How to make a custom ISO image

This document explains how to build a custom ISO image using the alpine-iso scripts.

Prerequisite

First make sure we have the needed tools

apk add alpine-sdk xorriso syslinux

Then create signing keys (-i installs them in /etc/apk/keys which is required for later)

abuild-keygen -i -a

Clone (or update) the alpine-iso git repository.

git clone git://git.alpinelinux.org/alpine-iso

Core Configuration

The alpine-iso scripts is a simple makefile which you need to feed with a <name>.conf.mk file and a <name>.packages.

In the <name>.conf.mk we specify

ALPINE_NAME: name of iso image

ALPINE_VERSION: (optional) version string. Will default to todays date.

KERNEL_FLAVOR: (optional) either grsec, vserver or pae. Will default to grsec.

MODLOOP_EXTRA: (optional) Extra kernel module packages for the modloop image. For example: dahdi-linux-vserver

APK_REPOS: (optional) Path to addidtional apk repository.

The <name>.packages is just a plaintext list of packages that should be included in the ISO image. You should always add alpine-base in there or the CD might not be able to boot. The dependencies for the packages will automatically be pulled in.

A rescue CD example

As an example, let us make a rescue ISO image with packages needed for rescue operations. We call it alpine-rescue

We create the alpine-rescue.conf.mk as follows:

ALPINE_NAME   := alpine-rescue
KERNEL_FLAVOR := grsec
MODLOOP_EXTRA :=

If you are going to use a custom kernel, don't forget to specify KERNEL_FLAVOR_DEFAULT which will set the default kernel to boot.

And then the alpine-rescue.packages as:

alpine-base
bkeymaps
openssh
e2fsprogs
mdadm
lvm2
parted
debootstrap
ntfs-3g

Tip: Make sure your public keys are placed in /etc/apk/keys/ (example: root-xxxxxxxx.rsa.pub):

ls /etc/apk/keys/

Learn apk-tools to find your home-built apk's:

echo "~/.cache/abuild/" >> /etc/apk/repositories

Make sure the apk index is up to date (so apk finds the packages):

apk update

We create the ISO image by telling the makefile the profile name. The makefile target is iso.

make PROFILE=alpine-rescue iso

Tip: If you are building inside an LXC guest, use fakeroot:

fakeroot make PROFILE=alpine-rescue iso

To generate the sha256 sum we use the sha256 make target.

make PROFILE=alpine-rescue sha256

Package lists

Beside the plaintext package lists in the git repository, there are more documented package lists contributed by Alpine users. Those lists can be transformed into a plain text description by apk search --exact -v $(cat alpine.packages).

So far the lists below are available (check here for more.)

Live Disk Setup with APKOVL

Once you have customized your custom ISO, you can now setup the live environment to operate outside of the standard installer as follows:

Generate an APKOVL file with lbu, lbu ci
Alpine ISO requires the OVL Volume to be hosted on a web server. Put the APKOVL file on a webserver and identify the url.
Uncomment the APKOVL line in the alpine flavor of your choice and set it to the address of your ovl volume.

Notes:

Any packages you add to /etc/apk/world of your lbu will automatically be installed onto the live system image.
If you don't have a web server you can run busybox's httpd temporarily - busybox -p 127.0.0.1:80
In general, lbu will only handle files in /etc, to customize this further, you need to add additional files.
If you want to make a customized installer, you need to create .default_boot_services which will cause mkinitfs to create the defaults for the live image.

Testing your ISO image

Qemu is useful for a quick test of your created ISO image.