I am cross compiling for my rpi4. I want to construct the most minimal userspace possible with 0 bloat for allowing login using ssh or by connecting to monitor and using a keyboard and access a shell prompt.

Landed on a few interesting links:

• https://www.linuxfromscratch.org/
• https://trac.clfs.org/
• https://kevinboone.me/pi_minimal.html

How can a system boot without /etc/passwd or users ? Or rather how much info does the linux kernel need about the userspace to function at its minimal level ? Who is the user of the first program launched by the kernel that does not have users on it ? How is this even possible ?

Please provide insights into the relation and dependencies between userspace concepts and kernel concepts and highlight their dependencies if any or if they are mutually exclusive .