Tutorial: boot Parallella from USB external hard drive (using standard SD image)

I’ve been using my Parallella for a few months now and I’ve already burnt a couple of SD Cards…

Therefore I thought that it would be better to load the OS from an USB attached Hard Disk, using the SD Card for the boot process only.

Parallella Board

In general Linux allows to easily change the root partition by passing the appropriate parameters to the Kernel (or through a bootloader). However in the standard image used by Parallella, a Device Tree is used. This means that you cannot pass directly the desired parameters to the Kernel, but you need modify the standard Device Tree. This is located in the Kernel package available at: http://www.parallella.org/create-sdcard/. See the point #2 (Parallella Linux Kernel – with ot without HDMI support, as you prefer) to download it.

Once you have decompressed the content (as explained in the instructions), you will see that one of the files is called “devicetree.dtb”. The file is compiled so we’ll need to decompile it. On the Parallella, make a copy of the file in another folder and launch the command:

dtc -I dtb -o dev.dts -O dts devicetree.dtb

if the command cannot be found, just install it using:

sudo apt-get install device-tree-compiler

 

Now the file dev.dts is in text again and can be customized.

Open the file with your favourite text editor and look for the line that begins with “bootargs”. In there you can specify any kernel boot options as described here.

In our case, we want to boot from a USB attached drive. In order to do so, we need to use the instructions we saw before at Parallella site to copy the official image to an Hard Disk (CAUTION, YOU WILL DELETE YOUR HARD DISK CONTENT – YOU’VE BEEN WARNED!!!). It’s quite simple as you just need to adapt the command to create the partitions by using the appropriate /dev/sdxx device that is related to your external hard disk.

 

Therefore the bootargs line will have to look like:

bootargs = "rootwait root=/dev/sda2 rw rootfstype=ext4";

 

Finally, re-compile the new Device Tree:

dtc -I dts -O dtb -o devicetree.dtb dev.dts

And now overwrite the old Device Tree with the new one. Happy OS loading from USB!

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