wt/finit
1
0 Fork 0
mirror of https://github.com/troglobit/finit.git synced 2026-10-22 11:36:07 +00:00
Code Issues Packages Projects Releases Wiki Activity

doc: massive refactor and simplification to migrate to mkdocs

Browse Source 
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg committed 2025-07-09 11:50:38 +02:00
1 parent a73e02afac
commit d77773d8ee
44 files changed
+2331 -2268
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

doc/config/Makefile.am
+7
View File
@@ -0,0 +1,7 @@
configdocsdir := @docdir@/doc/config
configdocs_DATA = README.md cgroups.md env.md files.md index.md \
limitations.md logging.md rescue.md runlevels.md \
runparts.md service-env.md service-opts.md \
service-sync.md service-wrappers.md services.md \
sysv.md task-and-run.md templating.md tty.md
EXTRA_DIST = $(configdocs_DATA)
doc/config/README.md
Symlink
+1
View File
@@ -0,0 +1 @@
index.md
doc/config/cgroups.md
+65
View File
@@ -0,0 +1,65 @@
There are three major cgroup configuration directives:
1. Global top-level group: `init`, `system`, `user`, or a custom group
2. Selecting a top-level group for a set of run/task/services
3. Per run/task/service limits
> [!NOTE]
> Linux cgroups and details surrounding values are not explained in the
> Finit documentation. The Linux admin-guide cover this well:
> <https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html>
Top-level Group Configuration
-----------------------------
# Top-level cgroups and their default settings. All groups mandatory
# but more can be added, max 8 groups in total currently. The cgroup
# 'root' is also available, reserved for RT processes. Settings are
# as-is, only one shorthand 'mem.' exists, other than that it's the
# cgroup v2 controller default names.
cgroup init cpu.weight:100
cgroup user cpu.weight:100
cgroup system cpu.weight:9800
Adding an extra cgroup `maint/` will require you to adjust the weight of
the above three. We leave `init/` and `user/` as-is reducing weight of
`system/` to 9700.
cgroup system cpu.weight:9700
# Example extra cgroup 'maint'
cgroup maint cpu.weight:100
By default, the `system/` cgroup is selected for almost everything. The
`init/` cgroup is reserved for PID 1 itself and its closest relatives.
The `user/` cgroup is for local TTY logins spawned by getty.
Selecting Cgroups
------------------
To select a different top-level cgroup, e.g. `maint/`, one can either
define it for a group of run/task/service directives in a `.conf` or per
each stanza:
cgroup.maint
service [...] <...> /path/to/foo args -- description
service [...] <...> /path/to/bar args -- description
or
service [...] <...> cgroup.maint /path/to/foo args -- description
The latter form also allows per-stanza limits on the form:
service [...] <...> cgroup.maint:cpu.max:10000,mem.max:655360 /path/to/foo args -- description
Notice the comma separation and the `mem.` exception to the rule: every
cgroup setting maps directly to cgroup v2 syntax. I.e., `cpu.max` maps
to the file `/sys/fs/cgroup/maint/foo/cpu.max`. There is no filtering,
except for expanding the shorthand `mem.` to `memory.`, if the file is
not available, either the cgroup controller is not available in your
Linux kernel, or the name is misspelled.
A daemon using `SCHED_RR` currently need to run outside the default cgroups.
service [...] <...> cgroup.root /path/to/daemon arg -- Real-Time process
doc/config/env.md
+31
View File
@@ -0,0 +1,31 @@
Environment Variables
---------------------
In Finit v4.3 support for setting environment variables in `finit.conf`,
and any `*.conf`, was added. It is worth noting that these are global
and *shared with all* services -- the only way to have a service-local
environment is detailed in [Services Environment](service-env.md).
The syntax for global environment variables is straight forward. In
Finit v4.4 the `set` keyword was added for completeness, but the old
syntax (without the `set ` prefix) is still honored:
set foo=bar
set baz="qux"
On reload of .conf files, all tracked environment variables are cleared
so if `foo=bar` is removed from `finit.conf`, or any `finit.d/*.conf`
file, it will no longer be used by Finit or any new (!) started
run/tasks or services. The environment of already started processes can
not be changed.
The only variables reset to sane defaults on .conf reload are:
PATH=_PATH_STDPATH
SHELL=_PATH_BSHELL
LOGNAME=root
USER=root
It is entirely possible to override these as well from the .conf files,
but be careful. Changing SHELL changes the behavior of `system()` and a
lot of other commands as well.
doc/config/files.md
+208
View File
@@ -0,0 +1,208 @@
Files & Layout
==============
Originally Finit was configured using a single file, `/etc/finit.conf`,
and although still possible to use a single configuration file, today
the following layout is recommended:
/
|- etc/
| |- finit.d/
| | |- available/
| | | `- my-service.conf
| : |- enabled/
| : | `- my-service.conf -> ../available/my-service.conf
| : :
| : |- static-service.conf
| : `- another-static.conf
| :
| `- finit.conf
|- lib
| `- finit/
| `- system/
| |- 10-hotplug.conf
| `- ...
`- run/
`- finit/
`- system/
|- dbus.conf
|- keventd.conf
|- runparts.conf
|- watchdogd.conf
`- ...
Configuration files in `/etc` are provided by the user, or projects like
[finit-skel](https://github.com/troglobit/finit-skel) and extended by
the user.
The files in `/lib/finit/system/*.conf` are system critical services and
setup provided by Finit, e.g. udev/mdev that must run very early at system
bootstrap. This system directory was introduced in Finit v4.4 to replace
the hard-coded services provided by plugins before. All .conf files in this
directory be either replaced by a system administrator or overridden by a
file with the same name in `/etc/finit.d/`.
The files in `/run/finit/system/*.conf` are created by plugins and Finit
bundled services like runparts, [watchdog](../watchdog.md), and
[`keventd`](../keventd.md) if they are enabled. Like
`/lib/finit/system/*.conf`, these files can be overridden by file with
the same name in `/etc/finit.d/`.
Services in the `available/` and `enabled/` sub-directories are called
dynamic services, in contrast to static services -- the only difference
being where they are installed and if the `initctl` tool can manage them
with the `enable` and `disable` commands. An administrator can always
create files and symlinks manually.
At bootstrap, and `initctl reload`, all .conf files are read, starting
with `finit.conf`, then `/lib/finit/system/*.conf`, `finit.d/*.conf`,
and finally all `finit.d/enabled/*.conf` files. Each directory is a
unique group, where files within each group are sorted alphabetically.
