@jms FOS is based on buildroot. Building your own custom init is definitely possible but we don’t have a nice wiki article on this.
On the other hand it’s all available in a script. Clone a copy of the FOS repo and run the build script:
git clone https://github.com/FOGProject/fos cd fos ./build.sh -fn -a x64Make sure you have enough of disk space available (roughly 7 GB as it downloads and compiles a huge amount of code) and lots of CPU power and RAM. On our designated compile workhorse it takes more than an hour to build. On my laptop it’s more like 8 hours.