finit/doc/bootstrap.md

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
10. Start built-in watchdog, if enabled and WDT_DEVNODE exists. This means any WDT that requires a kernel module need to be either compiled into the kernel, or insmod'ed in /etc/finit.conf
11. Load all /etc/finit.d/*.conf files and set hostname
12. Remount / read-write if / is listed in /etc/fstab without ro
13. Call 1st level hooks, HOOK_ROOTFS_UP
14. Mount all file systems listed in /etc/fstab and swap, if available. On mount error HOOK_MOUNT_ERROR is called. After mount, regardless of error, HOOK_MOUNT_POST is called
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

In (19) and (23) tasks and services defined in /etc/finit.conf and /etc/finit.d/*.conf are started.

Notice the seven 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 available, 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.