finit/man/finit.8

.\"                                      Hey, EMACS: -*- nroff -*-
.\" First parameter, NAME, should be all caps
.\" Second parameter, SECTION, should be 1-8, maybe w/ subsection
.\" other parameters are allowed: see man(7), man(1)
.Dd Jul 9, 2025
.\" Please adjust this date whenever revising the manpage.
.Dt FINIT 8 SMM
.Os Linux
.Sh NAME
.Nm finit
.Nd Fast init for Linux systems
.Sh SYNOPSIS
.Nm /sbin/finit --
.Op debug
.Op quiet
.Op rescue | recover
.Op single | S
.Op panic=SEC
.Op loglevel=<0-7>
.Op fsck.mode=[auto,skip,force]
.Op fsck.repair=[no,yes,preen]
.Op finit.debug=<true,false>
.Op finit.fstab=/path/to/fstab
.Op finit.cond=foo[,bar[,baz]]
.Op finit.config=/path/to/finit.conf
.Op finit.status_style=<classic,modern>
.Op finit.status=<on,off>
.Nm /sbin/telinit
.Op Fl hv
.Op q | Q | s | S | 0-9
.Sh 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.
.Sh OPTIONS
When
.Sy not
started as PID 1,
.Nm
behaves like
.Nm telinit ,
following classic UNIX command line syntax.  The options are:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Fl h
Show built-in help text.
.It Fl v
Show program version.
.El
.Pp
More options are implemented for SysV init support, but are ignored.
.Sh ARGUMENTS
When
.Sy not
started as PID 1,
.Nm ,
or
.Nm telinit ,
take these arguments:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It q | Q
Reload configuration, same as
.Cm initctl reload .
.It 0 - 9
Go to runlevel N, same as
.Cm initctl reload N .
.It s | S
Go to single user mode, runlevel 1.
.El
.Sh FEATURES
.Bl -bullet -width 1n -compact
.It
Runlevels, defined per service
.It
One-shot tasks, services (daemons), or SysV init start/stop scripts
.It
Runparts and
.Pa /etc/rc.local
support
.It
Process supervision similar to
.Xr systemd 8
.It
Sourcing environment files
.It
Conditions for network/process/custom dependencies
.It
Process readiness notification for synchronizing system startup as well
as reconfiguration at runtime.  Natively PID files are used, but systemd
.Cm sd_notify()
and s6 notification is also supported.
.It
Limited support for
.Xr tmpfiles.d 5 ,
no aging, attributes, or subvolumes
.It
Pre/Post script actions
.It
Tooling to enable/disable services
.It
Built-in getty
.It
Built-in watchdog, with support for hand-over to
.Lk https://troglobit.com/watchdogd.html watchdogd
.It
Built-in support for Debian/BusyBox
.Pa /etc/network/interfaces
.It
Cgroups v2, both configuration and monitoring in `initctl top`
.It
Plugin support for customization
.It
Proper rescue mode with bundled `sulogin` for protected maintenance shell
.El
.Sh BOOTPARAM
.Nm
support the following command line parameters to alter the behavior
at boot.  Notice the
.Cm --
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
.Xr bootparam 7 .
.Bl -tag -width pid -offset indent
.It Cm debug
Enable kernel debug.  Debug messages are printed to the console until
Finit starts up, unless
.Cm loglevel=7
(below) is used.
.It Cm fsck.mode=<auto,force,skip>
Defaults to
.Cm auto ,
unless Finit is built with
.Cm configure --enable-fastboot ,
in which case the default is
.Cm skip .
.It Cm fsck.repair=<preen,yes,no>
Defaults to
.Cm preen ,
unless Finit is built with
.Cm configure --enable-fsckfix ,
in which case the default is
.Cm yes .
This configure option also sets
.Cm fsck.mode=force ,
unless fastboot is also enabled.  I.e.,
.Cm configure --enable-fastboot
build option overrides the
.Cm fsck.mode
default value.
.It Cm finit.cond=foo[,bar[,baz]]
set
.Cm <boot/foo>
condition, optionally multiple conditions can be set using the same
option, separated with a comma.  Alternatively, multiple
.Cm foo.cond=arg
can be given.  Each will result in a
.Cm <boot/arg>
condition being set to control the rest of the system bootstrap.
.Pp
Very useful for selecting different boot modes, e.g. manufacturing test,
firmware upgrade, or rescue mode.
.Pp
.Sy Note:
.Cm <boot/...>
conditions cannot be cleared with
.Nm initctl !
.It Cm finit.config=/path/to/alternative/finit.conf
override the compile-time bootstrap config file, default:
.Bd -unfilled -offset indent
./configure --with-config=/etc/finit.conf
.Ed
Useful when starting up in various rescue mode, factory, or
production test setups.  Use the top-level configuration file
directive
.Cm rcsd Ar /path/to/finit.d
to override the default rcS.d directory.
.It Cm 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,
.Pa /dev/kmsg .
.It Cm finit.fstab=/path/to/fstab.alt
Tell
.Nm
to use an alternate
.Cm fstab
to mount the file system from.  Remember, this file must be on the
.Cm root=...
file system provided to Finit from the kernel.  If this file is missing,
.Nm
falls back to its built-in default, which can be changed at build time
using the
.Cm --with-fstab=/path/to/footab
configure option.  It is even possible to completely disable the
built-in using
.Cm --without-fstab ,
meaning
.Nm
.Sy must
be started with the
.Cm finit.fstab
option.
