The website ‘Linux Links’ has posted their selection of the top 20 free Linux books. Worth a look in case there’s something you weren’t aware of 
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Monthly Archive for April, 2009
Page 2 of 2
I’m scripting some sys admin tasks in Debian which require the installation of packages like Postfix. I don’t want it to prompt me with questions, so I knew I had to set the priority to something higher for this specific package (i.e. temporarily). There doesn’t appear to be a way to pass this to an apt-get command (which was a little disappointing) but debconf can set it system wide under /var/cache/debconf/config.dat, but that’s, well, ugly.
Turns out there’s an environment variable you can set to achieve what I want, DEBIAN_PRIORITY. So exporting this variable and unsetting it post install will do the trick, but I still think apt-get -p critical install postfix would be better
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Since getting Debian up and running on my D-Link DNS-323 NAS, I’ve blogged about the slowness of secure copy to the device. This is due to the CPU maxing out when de-crypting. Peter Lieverdink suggested I might get better performance using a different algorithm such as blowfish.
I thought I’d give it a shot and see. The default order for encryption for SSH2 is aes128-cbc, 3des-cbc, blowfish-cbc, cast128-cbc, arcfour128, arcfour256, arcfour, aes192-cbc, aes256-cbc, aes128-ctr, aes192-ctr, aes256-ctr. I set up a transfer of a 100MB uncompressed tarball using each of these protocols to see which one provided the best performance. For comparison purposes, I copied the same 100MB file over CIFS, NFS and plain FTP (but keep in mind that with scp there are a few seconds of key negotiation which the others don’t have). Here are the results.
Continue reading ‘Speed test on the DNS-323′
The other day I blogged about installing Debian on the D-Link DNS-323 NAS box, and it is really awesome (yay!). There were a few things missing however, most importantly for me was the fan to help cool the unit down. Well Martin Michlmayr built a new 2.6.29 kernel for me with a driver for the fan. THANKS!
I’ve a kernel for you now.
Edit the file /etc/apt/sources.list and add the following line:
deb http://people.debian.org/~tbm/orion lenny main
Now you can install the new kernel:
apt-get update
apt-get install linux-image-2.6.29-1-orion5xAfter a reboot, you can control the fan this way:
echo 0 > /sys/class/hwmon/hwmon1/device/pwm1 # turn it off
echo 255 > /sys/class/hwmon/hwmon1/device/pwm1 # turn it to full speedAny values between 0 and 255 will work.
This kernel also includes some performance patches from Marvell, so you
might see some performance increases too.
The new kernel works a treat, and indeed the fan does work. On my unit the device is under hwmon0, not hwmon1, but apart from that everything went smoothly. It will depend on your hard drive of course and how hot it runs, I just put mine on full-ball which isn’t too noisy (I think). AFAIK temperature sensing is not working yet, but if it was I could write a script to adjust the fan speed on the fly. For now I’m happy to just keep it at a comfortable level and keep an eye on the temps. Certainly without any fan working it was running too hot, so some fan is better than none at all!
I have yet to test any performance increase in the network performance, however I can confirm that scp is exactly the same slow speed at 2.x MB/sec and now I know why – thanks to top I can see scp and ssh maxing out the CPU. So it appears the unit just can’t decrypt fast enough, hence the bottleneck. I have installed nfs-kernel-server and will try this to see if performance is improved (I always use scp or rsync, so it might be good to have some speed increase!).
Thanks Martin!
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