Finit is a small SysV init replacement with process supervision similar to that of daemontools and runit. Its focus is on small and embedded GNU/Linux systems, although fully functional on standard server and desktop installations. It should also work on other UNIX systems, but this has yet to be proven.

Finit is fast because it starts services in parallel, it then supervises and automatically restarts them if they fail. This can be extended upon with custom callbacks for all services, hooks into the boot process, or plugins to extend the functionality and adapt Finit to your needs.

Finit is not only fast, it's arguably one of the easiest to get started with. A complete system can be booted with one simple configuration file, /etc/finit.conf, see below for syntax.

Process Supervision Start, monitor and restarting services if they fail.

Runlevels Finit supports standard runlevels if you want, but you don't need them for simple installations.

Plugins Extend and modify finit behavior. See examples in plugins/ directory. Plugin capabilities:

• Service callbacks — modify service arguments, run/restart/stop
• Task/Run callbacks — a one-shot commands, executed in sequence
• Hooks — hook into the boot at predefined points to extend finit
• I/O — listen to external events and control finit behavior/services

Extensions and functionality not purely related to what an /sbin/init needs to start a system are available as a set of plugins that either hook into the boot process or respond to various I/O.

Contrary to most script based init alternatives (SysV init, upstart, systemd, OpenRC and the likes) finit instead reads its configuration from /etc/finit.conf. Below is a brief list, see the source code for the full list:

check <DEV>

Run fsck on a file system before mounting it

module <MODULE>

Load a kernel module, with optional arguments

network <PATH>

Script or program to bring up networking, with optional arguments

runlevel <N>

N is the runlevel number 1-9, where 6 is reserved for reboot

run [RUN_LVLS] /path/to/cmd ARGS -- Optional description

One-shot command to run in sequence when entering a runlevel, with optional arguments and description. This command is guaranteed to be completed before running the next command.

task [RUN_LVLS] /path/to/cmd ARGS -- Optional description

One-shot like 'run', but starts in parallel with the next command

service [RUN_LVLS] /path/to/daemon ARGS -- Optional description

Service, or daemon, to be monitored and automatically restarted if it exits prematurely. Please note that you often need to provide a --foreground or --no-background argument to most daemons to prevent them from forking off to the background.

runparts <PATH>

Call run-parts(8) on a directory other than default /etc/finit.d

include <CONF>

Include another configuration file, /etc/finit.d, or runparts path is prepended to file if the file is not found or an absolute path is not given

tty [RUN_LVLS] <DEV | /bin/sh>

Start a getty on the given TTY device, in the given runlevels. When no tty setting is given in finit.conf, or if /bin/sh is given as argument instead of a device path, a single shell is started on the default console. Useful for really bare-bones systems

console <DEV>

Some embedded systems have a dedicated console port. This command tells finit to not start getty, but instead print a friendly message and wait for the user to activate the console with a key press before starting getty.

When running make install no default /etc/finit.conf will be provided since the system requirements differ too much. Try out the Debian 6.0 example /usr/share/doc/finit/finit.conf configuration that is capable of service monitoring SSH, sysklogd, gdm and a console getty!

At the end of the boot, when networking and all services are up, finit calls its built-in run-parts(8) on the /etc/finit.d/ directory, if it exists. Similar to how the /ec/rc.local file works in most other init daemons, only finit runs a directory of scripts. This replaces the earlier support for a /usr/sbin/services.sh script in the original finit.

Support for runlevels is included in Finit from v1.8. By default all services, tasks, run commands and TTYs listed without a set of runlevels get a default set [234] assigned. The default runlevel after boot is 2.

To specify an allowed set of runlevels for a service, run command, task, or tty, add [NNN] to it in finit.conf, like this:

run     [S]      /etc/init.d/acpid start -- Starting ACPI Daemon
task    [S]      /etc/init.d/kbd start -- Preparing console
service [S12345] /sbin/klogd -n -x -- Kernel log daemon
tty     [12345]  /dev/tty1
tty     [2]      /dev/tty2
tty     [2]      /dev/tty3
tty     [2]      /dev/tty4
tty     [2]      /dev/tty5
tty     [2]      /dev/tty6

In this example acpid is started once at bootstrap using a conventional SysV init script. Here the run command was used, meaning the following task command is not run until the init script has fully completed.

