Ubuntu Manpage: finit — Fast init for Linux systems

NAME

       finit — Fast init for Linux systems

SYNOPSIS

       /sbin/finit     [--]    [debug]    [finit.cond=foo[,bar[,baz]]]    [finit.config=/path/to/alt/finit.conf]
                   [finit.debug]              [finit.fstab=/etc/fstab.alt]               [finit.status=<on,off>]
                   [finit.status_style=<classic,modern>] [loglevel=<0-7>] [panic=SEC] [quiet] [rescue | recover]
                   [single | S]
       /sbin/telinit [-hv] [q | Q | 0-9]

DESCRIPTION

       Fast  init  for  Linux  systems.   Reverse  engineered  from the EeePC fastinit, 10+ years ago by Claudio
       Matsuoka, "gaps filled with frog DNA ...".  Focus is on small and embedded  systems,  although  Finit  is
       fully usable on server and desktop systems as well.

       Features include:
       •  Runlevels, defined per service
       •  One-shot tasks, services (daemons), or SysV init start/stop scripts
       •  Runparts and /etc/rc.local support
       •  Process supervision similar to systemd(8)
       •  Sourcing environment files
       •  Conditions for network/process/custom dependencies
       •  Process readiness notification for synchronizing system startup as well as reconfiguration at runtime.
          Natively PID files are used, but systemd sd_notify() and s6 notification is also supported.
       •  Limited support for tmpfiles.d(5), no aging, attributes, or subvolumes
       •  Pre/Post script actions
       •  Tooling to enable/disable services
       •  Built-in getty
       •  Built-in watchdog, with support for hand-over to watchdogd: https://troglobit.com/watchdogd.html
       •  Built-in support for Debian/BusyBox /etc/network/interfaces
       •  Cgroups v2, both configuration and monitoring in `initctl top`
       •  Plugin support for customization
       •  Proper rescue mode with bundled `sulogin` for protected maintenance shell

BOOTPARAM

finit support the following command line parameters to alter the behavior at boot. Notice the --
separator needed to tell the kernel which paramters should be given to PID 1. For more information on
this, and available kernel command line options, see bootparam(7).

debug
Enable kernel debug. Debug messages are printed to the console until Finit starts up, unless
loglevel=7 (below) is used.

finit.cond=foo[,bar[,baz]]
set <boot/foo> condition, optionally multiple conditions can be set using the same option,
separated with a comma. Alternatively, multiple foo.cond=arg can be given. Each will result
in a <boot/arg> condition being set to control the rest of the system bootstrap.

Very useful for selecting different boot modes, e.g. manufacturing test, firmware upgrade, or
rescue mode.

Note: <boot/...> conditions cannot be cleared with initctl!

finit.config=/path/to/alternative/finit.conf
override the compile-time bootstrap config file, default:

Useful when starting up in various rescue mode, factory, or production test setups. Use the
top-level configuration file directive rcsd /path/to/finit.d to override the default rcS.d
directory.

finit.debug
Enable Finit debug messages on system console and log. Sometimes useful when doing board
bringup. Before the system log daemon has started, Finit use the kernel ring buffer,
/dev/kmsg.

finit.fstab=/path/to/fstab.alt
Tell finit to use an alternate fstab to mount the file system from. Remember, this file must
be on the root=... file system provided to Finit from the kernel. If this file is missing,
finit falls back to its built-in default, which can be changed at build time using the
--with-fstab=/path/to/footab configure option. It is even possible to completely disable the
built-in using --without-fstab, meaning finit must be started with the finit.fstab option.

Should finit discover that there is no fstab file available, including the fallback, it
triggers the same failure mode as when fsck fails, starting sulogin(8), if that is availble.
When sulogin is missing, or when the user exits from sulogin, the system is rebooted.

