LINUX NEWS
RESOURCES & LINKS FROM BRAINBUZZ.COM
Thursday, April 26, 2001
Read By 5,000 Linux Enthusiasts Weekly!TABLE OF CONTENTS
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 Station3) Linux Resources
Application Directories
Using Stunnel to Secure IMAP Connections
More Honeynets
Building A Better Gaming Machine
Dynamic IPTables Firewalls4) 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 responsive.
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:
http://www.ertw.com/~sean/newsletter/March+8%2C+2001
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 server!
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 command:
nice mycommand
(check out the man pages for “nice” and “renice” for more usage)
That’s the process scheduling system in a nutshell. Those interested in the dirty details can check out
http://www.oreilly.com/catalog/linuxkernel/chapter/ch10.html
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:
http://boards.brainbuzz.com/boards/vbt.asp?b
Long live the Penguin,
Sean mailto:swalberg@brainbuzz.com
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 load.
http://www.ximian.com/
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.
http://itresources.brainbuzz.com/tutorials/tutorial.asp?t=S1TU1248
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!
http://www.zdnet.com/zdnn/stories/news/0,4586,2710728,00.html?chkpt
01
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.
http://www.linuxdevices.com/articles/AT3239582376.html
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?
http://freshmeat.net/articles/view/247/
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.
http://members.home.net/beldridg/imaps.htm
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.
http://project.honeynet.org/papers/honeynet/
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 upgrade.
http://linux.com/newsitem.phtml?sid&&aid=810
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.”
http://www-106.ibm.com/developerworks/linux/library/l-fw/index.html?dwzone=linux
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.
http://sourceforge.net/projects/foxserv/
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