Craig Younkins' Blog

Whenever I burn a CD from an ISO, I md5sum the CD to confirm the data was written correctly. Using the beauty of Linux, I can md5sum the cdrom device directly using "md5sum /dev/cdrom".

One day I was trying to burn OpenSolaris 2008.11 to check out the awesomeness of ZFS. After I burned the disk using Brasero, I tried to md5sum it. I was greeted with a rather strange error: "md5sum: /dev/cdrom: Input/output error". Input/output error? Is my drive going bad? I presumed it was the media. I put in another CD of the same brand and tried again. Nope. The batch of media was pretty old, so I decided to try another brand/batch. Maybe it's my drive? Five coasters later...

At this point I'm starting to think this is a software issue. Was there an update in 8.10 that made this not work? No, it worked on other disks. Googling, I came to this page at BigAdmin which describes the symptoms perfectly.

As it turns out, Brasero was burning the ISO using track-at-once. The problem with this is, as quoted from BigAdmin:

"the last block may be confused with the lead out area, and some drives will not read it properly. Thus your MD5 checksums will fail. You can pad the last blocks using the -pad option of cdrecord, but your checksums still might not match as you have added additional data to the CD that was not present in the original ISO image."

The solution? Make sure to set the record mode to disc-at-once (session-at-once may also work) in your CD burning software. I simply could not find this setting in Brasero, so I installed K3B and found it easily under "Writing Mode". Lesson learned.

Has this ever happened to you? Leave a comment!

Quite a while ago at the Ubuntu MD Team's release party for Intrepid Ibex, Ron Swift showed the group something really cool: The first issue of an educational comic about Linux called "Hackett and Bankwell." The first issue covers the adventures of characters Woody Hackett (tux) and Jerome Bankwell as they help a documentary production studio install and use Ubuntu. The thing is... it's really not dorky. No, seriously! Check out the first issue in PDF form here.

Hackett and Bankwell Worldwide, related characters, names, and all related indicia are trademarks and copyrights of Intarcorp LTD, licensed by Intarcorp LTD. Image copyright Intarcorp LTD.

After seeing Lifehacker blog about a number of Ubuntu speedups, I decided to test some of them to see their actual effectiveness.

The test machine was a Lenovo T61 with a Core 2 Duo T7500 @ 2.2 ghz and 3GB RAM. All boot times are from the grub menu (started when I pressed enter to start the boot) to the appearance of the login screen. I started with a completely fresh installation of Ubuntu 8.10 which I updated and rebooted 3 times. The default settings are "concurrency=none" in /etc/init.d/rc, but I'm unsure of the default readahead settings. It's possible Ubuntu tries to create a profile after installation, but I have no proof of that, so I assume there is no profile.

The results:

• No modifications (concurrency=none, no readahead profile) - 29.8 sec
• Concurrency=shell, no readahead profile - 29.2 sec
• Concurrency=shell, readahead profile - 28.7 sec
• Concurrency=none, rebuilt readahead profile - 29.2 sec

Also keep in mind all timings are subject to human error. My conclusion is that there are no notable improvements from implementing these tweaks, even with a dual core processor.

Here is my full action log:

• Install 8.10
• Update
• Restart x 2
  
• Restart, timed boot - 30.0 sec
• Restart, timed boot - 29.6 sec
• Set concurrency=shell in /etc/init.d/rc
• Restart, timed boot - 29.9 sec
• Restart, timed boot - 29.1 sec
• Restart, added "profile" to end of grub line
• Timed boot for profile creation - 1 min, 27.7 sec (This is normal)
• Restart, timed boot - 28.7 sec
• Restart, timed boot - 27.9 sec
• Restart, timed boot - 29.6 sec
• Set concurrency=none in /etc/init.d/rc
• Restart, added "profile" to end of grub line
• Timed boot for profile creation - 1 min, 29.1 sec (This is normal)
• Restart, timed boot - 29.3 sec
• Restart, timed boot - 29.1 sec

New with Ubuntu 8.10 "Intrepid Ibex" is the ability to create a bootable USB flash drive with a persistent filesystem.


I compared the time to start from when I pressed enter for "Try Ubuntu" until the desktop had loaded with the panel, icons, and wallpaper. Here's what I found:

USB flash drive: 1:44
CD: 2:40

That's a pretty significant improvement in speed! Also, since there's no CD to spin up, anything requiring data off the drive occurs with much less lag. Of course, your results may vary. Transfer speeds on flash drives do vary. I found that my Cruzer Micro 2GB was much faster than a PNY Attache 1GB.

This is so great, one of my flash drives will probably be dedicated to it. :-)