The CirrOS project provides linux disk and kernel/initramfs images. The images are well suited for testing as they are small and boot quickly. Please note that:

• Images are provided for test only. They should not be used in production.
• Images have well known login information. Users can log in with 'cirros:letsgocubs' locally or remotely and have passwordless sudo access to root.

CirrOS images have useful tools and function for debugging or developing cloud infrastructure. Supported architectures are:

• aarch64 (64-bit Armv8 often called arm64)
• arm (32-bit Armv7)
• ppc64le (64-bit Power little endian)
• x86_64 (64-bit x86 often called amd64)

Resulting images can be booted using QEMU. Several ways of booting are provided:

• UEFI (aarch64, arm, x86_64)
• BIOS (x86_64)
• OpenFirmware (ppc64le)
• direct kernel + initrd (all architectures)

The following works on Ubuntu 22.04 LTS, running on x86_64. Native building for other architectures is not recommended. Support for building under other distributions is limited and not tested.

• git clone https://github.com/cirros-dev/cirros.git or
• git clone git@github.com:cirros-dev/cirros.git

To get build going we need some packages installed. If you use Ubuntu 22.04 LTS then all you need to do is:

• cd cirros

• get the build dependencies:

   $ ./bin/system-setup

If you use other distribution then please check what script does and install required components using methods preferred by your distribution.

Once you fetched source code all you have to do something like:

• cd cirros
• bin/build-release daily

If you want to build for only a subset of supported architectures, use the ARCHES variable like:

• ARCHES=aarch64,x86_64,arm bin/build-release daily

Resulting images will be present in ../build-dYYMMDD/release directory.

To use it, you would do something like:

• download buildroot and setup environment

   $ br_ver="2022.02.4"
   $ mkdir -p ../download
   $ ln -snf ../download download
   $ ( cd download && wget http://buildroot.uclibc.org/downloads/buildroot-${br_ver}.tar.gz )
   $ tar -xvf download/buildroot-${br_ver}.tar.gz
   $ ln -snf buildroot-${br_ver} buildroot

• optionally update src/etc/ssl/certs/ca-certificates.crt file. This is not required, but can be done to make sure its up to date.

   $ wget https://github.com/mozilla/gecko-dev/raw/master/security/nss/lib/ckfw/builtins/certdata.txt -O certdata.txt
   $ ./bin/mkcabundle <certdata.txt > src/etc/ssl/certs/ca-certificates.crt

• apply any local cirros patches to buildroot

   ( cd buildroot && QUILT_PATCHES=$PWD/../patches-buildroot quilt push -a )

• download the buildroot sources

   $ ARCH=x86_64
   $ make ARCH=$ARCH br-source

• Build buildroot for a given arch (ARCH should be set to 'x86_64', 'arm', 'aarch64' or 'ppc64le')

   $ make ARCH=$ARCH OUT_D=$PWD/output/$ARCH

This will do a full buildroot build, which will take a while. The output that CirrOS is interested in is output/i386/rootfs.tar. That file is the full buildroot filesystem, and is used as input for subsequent steps here.

• Download a kernel to use. The kernel input to bundle must be in deb format. The ubuntu '-virtual' kernel is used as a starting point. Version can be taken from https://launchpad.net/ubuntu/+source/linux page.

   $ kver="5.15.0-48.54"
   $ ./bin/grab-kernels "$kver" $ARCH

• Download EFI grub to use (aarch64, arm, x86_64 only). The grub-efi input to bundle will be in tar.gz format. Version can be taken from https://launchpad.net/ubuntu/+source/grub2 page.

   $ gver="2.06-2ubuntu7"
   $ ./bin/grab-grub-efi "$gver" $ARCH

• build disk images using bin/bundle

   $ sudo ./bin/bundle -v --arch=$ARCH output/$ARCH/rootfs.tar \
      download/kernel-$ARCH.tar.gz download/grub-efi-$ARCH.tar.gz output/$ARCH/images

We provide simple script to test resulting image. You run it this way:

   $ RELEASE_DIR=$PWD/../build-*/release IMG=$PWD/../build-*/release/cirros-*-x86_64-disk.img bin/test-boot

Note: "RELEASE_DIR" variable is required only for aarch64 and arm images.

Once image boots you can login with 'cirros' user using 'gocubsgo' as password. Root access is granted with 'sudo' call.