Demystifying Systemd for Embedded Systems

This repository contains script used to create the presentation, they are targeted to run on a x86-64 machine that is already prepared to build the Linux Kernel and systemd itself. It was tested solely on ArchLinux.

Scripts:

• run-qemu.sh <kernel> <initramfs> after ./all.sh is executed, this will allow to boot a virtual machine with kernel and initramfs combinations.
• all.sh run all scripts but run-qemu.sh.
• fetch.sh download kernel and systemd source code tarballs. Results in download/
• extract.sh unpack kernel and systemd source code tarballs. Results in src/
• prepare.sh prepare source to build (./autogen.sh).
• compile.sh configure and compile various combinations of kernel and systemd builds. Results in kernel/ and systemd/*/install
• systemd-minimal-strip.sh copy systemd build easy_diet and remove some components that cannot be disabled using ./configure --disable-COMPONENT, such as udev and journal. Results in systemd/minimal*/install
• systemd-initramfs-all.sh create initramfs for all systemd builds.
• busybox-initramfs.sh create initramfs for busybox.
• report.sh print out sizes.

Helper Scripts:

• systemd-initramfs.sh <build-name> used by systemd-initramfs-all.sh to create initramfs for each build.
• systemd-install-strip.sh <systemd-install-dir> used by compile.sh to remove files that doesn't matter, like bash completion, locale and development (includes, pkgconfig)
• versions.sh various defines to be included by other scripts.

Kernel configuration:

• kernel-minimal-x86_64.config config fragment based on allnoconfig with minimum requirements to boot busybox. This configuration won't boot systemd.
• kernel-systemd-x86_64.config config fragment to extend kernel-minimal-x86_64.config following all https://github.com/systemd/systemd/blob/master/README recommendations. This enables IPv6, namespaces, tmpfs, SECCOMP...
• kernel-systemd-minimal-x86_64.config similar to the previous but instead of enabling everything, enable only the requirements, everything else is left disabled. That is, no IPv4/IPv6, namespaces or SECCOMP.