**Example:**
/lib/finit/system/10-hotplug.conf
/lib/finit/system/90-testserv.conf
/run/finit/system/dbus.conf
/run/finit/system/runparts.conf
/etc/finit.d/10-abc.conf
/etc/finit.d/20-abc.conf
/etc/finit.d/enabled/1-aaa.conf
/etc/finit.d/enabled/1-abc.conf
The resulting combined configuration is read line by line, each `run`,
`task`, and `service` added to an ordered list that ensures they are
started in the same order. This is important because of the blocking
properties of the `run` statement. For an example on the relation of
`service` and `run` statements, and dependency handling between them,
see [Conditional Loading](services.md#conditional-loading), below.
> [!NOTE]
> The names `finit.conf` and `finit.d/` are only defaults. They can be
> changed at compile-time with two `configure` options:
> `--with-config=/etc/foo.conf` and `--with-rcsd=/var/foo.d`.
>
> They can also be overridden from the [kernel command line](../cmdline.md)
> using: `-- finit.config=/etc/bar.conf` and in that file use the
> top-level configuration directive `rcsd /path/to/finit.d`.
Filesystem Layout
-----------------
Finit is most comfortable with a traditional style Linux filesystem
layout, as specified in the [FHS][]:
/.
|- bin/
|- dev/ # Mounted automatically if devtmpfs is available
| |- pts/ # Mounted automatically by Finit if it exists
| `- shm/ # Mounted automatically by Finit if it exists
|- etc/
| |- finit.d/
| | |- available/
| | `- enabled/
| `- finit.conf
|- home/
|- lib/
|- libexec/
|- mnt/
|- proc/ # Mounted automatically by Finit if it exists
|- root/
|- run/ # Mounted automatically by Finit if it exists
| `- lock/ # Created automatically if Finit mounts /run
|- sbin/
|- sys/ # Mounted automatically by Finit if it exists
|- tmp/ # Mounted automatically by Finit if it exists
|- usr/
`- var/
|- cache/
|- db/
|- lib/
| `- misc/
|- lock/
|- log/
|- run -> ../run
|- spool/
`- tmp/
Finit starts by mounting the critical file systems `/dev`, `/proc/`, and
`/sys`, unless they are already mounted. When all plugins and other,
core Finit functions, have been set up, all relevant filesystems (where
`PASS > 0`) are checked and mounted from the selected `fstab`, either
the default `/etc/fstab`, or any custom one selected from the command
line, or at build time.
To provide a smooth ride, file system not listed in the given `fstab`,
e.g. `/tmp` and `/run`, are automatically mounted by Finit, as listed
above, provided their respective mount point exists.
With all filesystems mounted, Finit calls `swapon`.
> [!TIP]
> To see what happens when all filesystems are mounted, have a look at
> the [`bootmisc.so` plugin](../plugins.md).
At shutdown, and after having stopped all services and other lingering
processes have been killed, filesystems are unmounted in the reverse
order, and `swapoff` is called.
[FHS]: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html
Managing Services
-----------------
Using `initctl disable my-service` the symlink (above) is removed and
the service is queued for removal. Several changes can be made to the
system, but it is not until `initctl reload` is called that the changes
are activated.
To add a new static service, drop a `.conf` file in `/etc/finit.d/` and
run `initctl reload`. (It is also possible to `SIGHUP` PID 1, or call
`finit q`, but that has been deprecated with the `initctl` tool). Finit
monitors all known active `.conf` files, so if you want to force a
restart of any service you can touch its corresponding `.conf` file in
`/etc/finit.d` and call `initctl reload`. Finit handles all conditions
and dependencies between services automatically, see the section on
[Service Synchronization](service-sync.md) for more details.
On `initctl reload` the following is checked for all services:
- If a service's `.conf` file has been removed, or its conditions are no
longer satisfied, the service is stopped.
- If the file is modified, or a service it depends on has been reloaded,
the service is reloaded (stopped and started).
- If a new service is added it is automatically started — respecting
runlevels and return values from any callbacks.
For more info on the different states of a service, see the separate
document [Finit Services](../service.md).
Alternate finit.d/
------------------
**Syntax:** `rcsd /path/to/finit.d`
The Finit rcS.d directory is set at compile time with:
./configure --with-rcsd=/etc/finit.d
A system with multiple use-cases may be bootstrapped with different
configurations, starting with the kernel command line option:
-- finit.config=/etc/factory.conf
This file in turn can use the `rcsd` directive to tell Finit to use
another set of .conf files, e.g.:
rcsd /etc/factory.d
> [!NOTE]
> This directive is only available from the top-level bootstrap .conf
> file, usually `/etc/finit.conf`.
Including Finit Configs
------------------------
**Syntax:** `include <CONF>`
Include another configuration file. Absolute path required.
doc/config/index.md
+30
View File
@@ -0,0 +1,30 @@
This section provides an overview of Finit's configuration system. For
detailed information on specific topics, see the individual sections in
the navigation menu.
Configuration File Syntax
--------------------------
The file format is line based, empty lines and comments, lines starting
with `#`, are ignored. A configuration directive starts with a keyword
followed by a space and the rest of the line is treated as the value.
As of Finit v4.4, configuration directives can be broken up in multiple
lines using the continuation character `\`, and trailing comments are
also allowed. Example:
```aconf
# Escape \# chars if you want them literal in, e.g., descriptions
service name:sysklogd [S123456789] \
env:-/etc/default/sysklogd \
syslogd -F $SYSLOGD_ARGS \
-- System log daemon \# 1 # Comments allowed
```
The .conf files `/etc/finit.conf` and `/etc/finit.d/*` support many
directives. Some are restricted, e.g., only available at bootstrap,
runlevel `S`. Read on in [Files & Layout](files.md) for more on how
to structure your .conf files.
For details on restrictions, see [Limitations](limitations.md).
doc/config/limitations.md
+21
View File
@@ -0,0 +1,21 @@
Limitations
===========
As of Finit v4 there are no limitations to where `.conf` settings can be
placed. Except for the system/global `rlimit` and `cgroup` top-level
group declarations, which can only be set from `/etc/finit.conf`, since
it is the first `.conf` file Finit reads.
Originally, `/etc/finit.conf` was the only way to set up a Finit system.
Today it is mainly used for bootstrap settings like system hostname,
early module loading for watchdogd, network bringup and system shutdown.
These can now also be set in any `.conf` file in `/etc/finit.d`.
