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How to produce a custom Linux OS image

A LCOW custom Linux OS image was divided into two parts: a Linux kernel module and a set of user-mode components. Both parts were highly customized for the purpose of supporting Linux Hyper-V container on Windows

How to build custom kernel module

Here you will find the steps to build a custom kernel for the Linux Hyper-V container on Windows (LCOW). To build the full image, please follow the instructions:

  • Have your kernel source tree ready

  • Apply additional LCOW patches to your kernel source tree

  • Use the matching recommended Kconfig to include all LCOW necessary kernel components

    Note: The key delta between the upsteam default setting and above kconfig is in the area of ACPI/NIFT/NVDIMM/OverlyFS/Vsock/HyerpV settings, which were set to be built-in instead of modules. The Kconfig above is still a work in process in terms of trimming any unnecessary components from the kernel image.

  • Build your kernel

Currently supported Linux kernel versions:

How to construct user-mode components

The expected user mode directory structure is required to constructed as follows: See the complete user-mode file list

Under the / directory, it should have the following subdirectories:

  • /tmp

  • /proc

  • /bin

  • /dev

  • /run

  • /etc

  • /usr

  • /mnt

  • /sys

  • /init

  • /root

  • /sbin

  • /lib64

  • /lib

Here are the expected contents of each subdirectory /file

  1. Subdirectories with empty contents:  /tmp /proc /dev /run /etc /usr /mnt /sys

  2. /init This is the init script file

  3. /root : this is the home directory of the root account.

  4. /sbin :

    • /sbin/runc

          Note:this is the "runc" binary for hosting the container execution environment.

    `runc -v` (where `runc` was installed using `go get`, `go install`, or `go build`) should output the following:
        runc version spec: 1.0.0

    `runc -v` (where `runc` was installed using the Makefile in the runc repo) should output the following:
        runc version 1.0.0-rc4+dev
        commit: 3f2f8b84a77f73d38244dd690525642a72156c64
        spec: 1.0.0

    • /sbin/udhcpc_config.script

  5. /lib64 :

    /lib64/ld-linux-x86-64.so.2

  6. /lib :

    /lib/x86_64-linux-gnu
/lib/x86_64-linux-gnu/libe2p.so.2
/lib/x86_64-linux-gnu/libcom_err.so.2
/lib/x86_64-linux-gnu/libc.so.6
/lib/x86_64-linux-gnu/libdl.so.2
/lib/x86_64-linux-gnu/libapparmor.so.1
/lib/x86_64-linux-gnu/libseccomp.so.2
/lib/x86_64-linux-gnu/libblkid.so.1
/lib/x86_64-linux-gnu/libpthread.so.0
/lib/x86_64-linux-gnu/libext2fs.so.2
/lib/x86_64-linux-gnu/libuuid.so.1
/lib/modules

  7. /bin : binaries in this subdir are categorised into four groups

    • GCS binaries

        /bin/exportSandbox
  /bin/gcs
  /bin/gcstools
  /bin/netnscfg
  /bin/remotefs
  /bin/tar2vhd
  /bin/vhd2tar

  Note : exportSandbox, vhd2tar, tar2vhd, remotefs, and netnscfg are actually hard links to the "gcstools' file

    • Required binaires: utilities used by gcs

         /bin/sh
   /bin/mkfs.ext4
   /bin/blockdev
   /bin/mkdir
   /bin/rmdir
   /bin/mount
   /bin/udhcpd
   /bin/ip
   /bin/iproute
   /bin/hostname

    • Required binaires: utilities used by docker

         /bin/cat
   /bin/kill
   /bin/ls
   /bin/pidof
   /bin/test

    • Debugging tools: mostly from busybox tool set

  8. / :

    • /gcs.commit Optional file containing the commit id of Microsoft/opengcs

Supported LCOW custom Linux OS packaging formats

A LCOW custom Linux OS could be packaged into two different supported formats:

  • Kernel + Initrd: vmlinuz and initrd.img
  • VHD: a VHDx file