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This month's answers created by:

[ Anderson Silva, Steve 'Ashcrow' Milner, Amit Kumar Saha, Ben Okopnik, Kapil Hari Paranjape, Karl-Heinz Herrmann, René Pfeiffer, Mulyadi Santosa, Neil Youngman, Paul Sephton, Raj Shekhar, Rick Moen, Suramya Tomar, Thomas Adam ]
...and you, our readers!

Our Mailbag

Multi-process CPU Benchmark

Deividson Okopnik [deivid.okop at gmail.com]

Thu, 5 Nov 2009 15:37:56 -0300

Hello everyone!

Im looking for a multi-process CPU benchmark to be run on linux (CLI is even better), as I need to test how well a kerrighed cluster is running. Anyone know of any of those programs?

Thanks Deividson

[ Thread continues here (4 messages/2.54kB) ]

HOWTO kill client when Xserver dies?

=?ISO-8859-2?Q?Petr_Vav=F8inec?= [pvavrinec at snop.cz]

Tue, 15 Dec 2009 10:44:36 +0100

Hello gurus,

I run a diskless, keyboard-less pc that boots into X11 (just plain twm as a window manager). The X clients I run remotedly, on a "database server". When someone switches off the Xserver PC (i.e. flips that big red switch), the X clients aren't killed - they remain on the "database server" forever (or at least 24 hours, that's for me the same as "forever"). Is there something that I could to to force them to die automa[t|g]ically?

Thanks in advance, Petr

[ Thread continues here (5 messages/5.55kB) ]

Hevea error

Amit Saha [amitsaha.in at gmail.com]

Mon, 7 Dec 2009 13:08:58 +0530

Hello TAG:

I know there are some 'hevea' users here. Could you help ? I am trying to convert this TeX article of mine into HTML and I run into:

Giving up command: \text
Giving up command: \@hevea@circ
./octave-p2.tex:227: Error while reading LaTeX:
       End of file in \mbox argument

The relevant lines in my LaTex file are:

226 \begin{align*}
227         Minimize        f(x) = c^\text{T}x \\
228         s.t.    Ax = b, x \geq 0 \\
229         where           b \geq 0
230 \end{align*}

What could be the problem ? I am using version 1.10 from Ubuntu repository.

Thanks a lot!

Best Regards, Amit

Journal: http://amitksaha.wordpress.com,
-blog: http://twitter.com/amitsaha

[ Thread continues here (3 messages/4.48kB) ]

Ubuntu boot problems

Ben Okopnik [ben at linuxgazette.net]

Mon, 16 Nov 2009 18:49:55 -0500

Earlier today, I had a problem with my almost-brand-new Ubuntu 9.10 install: my netbook suddenly stopped booting. Going into "rescue" mode showed that it was failing to mount the root device - to be precise, it couldn't mount /dev/disk/by-uuid/cd4efbe9-9731-40a5-9878-06deff19af06 (normally, a link to "/dev/sda1") on '/'. When the system finally timed out and dropped me into the "initramfs" environment/prompt, I did an "ls" of /dev/disk/by-uuid - which showed that the link didn't exist. Yoiks... had my hard drive failed???

I was quickly comforted by the existence of another device in there, one that pointed to /dev/sda5, a swap partition on the same drive, but that could still have meant damage to the partition table. I tried a few things, none of which worked (i.e., rebooting the system would always bring me back to the same point)... until I decided to create the appropriate symlink in the above directory - i.e.,

cd /dev/disk/by-uuid
ln -s ../../sda1 cd4efbe9-9731-40a5-9878-06deff19af06

and exit "initramfs". The system locked up when it tried to boot further, but when I rebooted, it gave me a login console; I remounted '/' as 'read/write', then ran "dpkg-reconfigure -plow ubuntu-desktop", the "one-size-fits-all" solution for Ubuntu "GUI fails to start" problems, and the problem was over.

NOW, Cometh The REALLY Big Problem.

1) What would cause a device in /dev/disk/by-uuid to disappear? Frankly, the fact that it did scares the bejeebers out of me. That shouldn't happen randomly - and the only system-related stuff that I did this morning was installing a few packages (several flavors of window manager so I could experiment with the Ubuntu WM switcher.) I had also rebooted the system a number of times this morning (shutting it down so I could take it off the boat and to my favorite coffee shop, etc.) so I knew that it was fine up until then.

2) Why in the hell did changing anything in the "initramfs" environment - i.e., creating that symlink - actually affect anything? Isn't "initramfs", as indicated by the 'ram' part, purely temporary?

3) What would be an actual solution to this kind of thing? My approach was based on knowing about the boot process, etc., but it was part guesswork, part magical hand-waving, and a huge amount of luck. I still don't know what really happened, or what actually fixed the problem.

I'd be grateful for any insights offered.

* Ben Okopnik * Editor-in-Chief, Linux Gazette * http://LinuxGazette.NET *

[ Thread continues here (12 messages/27.96kB) ]

Industrial PC booting issues

=?ISO-8859-2?Q?Petr_Vav=F8inec?= [pvavrinec at snop.cz]

Thu, 12 Nov 2009 11:35:44 +0100

Allmighty TAG!

first, sorry for a longish post. I'm almost at my wit's end.

I have an industrial PC, equipped with a touch screen and "VIA Nehemiah" CPU (that behaves like i386). The PC has no fan, no keyboard, no harddisk, nor flash drive - only ethernet card. It boots via PXE from my database server. The /proc/meminfo on the PC says, that the PC has MemTotal: 452060 kB. I'm booting the "thinstation" (http://thinstation.sourceforge.net) with kernel The PC uses ramdisk. I boot Xorg with twm window manager. Then I start client of the "Opera" browser on my database server and "-display" it on the X server on the PC. This setup has worked flawlessly for a couple of months.

Then my end-users came with complains, that the PC doesn't boot anymore after flipping the mains switch. For the moment, I have found following:

1. The PC sometimes doesn't boot at all. The boot process stops with the message:

   Uncompressing linux... OK, booting the kernel.

...and that's all. Usually, when I switch the PC again off and on, it boots OK, I mean I don't change anything, just flip that big button.

2. When it really does boot all the way into X, the opera browser isn't able to start properly. I tried to investigate further the matter. I modified the setup, now I'm booting only into X+twm. This works.

Now I tried to run following test on my database server:

    xlogo -display <ip_address_of_the_pc>:0

This works, the X logo is displayed on the screen of the PC.

Now I tried this test on the database server:

    xterm -display <ip_address_of_the_pc>:0

Result is this error message on the client side (i.e. on the database server):

   xterm:  fatal IO error 104 (Connection reset by peer) or KillClient 
on X server ""

...and the X server on the PC is really killed (I can't find him anymore in the process list on the PC).

This is, what I have found in the /var/log/boot.log on the PC:

------------ /var/log/boot.log starts here ----------------------------
X connection to :0.0 broken (explicit kill or server shutdown).
/etc/init.d/twm: /etc/init.d/twm: 184: xwChoice: not found
twm:  unable to open display ":0.0"
------------ /var/log/boot.log ends here ------------------------------

...and this is from /var/log/messages on the PC:

[ ... ]

[ Thread continues here (11 messages/16.28kB) ]

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Published in Issue 170 of Linux Gazette, January 2010