There is, however, nothing preventing you from having all configuration
settings in `/etc/finit.conf`.
> [!IMPORTANT]
> The default `rcsd`, i.e., `/etc/finit.d`, was previously the Finit
> [runparts](runparts.md) directory. Finit >=v4.0 no longer has a
> default `runparts` directory, make sure to update your setup, or the
> finit configuration, accordingly.
doc/config/logging.md
+41
View File
@@ -0,0 +1,41 @@
General Logging
===============
**Syntax:** `log size:200k count:5`
Log rotation for run/task/services using the `log` sub-option with
redirection to a log file. Global setting, applies to all services.
The size can be given as bytes, without a specifier, or in `k`, `M`,
or `G`, e.g. `size:10M`, or `size:3G`. A value of `size:0` disables
log rotation. The default is `200k`.
The count value is recommended to be between 1-5, with a default 5.
Setting count to 0 means the logfile will be truncated when the MAX
size limit is reached.
Redirecting Output
------------------
The `run`, `task`, and `service` stanzas also allow the keyword `log` to
redirect `stderr` and `stdout` of the application to a file or syslog
using the native `logit` tool. This is useful for programs that do not
support syslog on their own, which is sometimes the case when running
in the foreground.
The full syntax is:
log:/path/to/file
log:prio:facility.level,tag:ident
log:console
log:null
log
Default `prio` is `daemon.info` and default `tag` is the basename of the
service or run/task command.
Log rotation is controlled using the global `log` setting.
**Example:**
service log:prio:user.warn,tag:ntpd /sbin/ntpd pool.ntp.org -- NTP daemon
doc/config/rescue.md
+62
View File
@@ -0,0 +1,62 @@
Rescue Mode
===========
Finit supports a rescue mode which is activated by the `rescue` option
on the kernel command line. See [cmdline docs](../cmdline.md) for how to
activate it.
This rescue mode can be disabled at configure time using:
configure --without-rescue
The rescue mode comes in two flavors; *traditional* and *fallback*.
> [!NOTE]
> In this mode `initctl` will not work. Use the `-f` flag to force
> `reboot`, `shutdown`, or `poweroff`.
Traditional
-----------
This is what most users expect. A very early maintenance login prompt,
served by the system `sulogin` program from util-linux, or BusyBox. If
that is not found in `$PATH`, the bundled `/libexec/finit/sulogin`
program is used instead. If a successful login is made, or if the user
exits (Ctrl-D), the rescue mode is ended and the system boots up
normally.
> [!WARNING]
> The bundled sulogin in Finit can at configure time be given another
> user than the default (root). If the sulogin user does not have a
> password, or __the account is locked__, the user is presented with a
> prompt: `"Press enter to enter maintenance mode."`, which will open
> up a root shell *without prompting for password*!
Fallback
--------
If no `sulogin` program is found, Finit tries to bring up as much of its
own functionality as possible, yet limiting many aspects, meaning; no
network, no `fsck` of file systems in `/etc/fstab`, no `/etc/rc.local`,
no `runparts`, and most plugins are skipped (except those that provide
functionality for the condition subsystem).
Instead of reading `/etc/finit.conf` et al, system configuration is read
from `/lib/finit/rescue.conf`, which can be freely modified by the
system administrator.
The bundled default `rescue.conf` contains nothing more than:
runlevel 1
tty [12345] rescue
The `tty` has the `rescue` option set, which works similar to the board
bring-up tty option `notty`. The major difference being that `sulogin`
is started to query for root/admin password. If `sulogin` is not found,
`rescue` behaves like `notty` and gives a plain root shell prompt.
If Finit cannot find `/lib/finit/rescue.conf` it defaults to:
tty [12345] rescue
There is no way to exit the *fallback* rescue mode.
doc/config/runlevels.md
+168
View File
@@ -0,0 +1,168 @@
Runlevels
=========
Finit supports runlevels, but unlike other init systems runlevels are
declared per service/run/task/sysv command. When booting up a system
Finit pass through three phases:
1. Setting up the console, parsing any command line options, and other
housekeeping tasks like mounting all filesystems, and calling `fsck`
2. Starting all run/task/services in runlevel S, then waiting for all
services to have started, and all run/tasks to have completed
3. Go to runlevel 2, or whatever the user has set in the configuration
Available runlevels:
- ` S`: bootStrap
- ` 1`: Single user mode
- `2-5`: traditional multi-user mode
- ` 6`: reboot
- `7-9`: multi-user mode (extra)
- ` 0`: shutdown
Runlevel S (bootStrap), is for tasks supposed to run once at boot, and
services like `syslogd`, which need to start early and run throughout
the lifetime of your system.
Example:
task [S] /lib/console-setup/console-setup.sh
service [S12345] env:-/etc/default/rsyslog rsyslogd -n $RSYSLOGD_ARGS
When bootstrap has completed, Finit moves to runlevel 2. This can be
changed in `/etc/finit.conf` using the `runlevel N` directive, or by a
script running in runlevel S that calls, e.g., `initctl runlevel 9`.
The latter is useful if startup scripts detect problems outside of
Finit's control, e.g., critical services/devices missing or hardware
problems.
Each runlevel must be allowed to "complete". Meaning, all services in
runlevel S must have started and all run/tasks have been started and
collected (exited). Finit waits 120 seconds for all run/tasks in S to
complete before proceeding to 2.
Finit first stops everything that is not allowed to run in 2, and then
brings up networking. Networking is expected to be available in all
runlevels except: S, 1 (single user level), 6, and 0. Networking is
enabled either by the `network script` directive, or if you have an
`/etc/network/interfaces` file, Finit calls `ifup -a` -- at the very
least the loopback interface is brought up.
> [!NOTE]
> When moving from runlevel S to 2, all run/task/services that were
> constrained to runlevel S only are dropped from bookkeeping. So when
> reaching the prompt, `initctl` will not show these run/tasks. This is
> a safety mechanism to prevent bootstrap-only tasks from accidentally
> being run again. E.g., `console-setup.sh` above.
Runlevel Configuration
----------------------
**Syntax:** `runlevel <N>`
The system runlevel to go to after bootstrap (S) has completed. `N` is
the runlevel number 0-9, where 6 is reserved for reboot and 0 for halt.
Completed in this context means all services have been started and all
run/tasks have been started and collected.
It is recommended to keep runlevel 1 as single-user mode, because
Finit disables networking in this mode.
*Default:* 2
> [!NOTE]
> Only read and executed in runlevel S (bootstrap).
