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Rolf's tech blog

This is my tech blog. I'll document all kinds of computer related activties, which may be useful for myself in the future or even useful for others. The blog entries may refer to specific topics, which are documented in more detail here.


Pi running on F2FS

SD cards show to be vulnerable media when using as Raspberry Pi storage: whenever there's a powerfailure (e.g. when I remove the power adapter from the outlet) there's a considerable risk of running into filesystem corruptions (I think this is especially the case when I'm removing the power during write access). Today the SD card even showed to be broken, beyond repair.

So today I decided to get F2FS (Flash Friendly File System) running on my Pi. It took quite some effort to make it happen:

  • I rebuilt a Pi kernel with F2FS support
  • I rebuilt a Fedora kernel with F2FS support on my PC to build an F2FS image for the Pi
  • I rebuilt F2FS-tools because Fedora's 1.0.0 release wasn't building a Filesystem that de 3.9 kernel understood; had to build 1.1.0

After that all went really smooth. A few things should be noted thogh:

  • A standard Raspbian image needs 1.7 GB on ext4 and 2.3 GB on F2FS. This is probably caused by (default) allocation units, I need to look into that later.
  • There's no f2fs.fsck yet, so checking the FS during boot is not an option
  • No swapfile is possible on F2FS


My MiFi has arrived!

After coming home from our skiing our holiday, I was fed up with the nine hours drive without internet because data roaming is too expensive. So I ordered a Huawei e355 MiFi (mobile Wifi) which allows us to use a German or Swiss SIM for cheap internet connectivity during the drive! Now I only have to buy a German SIM (like Aldi Talk) for the drive and a Swiss SIM (Like Swisscom Natel) for the chalet to actually be online.

Of course I could just replace the SIM of my phone by a German or Swiss one to achieve this, but that would imply that I'm no longer reachable on my own Phone number. By means of the MiFi both my wife and me are online, while being fully reachable as well.

To test the MiFi I bought a 10 Euro *Bliep SIM. After setting up the right APN, all works like a charm! The next step is buy a German SIM right across the border (we live nearby) and we ready for the next long trip to Switzerland.

Of course I'm aware of alternatives like Droam (, but … well … I'd like to have my own MiFi. And I think In the end it will be cheaper.


Documented AirPrint gateway for Apple iOS devices

Today I finally finished my 'AirPrint gateway for Apple iOS devices' page. It wasn't all that hard, just had to flash a fresh SD card and reinstall Airprint step by step. Now the 'Mail gateway' page is left to document.

No more 'BUG: soft lockup' situtations

Since I stopped using X on the C60M-I 'server' the awkward messaged BUG: soft lockup - CPU#… stuck for …s have gone and the machine is stable again. I'm also running a Windows 7 VM in KVM on this machine (yeah, I know, It's not the most powerful CPU), so shear load is not the cause of the instability.


CPU stuck during Firefox usage

To my surprise I had my X hang during Firefox usage. First some video corruption, some kind of recovery and than a hang. I found messages in syslog stating something like 'Bug: soft lockup - CPU#2 stuck for 22s! [Xorg:10022]', and an the end I was forced to do a reboot. After that, none of the messages were in the syslog, seems like data loss.

The Motherboard is a Asus C60M-I, and I'm running Fedora 17 x86_64. The PC normally isn't used via X since it's only meant for NAS like purposes and firewalling. Could be an ATI video driver issue?

Google shows me lots of “BUG: soft lockup - CPU#… stuck for …s” problems, but no clear answer. So I'll stop using X on this PC, see if the problems stay away.


Multipurpose Raspberry Pi

Today I installed a Raspberry Pi at the office to handle all kinds of network related actities:


Ingress traffic shaping using veth devices

Having a router that routes traffic between the internet and all my PC's, phones, etc allows to do great traffic shaping by using the HTB qdisc in both directions. However if your router is a PC itself, it's impossible to use HTB to do traffic shaping on it's own inbound network traffic. I came up with a funny solution: use Virtual Ethernet devices to introduce an additional bridge 'in front of' your PC.

More info can be found here

iptables with bridging: NAT broken?

I had this idea of doing traffic shaping bij adding a single NIC router (E.g. Raspberry Pi) in an existing network:

  • This router does it's own DHCP, advertising itself as the gateway.
  • Then all pachets are forwarded to the real gateway.
  • Which requires NAT, so the return packets are also forwarded to this intermediate router
  • In the process of forwarding the packets the intermediate router has the opportunity to do some traffic shaping.

After struggling with this for quite a while with the fact that the returnpackets arrived at the routerm but got lost, it became clear that disabling iptables on bridging was the solution. See also


Tech blog

Today I started a tech blog. It's a kind of experiment, I'm not sure if it'll really help me, but I expect it will. Just because I'm familiar with it, I'm using dokuwiki as a tool to serve my blog. It's not what wiki's are meant for, so I'll find out if this works.

start.txt · Last modified: 2013/06/09 19:49 by rolf