|BASH COMPLETION SHORTCUTS
Don't drive yourself nuts typing lengthy directory names, filenames, or command names. Let bash do it for you. Try typing a few characters of the name, and press [Tab] or [Ctrl]I. Chances are bash will be able to complete the item for you. If not, try pressing [Tab] or [Ctrl]I again. You'll see a list of possible completions. If you'd like to restrict the possibilities, you can request completions for filenames only by pressing [Alt]I, host names only by pressing [Alt]@, or user names only by pressing [Alt]~. To find command names only, press [Alt]!, and to find variable names only, press [Alt]$. If these commands don't work, your system may be set up so that these commands are mapped to [Esc] or some other key, such as the Command key on Power Macintosh systems. To view the current key assignments, take a look at /etc/inputrc (assignments for the whole system) and the .inputrc file in your home directory (assignments for your user account only).
THE BRAVE GNU WORLD ONLINE MAGAZINE
Brave GNU World is a multilingual monthly column that provides information about internal developments of the GNU Project and GNU community. It is available online at http://www.gnu.org/brave-gnu-world/
Alternatively, you can subscribe to a mailing list to be informed of new issues as soon as they are released.
THE DISPLAY GHOSTSCRIPT SYSTEM
The Display GhostScript System (DGS) provides a device-independent imaging model for displaying information and graphics on a screen, regardless of display-specific details like screen resolution and color issues. The imaging model of DGS uses the PostScript language, which has powerful graphics capabilities.
DGS is composed of a PostScript language interpreter called GhostScript, the client library, and the pswrap translator. The pswrap translator enables you to take PostScript programs and wrap them with a C function interface, thereby allowing your applications to call them directly. DGS is available at ftp://ftp.gnustep.org/pub/gnustep/dgs/
RESUMPTIVE AND NONRESUMPTIVE EXCEPTION HANDLING
In a resumptive exception handling model, after an exception has been
handled, the program continues execution at the point where the
exception was thrown. This is how Structured Exception Handling (SEH)
works in C (note that SEH is a no-standard extension to ANSI C). On
the other hand, the C++ standard exception handling model is
nonresumptive. This means that program execution resumes at the next
statement following the catch-block. The C++ program does not return
to the point where the exception was thrown after that exception has
been handled. This is a source of confusion among C++ novices, who
mistakenly assume that the program automatically returns to the point
from which an exception was thrown, but it doesn't.
THE COMMON UNIX PRINTING SYSTEM
The Common UNIX Printing System (CUPS) provides a portable printing
layer for various UNIX operating systems and Linux distributions. CUPS
supports both the System V and Berkeley command-line interfaces. CUPS
also includes a customized version of GNU GhostScript and an image
file RIP that can be used to support non-PostScript printers. CUPS can
be downloaded from
THE MIDGARD PROJECT
The Midgard Project is responsible for the development of an open
source application--the Midgard Application Server. The product
consists of Midgard core libraries, a PHP-based Web Application Server
for Apache platform, and Web-based administration tools. For further
information and software download, visit the Midgard Web site at
WINMODEM ON LINUX?
Although many Linux users balk at the idea of using Winmodem, it still
has many useful applications on Linux: it can serve as an answering
machine, pager interface, phone emulation, etc. The following Web site
is dedicated to Winmodems on Linux. You can download related software,
view a list of Winmodem chipsets, and find related links:
THE PHP SCRIPTING LANGUAGE
PHP is an open source server-side, cross-platform, HTML-embedded
scripting language. It enables you to create dynamic Web pages that
are treated just like regular HTML pages. PHP's syntax is reminiscent
of C. However, it is much simpler than C and it is free from the
hassles of memory management and pointers. For more information, visit
the PHP Web site at
THE VIM EDITOR
VIM is an open source and enhanced version of vi, one of the standard text editors on UNIX. VIM features include unlimited undo, syntax coloring, split windows, visual selection, GUI support, and more. Besides Linux and Unix, VIM runs on many other operating systems, including BeOS, DOS, MacOS, OS/2, RiscOS, VMS, and Windows32. You can obtain further information about the VIM editor and download it from http://www.vim.org/
Project Linux is aimed at Linux users and the Open Source community in
general. Starting November 8, the organization will present the
following two Web sites: Get Linux and Open Talk. Get Linux provides
information for people new to Linux. It will include a list of
available distributions, reviews, and articles. The Open Talk section
will host forums of discussion about all things relating to open
source technologies. You can find the Project Linux Web site at
REENTRANT AND NONREENTRANT SIGNALS
What happens when a signal is sent to a process that is already
handling that signal? In theory, the kernel can interrupt the process
and invoke the signal handler again. This approach requires that the
signal handler can function properly if it is invoked while it is
already executing. Such a handler is said to be reentrant. Writing
reliable and efficient reentrant handlers is not a trivial task.
Imagine what would happen if the signal handler locks a file, and at
that point, the kernel interrupts it and invokes that handler once
more. The second invocation will result in a deadlock because the
handler infinitely waits for the lock to be released. The lock,
however, cannot be released because the first handler call was
In Linux, this situation doesn't occur, because the kernel withholds
the signal until the process to which it is sent has finished handling
the previous signal (the second signal is said to be pending). Only
then is the pending signal sent to that process. This approach was
chosen to avoid the complexities of reentrant signal handlers.
THE WINE COMPATIBILITY LAYER
Wine is a Windows compatibility layer that facilitates porting of
Windows sources to Unix and Linux. Wine also includes a program loader
that enables unmodified Windows 3.1/95/NT binaries to execute under
Intel Unix and Linux systems. Wine does not require Microsoft Windows,
since it consists of 100 percent free code. It supports many Windows
features, including multimedia and OLE DLLs reorganization, Clipboard,
and support for Win16 and Win32 function calls. You can find more
information about Wine and download it from
THE QUANDARIES OF FLOATING POINT NUMBERS
People sometimes complain about the inaccuracy of floating point
arithmetic. To demonstrate that, try the following program:
float f1 = 2000.58;
float f2 = 2000.0;
printf("%f", f1 - f2);
On an Intel-based machine, this program prints 0.579956 instead of
0.58. More complex calculations yield higher inaccuracy. What is going
on here? First, remember that rounding, approximation, and truncation
are not the responsibility of a particular programming language or
compiler. Rather, they depend on the hardware that your machine uses.
Floating point numbers are merely an approximation based on the IEEE
standard. On most machines, the type float occupies 32 bits. The IEEE
standard for 32-bit floating point numbers requires that 1 bit be used
for the sign representation, 8 bits for exponent, and the remaining 23
bits are for the mantissa. Since a mantissa always has the form
1.nnnn..., the leading 1 can be dropped, so there are actually 24 bits
allocated for the mantissa. This 24-bit accuracy can have a deviation
of plus or minus %0.0000062 from the original number. For higher
accuracy, you can use the type double, which provides 53 bits of
mantissa. This is more accurate than 24 bits, but you can never get
absolute accuracy with built-in data types.
THE SAWMILL WINDOW MANAGER
Sawmill is a highly configurable window manager for Linux and several
Unix flavors. Its major advantage over the Enlightenment window
manager is its minimal system requirements. Thus, it can run on Linux
machines that have slow processors and minimal memory.