Networking
----------
**Syntax:** `network <PATH>`
Script or program to bring up networking, with optional arguments.
Deprecated. We recommend using dedicated task/run stanzas per runlevel,
or `/etc/network/interfaces` if you have a system with `ifupdown`, like
Debian, Ubuntu, Linux Mint, or an embedded BusyBox system.
> [!NOTE]
> Only read and executed in runlevel S (bootstrap).
System Hostname
---------------
**Syntax:** `host <NAME>`, or `hostname <NAME>`
Set system hostname to NAME, unless `/etc/hostname` exists in which case
the contents of that file is used.
Deprecated. We recommend using `/etc/hostname` instead.
> [!NOTE]
> Only read and executed in runlevel S (bootstrap).
Kernel Modules
--------------
**Syntax:** `module <MODULE> [ARGS]`
Load a kernel module, with optional arguments. Similar to `insmod`
command line tool.
Deprecated, there is both a `modules-load.so` and a `modprobe.so` plugin
that can handle module loading better. The former supports loading from
`/etc/modules-load.d/`, the latter uses kernel modinfo to automatically
load (or coldplug) every required module. For hotplug we recommend the
BusyBox mdev tool, add to `/etc/mdev.conf`:
$MODALIAS=.* root:root 0660 @modprobe -b "$MODALIAS"
> [!NOTE]
> Only read and executed in runlevel S (bootstrap).
Resource Limits
---------------
**Syntax:** `rlimit [hard|soft] RESOURCE <LIMIT|unlimited>`
Set the hard or soft limit for a resource, or both if that argument is
omitted. `RESOURCE` is the lower-case `RLIMIT_` string constants from
`setrlimit(2)`, without prefix. E.g. to set `RLIMIT_CPU`, use `cpu`.
LIMIT is an integer that depends on the resource being modified, see
the man page, or the kernel `/proc/PID/limits` file, for details.
Finit versions before v3.1 used `infinity` for `unlimited`, which is
still supported, albeit deprecated.
# No process is allowed more than 8MB of address space
rlimit hard as 8388608
# Core dumps may be arbitrarily large
rlimit soft core infinity
# CPU limit for all services, soft & hard = 10 sec
rlimit cpu 10
`rlimit` can be set globally, in `/etc/finit.conf`, or locally per
each `/etc/finit.d/*.conf` read. I.e., a set of task/run/service
stanzas can share the same rlimits if they are in the same .conf.
Miscellaneous Settings
----------------------
**Syntax:** `reboot-delay <0-60>`
Optional delay at reboot (or shutdown or halt) to allow kernel
filesystem threads to complete after calling `sync(2)` before
rebooting. This applies primarily to filesystems that do not
have a reboot notifier implemented. At the point of writing,
the only known filesystems affected are: ubifs, jffs2.
*Default:* 0 (disabled)
When enabled (non-zero), this delay runs after file systems have been
unmounted and the root filesystem has been remounted read-only, and
sync(2) has been called, twice.
> "On Linux, sync is only guaranteed to schedule the dirty blocks for
> writing; it can actually take a short time before all the blocks are
> finally written.
doc/config/runparts.md
+51
View File
@@ -0,0 +1,51 @@
Run-parts Scripts
-----------------
**Syntax:** `runparts [progress] [sysv] <DIR>`
Call [run-parts(8)][] on `DIR` to run start scripts. All executable
files in the directory are called, in alphabetic order. The scripts in
this directory are executed at the very end of runlevel `S`.
A common use-case for runparts scripts is to create and enable/disable
services, which Finit will then apply when changing runlevel from S to
whatever the next runlevel is set to be (default 2). E.g., generate a
`/etc/chrony.conf` and call `initctl enable chronyd`.
**Options:**
- `progress`: display the progress of each script being executed
- `sysv`: run only SysV style scripts, i.e., `SNNfoo`, or `KNNbar`,
where `NN` is a number (0-99).
If global debug mode is enabled, the `runparts` program is also called
with the debug flag.
**Limitations:**
Scripts called from `runparts`, or hook scripts (see below), are limited
in their interaction with Finit. Like the standalone `run` stanza and
the `/etc/rc.local` shell script, Finit waits for their completion
before continuing. None of them can issue commands to start, stop, or
restart other services. Also, ensure all your services and programs
either terminate or start in the background or you will block Finit.
> [!NOTE]
> `runparts` scripts are only read and executed in runlevel S. See
> [hook scripts](../plugins.md#hooks) for other ways to run scripts at
> certain points during the complete lifetime of the system.
**Recommendations:**
It can be beneficial to use `01-name`, `02-othername`, etc., to ensure
the scripts are started in that order, e.g., if there is a dependency
order between scripts. Symlinks to existing daemons can talso be used,
but make sure they daemonize (background) themselves properly, otherwise
Finit will lock up.
If `S[0-9]foo` and `K[0-9]bar` style naming is used, the executable will
be called with an extra argument, `start` and `stop`, respectively.
E.g., `S01foo` will be called as `S01foo start`. Of course, `S01foo`
and `K01foo` may be a symlink to to `another/directory/foo`.
[run-parts(8)]: http://manpages.debian.org/cgi-bin/man.cgi?query=run-parts
doc/config/service-env.md
+27
View File
@@ -0,0 +1,27 @@
Service Environment
-------------------
Finit supports sourcing environment variables from `/etc/default/*`, or
similar `--with-sysconfig=DIR`. This is a common pattern from SysV init
scripts, where the start-stop script is a generic script for the given
service, `foo`, and the options for the service are sourced from the
file `/etc/default/foo`. Like this:
* `/etc/default/foo`:
FOO_OPTIONS=--extra-arg="bar" -s -x
* `/etc/finit.conf`:
service [2345] env:-/etc/default/foo foo -n $FOO_OPTIONS -- Example foo daemon
Here the service `foo` is started with `-n`, to make sure it runs in the
foreground, and the with the options found in the environment file. With
the `ps` command we can see that the process is started with:
foo -n --extra-arg=bar -s -x
> [!NOTE]
> The leading `-` in `env:` determines if Finit should treat a missing
> environment file as blocking the start of the service or not. When
> `-` is used, a missing environment file does *not* block the start.
doc/config/service-opts.md
+111
View File
@@ -0,0 +1,111 @@
If a service should not be automatically started, it can be configured
as manual with the optional `manual` argument. The service can then be
started at any time by running `initctl start <service>`.
