Mini home server with MK802

Note: I’m currently using a Raspberry Pi 2 and Arch Linux ARM

My first attempt to set up a mini home server was using a Raspberry Pi as a torrent and a DLNA server running with an external HDD. Unfortunately it had a lot of USB related issues that caused the HDD and the network to disconnect very often. I tried several workarounds, from tweaks in the boot-loader to fixes in the kernel without success.

Because of that, almost two years ago I bought a MK802 android stick from DealExtreme to replace my old Raspberry Pi. In general, the MK802 has been able to run a torrent and DLNA server for long periods of time without any further problems. But I noticed that sporadically the root FS was getting corrupted causing the MK802 to hang. Most of the times, a simple fsck was enough. But on the last hang the FS on the SD card was completely corrupted and I had to do a fresh reinstall.

The MK802 has an internal storage that comes with android pre-installed on it. The simplest way to get Linux running on it is using a SD card with one of several images available from miniand and rikomagic sites. However I chose to use a Fedora 20 Remix for Allwinner A10’s and A20’s available here because it has a series of nice modules already compiled into it.

Considering that SD cards have limited write cycles and I was having FS corruptions with an increasing frequency, I decided to move the root partition to my external HDD. My first step was to copy the root partition to the external HDD and update the root parameter that uboot passes to the kernel with the new root partition. That can be done changing the uEnv.txt file in the boot partition:

console=tty0
loglevel=5
root=/dev/sda3 ro rootwait rootfstype=ext4
extraargs=console=ttyS0,115200 disp.screen0_output_mode=EDID:1280x720p60 hdmi.audio=EDID:0 sunxi_g2d_mem_reserve=0 sunxi_ve_mem_reserve=0 sunxi_fb_mem_reserve=20 sunxi_no_mali_mem_reserve

And…. that didn’t work. After a few minutes investigating the original system booted from the SD card I noticed that the module needed to access USB storages was not built into the kernel. The only option was to rebuild the kernel including usb-storage in it.

Rebuilding the Fedora 20 ARM for Allwinner A10 disk image

You can find all the instructions to rebuild the image in the README file. But I added bellow the steps that I did to rebuild my custom Fedora 20 disk image.

Installing dependencies

Since we’re going to cross-compile a new kernel targeting an ARM platform, we will need to install a few dependencies in addition to what is necessary to build a regular kernel. I had to install the following packages:

libusb1
gcc-arm-linux-gnu
uboot-tools
sunxi-tools

If your distro doesn’t provide a package for sunxi-tool you can checkout its source from https://github.com/linux-sunxi/sunxi-tools and build it manually.

Getting the sources

In order to generate the boot and root file systems and to create the disk image, jwrdegoede has provided a series of git repositories containing the kernel source for A10 and A20 devices, kernel configs, board-specific files, and scripts that automatizes the building process.

The first repository to download is sunxi-fedora-scripts:

git clone https://github.com/jwrdegoede/sunxi-fedora-scripts.git

This repository contains the scripts to build the boot and root FS and to generate the disk image. All the other repositories need to be placed inside the sunxi-fedora-scripts directory:

cd ./sunxi-fedora-scripts/
git clone https://github.com/jwrdegoede/linux-sunxi.git
git clone https://github.com/jwrdegoede/sunxi-kernel-config.git
git clone https://github.com/jwrdegoede/sunxi-boards.git
git clone https://github.com/jwrdegoede/u-boot-sunxi.git

Changing kernel config

That is the reason for all this process. We need to change the kernel config files to build usb-storage inside the kernel instead of as a module.

Edit sunxi-kernel-config/config-generic and change:

CONFIG_USB_STORAGE=m

To:

CONFIG_USB_STORAGE=y

Generating the boot and root file systems

That is performed by the script build-boot-root.sh. It compiles a series of different boot-loaders and kernels to a big range of different boards. Since I just need support for MK802 that uses a sun4i chip, I changed the script to just build what was really necessary. That is my [modified script]().

After that you just need to run:

./build-boot-root.sh

This will create the files uboot.tar.gz and rootfs.tar.gz.

Generating the disk image

The next step is to put everything together in a disk image that can be written to a SD card. That is done by the script build-image.sh, it uses the uboot.tar.gz and rootfs.tar.gz files located at the current directory and receives two arguments. The first one is a Fedora disk image for PandaBoard, the script will use it as a skeleton and replace everything that is necessary. The second argument is the output disk image file.

I intend to use my MK802 as a headless server, so instead of using the disk image for PandaBoard as input I decided to use an ARMHFP minimal disk image that can be downloaded here.

wget http://fedora.c3sl.ufpr.br/linux/releases/20/Images/armhfp/Fedora-Minimal-armhfp-20-1-sda.raw.xz
unxz Fedora-Minimal-armhfp-20-1-sda.raw.xz
./build-image.sh Fedora-Minimal-armhfp-20-1-sda.raw Fedora-Minimal-armhfp-20-1-sda.raw-USB.raw

Preparing the hard drive disk

dd if=Fedora-Minimal-armhfp-20-1-sda.raw-USB.raw of=/dev/sdX

Notice that I’m copying the whole image to the external HDD, this will also copy the boot-loader and boot partition that will not be used. I opted to keep the same partition structure to avoid any further changes in the root partition to adjust mount point’s UUIDs and anaconda scripts.

Preparing the SD card

Since the root partition is not located at the SD card anymore I decided to save my 8GB SD card and use a smaller card with 256MB. The SD card will need to have a reserved region to the boot-loader and a boot partition (check the linux-sunxi site).

sfdisk -R /dev/mmcblk0
{ echo '1,16,c'; echo ',,L' } | sfdisk --in-order -uM /dev/mmcblk0

That will create the space needed to the boot-loader and a boot partition.

mkfs.ext3 /dev/mmcblk0p1
mount /dev/mmcnblk0p1 /mnt
tar -xzf ubootfs.tar.gz -C /mnt
cd /mnt
./select-board.sh mk802-1gb
cd -
umount /mnt
sync

That will copy all the necessary files and install the boot-loader.

Final steps

The last thing to do is to insert the SD card and plug the external HHD, turn the device on and follow all the installer steps.