Sawmill is distributed under the terms of the GNU GPL license. You can
find more information on Sawmill and download it from http://www.dcs.warwick.ac.uk/~john/sw/sawmill/
LINUX C++ MAILING LISTS
The Linux C++ Mailing List was recently established. The purpose of
this mailing list is to help and support Linux programmers who use
C++. To subscribe to the list, send this e-mail with an empty subject
and message: mailto:tuxCPProgrammingfirstname.lastname@example.org
You will receive a reply with further instructions on how to confirm your subscription, post messages, post replies, and unsubscribe from the list.
AVOID PASSING ARGUMENTS WITH SIDE EFFECTS
Many of the ANSI C functions are in fact macros in disguise.
routines, memset(), strcpy(), and other runtime library
functions are examples of such macros in disguise. You should beware
of passing expressions with a side effect as arguments to these
functions, because the results may be undefined. Consider the
int n = 0;
memset(buff, ++n, sizeof(buff); /* ++n has a side-effect; bad idea */
If memset() happens to be a macro that passes its arguments to another
function, the value of n may be incremented twice before it is used.
LINUX 2000 ORGANIZATION
Linux 2000 Online is a resource site for Linux users--beginners and
experienced alike. The site contains forums, links to portals,
hardware and software vendors, and newsgroups from all over the world.
The Linux 2000 Online site is at: http://www.linux-2000.org/
THE UTOPIX WEB SITE
Utopix is a Web site dedicated to Linux and Windows users alike. It
provides news from the Linux industry and promotes the adoption of
Linux as a mainstream OS. The site offers a chat room, a forum, and
online polls. You can find Utopix at: http://utopix.cjb.net/
When you invoke the fork() command, Linux creates a new process that
is an exact copy of the existing one. When Linux instantiates the new
process, it uses an optimization method called "copy-on-write."
Instead of copying the memory block that contains the original
process's attributes, the new process's attributes are mapped to the
original memory block and marked as "read-only." When the new process
changes any of its attributes, it attempts to write to that read-only
memory block. Consequently, the exception handler allocates a new
block of memory, copies the data into it, marks the newly allocated
block as "write-enabled," and changes the mapping of the new process
to it. Thus, no actual copy takes place as long as the new process
doesn't change any of its attributes.
WHAT IS A SIDE EFFECT?
In standard C and C++, a side effect is defined as a "change in the
state of the execution environment." Modifying an object, accessing an
object that is declared volatile, invoking an I/O function, or calling
a function that does any of these operations are all side effects. The
validity of many operations depends on the existence of a side effect
(or lack thereof). The following are instances of side effects:
volatile int n = 0; int j = 0;
++j; /* object modification */
j = n; /* two side effects: accessing a volatile object and modifying
printf( "hello world"); /* I/O function call */
CHECKING AVAILABLE RAM FROM THE COMMAND LINE
Linux can highlight the available amount of RAM on a system at any
given moment. Both command-line (text only) and GUI-type tools are
available. The command-line tool for system RAM usage comes in two
forms: dynamic and static. The dynamic tool is called Top (in fact, the
command to execute this tool is top). Top offers two types of output.
The system's resources are listed at the top of the output. These
include CPU status, available RAM, and number and status of processes.
The CPU status and available RAM are most helpful.
The CPU status is broken into four categories: system, user, nice, and
idle. System is the percentage of the CPU that the OS is currently
using; user is the percentage of the CPU that the user-space programs
are using; nice is the percentage of CPU being used by prioritized
applications; and idle is the remaining percentage of the CPU.
Should your system begin to show signs of slowing down, run top. If you
consistently see the system CPU status at 15 percent or higher, you
should check into the lower half of Top's output to see what's causing
The lower portion of Top's output details every process running on the
system. This is very handy when used to analyze the state of a system.
Should the user see a high CPU percentage, he or she can look into the
lower half of the output, determine what is causing the issue, and if
necessary, terminate the process, thereby freeing up critical CPU
Probably the most helpful listing in Top is the process identifier
(PID). The PID is an integer assigned to a given process that allows
the user to identify (for purposes of killing or restarting) that
CHECKING AVAILABLE RAM FROM THE KDE GUI
The Gnome and KDE Linux GUI desktops offer graphical tools for viewing
system resources. Both tools give the user exhaustive output on the
particular system in question, and each tool has its own unique
features. Today we'll discuss how to check available RAM from KDE's
GUI, and next time we'll explain how to do so from Gnome's.
Ktop is a very solid graphical tool for analyzing system resources.
Ktop (also known as KDE Taskmanager) offers three different tabs within
a single window: Process List, Process Tree, and Performance.
The Process List tab is basically a simple representation of the lower
half of the top command. Each process on the system is listed along with its
PID, username, CPU, time running, status, and various memory
indicators (amount used/shared/cached).
The next tab, the Process Tree, is a very useful representation of the
dependencies of a process. When a parent process spawns a child
process, the Process Tree offers an Explorer-like view of this
dependency. For example, when you run the command Ktop from a "Konsole," the
Konsole is the parent of Ktop--the one is spawned from the other.
The final tab is the Performance tab, which is simply a dynamic
graphical representation of the system resources offered with the basic
CHECKING SYSTEM RESOURCES
On what operating system can you find both textual and graphical tools
to check system resources? Linux, of course. While the Windows
operating system offers the user just a few ways to check resources,
Linux gives users several ways to test various resources.
To check for percentage of used hard drive (or floppy disk) space, run
the command df. You'll see something similar to:
[jacula@lab3 jacula]$ df
Filesystem Size Used Avail Use% Mounted On
/dev/hda 3968M 576M 341M 63% /
This output shows a particular dual-booting machine (only the Linux
partition shows) with Linux residing on the hda3 partition. The numbers
are self-explanatory, with the possible exception of Mounted On. This
listing shows the point at which this partition starts.
KDE has its own GUI tool for checking available disk space. KDiskFree
gives the user a (somewhat) graphical representation of what the df
command offers. This application can be found in the System submenu of
the main K menu.
CHECKING AVAILABLE RAM FROM THE GNOME GUI
Gnome has its own version of the front-end application for the top
command. Gtop is a powerful application that takes Top to new levels.
With a handsome interface, Gtop enables the user to kill processes with
a right-click menu, to view all system resources (both dynamically and
statically), to view system status (e.g., the machine's run time, load
average, etc.), and to start and stop sampling the system. Unlike Ktop,
Gtop (in typical Gnome fashion) allows the user to customize the look
and feel AND the output of the application.
Gtop can be run from the command line by typing gtop or from the Gnome
main menu under the Utilities submenu (System Monitor is the name of
the menu entry).
A DIFFERENT WAY TO START X
A simple way to start X (from the console boot prompt) and give yourself a nice viewable boot log is to create a simple startup shell script that will catalog the boot message output to a file.
This shell script, which we'll call logx, looks like this:
startx > log_of_x 2>&1
Name this script logx and put it into a directory that lies in your $PATH. This will result in the logx command being global and executable by a user (chmod u+x logx).
When you're ready to log on at your console bash prompt, simply type logx and your GUI will begin. To view the newly created log, simply open the file log_of_x with your favorite text editor.