manual:yes
The name of a service, shown by the `initctl` tool, defaults to the
basename of the service executable. It can be changed with the
optional `name` argument:
name:<service-name>
If multiple instances of a service, with the same `name`, exist. Set
the identifier `:ID` to prevent Finit from replacing previous instances:
service :eth1 ssdpd eth1 -- Windows discovery on eth1
service :eth2 ssdpd eth2 -- Windows discovery on eth2
If you have conflicting services and want to prevent them from starting,
use the `conflict:` argument:
service [S12345789] udevd -- Device event management daemon
run [S] conflict:udevd mdev -s -- Populating device tree
Multiple conflicting services can be separated using `,`:
service :1 abc
service :2 abc
service conflict:abc:1,abc:2 cde
As mentioned previously, services are automatically restarted, this is
configurable with the following options:
* `restart:NUM` -- number of times Finit tries to restart a crashing
service, default: 10, max: 255. When this limit is reached the
service is marked *crashed* and must be restarted manually with
`initctl restart NAME`
* `restart_sec:SEC` -- number of seconds before Finit tries to restart
a crashing service, default: 2 seconds for the first five retries,
then back-off to 5 seconds. The maximum of this configured value
and the above (2 and 5) will be used
* `restart:always` -- no upper limit on the number of times Finit
tries to restart a crashing service. Same as `restart:-1`
* `norestart` -- dont restart on failures, same as `restart:0`
* `respawn` -- bypasses the `restart` mechanism completely, allows
endless restarts. Useful in many use-cases, but not what `service`
was originally designed for so not the default behavior
* `oncrash:reboot` -- when all retries have failed, and the service
has *crashed*, if this option is set the system is rebooted
* `oncrash:script` -- similarly, but instead of rebooting, call the
`post:script` action with exit code `crashed`, see below
* `reload:script [args]` -- some services do not support `SIGHUP` but
may have other ways to update the configuration of a running daemon.
When `reload:script` is defined it is preferred over `SIGHUP`. Like
systemd, Finit sets `$MAINPID` as a convenience to scripts, which in
effect also allow `reload:'kill -HUP $MAINPID'`
* `stop:script [args]` -- some services may require alternate methods
to be stopped. When `stop:script` is defined it is preferred over
`SIGTERM` and `stop` for `service` and `sysv` stanzas, respectively.
Similar to `reload:script`, Finit sets `$MAINPID`
> [!CAUTION]
> Both `reload:script` and `stop:script` are called as PID 1, without
> any timeout! Meaning, it is up to you to ensure the script is not
> blocking for seconds at a time or never terminates.
When stopping a service (run/task/sysv/service), either manually or when
moving to another runlevel, Finit starts by sending `SIGTERM`, to allow
the process to shut down gracefully. However, if the process has not
been collected within 3 seconds, Finit will send `SIGKILL`. To stop the
process using a different signal than `SIGTERM`, use `halt:SIGNAL`,
e.g., `halt:SIGPWR`. To change the delay between the stop signal and
KILL, use the option `kill:<1-60>`, e.g., `kill:10` to wait 10 seconds
before sending `SIGKILL`.
Services, including the `sysv` variant, support pre/post/ready and
cleanup scripts:
* `pre:[0-3600,]script` -- called before the sysv/service is stated
* `post:[0-3600,]script` -- called after the sysv/service has stopped
* `ready:[0-3600,]script` -- called when the sysv/service is ready
* `cleanup:[0-3600,]script` -- called when run/task/sysv/service is removed
The optional number (0-3600) is the timeout before Finit kills the
script, it defaults to the kill delay value and can be disabled by
setting it to zero. These scripts run as the same `@USER:GROUP` as the
service itself, with any `env:file` sourced. The scripts are executed
from the `$HOME` of the given user. The scripts are not called with any
argument, but get a set of environment variables:
* `SERVICE_IDENT=foo:1`
* `SERVICE_NAME=foo`
* `SERVICE_ID=1`
The `post:script` is called with an additional set of environment
variables. Yes, the text is correct, the naming was an accident:
- `EXIT_CODE=[exited,signal,crashed]`: normal exit, signaled, or
crashed
- `EXIT_STATUS=[num,SIGNAME]`: set to one of exit status code from
the program, if it exited normally, or the signal name (`HUP`,
`TERM`, etc.) if it exited due to signal
When a run/task/sys/service is removed (disable + reload) it is first
stopped and then removed from the runlevel. The `post:script` always
runs when the process has stopped, and the `cleanup:script` runs when
the the stanza has been removed from the runlevel.
> [!IMPORTANT]
> These script actions are intended for setup, cleanup, and readiness
> notification. It is up to the user to ensure the scripts terminate.
doc/config/service-sync.md
+74
View File
@@ -0,0 +1,74 @@
Service Synchronization
=======================
Finit was created for fast booting systems. Faster than a regular SysV
Init based system at the time. Early on the need for a guaranteed start
order of services (daemons) arose. I.e., service `A` must be guaranteed
to have started (and be ready!) before `B`. The model that was chosen
to determine this was very simple: PID files.
Early on in UNIX daemons were controlled with basic IPC like signals,
and the way for a user to know that a daemon was ready to respond to
signals (minimally having set up its signal handler), was to tell the
user;
> "Hey, you can send signals to me using the PID in this file:
> `/var/run/daemon.pid`".
Since most systems run fairly unchanged after boot, Finit could rely on
the PID file for `A` being created before launching `B`. This method
has worked well for a long time, and for systems based on Open Source it
was easy to either add PID file support to a daemon without support for
it, or fix ordering issues (PID file created before signal handler is
set up) in existing daemons.
However, with the advent of other Init systems (Finit is rather old),
most notably systemd and s6, other methods for signaling "readiness"
arrived and daemons were adapted to these new schemes to a larger
extent.
As of Finit v4.4 partial support for systemd and s6 style readiness
notification is available, and the native PID file mode of operation is,
as of Finit v4.6 optional, by default it is still enabled, but this can
be changed in `finit.conf`:
readiness none
This will be made the default in Finit 5.0. In this mode of operation,
every service needs to explicitly declare their readiness notification,
like this:
service notify:pid watchdogd
service notify:systemd foo
service notify:s6 bar
service notify:none qux
The `notify:none` syntax is for completeness in systems which run in
`readiness pid` mode (default). Services declared with `notify:none`
will transition to ready as soon as Finit has started them, e.g.,
`service/qux/ready`.
To synchronize two services the following condition can be used:
service notify:pid watchdogd
service <service/watchdogd/ready> stress-ng --cpu 8
For details on the syntax and options, see below.
