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Bootstrap

  1. Prepare emergency shell, if enabled
  2. Set up initial signal handlers
  3. Set up default $PATH early
  4. Mount /proc and /sys
  5. Check kernel command line for debug to figure out log level
  6. Load all .so plugins
  7. Call fsck on file systems listed in /etc/fstab
  8. Populate /dev using either udev or mdev, depending on system type
  9. Parse /etc/finit.conf and all /etc/finit.d/*.conf files
  10. Start built-in watchdog, if enabled
  11. Set hostname
  12. Pivot root, or remount / read-write, depending on system type
  13. Call 1st level hooks, HOOK_ROOTFS_UP
  14. Mount all file systems listed in /etc/fstab and swap, if available
  15. Enable SysV init signals
  16. Call 2nd level hooks, HOOK_BASEFS_UP
  17. Cleanup stale files from /tmp/* et al, handled by bootmisc plugin
  18. Load kernel params from /etc/sysctl.d/*.conf, /etc/sysctl.conf et al. (Supports all locations that SysV init does.), handled by procps plugin
  19. Start all 'S' runlevel tasks and services
  20. Bring up loopback interface and all /etc/network/interfaces, if the .conf setting network <SCRIPT> is set, it is called instead
  21. Call 3rd level hooks, HOOK_NETWORK_UP
  22. If runparts <DIR> is set, run-parts(8) is called on <DIR>
  23. Switch to the configured runlevel from /etc/finit.conf, default 2. At every runlevel change all *.conf files in /etc/finit.d/ are (re)loaded and new services, tasks, and blocking run commands are started. Provided they are allowed in the new runlevel and all of their conditions, if any, are set.
  24. Call 4th level hooks, HOOK_SVC_UP
  25. Call /etc/rc.local, if it exists and is an executable shell script
  26. Call 5th level (last) hooks, HOOK_SYSTEM_UP
  27. Start all configured TTYs, or a fallback shell on /dev/console

In (19) and (22) tasks and services defined in /etc/finit.conf and /etc/sysctl.d/*.conf are started. Remember, all service and task stanzas are started in parallel and run in sequence, and in the order listed. Hence, to emulate a SysV /etc/init.d/rcS one could write a long finit.conf with only run statements.

Notice the five hook points that are called at various point in the bootstrap process. This is where plugins can extend the boot in any way they please. There are other hook points, e.g. HOOK_MOUNT_ERROR, for more on this see plugins.md.

For instance, at HOOK_BASEFS_UP a plugin could read an XML file from a USB stick, convert/copy its contents to the system's /etc/ directory, well before all 'S' runlevel tasks are started. This could be used with system images that are created read-only and all configuration is stored on external media.