LINUX VIRTUAL SERVERS
A virtual server is a scalable and highly available server built on a cluster of real servers. The architecture of the cluster is transparent to the end users, who see only a single virtual server. Thus, a virtual server offers a very high computation power as well as exceptionally high fault tolerance. You can find more info on this technology and its uses at: http://www.linuxvirtualserver.org/
THE DIFF3 COMMAND
The diff3 is useful when two people change a common file and create two independent versions thereof. Diff3 compares the original file, as well as the two files derived from it, all at once. Diff3's syntax is diff3 derived1 originalfile derived2 Where originalfile is the common ancestor from which derived1 and derived2 are derived.
THE GEEKNEWS ORGANIZATION
The Geeknews site is devoted to reporting Linux-related technology news from around the Web. The site includes news flashes, reviews, and downloads of open source software tools. The Geeknews Web site is at: http://www.Geeknews.org
THE LINUX MICRO-CONTROLLER PORT
The uCLinux (Linux Micro-controller, the lowercase u stands for the Greek letter "mu") project is a port of Linux 2.0 to embedded systems that don't have a memory management unit. The end goal of this project is to port Linux to handheld devices and embedded controllers that do not have a built-in memory management unit. uCLinux is an Open Source product distributed under the GNU Public License. For further info, visit the uCLinux Web site at: http://www.uclinux.org/
THE REBOL PROGRAMMING LANGUAGE
REBOL (Relative Expression-Based Object Language) is a new, portable, general purpose, and efficient programming language for intercommunications and interoperability. The language supports almost 40 hardware platforms, including Win32, Solaris, various Unix flavors, Macintosh, and Linux. REBOL has a simple and intuitive structure with English-like syntax. You can find further info on REBOL at: http://www.rebol.com
LISTING FILES WITH LS
The command ls is a useful tool that allows you to view various information about files and directories. The basic use of ls is to list files within a directory--from within the directory, type ls (without arguments) and you'll get a content listing for that directory.
The ls command is, of course, potentially much more powerful than this basic application. For example, instead of jumping through your directory structure just to view directories' contents, use ls instead. Let's say you're in your home directory and want to list the contents of the /etc directory. Simply type ls /etc and you'll be rewarded with a content listing of the directory /etc.
The ls command has other power applications. Users can list all files by adding the -a flag (including hidden files) and list permissions and ownership of files with the -l flag.
After you've installed Linux, you'll notice that sound output doesn't work automatically. You must do a post-install configuration of either the proper sound driver or kernel module (depending on the Linux distribution you're using). With Red Hat Linux (both Mandrake and Macmillan), you'll have to run the sndconfig application. To run this simple app as root, type /usr/sbin/sndconfig and choose the proper driver and settings for your soundcard.
When dealing with a distribution such as Caldera, you'll have to run the COAS app as root (from the 'k' menu) and load the proper sound module into the kernel.
CREATING EMPTY FILES THE EASY WAY
You often need to create an empty file for any number of reasons. Obviously, you can open your favorite text editor, create an empty file, and then save the file.
Linux, however, gives you a simpler alternative. Using the touch command, you can create an empty file (with user permissions and ownerships) to be used for any purpose. Let's say you need to create an empty file called check. To create the empty check file, enter the command touch check and voila--there's your empty file.
GUI LOGIN OR NO?
One compulsion for many users (a holdover from their Windows world) is the need for a graphical login screen. Linux offers such a beast (in various forms) that can be configured during install or upon running Xconfigurator. But it's best to avoid this temptation.
Why, you ask? The system you're using may find itself victim of a broken X server. Should this occur when your machine is configured to automatically boot to X, you'll have trouble dropping into the console to save yourself from impending doom. To avoid this, configure your system for a console login. With an automatic console login, you're immediately free to solve any sort of X problems that might come up.
LOADABLE KERNEL MODULES
A Loadable Kernel Module (LKM) can be added and removed while the system is running. Modern device drivers are written as LKMs. This form is a significant improvement over statically linked kernel device drivers because it eliminates the need to recompile, relink, and reinstall the kernel every time you modify any of its supported device drivers. Another advantage of LKMs is that they are not subjected to the GPL licensing rules because they are not linked into the kernel image.
STATICALLY LINKED KERNEL DEVICE DRIVERS
Device drivers can be compiled and linked directly into the kernel. This type of driver is called a statically linked device driver. Such a driver is integrated into the kernel image and remains attached to it until the next time the kernel is rebuilt. This is not the preferred technique of writing device drivers because you need to recompile, relink, and reinstall the kernel every time you want to add, remove, or update a device driver. Still, in older versions of Linux, this technique was rather popular.
TAKING CONTROL OF BOOT MESSAGES
When booting a Linux system, you'll notice that a vast number of on-screen messages go flying by. This information can be critical in analyzing your system's boot process. In many instances (and many OSs), the speed at which these messages fly by hampers your ability to gather and retain any valuable information.
Linux, fortunately, has a solution to this problem. After a successful boot, go to a console terminal and run the command dmesg--you'll see thesame messages go flying by. If you'd like to examine them more closely, you can copy the output of the command to a file with the command dmesg > boot.message
Then, all that's left to do is view the newly created file, boot.message, with your favorite text editor.
BURNING CDS WITH LINUX
With blank CD-R discs selling for a buck or less, CD-R drives enable
users to back up their data inexpensively--and what's more, any
computer with a CD-ROM drive can read the burned disc, thanks to the
cross-platform file system that CDs use. You can use this capability to
create a very low-cost, cross-platform sneakernet that enables Linux
users to exchange data files with their Windows- and Mac-using
colleagues. Among Linux CD burners, the most popular is an X
application called X-CD-Roast. However, its interface is rather
confusing. Equally capable, but with a much better interface, is
gcombust. Gcombust looks best in the GNOME desktop environment, but it
will run on any X-capable system that's equipped with the GTK+
Copy and paste this URL into your browser:
CHANGING WINDOW MANAGERS IN GNOME
The Gnome desktop environment allows users to change their window
managers at will and on the fly. Although Gnome prefers to deal with
"session management compliant" window managers, it will play well with
nearly all the available WMs.
To change the current WM in Gnome, simply go to the Control Center,
open the Window Manager section, highlight the WM you wish to switch
to, and click OK. If the WM you wish to switch to is not listed, click
Add and provide the necessary information. (NOTE: This assumes the WM
is properly installed.) When that's finished, you should have no
problem making the switch.
COPYING AND PASTING TEXT IN LINUX CONSOLE
To copy and paste in Linux console, you'll rely on your mouse alone. So
when you install (or configure) a two-button mouse, you'll need to set
it for three-button emulation. In order to copy a block of text in your
console emulator, simply highlight that text with the left mouse
button. To paste, place the cursor where you want to reposition the
text and click the left and right mouse buttons simultaneously--hence
the need for three-button mouse emulation.
If you have a three-button mouse (such as an IntelliMouse or other
wheelmouse) you do not need three-button emulation. With a three-button
mouse, pasting text is accomplished by simply clicking the middle mouse
button (once your text is copied to the clipboard).