> [!NOTE]
> On `initctl reload` conditions are set in "flux", while figuring out
> which services to stop, start or restart. Services that need to be
> restarted have their `ready` condition removed before Finit issue a
> SIGHUP (if they support that), or stop-starting them. A daemon is
> expected to reassert its readiness, e.g. systemd style daemons to
> write `READY=1\n`.
>
> However, the s6 notify mode does not support this because in s6 you
> are expected to close your notify descriptor after having written
> `\n`. This means s6 style daemons currently must be stop-started.
> (Declare the service with `<!>` in its condition statement.)
>
> For default, PID file style readiness notification, daemons are
> expected to either create their PID files, or touch it using
> `utimensat()` to reassert readiness. Triggering both the `<pid/>`
> and `<.../ready>` conditions.
doc/config/service-wrappers.md
+31
View File
@@ -0,0 +1,31 @@
Service Wrapper Scripts
=======================
If your service requires to run additional commands, executed before the
service is actually started, like the systemd `ExecStartPre`, you can
use a wrapper shell script to start your service.
The Finit service `.conf` file can be put into `/etc/finit.d/available`,
so you can control the service using `initctl`. Then use the path to
the wrapper script in the Finit `.conf` service stanza. The following
example employs a wrapper script in `/etc/start.d`.
**Example:**
* `/etc/finit.d/available/program.conf`:
service [235] <!> /etc/start.d/program -- Example Program
* `/etc/start.d/program:`
#!/bin/sh
# Prepare the command line options
OPTIONS="-u $(cat /etc/username)"
# Execute the program
exec /usr/bin/program $OPTIONS
> [!NOTE]
> The example sets `<!>` to denote that it doesn't support `SIGHUP`.
> That way Finit will stop/start the service instead of sending SIGHUP
> at restart/reload events.
doc/config/services.md
+200
View File
@@ -0,0 +1,200 @@
Services
========
**Syntax:** `service [LVLS] <COND> /path/to/daemon ARGS -- Optional description`
Service, or daemon, to be monitored and automatically restarted if it
exits prematurely. Finit tries to restart services that die, by default
10 times before giving up and marking them as *crashed*. After which
they have to be manually restarted with `initctl restart NAME`. The
limits controlling this are configurable, see the options below.
> [!TIP]
> To allow endless restarts, see below option `respawn`
For daemons that support it, we recommend appending `--foreground`,
`--no-background`, `-n`, `-F`, or similar command line argument to
prevent them from forking off a sub-process in the background. This is
the most reliable way to monitor a service.
However, not all daemons support running in the foreground, or they may
start logging to the foreground as well, these are forking daemons and
are supported using the same syntax as forking `sysv` services, using
the `pid:!/path/to/pidfile.pid` syntax. There is an alternative syntax
that may be more intuitive, where Finit can also guess the PID file
based on the daemon's command name:
service type:forking ntpd -- NTP daemon
This example lets BusyBox `ntpd` daemonize itself. Finit uses the
basename of the binary to guess the PID file to watch for the PID:
`/var/run/ntpd.pid`. If Finit guesses wrong, you have to submit the
full `pid:!/path/to/file.pid`.
**Example:**
In the case of `ospfd` (below), we omit the `-d` flag (daemonize) to
prevent it from forking to the background:
service [2345] <pid/zebra> /sbin/ospfd -- OSPF daemon
`[2345]` denote the runlevels `ospfd` is allowed to run in, they are
optional and default to level 2-5 if omitted.
`<...>` is the condition for starting `ospfd`. In this example Finit
waits for another service, `zebra`, to have created its PID file in
`/var/run/quagga/zebra.pid` before starting `ospfd`. Finit watches
*all* files in `/var/run`, for each file named `*.pid`, or `*/pid`,
Finit opens it and find the matching `NAME:ID` using the PID.
Some services do not maintain a PID file and rather than patching each
application Finit provides a workaround. A `pid` keyword can be set
to have Finit automatically create (when starting) and later remove
(when stopping) the PID file. The file is created in the `/var/run`
directory using the `basename(1)` of the service. The default can be
modified with an optional `pid:`-argument:
pid[:[/path/to/]filename[.pid]]
For example, by adding `pid:/run/bar.pid` to the service `/sbin/bar`,
that PID file will, not only be created and removed automatically, but
also be used by the Finit condition subsystem. So a service/run/task
can depend on `<pid/bar>`, like this foo will not be started until bar
has started:
service pid:/run/bar.pid bar -- Bar Service
service <pid/bar> foo -- Foo Service
Needless to say, it is better if `bar` creates its own PID file when it
has completed starting up and is ready for service.
As an alternative "readiness" notification, Finit supports both systemd
and s6 style notification. This can be enabled by using the `notify`
option:
* `notify:systemd` -- tells Finit the service uses the `sd_notify()`
API to signal PID 1 when it has completed its startup and is ready
to service events. The [sd_notify()][] API expects `NOTIFY_SOCKET`
to be set to the socket where the application can send `"READY=1\n"`
when it is starting up or has processed a `SIGHUP`.
* `notify:s6` -- puts Finit in s6 compatibility mode. Compared to the
systemd notification, [s6 expect][] compliant daemons to send `"\n"`
and then close their socket. Finit takes care of "hard-wiring" the
READY state as long as the application is running, events across any
`SIGHUP`. Since s6 can give its applications the descriptor number
(must be >3) on then command line, Finit provides the following
syntax (`%n` is replaced by Finit with then descriptor number):
service [S12345789] notify:s6 mdevd -O 4 -D %n
[sd_notify()]: https://www.freedesktop.org/software/systemd/man/sd_notify.html
[s6 expect]: https://skarnet.org/software/s6/notifywhenup.html
When a service is ready, either by Finit detecting its PID file, or
their respective readiness mechanism has been triggered, Finit creates
then service's ready condition which other services can depend on:
$ initctl -v cond get service/mdevd/ready
on
This can be used to synchronize the start of another run/task/service:
task [S] <service/mdevd/ready> @root:root mdevd-coldplug
Finit waits for `mdevd` to notify it, before starting `mdevd-coldplug`.
Notice how both start in runlevel S, and the coldplug task only runs in
S. When the system moves to runlevel 2 (the default), coldplug is no
longer part of the running configuration (`initctl show`), this is to
ensure that coldplug is not called more than once.
> For a detailed description of conditions, and how to debug them,
> see the [Finit Conditions](../conditions.md) document.
