Modifying install images

Overview

Modifying packages that are part of the install diskless boot (e.g. on install media), or the parameters that can be accepted by the boot process, is a little more involved than modifying individual packages, especially for netboot images. This author discovered that then when working on feat: answerfile kernel cmdline parameter (#26) · Issues · alpine / mkinitfs · GitLab an issue he opened to request / offer to develop an improvement to unattended installation by adding the option of applying a setup-alpine ‘answerfile’ automatically via netboot, by providing a URL to a new answerfile kernel commandline parameter.

The easy part

  • Update the list of options accepted by the installer using the kernel command line by modifying mkinitfs initramfs-init.in and updating the man page in mkinitfs-bootparam.7.in.
  • Install the new mkinitfs into one’s build environment using make install in mkinitfs.
  • Build a new image using scripts/mkimage.sh from aports with the appropriate parameters.
  • You new have an image that will accept your new parameter.

Challenge #1

  • In the case of answerfile an additional change needs to be make to the firstboot initscript, which is part of the openrc package.
  • That means building a new openrc package and getting it into the generated image.
  • To do that one has to point scripts/mkimage.sh at the package repository created when building the modified openrc package.
  • This is sufficient for images where all the packages used during boot and install are present on the install media.

Challenge #2 (netboot)

  • For netboot, however, the process is more involved because the openrc package has to be downloaded from an external repository during the boot process.
  • This would seem easy; one might think you one could just supply put the packages directory created during the openrc build on a web server and using the alpine_repo=<URI_of_repo>, but the problem is that alpine_repo only accepts a single repository.
  • In addition the package list must be signed by a key which appears in the image (that part is easy using the mkimage.sh parameters).
  • This means one must have include all the packages netboot and install will require in the new repository.
  • There is one more gotcha; One must include all the dependencies for the packages in the repository or the packages will fail to install.

One method of creating the necessary signed repository

Identify all the base packages needed by netboot

  • In the mkinitfs repository issue grep pkgs initfamfs-init.in and make note of all the packages that may be used by the initramfs.
  • In aports, grep apks scripts/*. This will identify all base packages added by the mkimage.sh script.
  • You also need linux-lts linux-virt wireless-regdb scanelf alpine-conf alpine-base openssl

Identify all the dependencies of the base packages

  • Create a file with the list of base packages on a single line, separated by spaces. For example a file named ~/base-packages.lst containing:

    package1 package2 package3

  • Install the package lua-aports

  • From a package directory in a package from aports, issue the following command:

    ap recursive-deps $(cat ~/base-packages.lst) >~/base-deps.lst

Build all required packages

Create required list of package directories in aports

  • Take the list of base packages and dependencies above and create a single file with all packages on a single line, separated by spaces. For ~/base-deps.lst above you could do:

    cat ~/base-deps.lst ~/base-pkgs.lst | tr $'\n' ' ' >~/oneline-deps.lst

  • From a package directory in a package from aports, issue the following command:

    ap builddirs $(cat ~/oneline-deps.lst) >~/packages-to-build.lst
Create a directory for the package repository
mkdir -p ~/packages/main
Add this directory to the system APK repositories

  • NOTE: This will break things if you are not running latest (edge) Alpine in your build environment

  • Assuming your user home dir is /home/user, then to the file /etc/apk/repositories add

    /home/user/packages/main
Build the packages
cd ~
for pdir in $(cat ~/packages-to-build.lst); do (cd $pdir && abuild -r -m | tee -a ~/build.log); done

Build a netboot image

From the aports directory:

./scripts/mkimage.sh --profile netboot --repository /home/user/packages/main

Copy to your netboot server and netboot

See Netboot Alpine Linux using iPXE and adjust paths as necessary.

See Also