CURING THE VIRTUAL DESKTOP BLUES
After installing Red Hat Linux and GNOME, users may complain that their
displays don't show the whole GNOME desktop; they must move the mouse
toward the screen's edge to bring the rest of the desktop into view--
and that's true even if they've configured their window manager to use
only one desktop area. Some users just hate this and give up on Linux
That's too bad, because there's a simple solution: Edit
/etc/X11/XF86Config so that X doesn't use a virtual desktop that's
larger than the display. In this file's Screen section, comment out any
line that begins with Virtual by typing a hash mark [#] at the
beginning of the line. If you don't find a line with a Virtual setting,
look at the Modes line for each color depth. By default, most X servers
automatically set the screen size to the largest size they find in this
line. If the largest resolution listed on the Modes line is greater
than the display's maximum resolution, delete the largest resolution.
For example, if the display's maximum resolution is 1024 x 768, delete
1280 x 1024. Save the file and restart X, and you'll find that the
desktop and screen are now the same size.
When you create your new dial-up account in Linux, make sure you click
User May Activate/Deactivate. By clicking this button you avoid the
issue of having to su to root to bring up your modem. With this option
you can, from console, bring the modem up with /sbin/ifup ppp0 and
bring it down with /sbin/ifdown ppp0 (that is, if your modem is
connected to ppp0).
Want to dual boot between Linux and Windows 9x? Here's a tip that will
save you a great deal of headache. Load Windows first! The Windows boot
loader (this does not include the NT boot loader) is not intelligent
enough to work with any other OS, and since the Linux Loader (LILO) is,
it only makes sense to put it on last.
So to set up a dual-booting machine, follow this tried-and-true
FOR THE GEEKS
1. Partition your hard drive so that you have a FAT partition (for
Windows) taking up only a certain percentage of your hard space (this
percentage will depend on whether the user prefers Linux or Windows).
Once the partition for Windows is set, LEAVE THE REMAINING HARD SPACE
UNPARTITIONED. Linux is smart enough to use all the remaining free
space left after your Windows partition is created.
2. Install Windows 9x.
3. Install Linux and allow for LILO to be placed on the MBR.
FOR THE NON-GEEKS
1. Install Windows.
2. Install Partition Magic and shrink your Windows partition to make
room for Linux.
3. Install Linux and allow for LILO to be placed on the MBR.
Simple enough. When you start up your machine, you will be greeted with
the LILO: boot prompt. At this prompt, either hit [Enter] (to boot
Linux) or type dos followed by [Enter] (to boot Windows).
Red Hat Linux offers up a great errata page from which users can
download, for free of course, the latest security patches and updates
for the Red Hat Linux distribution.
On this site you'll want to take special notice of the Security
Advisories and the Bug Fixes sections. Take caution, however. The Red
Hat Errata site is in a constant state of busy! If you have problems
getting packages, click Red Hat's convenient mirrors link.
Need a Linux application? Browse on over to freshmeat, where you'll
find categorized and searchable indices of the thousands of apps (both
console- and X-based) available for Linux.
Each day the main freshmeat page is updated to reflect new entries
within its software map, so if you want to stay on top of the curve,
this is the place to be!
GRAPHICS WITH THE GIMP
The Gnu Image Manipulation Project (GIMP) is one of the most powerful
open source applications to date. Nearly rivaling Photoshop in its
power and flexibility, the GIMP is an amazing testament to what the
open source community can accomplish.
The GIMP contains nearly all the features that make Photoshop the
industry standard. From layering to plug-ins to original effects and
lighting, the GIMP allows those with a bent for artistic creativity and
design to happily flex their right-hemisphere muscles.
HOST NAME RESOLUTION
To allow your Linux machine to use host names for various networked
machines, you simply have to add the new aliases to your /etc/hosts
file. Let's assume that on your network you have three machines: Sammo
(IP 172.22.1.0), Jackie (IP 172.22.1.1), and Maggie (172.22.1.3), all
of which are part of the .goofydragon net. To allow your machines to
resolve the IP addresses to host names, you'll want to enter them into
your hosts file as such:
172.22.1.0 Sammo.goofydragon Sammo
172.22.1.1 Jackie.goofydragon Jackie
172.22.1.3 Maggie.goofydragon Maggie
You'll have to edit and save this file as root. Once you save this
file, you can test the settings by pinging each alias (e.g., ping
LAPTOP BATTERY MONITORS
Both Gnome and KDE offer monitors for laptop battery states. Both
applets show you the machine's current power source and give both
graphical and textual representations of how much charge your battery
For Gnome: Right-click the panel, select Add Applet, and choose Battery
Charge Monitor from the Monitors menu.
For KDE: From the main menu (k menu), go to the Settings menu and then
to the Laptop submenu. From the Laptop submenu, choose the Battery
Monitor, and it will automatically be placed on your panel.
MOUNTING NFS AT THE COMMAND LINE
Mounting an NFS (Network File System) from the command line is a very
simple process. This tip assumes you have the NFS properly working on
your Linux box and want to mount or unmount either an automounted
partition or a partition that is available but not mounted.
As root, you will mount the file system as you would mount any other
device (only with different flags and mount points). So, type mount -t
nfs DEVICE_TO_BE_MOUNTED DIRECTORY_WHERE_NFS_IS_TO_BE_MOUNTED.
Notice the space between DEVICE_TO_BE_MOUNTED and
DIRECTORY_WHERE_NFS_IS_TO_BE_MOUNTED, as this space is critical. Should
you want to mount an NFS device over a network, you'd simply add the
hostname of the remote device before DEVICE_TO_BE_MOUNTED and separate
it by a colon [:]. So, if you want to mount DEVICE_TO_BE_MOUNTED on the
remote host "Buffy," you'd type:
mount -t nfs Buffy:DEVICE_TO_BE_MOUNTED
as one line.
To unmount these devices you'd simply run:
PROBLEMS WITH OLDER GNOME
If you're using an older version of GNOME, you'll more than likely run
into problems with "core dumping," and your log out button may no
longer work. There are many reasons for this and one simple (but
frustrating) solution. (To check which GNOME version you have, run rpm
-q gnome-core. If the version number that's returned is prior to 1.0.7,
you're running an old one.)
Once you notice this behavior you need to remove the .gnome and .gnome-
desktop directories, as well as the .ICE-authority file in your normal
user account. By removing these you force GNOME to rebuild itself when
the user logs back in. NOTE: This will cause you to have to completely
reconfigure your personal GNOME desktop settings (including your panel
settings), but it's a small price to pay for getting a modicum of
stability back into your system. The best solution--upgrade to the
latest GNOME, of course.
USING TRANSPARENCIES IN CONSOLE WINDOWS
Want to completely impress your friends with the amazing aesthetics of
Linux? Use transparencies for your console windows. A number of
different terminal window emulators handle transparent backgrounds very
well. Of the console emulators, aterm, eterm, and gnome-terminal are
the best at creating this look. With them, adding transparencies is as
simple as calling the application with the tr argument. Each terminal
emulator deals with the argument differently. With either aterm or
eterm, you add the tr flag with a hyphen (-) as in aterm -tr or eterm -
tr. For the gnome-terminal emulator, add transparencies with the plus
symbol (+), as in gnome-terminal +tr.
Aterm takes the transparencies one step further and adds the ability to
tint your windows in various colors (a limited palette, mind you). So,
to add a magenta tint to your transparent aterm window, type (in a
console) aterm -tr -tint magenta.
UPGRADING WITH RPM
The Red Hat Package Manager (RPM) is one of the simplest and most
powerful ways to update a Linux system. Although created by and for Red
Hat Linux, RPM works with a number of distributions and has been worked
into both the Gnome and KDE GUI applications.