.Pp
Should
.Nm
discover that there is no fstab file available, including the fallback,
it triggers the same failure mode as when
.Cm fsck
fails, starting
.Xr sulogin 8 ,
if that is availble.  When
.Cm sulogin
is missing, or when the user exits from
.Cm sulogin ,
the system is rebooted.
.Pp
Default fstab, unless changed at build-time:
.Pa /etc/fstab
.It Cm finit.status=<on,off>
Control finit boot progress, including banner.  This used to be called
.Cm finit.show_status ,
which still works but is deprecated.
.It Cm finit.status_style=<classic,modern>
Set Finit boot progress style, when enabled.
.It Cm loglevel=<0-7>
set the kernel's log level, which is more granular than
.Cm debug .
Also, when
.Cm loglevel=7 ,
Finit will
.Em not disable
kernel logs to the console.  This is very useful when debugging the
kernel at system bring-up.  Since
.Cm loglevel=7
is the same as
.Cm debug
this means you have to use
.Cm quiet
for a quiet boot, until sysklogd takes over logging of kernel events.
.It Cm panic=SEC
By default the kernel does not reboot after a kernel panic.  This
setting will cause a kernel reboot after
.Ar SEC
seconds.
.It Cm quiet
Suppress kernel logging to console, except for warnings and errors.
Also, see
.Cm loglevel
and
.Cm quiet
above.
.It Cm rescue | recover
Start rescue/maintenance mode.  If your system comes with the bundled
.Cm sulogin
program (Finit, or from util-linux/Busybox), you will be given a root
login to a maintenance shell.  However, if
.Cm sulogin
is missing, the file
.Pa /lib/finit/rescue.conf
is read and the system booted in a limited fallback mode.  See
.Xr finit.conf 5
for more information.
.It Cm single | S
Single user mode, runlevel 1, in Finit.  Useful to debug problems with
the regular runlevel.  All services and TTYs in
.Cm [1]
will be started, e.g., a
.Cm tty [1] @console nologin
configuration presents you with a root console without login.
.Pp
.Sy Note:
by definition, single user mode does not have networking enabled.  This
is also true for runlevel 1.
.El
.Sh BOOTING
.Pp
Before laucnhing services, the system needs to be bootstrapped.  This
involves mounting all filesystems (not already mounted by an initramfs)
in
.Pa /etc/fstab ,
or any alternate
.Pa fstab
file provided on the Finit command line using
.Cm finit.fstab ,
ensuring that necessary filesystems like:
.Pa /dev ,
.Pa /proc ,
.Pa /sys ,
and
.Pa /run
are available and can provide the system with the services required.
.Pp
With that out of the way, a set of plugins take over:
.Pp
.Bl -tag -width bootmisc.so -offset indent
.It Cm bootmisc.so
Cleans up stale files from previous boots and default directories are
created in tmpfs filesystems
.It Cm modprobe.so
Probes kernel modules required by the system
.It Cm procps.so
Set kernel variables from
.Pa /etc/sysctl.conf
et al
.El
.Pp
When the plugins are done, finit reads
.Pa /etc/finit.conf
and all other enabled services in
.Pa /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.
.Pp
When all services and run/tasks have been started, the console progress
is disabled and all configured getty services are started.
.Sh 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.
.Pp
The following condition families are available today:
.Pp
.Bl -tag -width service -offset indent
.It Cm net
Linux netlink events, e.g. net/route/default, net/eth0/up, and
net/et0/running
.It Cm pid
PID files based on the service declaration
.Cm name:id ,
gives the condition pid/name:id
.It Cm service
Tracks run/task/service state stansitions, including readiness.  E.g.,
.Cm service/foo/ready
can be used as a condition for service
.Cm bar ,
provided
.Cm foo
properly signals its readiness to Finit.
.It Cm sys
System conditions, e.g. sys/key/ctrlaltdel and sys/pwr/fail
.It Cm usr
User conditions, assert and deassert using
.Cm initctl cond [set|clr] foo
.El
.Sh 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
.Xr initctl 8
tool.
.Pp
.Bl -tag -width TERM
.It HUP
Tell
.Nm
to reload its configuration file(s), same as
.Cm initctl reload
.It USR1
Restart API
.Cm ( initctl )
socket.
.It USR2
Tell
.Nm
to perform a system shutdown, same as
.Cm initctl poweroff
.It TERM
Like SIGUSR2 but performs a reboot, same as
.Cm initctl reboot
.It 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
.It PWR
Sent from a a power daemon on changes to UPS status, Finit asserts
the sys/pwr/fail condition
.El
.Sh FILES
.Bl -tag -width /etc/finit.d/available/*.conf -compact
.It Pa /etc/finit.conf
Main configuration file
.It Pa /etc/finit.d/*.conf
Static service definitions
.It Pa /etc/finit.d/available/*.conf
Available services
.It Pa /etc/finit.d/enabled/*.conf
Symlinks from available
.It Pa /run/finit/
Runtime files, including the condition subsystem
.El
.Sh SEE ALSO
.Xr finit.conf 5
.Xr initctl 8
.Xr tmpfiles.d 5
.Sh AUTHORS
.Nm
was conceived and reverse engineered by Claudio Matsuoka.  Since v1.0,
maintained by Joachim Wiberg, with contributions by many others.