2001 04 26

                    LINUX NEWS
             Thursday, April 26, 2001
       Read By 5,000 Linux Enthusiasts Weekly!


1) Sean’s Notes

2) Linux News

Ximian GNOME 1.4 is Out!
Perl: The Complete Reference (2ed)
IBM Takes to the Street
Linux as a Radio Station

3) Linux Resources

Application Directories
Using Stunnel to Secure IMAP Connections
More Honeynets
Building A Better Gaming Machine
Dynamic IPTables Firewalls

4) App o’ the week

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1) Sean's Notes
I was browsing around the web the other day, and came across
a helpful hint that should make your X-Windows session more

renice -10 -p PIDOF_X

where PIDOF_X is the processid of your X-Windows server.
Recall from the March 8th issue of this newsletter, each task
in the system is given a processid:


Each processid also has a "nice level" attached to it, a
value of -20 to +20 (or +19, depending on who you ask), with
-20 being the highest priority.  So, a process is considered
"nice" if it doesn't want too much of the CPU.  What we're
doing in the above command is giving the X process a higher
priority. Note that you probably don't want to do this on a

UNIX is a pre-emptive multitasking operating system.
"Pre-emptive" means that processes don't have to be aware
they're running alongside others -- the operating system will
dole out (and take away) their use of the CPU as it sees fit.
Contrast this with a non pre-emptive system like Windows 3.1,
where the application had to relinquish control of the CPU
when it was done.

So, the Linux scheduler (part of the kernel) works hard at
giving CPU time to processes, timing them, and then moving on.
But how does it choose which process to put on the burner?
Enter priorities.

In a nutshell, each process gets a priority based on the nice
level and some other factors, such as how long it's been
sitting idle.  This is all mashed into a number between 0-99,
and is considered to be the process's priority.  The kernel
looks in the top priority bin to see if any processes are in
there.  If so, they get the CPU for a time slice.  When it's
done with it's slice, the process goes to the end of the queue
(within the same priority).  So, as long as a process with a
higher priority is ready for the CPU, lower ones won't execute.

As I said above, the priority depends on other factors.  The
kernel is tuned so that a process can't hog the CPU -- if it
stays on the burner too long, its priority is slowly
decremented until the system is normal again.

The next thing to remember is that the computer is super fast
compared to the IO system (including the users!).  A process
may need to access the disk or other input device.  While
it's waiting for the data, the kernel marks it as waiting for
IO and puts it to sleep.  While in this state, it doesn't get
the CPU.  Once the data arrives, this process will pre-empt a
lower priority process that is on the CPU, if applicable.  On
most systems, this is enough to keep the system usable.  Put a
few CPU bound processes in, and that's when the administrator
is going to have to step in with the renice command.

renice isn't just for administrators, users can use it too,
subject to some restrictions.  A normal user can only assign
priorities between 0 and 20 -- negative numbers aren't allowed.
Furthermore, you can only increase the nice level, you can't
decrease it. You can also start the process at a nice level of
10 (most processes by default are 9 or less) with the nice

nice mycommand

(check out the man pages for "nice" and "renice" for more

That's the process scheduling system in a nutshell.  Those
interested in the dirty details can check out


sched_setscheduler manpage, and the pages in the see also
section /usr/src/linux/kernel/sched.c  (it is well commented).

Don't forget about the Brainbuzz Linux News Board, where you
can post your comments about the newsletter and talk with
other readers:


Long live the Penguin,


2) Linux News

Ximian GNOME 1.4 is Out!
Ximian, formerly Helix Code, are the guys that put together
a great distribution of GNOME related stuff. Their latest
release incorporates GNOME 1.4 and Mozilla. Installation is
super easy, but at the moment is pretty slow due to the huge


Perl: The Complete Reference (2ed)
If you're looking for a book that will teach you PERL, and
then act as a great reference, this is for you. Starting
off with the basics, it takes you through the language,
with plenty of examples to help you along.


IBM Takes to the Street
IBM's Peace, Love, and Linux slogan which was slapped on
billboards has graced the pavement of San Francisco. You'd
think geeky stuff like this would go over well, but some
key people weren't impressed. At least they were able to
wash it off!


Linux as a Radio Station
In the "fascinating, but completely useless category", Real
Time Linux has been used to turn a Linux box into a radio
transmitter. That's right -- it toggles voltages on the
parallel cable to act as an antenna. This article explains
what RTL is, and how it differs from normal Linux operation.


3) Linux Resources

Application Directories
This Freshmeat editorial asks why the current filesystem
is laid out the way it is. Windows 3.1 had something going
for it, as most everything was stored in its own directory.
In UNIX, though, all the binaries are crammed into a handful
of directories. When package management doesn't cut it, what
do you do?


Using Stunnel to Secure IMAP Connections
Stunnel is a utility that allows you to tunnel protocols
over SSL. In this example, IMAP is the target. Various
methods of doing it are explained, depending on what your
client can support.


More Honeynets
The folks at the Honeynet project have updated their "Know
Your Enemy" series of papers. This time, a detailed analysis
of the implementation of their Honeynets is presented. For
those that were wondering how they prevent crackers from
doing serious damage to other sites after cracking a
honeypot, this question has been answered.


Building A Better Gaming Machine
Building a better gaming machine is different from building
that perfect web server. There are different bottlenecks to
overcome, and different items to add on. This article walks
through the things you'll want to keep in mind for that next


Dynamic IPTables Firewalls
"Firewalls are good and fun, but what do you do when you
need to make rapid, complex changes to your firewall rules?
Easy. Use Daniel Robbins' dynamic firewall scripts that are
demonstrated in this article. You can use these scripts to
increase your network security and responsiveness, and to
inspire your own creative designs."


4) App o' the week
This week's app isn't for Linux, it's for Windows.  Crazy,
you say? Probably. Foxserv is an installer for the Windows
versions of Apache/PHP/MySQL. If you can't spare a box for
Linux, but need a great web development platform, give this
a shot.


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