The easiest method of upgrading a package is doing it all at once. This
allows for dependency checks on an entire array of packages. Let's say
you want to upgrade your current Gnome package: Create a new directory
called "rpms" and move all of your relevant Gnome .rpm files into this
new directory. Once all your files are moved, cd into this new
directory and run (as root) rpm -Uvh *rpm and, barring dependency
errors, you'll see hash marks fly by as the packages are upgraded.
ADDING SHORTCUTS TO YOUR .PROFILE FILE
The bash command shell automatically executes the .profile file that is located in the user's default directory upon log in (.profile is similar to the autoexec.bat file in DOS). You can add aliases, environment variables, and hard links to your .profile file so that they remain defined permanently.
BASIC INLINE ASSEMBLY
Standard C and C++ enable you to embed inline assembly code in your program. The reserved keyword "asm" takes a quoted string that is a native assembly directive. For example:
is a no-operation assembly directive, and
disables all interrupts. The __asm__ token is identical to asm. You can use __asm__ instead of standard asm if the latter conflicts with other identifiers in your program. Still, it is best to stick to the standard asm keyword whenever possible to ensure compatibility with other compilers and UNIX versions.
BENEFITS OF RECOMPILING YOUR KERNEL
When upgrading your compiler, you may consider recompiling your kernel. The new compiler version may provide better optimizations and bug fixes so the overall performance gain can be significant. Note that this tweak is recommended for experienced users and that you should follow the documentation regarding kernel compilation that is included in your Linux distribution.
DEFINING AN ALIAS
To avoid typing a long command that you use frequently, define an alias for it. For example, the following line:
$ alias chkcode = 'gcc --fsynatx-only test.cxx'
defines an alias chkcode, which is synonymous with the long-winded "gcc --fsynatx-only test.cxx" command.
DYNAMIC ALLOCATION OF STACK MEMORY
The function alloca() allocates memory at runtime. Note, however, that unlike malloc() and calloc(), alloca() allocates memory from the stack, not from the heap. This is advantageous because the allocated memory is automatically released when the function that invoked alloca() exits. In the following example, alloca() is used to create a memory buffer that is automatically released when the function exits:
char * p = (char *) alloca(12); /*allocate 10 bytes*/
strcpy(p, "hello world");
} /*memory is reclaimed automatically*/
Note that alloca() is not defined by ANSI C.
IMPLEMENTING A DEVICE DRIVER AS A SHARED LIBRARY
In addition to statically linked kernel device drivers and loadable kernel modules, you can implement a device driver as a shared library. This is useful when the driver has specific timing requirements or privileges.
LINUX KERNEL CRASH DUMP
The Linux Kernel Crash Dump project attempts to provide a more reliable method of examining system failures after the machine recovers. The project contains kernel and user level code that is designed to save kernel memory information when the system crashes due to a software failure. When the system is rebooted, the saved kernel memory information can be recovered and analyzed to determine the cause of the failure. The documentation, source code, and RPMs of Linux Kernel Crash Dump are now available at: http://oss.sgi.com/projects/lkcd/
PSEUDO CHARACTERS IN NCURSES
Ncurses is an Open Source implementation of the traditional UNIX curses library. It provides a uniform, simple, and high-level interface for controlling the screen and capturing mouse and keyboard input. Ncurses beginners should notice that many of the library's functions take parameters of the type "chtype", rather than plain char. Such a character is also called a "pseudo character" because it is represented as an unsigned long integer, in which the low order eight bits hold the original character and the higher order bits carry additional information, such as video attributes.
SWAPPING A RUNNING TASK FROM THE FOREGROUND INTO THE BACKGROUND
Suppose you've just started to run a long process (a compilation of a huge program, for example) and you forgot to append an ampersand to that command. The task will run in the foreground, which means that you cannot type other commands in the shell prompt until that task finishes. You don't have to abort that task or wait for it to finish. Simply redirect the running task to the background as follows: press trl-Z, then type bg (for background), and press Enter. The command prompt will appear again, and the task will continue to run in the background.
THE KDBG GRAPHICAL DEBUGGER INTERFACE
KDbg is a graphical debugger interface to the GNU gdb debugger. It requires the KDE runtime libraries. Major features of KDbg include inspection of variable values in a concise tree structure, debugging of core dumps, attaching to running processes, conditional breakpoints, and function keys for frequent debugging commands. KDbg supports C and C++ and is an Open Source product. KDbg is available at: http://members.telecom.at/~johsixt/kdbg.html
THE LINUXONE DISTRIBUTION
LinuxOne Lite is a simplified version of Linux that has been especially crafted for first-time users. It is targeted at curious PC enthusiasts, educators, and students who are looking for a Linux version that is easy to set up and use. For example, unlike other distributions, LinuxOne Lite doesn't require that users know how to partition their hard disk. For further info and a free download, see: http://www.linuxone.net
THE RETURN STATUS OF MAIN()
When main() exits, either implicitly or explicitly (that is, by an explicit call to exit() or due to a return statement), it returns to the environment a status code that indicates successful or failed termination. Remember, though, that the return code is truncated to eight bits. Therefore, you should return only values in the range of -127 through 127.
THE TINY COBOL PROJECT
The tiny COBOL project attempts to develop an open source COBOL compiler for Linux that is as close as possible to the COBOL-74 ANSI standard. For more information about this project, visit: http://tiny-cobol.sourceforge.net/index.html
ABIWORD--A FREE WORD PROCESSOR FOR LINUX
AbiWord is a cross-platform word processor with a graphical user
interface that can import Word files. It is available on Linux, UNIX,
Win32, BeOS, and MacOS. AbiWord is an Open Source product distributed
under the GNU GPL terms. You can find more info on AbiWord and
download it from: http://www.abisource.com/
BASH COMMAND PROMPTS
The bash command shell uses different prompts to indicate what your
user privileges are. For example, the default prompt for a root user
is #, whereas a regular user's default prompt is $. You should pay
attention to the bash prompt you get to avoid inadvertent deletion of
files when you're logged in with super user privileges--and, in
particular, after executing the su (switch user) command.
DETECTING LOG ALTERATION
Linux regularly monitors the activity of every user and process and
logs that information. Crackers sometimes try to alter the system logs
to hide their malicious activity. chkwtmp is a software tool that
detects such alterations in wtmp and reports deleted entries in it.
You can find more info on chkwtmp and download it from: http://sunsite.ics.forth.gr/pub/systools/chkwtmp/
Intrusion detection is a relatively new methodology in the science of
system security. In essence, it is based on the use of automated and
intelligent software tools that detect intrusion attempts in real-time
and then react accordingly. An Intrusion Detection System (IDS) can do
one or more of the following when it detects such an attempt:
- Page the system administrator.
- Distribute misinformation. Linux can pretend to be an NT server, for
instance, and mislead the attacker.
