Minimal filesystem

  • In order to work, a Linux system needs at least a few applications
  • An init application, which is the first user space application started by the kernel after mounting the root filesystem
    • The kernel tries to run /sbin/init, /bin/init, /etc/init and /bin/sh.
    • In the case of an initramfs, it will only look for /init. Another path can be supplied by the rdinit kernel argument.
    • If none of them are found, the kernel panics and the boot process is stopped.
    • The init application is responsible for starting all other user space applications and services
  • A shell, to implement scripts, automate tasks, and allow a user to interact with the system
  • Basic Unix applications, to copy files, move files, list files (commands like mv, cp, mkdir, cat, etc.)
  • These basic components have to be integrated into the root filesystem to make it usable

Overall booting process

Overall booting process with initramfs

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