the CPU processor type of the
system (such as i586, PowerPC, etc.); specify this with the `-m'
option. The `-a' option is also useful; it outputs all
information about the system that it can, including all of the mentioned
options, plus the version date and number of the operating system and
the machine's hostname.
-
To output the CPU processor type of the system, type:
-
To output all of the
uname information for the system you are on,
type:
A.5.3 What Version of Debian Am I Running?
On a Debian system, the file `/etc/debian_version' (see section Files and Directories) contains the release name of
the Debian installed.
Use cat to output the contents of this file (see section Concatenating Text).
-
To output the release name of the Debian system you are on, type:
| | $ cat /etc/debian_version RET
|
NOTE: Debian releases have historically been named after
characters from the motion picture Toy Story.
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