Default fstab, unless changed at build-time: /etc/fstab

finit.status=<on,off>
Control finit boot progress, including banner. This used to be called finit.show_status,
which still works but is deprecated.

finit.status_style=<classic,modern>
Set Finit boot progress style, when enabled.

loglevel=<0-7>
set the kernel's log level, which is more granular than debug. Also, when loglevel=7, Finit
will not disable kernel logs to the console. This is very useful when debugging the kernel at
system bring-up. Since loglevel=7 is the same as debug this means you have to use quiet for a
quiet boot, until sysklogd takes over logging of kernel events.

panic=SEC
By default the kernel does not reboot after a kernel panic. This setting will cause a kernel
reboot after SEC seconds.

quiet
Suppress kernel logging to console, except for warnings and errors. Also, see loglevel and
quiet above.

rescue | recover
Start rescue/maintenance mode. If your system comes with the bundled sulogin program (Finit,
or from util-linux/Busybox), you will be given a root login to a maintenance shell. However,
if sulogin is missing, the file /lib/finit/rescue.conf is read and the system booted in a
limited fallback mode. See finit.conf(5) for more information.

single | S
Single user mode, runlevel 1, in Finit. Useful to debug problems with the regular runlevel.
All services and TTYs in [1] will be started, e.g., a tty [1] @console nologin configuration
presents you with a root console without login.

Note: by definition, single user mode does not have networking enabled. This is also true for
runlevel 1.

BOOTING

       Before laucnhing services, the system needs to be bootstrapped.  This involves mounting  all  filesystems
       (not  already  mounted  by an initramfs) in /etc/fstab, or any alternate fstab file provided on the Finit
       command line using finit.fstab, ensuring that necessary filesystems like: /dev, /proc, /sys, and /run are
       available and can provide the system with the services required.

       With that out of the way, a set of plugins take over:

             bootmisc.so  Cleans up stale files from previous boots and default directories are created in tmpfs
                          filesystems

             modprobe.so  Probes kernel modules required by the system

             procps.so    Set kernel variables from /etc/sysctl.conf et al

       When the plugins are done, finit reads /etc/finit.conf and all other enabled services in  /etc/finit.d/*.
       First  all  services, run/tasks in runlevel S (bootStrap) are started, When all run/tasks have completed,
       Finit changes to the configured runlevel (default 2), Processes are started in  parallel,  in  dependency
       order according to their conditions.

       When  all  services  and run/tasks have been started, the console progress is disabled and all configured
       getty services are started.

CONDITIONS

       The condition subysystem in Finit was initially created to track PID files of daemons.  If service/task B
       requires service A to have started, Finit waits for the PID file  of  service  A  to  be  created/updated
       before  it  starts service B.  Conversely, if service A is stopped and its PID file removed, service B is
       also stopped.

       The following condition families are available today:

             net      Linux netlink events, e.g. net/route/default, net/eth0/up, and net/et0/running

             pid      PID files based on the service declaration name:id, gives the condition pid/name:id

             service  Tracks run/task/service state stansitions, including readiness.   E.g.,  service/foo/ready
                      can be used as a condition for service bar, provided foo properly signals its readiness to
                      Finit.

             sys      System conditions, e.g. sys/key/ctrlaltdel and sys/pwr/fail

             usr      User conditions, assert and deassert using initctl cond [set|clr] foo

SIGNALS

       PID  1 is the only process that by default blocks all signals.  Finit allows for the following signals to
       control operation, but recommends instead using the initctl(8) tool.

       HUP   Tell finit to reload its configuration file(s), same as initctl reload

       USR1  Restart API (initctl) socket.

       USR2  Tell finit to perform a system shutdown, same as initctl poweroff

       TERM  Like SIGUSR2 but performs a reboot, same as initctl reboot

       INT   Sent from kernel when Ctrl-Alt-Del is pressed (on the console), this asserts the sys/key/ctrlaltdel
             condition, which can be used to start tasks or services

       PWR   Sent from a a power daemon on changes to UPS status, Finit asserts the sys/pwr/fail condition

FILES

       /etc/finit.conf                Main configuration file
       /etc/finit.d/*.conf            Static service definitions
       /etc/finit.d/available/*.conf  Available services
       /etc/finit.d/enabled/*.conf    Symlinks from available
       /run/finit/                    Runtime files, including the condition subsystem

AUTHORS

       finit was conceived and reverse engineered by  Claudio  Matsuoka.   Since  v1.0,  maintained  by  Joachim
       Wiberg, with contributions by many others.

Linux                                             Apr 22, 2023                                          FINIT(8)