Tasks and services are started in parallel, while run commands are run in the order listed and subsequent commands are not started until a run command has completed.

Existing finit.conf files that lack runlevel setting will get a default runlevel assigned, [234].

Switching between runlevels can be done by calling init with a single argument, e.g., 'init 5' switches to runlevel 5.

Finit handles SIGUSR1 and SIGUSR2 for reboot and halt, and listens to /dev/initctl so standard Linux reboot and halt commands should also work.

The finit build system does not employ the GNU Configure and Build System, instead standard makefiles are used. The user is encouraged to make source code changes, using defines and conditionally building plugins instead to alter the behavior of finit.

The following environment variables are checked by the makefiles and control what is built and where resulting binaries are installed.

ROOTDIR=

Top directory for building complete system, used in pretty printing

VERSION=

Defaults to the currently released version of finit, e.g., 1.3 but can be overridden by packages to add a suffix or completely alter the version.

CFLAGS=

Standard CFLAGS are inherited from the build environment.

CPPFLAGS=

Standard CPPFLAGS are inherited from the build environment.

LDFLAGS=

Standard LDFLAGS are inherited from the build environment.

LDLIBS=

Standard LIBLIBS are inherited from the build environment.

prefix=

Base prefix path for all files, except sbinbdir and sysconfdir. Used in concert with the DESTDIR variable. Defaults to /usr

sbindir=

Path to where resulting binaries should install to. Used in concert with the DESTDIR variable. Defaults to /sbin

sysconfdir=

Path to where finit configuration files should install to. Used in concert with the DESTDIR variable. Defaults to /etc, but is currently unused.

PLUGINS=

List of stock finit plugins to build and install.

plugindir=

Absolute path to where finit should look for dynamically loadable plugins at runtime. At installation prepended by DESTDIR and prefix. Defaults to /lib/finit/plugins

DESTDIR=

Used by packagers and distributions when building a relocatable bundle of files. Always prepended to the prefix destination directory.

Example:

$ tar xfJ finit-1.3.tar.xz
$ PLUGINS="initctl.so hwclock.so" DESTDIR=/tmp/finit/dst \
  make -C finit-1.3/ clean install
make: Entering directory `/home/troglobit/finit-1.3'
  CC      finit.o
  CC      conf.o
  CC      helpers.o
  CC      sig.o
  CC      svc.o
  CC      plugin.o
  CC      strlcpy.o
  LINK    finit
  CC      plugins/initctl.o
  PLUGIN  plugins/initctl.so
  CC      plugins/hwclock.o
  PLUGIN  plugins/hwclock.so
  INSTALL /tmp/finit/dst/sbin/finit
  INSTALL /tmp/finit/dst/lib/finit/plugins/initctl.so
  INSTALL /tmp/finit/dst/lib/finit/plugins/hwclock.so
make: Leaving directory `/home/troglobit/finit-1.3'

In this example the finit-1.3.tar.xz archive is unpacked to the user's home directory, built and installed to a temporary staging directory. The environment variables DESTDIR and PLUGINS are changed to suit this particular build.

The default install does not setup finit as the system default /sbin/init, neither does it setup an initial /etc/finit.conf.

It is assumed that users of finit are competent enough to either setup finit as their default /sbin/init or alter their respective Grub, LOADLIN, LILO, U-Boot/Barebox or RedBoot boot loader configuration to give the kernel the following extra command line:

init=/sbin/finit

Add finit_debug, or --debug, to the kernel command line to enable trace messages. A console getty is always started, see the file finit.h for more useful compile-time tweaks:

init=/sbin/finit --debug

This is the continuation of the original finit by Claudio Matsuoka, which in turn was reverse engineered from syscalls of the EeePC fastinit -- "gaps filled with frog DNA ...". It is currently being developed and maintained by Joachim Nilsson at GitHub. Please file bug reports, clone it, or send pull requests for bug fixes and proposed extensions.