Non-privileged Services
-----------------------
Every `run`, `task`, or `service` can also list the privileges the
`/path/to/cmd` should be executed with. Prefix the command with
`@USR[:GRP]`, group is optional, like this:
run [2345] @joe:users logger "Hello world"
For multiple instances of the same command, e.g. a DHCP client or
multiple web servers, add `:ID` somewhere between the `run`, `task`,
`service` keyword and the command, like this:
service :80 [2345] httpd -f -h /http -p 80 -- Web server
service :8080[2345] httpd -f -h /http -p 8080 -- Old web server
Without the `:ID` to the service the latter will overwrite the former
and only the old web server would be started and supervised.
Conditional Loading
-------------------
Finit support conditional loading of stanzas. The following example is
take from the `system/hotplug.conf` file in the Finit distribution.
Here we only show a simplified subset.
Starting with the `nowarn` option.
service nowarn name:udevd pid:udevd /lib/systemd/systemd-udevd
service nowarn name:udevd pid:udevd udevd
When loading the .conf file Finit looks for `/lib/systemd/systemd-udevd`
if that is not found Finit automatically logs a warning. The `nowarn`
option disables this warning so that the second line can be evaluated,
which also provides a service named `udevd`.
run nowarn if:udevd <pid/udevd> :1 udevadm settle -t 0
This line is only loaded if we know of a service named `udevd`. Again,
we do not warn if `udevadm` is not found, Execution will also stop here
until the PID condition is asserted, i.e., Finit detecting udevd has
started.
run nowarn conflict:udevd [S] mdev -s -- Populating device tree
If `udevd` is not available, we try to run `mdev`, but if that is not
found, again we do not warn.
Conditional loading statements can also be negated, so the previous stanza
can also be written as:
run nowarn if:!udevd [S] mdev -s -- Populating device tree
The reason for using `confict` in this example is that a conflict can be
resolved. Stanzas marked with `conflict:foo` are rechecked at runtime.
Conditional Execution
---------------------
Similar to conditional loading of stanzas there is conditional runtime
execution. This can be confusing at first, since Finit already has a
condition subsystem, but this is more akin to the qualification to a
runlevel. E.g., a `task [123]` is qualified to run only in runlevel 1,
2, and 3. It is not considered for other runlevels.
Conditional execution qualify a run/task/service based on a condition.
Consider this (simplified) example from the Infix operating system:
run [S] name:startup <pid/sysrepo> confd -b --load startup-config
run [S] if:<usr/fail-startup> name:failure <pid/sysrepo> confd --load failure-config
The two run statements reside in the same .conf file so Finit runs them
in true sequence. If loading the file `startup-config` fails confd sets
the condition `usr/fail-startup`, thus allowing the next run statement
to load `failure-config`.
Notice critical the difference between `<pid/sysrepo>` condition and
`if:<usr/fail-startup>`. The former is a condition for starting and the
latter is a condition to check if a run/task/service is qualified to
even be considered.
Conditional execution statements can also be negated, so provided the
file loaded did the opposite, i.e., set a condition on success, the
previous stanza can also be written as:
run [S] if:<!usr/startup-ok> name:failure <pid/sysrepo> confd ...
doc/config/sysv.md
+94
View File
@@ -0,0 +1,94 @@
SysV Init Compatibility
=======================
It is not possible to run unmodified SysV init systems with Finit. This
was never the intention and is not the strength of Finit. However, it
comes with a few SysV Init compatibility features to ease the transition
from a serialized boot process.
SysV Init Scripts
-----------------
**Syntax:** `sysv [LVLS] <COND> /path/to/init-script -- Optional description`
> `<COND>` is described in the [Services](services.md) section.
Similar to `task` is the `sysv` stanza, which can be used to call SysV
style scripts. The primary intention for this command is to be able to
reuse much of existing setup and init scripts in Linux distributions.
When entering an allowed runlevel, Finit calls `init-script start`, when
entering a disallowed runlevel, Finit calls `init-script stop`, and if
the Finit .conf, where `sysv` stanza is declared, is modified, Finit
calls `init-script restart` on `initctl reload`. Similar to how
`service` stanzas work.
Forking services started with `sysv` scripts can be monitored by Finit
by declaring the PID file to look for: `pid:!/path/to/pidfile.pid`.
Notice the leading `!`, it signifies Finit should not try to create the
file, but rather watch that file for the resulting forked-off PID. This
syntax also works for forking daemons that do not have a command line
option to run it in the foreground, more on this below in `service`.
> [!TIP]
> See also [SysV Init Compatibility](#sysv-init-compatibility).
`runparts DIRECTORY`
--------------------
For a directory with traditional start/stop scripts that should run, in
order, at bootstrap, Finit provides the `runparts` directive. It runs
in runlevel S, at the very end of it (before calling `/etc/rc.local`)
making it perfect for most scenarios.
For syntax details, see the [Run-parts Scripts](runparts.md) section.
Here is an example take from a Debian installation:
runparts /etc/rc2.d
Files in these directories are usually named `SNNfoo` and `KNNfoo`,
which Finit knows about and automatically appends the correct argument:
/bin/sh -c /etc/rc2.d/S01openbsd-inetd start
or
/bin/sh -c /etc/rc0.d/K01openbsd-inetd stop
Files that do not match this pattern are started similarly but without
the extra command line argument.
Start/Stop Scripts
------------------
For syntax details, see [SysV Init Scripts](#sysv-init-scripts), above.
Here follows an example taken from a Debian installation:
sysv [2345] <pid/syslogd> /etc/init.d/openbsd-inetd -- OpenBSD inet daemon
The init script header could be parsed to extract `Default-Start:` and
other parameters for the `sysv` command to Finit. There is currently no
way to detail a generic syslogd dependency in Finit, so `Should-Start:`
in the header must be mapped to the condition system in Finit using an
absolute reference, here we depend on the sysklogd project's syslogd.
`/etc/rc.local`
---------------
One often requested feature, early on, was a way to run a site specific
script to set up, e.g., static routes or firewall rules. A user can add
a `task` or `run` command in the Finit configuration for this, but for
compatibility reasons the more widely know `/etc/rc.local` is used if
it exists, and is executable. It is called very late in the boot process
when the system has left runlevel S, stopped all old and started all new
services in the target runlevel (default 2).
> In Finit releases before v4.5 this script blocked Finit execution and
> made it as good as impossible to call `initctl` during that time.
