The system-init program

system-init is a minimal, scripted init to bring up a goetia based system.

Interface

     system-init

system-init takes no arguments.
It makes /dev/console its stdout and stderr.
It reads the environment variable BUNDLE, which can be specified on the Kernel command line. If it is undefined, it uses default as the value.
It reads the environment variable PATH, which can be specified on the Kernel command line. If it is undefined, it uses /command:/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/libexec:/usr/local/libexec as the value.
It sets the PATH environment variable to the value chosen above.
It chdirs to /.
It runs s6-setsid to become the session leader.
It creates the runtime directory if it does not already exist.
It mounts the runtime directory tmpfs.
It copies the old system logs from the system/uncaught-logs subdirectory of the log directory to the system/ subdirectory of the runtime directory if they exist.
It runs prepare-svscan with the proper arguments.
Finally, it executes into s6-svscan on the scandir represented by the system/service subdirectory of the runtime directory.

system-init usually executes into s6-svscan which exits according to its page.
Since system-init is an execline script, it exits with an approximation of employed program that failed.
system-init mostly uses execline and s6 software, the exit behaviour of which can be looked up on their respective pages.
See also: execline exit code handling.

system-init is primarily intended to be used as an init for an acutal boot process, not for containers.