OpenWRT and the TP Link WR841N

The WR841N has no USB port on the case but USB is available on the PCB if you can solder and don't mind a bit of work to get it going. I had a problem getting the USB connection I made to the WR841N PCB working. I tried various flavours of patched firmware with no success, however on the OpenWRT Forum someone mentioned just use the TP Link MR3420 firmware. This I did and it worked straight away, smiles all round. I then got extroot to a 2GB memory stick working, this allowed me to add more packages. I added a USB hub to allow the connection of a USB webcam.

Getting the Arnova 9 G2 into Recovery Mode

To enter Arnova 9 G2 recovery mode, press the esc button then using a paperclip press the recessed reset button (its located on the top edge of the Arnova). It will now enter the recovery mode. A rooted verion of the Arnova9G2 firmware is available here. Plug in the micro USB to your computer I have Windows 7 installed. After a time it should show in the Windows 7 Device Manager with a RK29? Device, ignore the ? Now right click on the RK29? entry and select update driver. Then choose the browse option and navigate to the folder where you unzipped the file you downloaded previously, usually the Downloads folder, "arnova G2_full_root_rom_V1.0_arctools\drivers\32bit\win7" that contains the driver for your flavour of Windows 7, mine was the 32 bit driver. Once Windows has indicated that the driver install was successful you can now run the firmware update tool RK29update.exe located in the root of the arnova G2_full_root_rom_V1.0_arctools folder.

Update
I found that after the update I couldn't enter recovery mode it appears to be as described on Recovery Mode

OpenWRT MR3220 Command Snippets

Reset the OpenWRT on Router back to the default use the command mtd -r erase rootfs_data

Turn Wifi off uci set wireless.@wifi-device[0].disabled=1; wifi

Using a clone image on new hardware.

The Centos networking will not work after the new hardware is using a clone image. The problem occurs because the MAC addresses on the new hardware don't match the MAC addresses in the config files of the clone image, these are the MAC addresses of the original hardware the image was taken from.

To get Networking working on Centos when using a cloned image, just modify the entries in /etc/sysconfig/network-scripts/ifcfg-eth0 ifcfg-eth1 and the /etc/udev/rules.d/70-persistent-net.rules files so that the eth0 and eth1 entries match the new hardware MAC addresses.

Restart the networking using service network restart and networking should now be working.

Add SSH public keys to a remote host

Nice quick way to add public keys to the authorized_keys file on a remote host
ssh-copy-id -i ~/.ssh/id_rsa.pub user@hostname

Rocks Cluster Compute nodes Ask for Password

After installing the compute nodes on a new Rocks Cluster it was found that a few nodes kept asking for SSH password. These should have been passwordless SSH and it was working on some of the compute nodes.

Try the following #rocks sync host sharedkey compute 

Try #rocks run host "/opt/rocks/bin/411get --all" 

if that works, 

Try #rocks sync users on the frontend

This cured the password prompt problem on the cluster.

4 Litre Silver Mini Fridge Repair

After just over a year of use (just out of warranty) the fridge stopped keeping things cool.
After taking out the 7 screws from the back panel the power supply PCB was revealed. On close examination it was found that the two 1000uF 25Volt electrolytic Capacitors on the power supply board were swollen (see picture below and note the pressure seals on the capacitors, both are leaking electrolyte), they were replaced and the fridge began to cool again, Result!
Do these repairs at your own risk, electricity is dangerous, you have been warned.