`init q`
--------
When `/sbin/finit` is installed as `/sbin/init`, it is possible to use
`init q` to reload the configuration. This is the same as calling
`initctl reload`.
doc/config/task-and-run.md
+46
View File
@@ -0,0 +1,46 @@
run (sequence)
--------------
**Syntax:** `run [LVLS] <COND> /path/to/cmd ARGS -- Optional description`
> `<COND>` is described in the [Services](services.md) section.
One-shot command to run in sequence when entering a runlevel, with
optional arguments and description. `run` commands are guaranteed to be
completed before running the next command. Useful when serialization is
required.
> [!WARNING]
> Try to avoid the `run` command. It blocks much of the functionality
> in Finit, like (re)starting other (perhaps crashing) services while a
> `run` task is executing. Use other synchronization mechanisms
> instead, like conditions.
Incomplete list of unsupported `initctl` commands in `run` tasks:
- `initctl runlevel N`, setting runlevel
- `initctl reboot`
- `initctl halt`
- `initctl poweroff`
- `initctl suspend`
To prevent `initctl` from calling Finit when enabling and disabling
services from inside a `run` task, use the `--force` option. See
also the `--quiet` and `--batch` options.
task (parallel)
---------------
**Syntax:** `task [LVLS] <COND> /path/to/cmd ARGS -- Optional description`
> `<COND>` is described in the [Services](services.md) section.
One-shot like 'run', but starts in parallel with the next command.
Both `run` and `task` commands are run in a shell, so basic pipes and
redirects can be used:
task [s] echo "foo" | cat >/tmp/bar
Please note, `;`, `&&`, `||`, and similar are *not supported*. Any
non-trivial constructs are better placed in a separate shell script.
doc/config/templating.md
+39
View File
@@ -0,0 +1,39 @@
Templating
==========
Finit comes with rudimentary support for templating, similar to that of
systemd. Best illustrated with an example:
$ initctl show avahi-autoipd@
service :%i avahi-autoipd --syslog %i -- ZeroConf for %i
To enable ZeroConf for, e.g., `eth0`, use
$ initctl enable avahi-autoipd@eth0.conf
The enabled symlink will be set up to `avahi-autoipd@.conf` and every
instance of `%i` will in the instantiated directive be replaced with
`eth0`. Inspect the resulting instantiated template with `initctl show
avahi-autoipd:eth0` and check the status of a running instance with:
```
$ initctl status avahi-autoipd:eth0
Status : running
Identity : avahi-autoipd:eth0
Description : ZeroConf for eth0
Origin : /etc/finit.d/enabled/avahi-autoipd@eth0.conf
Environment : -/etc/default/avahi-autoipd-eth0
Command : avahi-autoipd $AVAHI_AUTOIPD_ARGS eth0
PID file : /run/avahi-autoipd.eth0.pid
PID : 4190
User : root
Group : root
Uptime : 24 sec
Restarts : 0 (0/10)
Runlevels : [---2345-789]
Memory : 20.0k
CGroup : /system/avahi-autoipd@eth0 cpu 0 [100, max] mem [0, max]
└─ 4190 avahi-autoipd: [eth0] bound 169.254.1.9
Jul 8 11:51:42 infix-c0-ff-ee finit[1]: Starting avahi-autoipd:eth0[4190]
```
doc/config/tty.md
+86
View File
@@ -0,0 +1,86 @@
TTYs and Consoles
=================
**Syntax:** `tty [LVLS] <COND> DEV [BAUD] [noclear] [nowait] [nologin] [TERM]`
`tty [LVLS] <COND> CMD <ARGS> [noclear] [nowait]`
`tty [LVLS] <COND> [notty] [rescue]`
The first variant of this option uses the built-in getty on the given
TTY device DEV, in the given runlevels. DEV may be the special keyword
`@console`, which is expanded from `/sys/class/tty/console/active`,
useful on embedded systems.
The default baud rate is 0, i.e., keep kernel default.
> The `tty` stanza inherits runlevel, condition (and other feature)
> parsing from the `service` stanza. So TTYs can run in one or many
> runlevels and depend on any condition supported by Finit. This is
> useful e.g. to depend on `<pid/elogind>` before starting a TTY.
**Example:**
tty [12345] /dev/ttyAMA0 115200 noclear vt220
The second `tty` syntax variant is for using an external getty, like
agetty or the BusyBox getty.
The third variant is for board bringup and the `rescue` boot mode. No
device node is required in this variant, the same output that the kernel
uses is reused for stdio. If the `rescue` option is omitted, a shell is
started (`nologin`, `noclear`, and `nowait` are implied), if the rescue
option is set the bundled `/libexec/finit/sulogin` is started to present
a bare-bones root login prompt. If the root (uid:0, gid:0) user does
not have a password set, no rescue is possible. For more information,
see the [Rescue Mode](rescue.md) section.
By default, the first two syntax variants *clear* the TTY and *wait* for
the user to press enter before starting getty.
**Example:**
tty [12345] /sbin/getty -L 115200 /dev/ttyAMA0 vt100
tty [12345] /sbin/agetty -L ttyAMA0 115200 vt100 nowait
The `noclear` option disables clearing the TTY after each session.
Clearing the TTY when a user logs out is usually preferable.
The `nowait` option disables the `press Enter to activate console`
message before actually starting the getty program. On small and
embedded systems running multiple unused getty wastes both memory
and CPU cycles, so `wait` is the preferred default.
The `nologin` option disables getty and `/bin/login`, and gives the
user a root (login) shell on the given TTY `<DEV>` immediately.
Needless to say, this is a rather insecure option, but can be very
useful for developer builds, during board bringup, or similar.
Notice the ordering, the `TERM` option to the built-in getty must be
the last argument.
Embedded systems may want to enable automatic `DEV` by supplying the
special `@console` device. This works regardless weather the system
uses `ttyS0`, `ttyAMA0`, `ttyMXC0`, or anything else. Finit figures
it out by querying sysfs: `/sys/class/tty/console/active`. The speed
can be omitted to keep the kernel default.
> Most systems get by fine by just using `console`, which will evaluate
> to `/dev/console`. If you have to use `@console` to get any output,
> you may have some issue with your kernel config.
**Example:**
tty [12345] @console noclear vt220
On really bare bones systems, or for board bringup, Finit can give you a
shell prompt as soon as bootstrap is done, without opening any device
node:
tty [12345789] notty
This should of course not be enabled on production systems. Because it
may give a user root access without having to log in. However, for
board bringup and system debugging it can come in handy.
One can also use the `service` stanza to start a stand-alone shell:
service [12345] /bin/sh -l