When the Linux kernel finishes booting, it runs an executable as the first and only userland process.
The default path is /init, but we an set a custom one with the init= kernel command line argument.
This process is then responsible for setting up the entire userland (or destroying everything when you want to have fun).
This typically means reading some configuration files (e.g. /etc/initrc) and forking a bunch of userland executables based on those files.
systemd is a "popular" /init implementation for desktop distros as of 2017.
BusyBox provides its own minimalistic init implementation which Buildroot uses by default.
Is the default BusyBox /init too bloated for you, minimalism freak?
No problem, just use the init kernel boot parameter:
./run -e 'init=/sleep_forever.out'
Remember that shell scripts can also be used for init https://unix.stackexchange.com/questions/174062/init-as-a-shell-script/395375#395375:
./run -e 'init=/count.sh'
Also remember that if your init returns, the kernel will panic, there are just two non-panic possibilities:
- run forever in a loop or long sleep
poweroffthe machine
The default BusyBox init scripts enable networking, and there is a 15 second timeout in case your network is down or if your kernel / emulator setup does not support it.
To disable networking, use:
./build -p -n
To restore it, run:
./build -t initscripts-reconfigure