- Act according to a set of predefined rules, for example: "terminate
all processes and shut the system down when the attacker has a certain
PLUGGABLE AUTHENTICATION MODULES
Pluggable Authentication Modules (PAM) is a software library that was
specifically designed for configuring authentication on a system. The
PAM library is implemented on Linux and most flavors of Unix. It has a
standard and rather intuitive interface for changing authentication
information (such as a user's password) and authentication checks. You
can read more about the PAM specifications and download the source
code from: http://www.kernel.org/pub/linux/libs/pam
SHELL COMMAND AUTO-COMPLETION
The bash shell command supports autocompletion. To complete the full
name of a file that is located in the current directory, simply type
the first letters of the file that uniquely identify that file. For
example, suppose you have the following three files in the current
and you want to delete the file nightingale. First, type
$ rm nig
and press Tab. Because nightingale is the only file in the current
directory that starts with the characters nig, the command shell
automatically extends what you've just typed to
$ rm nightingale
Now you can press Enter to delete that file.
TCP WRAPPERS AND NETWORK ACCESS CONTROL
TCP Wrappers is one of the most widely used toolkits for enforcing
network access control. If you own a recent Linux distribution
version, you probably already have TCP Wrappers installed on your
system. TCP Wrappers enables you to allow users and hosts to connect
to one another selectively. For example, you can force a user to
connect to a server from a particular machine by forcing him or her to
have a particular IP address. By combining this restriction with the
general username and password protection, you can get a higher level
of system security.
THE ENTROPY POOL
The entropy pool stores random information from external events such
as mouse clicks and keyboard keypresses. These random data can later
be used by programs and scripts that need truly random and
nonreplicable numbers. You can read the random numbers in the entropy
pool from dev/random and dev/urandom devices. Whenever you read from
any of these devices, a hash algorithm first manipulates the random
data in the entropy pool and returns the resultant numbers. The random
driver's code (located at drivers/char/random.c) contains extensive
documentation on the generation of random numbers and the hash
"HELP! I SWITCHED OFF MY SYSTEM WITHOUT SHUTTING DOWN--AND IT SCRAMBLED
Try to refrain from saying "I told you so." OK, they flipped off the
power switch instead of shutting down properly--and some data that
should have been written to disk went to byte heaven. What's probably
happening now is that the user's system is failing the boot-process
filesystem check. Instead of continuing, Linux displays a command
prompt and gives the user all kinds of frightening messages about
horrible things wrong with various partitions.
In most cases, the problems here aren't serious--but they're just
serious enough that the filesystem checking utility (fsck) can't fix
the problems the way it's configured to run during the boot sequence.
Instead, fsck keeps its more radical tools in check until there's a
human being around to confirm the somewhat more drastic measures that
may be needed to fix the problems. Chances are good that the following
procedure will get the system running smoothly again. First, make sure
the damaged partitions are unmounted--don't ever run fsck on a mounted
filesystem! If the problems were found on /dev/hda8, and this partition
contains the native Linux filesystem, type the following: fsck -t ext2
/dev/hda8. This command runs in interactive mode, so you may need to
approve some repairs; chances are good they won't destroy any critical
data. Once you've restarted the system, all should be well. Now you can
say, "Repeat after me: 'I promise to shut down my system properly!'"
"I KNOW THAT FILE'S IN HERE SOMEWHERE!"
You created a file just a few hours ago, and now you can't find it. You
can search for it using text-mode utilities, but there's a GUI way,
thanks to the KDE File Manager (kfm). What's more, it works almost
exactly the way a similar feature works in Microsoft Windows.
To search for a recently created file with kfm, select Find from the
File menu (or press [Ctrl]F). Now you'll see the Kfind dialog box. In
the Named text box, type the filename. In the Look In area, type the
directory you want to search. (Be sure to select Include Subfolders if
you think the file might be buried down there somewhere.) Now, click
Date Modified, select Find All Files Created Or Modified, and select
During The Previous 1 Day.
Finally, do one of the following:
* Click Start Search on the toolbar.
* Choose Start Search from the File menu.
* Press [Ctrl]F.
"THIS EDGE FLIPPING IS DRIVING ME NUTS!"
You'll often hear the above complaint from new users of the Red Hat
Gnome/Enlightenment duo, which is configured by default with edge
flipping enabled. In brief, edge flipping moves the focus to an
adjacent desktop area when the user moves the pointer near the screen's
edge. All too often, users don't actually want to jump to the adjacent
desktop area; they just moved the pointer too close to the screen's
Because this feature can prove very frustrating to new users, you'd be
wise to disable it--or at least introduce a much greater delay before
edge flipping kicks in. You can perform the necessary modifications by
accessing the Gnome Desktop Settings dialog box, choosing the Window
Manager option, and running the configuration manager for
Enlightenment. Just click Desktops and deselect the Enable option in
the Edge Flip Resistance Area. Optionally, you can increase the edge
DEFRAGMENTATION? FORGET IT
Remember what it was like using Windows? Periodically, you'd find that
your hard drive's performance would slow down considerably, and you'd
be in for a time-consuming bout with a defragmentation utility. Your
ex-Windows users are probably wondering when they'll have to go through
this painful experience with their Linux systems, and they might even
start nosing around, looking for a defragmentation utility.
Tell them two things, and right away: first, it's rarely necessary to
defragment a Linux filesystem; second, the defrag utility that's out is
old, unsupported, and dangerous to use. Why isn't defragmentation
necessary? You can thank the ext2 filesystem's advanced design, which
proactively keeps the various segments of files together as much as
possible. Consequently, fragmentation rarely causes the kind of
performance degradation that's commonplace on Windows systems.
DESKTOP PAGERS: NICE, IF YOU'VE GOT LOTS OF RAM
The latest versions of Enlightenment and the KDE window manager offer a
very cool desktop pager, which displays miniature graphical versions of
all your system's desktop areas. For each area, you'll see a miniature
version of the desktop, including the windows that you've positioned
on-screen. By dragging these pager thumbnails, you can move them from
one desktop area to the next. You can even choose an option that mimics
the appearance of what's displayed in the window--as you can imagine,
this looks very cool.
After toying with a desktop pager for a while, though, you'll realize
that this feature consumes system resources with the type of voracity
normally encountered only with window managers or Netscape. I'm running
the KDE desktop pager right now, and it's taken a 10 percent bite out
of my CPU. What's more, it's consuming a whopping 10 MB of RAM.
With the KDE pager, you can cut down the resource consumption
significantly by switching to the plain display mode, but it isn't
anywhere near as nifty. Maybe I will upgrade my system, after all.
DIGITAL PHOTOGRAPHY THANKS TO gPHOTO
Digital cameras are changing photography, especially in business
settings. In real estate, for example, realtors can take a few
snapshots and get that hot new listing up on the Web within a couple
hours. Thanks to gPhoto, a GTK+ application, Linux is now a very good
platform for digital photography--perhaps even an ideal one.
One of the most impressive of all GTK+ applications, gPhoto is a
beautifully designed, easy-to-use program, and it works with a whopping
90 cameras, including popular makes such as Agfa, Kodak, Nikon,
Olympus, and Sony. Note, though, that gPhoto supports image downloads
through a serial port. (USB support is coming to Linux, but it's not
yet fully implemented.) A very cool gPhoto feature is an almost totally
automatic Web gallery generator that creates HTML-encoded
presentations, ready for uploading, that feature pix you've arranged
FIXING A FILE OWNERSHIP MESS
On single-user Linux systems where users know the root password, they
often get themselves into a fix by switching to superuser status and
writing files to their home directories. The result? The files belong
to root, not to the user. After switching back to their ordinary user
account, users won't be able to delete or alter these files and may not
realize why--and sometimes, they won't be able to run programs that
require certain files to have the user's write or execute permissions.
