Month: April 2016

Wow! Talk about a crazy week. And it couldn’t have been better. After many days trying to get a working kernel in Snappy Ubuntu Core with customized Kernel Modules built against the kernel into a single snap bundle was easy is like saying giving a cat a bath is easy (I did that today as well, waiting for the kernel to finish building…)

Anyways, this blog post is about how I managed to get it working using snapcraft 2.8.4, running on Ubuntu 16.04, with kernel 4.4.0-21-generic from the Ubuntu kernel repository, and building the modules and then depmod’ing them and making sure they get put into the final snap.

First thing I did, download snapcraft. Easy to do now that it is in the main repository for Ubuntu 16.04. All you do is sudo apt update then sudo apt install snapcraft -y. Once that is complete, then you can run snapcraft init and you have a blank snapcraft.yaml file waiting for you to tell it what you are going to build. Below is an example that I used for my kernel snap:

name: custom-kernel
 version: 4.4.6
 summary:  custom kernel
 description:  custom kernel for Snappy
 type: kernel
 parts:
    kernel:
      plugin: kernel
      source: .
      kconfigfile: 4.4-config
      kconfigs:
        - CONFIG_SQUASHFS=m
      kernel-initrd-modules:
        - squashfs
        - ahci

I then ran sudo apt source linux-image-`uname -r` to get the latest kernel source that is running on Xenial. After that, I copied my snapcraft.yaml file to the location I downloaded the kernel source files to and copied the default kernel config file from /boot/config-4.4.0-21-generic to the kernel source directory and renamed it to 4.4-config. I then ran snapcraft build and after two hours, and giving my cat a bath, it was done. I was then able to build my custom kernel modules against these headers so that I knew they would have the same symbols for it. All I did was modify my makefile so that instead of it looking in /lib/modules/`uname -r`/build for my modules, I pointed it to /home/wililupy/linux-4.4.0/parts/kernel/build and modified the kernel version to 4.4.6. I then ran make all and it built my *.ko files I needed.

I then copied the *ko files to /home/wililupy/linux-4.4.0/parts/install/lib/4.4.6/extra (I had to create the extra directory mkdir -p extra) and then ran depmod -b ~wililupy/linux-4.4.0/parts/install 4.4.6 to update the modules symbols for the compiled kernel. I then ran  snapcraft snap. It then built my kernel.snap file. I then ran ubuntu-device-flash, which you will need to download from here. Run sudo ./ubuntu-device-flash core 16 --channel=edge --kernel=custom-kernel_4.4.6_amd64.snap --gadget=canonical-pc --os=ubuntu-core -o custom-snappy.imgand you will have your custom image that you are now ready to install on your device.

Since I work heavily in the Whitebox switching area, I use ONIE to install my software on whitebox switches. Read up on how this works from their Github or if you want, ask me in the comments below.

Happy Hacking!!

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Hello,

Don’t think too many of you noticed this site being down, but I had to rebuild it. I had a firewall issue that had to be corrected, and during the initial configurations, all the moving pieces wouldn’t play nice, so it was easier to rip it all down and start over from scratch.

So, now that I am all back, be looking forward to some randomness of information, mostly for my own need, but if you find it helpful, let me know in the comments and I’ll keep up with it.