To fix the problem, you could right-click the files individually in the
GNOME or KDE file managers and adjust the ownership settings one-by-
one--but this task could very well take hours. If there was ever a good
argument for switching to the shell, here it is: You can run the chown
command with the -R (recursive) switch, which goes to work on every
last file in the directory (and all associated subdirectories). To
restore the correct file ownership for all the files in /home/suzanne
and associated subdirectories, open a terminal window, switch to
superuser, and type chown -R suzanne /home/suzanne. If you'd like to
fix group ownership settings too, type a period after the username and
type the group name, as in the following example: chown -R
suzanne.users /home/suzanne. Sometimes, using the shell really is
FROM UPPERCASE TO LOWERCASE IN ONE EASY SCRIPT
If you're importing lots of files from Windows, you'll wind up with all
kinds of weird capitalization patterns in filenames--some are all
uppercase, some are lowercase, and some combine the two. Because most
Linux utilities list files in case-sensitive order, such anomalies can
make directory listings look rather random. The following shell script
cures the problem:
$for file in *
name=$(echo $file | tr A-Z a-z)
mv $file $name
To use this shell script, type the first line (for file in *) and press
[Enter]; press [Enter] after typing each subsequent line as well.
GETTING ALL YOUR CLOCKS IN A ROW
Setting the time and date on a Windows or Mac system is simple enough:
You just change the setting, and bingo! You see the correct time and
date. On Linux, it's not quite so simple. Users may try to set the time
and date using various utilities, only to find that their setting
doesn't actually change what's displayed on-screen. Here's why.
A Linux system actually has two clocks: the system clock and the
hardware clock. On Linux, the system clock has absolutely nothing to do
with hardware; it's a kernel utility, and the time it's tracking is
lost when the power is shut off. Still, the system clock is the one
that generates the time and date display that programs use. The
hardware clock, in contrast, is the battery-powered time-keeping clock
that's built into the computer's motherboard; it stores the time while
your computer is switched off. When you start a Linux system, scripts
run utilities that fetch the time and date from the hardware clock and
synchronize this data with the system clock. Got it? Here's where users
get into trouble. Time and date utilities sternly warn users against
changing the system clock while their systems are running programs, and
for good reason: Doing so could bring down time-synchronized programs.
So they follow the time and date utility's advice and change the
hardware clock--but this doesn't affect the on-screen time and date
To keep users from getting frustrated, teach them the proper procedure:
Before logging out, open a terminal window, switch to superuser, and
type hwclock --set --date=newdate, where newdate is a quotation-
enclosed string containing MM/DD/YY HH:MM, as in "05/21/03 12:56."
After setting the hardware clock, users should restart their system.
Voila! Both clocks are now in sync.
GETTING BEYOND THE MPEG HERKY-JERKY
No matter which OS you're running, PCs are far from ideal as a movie-
viewing platform. Still, there are times when nothing short of full-
motion video will do, even if it's visible only in a relatively small
If you've tried running XAnim (an X movie player) or aKtion (a KDE
player that relies on XAnim), you probably weren't impressed with the
utilities' performance when playing MPEG videos. But there's a reason:
The required video codecs can't be readily distributed in GPLed
distributions of Linux due to licensing restrictions. Consequently,
XAnim is running with only half of a brain. And believe me, it shows.
Thanks to David Sweet, you can download a version of XAnim that's fully
equipped with the needed codecs. Performance improves, but as you'll
see, it still isn't anything to write home about. If you need MPEG
movie-playing capabilities to get those essential points across to
colleagues and customers, take a look at the shareware at MpegTV.
You'll get Windows-Media-Player quality, and at $10 per seat, it's not
going to break the bank. The software is free for personal or
GETTING YOUR WINDOWS IN FOCUS
Users migrating from a Windows or Mac OS may find default X window
focus behaviors annoying. For example, the default version of
Enlightenment that shipped with Red Hat 6.0 and 6.1 doesn't
automatically move the focus to new windows when they appear on-screen;
you can't type in the window until you click within it. To change these
settings with Enlightenment, use the Enlightenment configuration editor
(accessible from the GNOME desktop settings utility), click Behavior,
and choose all the options that automatically move the focus to new
windows when they appear on-screen.
IT'S ONLY AS TRUE AS YOUR TYPE
You can get TrueType fonts working on a Linux system, but there might
not be much point in doing so: With X, what you see on-screen is not
what you get at the printer. That's why AbiWord, Gnumeric, and
StarOffice will cheerfully ignore the screen fonts you've installed
unless there's a printer font that exactly matches the screen font.
Why not forget installing TrueType support and convert all those pretty
TrueType fonts into Typ1 format? It's easy, thanks to a very neat
utility called ttf2pt1. After you download and install ttf2pt1, check
out the README files and documentation; you'll find there's a script
that automates the entire conversion process once you've made a few
changes to the default configuration file. Alternatively, you can run
the script on one font at a time. For example, type ttf2pt1 arial.ttf
arial to transform the Arial font into the arial.pfa and arial.afm
files that X applications need to display and print it.
KDE CAN KILL, TOO (GETTING THE SKULL-AND-CROSSBONES POINTER)
One nice thing about Enlightenment is the ease with which you can
dispatch comatose processes--you just right-click the window close box
to throw the equivalent of a kill switch. (This comes in very handy
with Netscape, which goes belly-up with disconcerting frequency.)
As you'll quickly discover with KDE, though, right-clicking a window
close box won't kill it. But there is a deadly trick you can use. Just
press [Ctrl][Alt][Esc], and a skull-and-crossbones pointer will appear
on-screen. With this thing, you can kill anything you click.
MANAGING FILES WITH THE K FILE MANAGER
Even those partial to GNOME will concede that the GNOME File Manager
leaves a great deal to be desired. File Manager's strength lies in its
great drag-and-drop implementation, but users find that they can't use
the standard clipboard commands--[Ctrl]C, [Ctrl]X, and [Ctrl]V--to copy
or move files.
One look at the KDE file manager, called kfm, is enough to see what
you've been missing: It's fully the equal of the best file managers in
the Windows and Mac worlds. In addition, it's loaded with cool
features, including an option that displays Mac-like thumbnails for
graphics files. Does kfm's superiority mean that it's advisable to
switch from GNOME to KDE? That's not necessary, thanks to GNOME's
ability to run KDE applications. If you've installed KDE, you can
choose the K File Manager from the GNOME Main Menu--point to KDE Menus
and choose Home Directory from the pop-up menu. Try it; you'll love it.
(Note that the GNOME File Manager is slated for a major overhaul for
version 2.0. Don't be surprised if the new GNOME utility looks a lot
more like today's kfm.)
RPM BLUES: WHERE OH WHERE DID MY NEW FILES GO?
It's easy to install software with the Red Hat Package Manager (RPM)--
that is, it's easy once you've learned how to invoke the correct
command. Generally, this syntax is rpm -ivh, followed by the package
name. With this skill down, you're ready to install like mad.
It's quite another thing, however, to figure out where all the program
components wound up. Where's the configuration file? Where's the
documentation? Where are the darned icons? If you're wondering where to
find all this stuff, here's a nifty query command that displays a
complete list of all the files that were installed with the package.
rpm -ql package-name
to get an exhaustive listing of information.
For example, rpm -ql enlightenment will display a complete list--a very
lengthy list--of all the files installed with the Enlightenment window
manager. You may prefer to route the output to the printer (rpm -ql
package-name | lpr) or pass the less parameter (rpm -ql | less) so that the
info is more convenient to read.
SCANNING AND LINUX? IT'S SANE, AT LAST
Formerly an oxymoron, the phrase "scanning with Linux" can now be
discussed sensibly, thanks to the SANE project. SANE is essentially a
library of scanner drivers and an API that application authors can use
to communicate with scanning hardware.
Now in a stable version 1.0, SANE supports a wide variety of scanners,
including models made by Agfa, Apple, Canon, Epson, HP, MicroTek,
Nikon, Polaroid, Tamarack, Umax, and more. Unlike the TWAIN interface
common in Windows and Mac worlds, SANE separates the scanning interface
from the code that connects to the scanner--a more logical and elegant
approach. What's more, SANE enables network access to scanners, a
development that could make Linux the platform of choice for scanning-
Several graphics applications are designed to work with SANE; among
them is Xsane, a front-end program for SANE that can also function as a
SHARPEN YOUR MAN-HUNTING SKILLS
Man (manual) pages offer a tremendous repository of knowledge
concerning Linux systems, and they're generally well prepared, thanks
to the standard heading format to which every man page author must
conform. But there's so many of them! Worse, few users know how to
search for man pages in anything like an organized fashion.
Here's a quick rundown. Use apropos to perform a substring search for
man page titles and brief descriptions. For example, type:
to see an on-screen list (automatically routed to less) of all the man
pages that contain the string "time" in their titles or brief
descriptions. If apropos doesn't bring home the big game, you can use
the man command with the -K switch to search through the full text of
all man pages accessible on the system.
Because many man pages pertain to system calls, library calls, and
other arcane things that probably don't interest the average user, you
may wish to restrict the search to utilities or executables by
specifying the appropriate section number (1 and 8, respectively).
For example, the command
man 1 -K file
retrieves a list of all the man pages in Section 1 (utilities) that
mention the word "file." You'll see a prompt asking if you'd like to
see the first file that contains this word. Type y to view the file, n
to skip to the next file (if any), or q to quit.
TAKE A LITTLE PEEK AT /ETC/SERVICES--YOU'LL SLEEP BETTER
One of the not-so-nice things about too many Linux distributions is
their propensity to let naive users install all kinds of things that
they shouldn't really be running, such as telnet, ftp, finger, and
other easily exploited services. Sure, users could opt for the
"Workstation" install, which is supposed to protect beginners from the
dangers of a poorly configured server installation--but that's not what
most beginners will choose if left to their own devices. The typical
attitude is "Hey, I want it all!" So guess what? They're running
sendmail, ftp (and of course, it's the older version with the wide-open
security hole), and who knows what else. Make a friendly visit to every
Linux user's office, log on as root, and have a look at /etc/services--
and put that nice, big hash mark [#] in front of every service that the
user doesn't really need to run.
THE CAPS LOCK ATTACK, OR, HERE'S ONE PROBLEM THAT'S EASY TO SOLVE
The anguished voice on the other end of the phone says, "I can't log
in. I've tried everything. I know my password. I even know my root
password. The system won't accept either one! I can't get to my work!
You got me into all this Linux stuff and now look, I'm dead!"
Sounds serious, right? Chances are it's really very simple. Tell the
anguished user, "Take a look at your keyboard. Do you see a little
light next to the Caps Lock indicator? Ah, I thought so. Press the Caps
Lock key, and try again."
It's amazing how many users make this mistake. Just bear in mind that
as a UNIX derivative, Linux is generally case-sensitive. It's often
safe to assume that capitalization matters, unless you can prove that's
not the case.
Reflections on Multithreading
by Danny Kalev
While it is true that a multithreaded app is usually more
responsive than a single-threaded one, programmers new to
multithreading are often misled into thinking that a multithreaded
app executes faster than a single-threaded one. This is not always
the case, however. On a machine that has a single CPU, adding
threads will usually increase the overall processing time. This is
because the CPU instructions required to perform the scheduling and
switching between threads add more overhead in terms of execution
speed and application size.
Of course, in interactive applications such as word processing, Web
browsers, and graphical editors, multithreading is unavoidable;
otherwise, the application may become annoyingly nonresponsive.
However, processes that always run in the background usually
execute faster as multithreaded applications on machines that have
a single CPU. In some cases, even interactive applications can do
well without threads if they run on a machine that has a single
CPU. For instance, a text-based interactive calculator that accepts
an expression and displays the result doesn't necessarily have to
split the user interface logic and the number-crunching task into
two separate threads. The time wasted in performing the context
switch between those threads is probably longer than the time
needed for parsing the expression and computing the result.
Likewise, for applications that only run in the background, the use
of threads may not be necessary.
Only machines that have two or more processors offer true parallel
processing. In this case, the overall processing time can be
reduced by allocating a distinct processor to each thread.
Web Browsers for Linux
by Danny Kalev
Currently, there are at least four Web browsers that run on Linux.
This column is a quick overview of those browsers and their
major advantages and weaknesses.
- Netscape -
Netscape is included with most Linux distributions. The
latest version, Communicator 4.7, supports the latest standards,
including HTML 4.0, XML, and CSS. However, its resource-gluttony and
instability are two noticeable weaknesses. For acceptable
performance, you need at least 64Mb of RAM and a Pentium 233 or
higher. Netscape still crashes occasionally, although recent
versions have shown continuous improvements in this respect. The
latest version is available from http://www.netscape.com.
Pros: fully-featured, supports the latest standards, free, includes
a mail client.
Cons: bulky, resource hungry, still unstable.
- Mozilla -
The Mozilla project has been working, over the past couple of
years, on an Open Source Web browser. Originally, Mozilla relied on
Netscape's legacy browsing engine, but later it was abandoned in
favor of an entirely new engine written from scratch. Thus, Mozilla
is independent of Netscape. M13, the latest release, is still an
alpha version, yet fully-featured. Future releases, however, will
add missing functionality. The latest binaries and source files are
available from http://www.mozilla.org.
Pros: free, open source, graphical, written from scratch; includes
a mail client.
Cons: bulky, still unstable, not fully-featured.
- Opera -
Opera offers a small, fast, and efficient browser that performs
satisfactorily, even on old PCs with vintage processors and little
memory. The latest release, Opera for Linux 4.0a, is still an alpha
version. While it offers an interesting alternative to the more
cumbersome mainstream browsers, it's not free: a registered copy
costs $35. Still, Opera's creators claim that the product offers
incontestable qualities in terms of compactness and speed. You can
download a 30-day trial version from http://www.opera.com and
decide whether it's worth the price.
Pros: small, fast, can run on old PCs.
Cons: costs money, still a preview version.
- Lynx -
Lynx, a text-based Web browser, is included with most Linux
distributions. What's the use of an age-old browser that displays
only text without graphics? For some folks, this is a plus -- many
sites are replete with ads, banners, and animation that take
forever to download and consume precious bandwidth and connection
time. Lynx filters out non-textual contents such as applets,
images, animation, and audio files, thereby significantly
decreasing download time.
Pros: free, small, fast, and secure.
Cons: displays only text, command line operated.