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136 lines
5.1 KiB
Markdown
136 lines
5.1 KiB
Markdown
Hooks & Plugins
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===============
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* [Plugins](#plugins)
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* [Hooks](#hooks)
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* [Bootstrap Hooks](#bootstrap-hooks)
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* [Runtime Hooks](#runtime-hooks)
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* [Shutdown Hooks](#shutdown-hooks)
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Finit can be extended to add general functionality in the form of I/O
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monitors, or hook plugins.
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The following sections detail existing plugins and hook points. For
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more information, see the plugins listed below.
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Plugins
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-------
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For your convenience a set of *optional* plugins are available:
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* *alsa-utils.so*: Restore and save ALSA sound settings on
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startup/shutdown. _Optional plugin._
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* *bootmisc.so*: Setup necessary files and system directories for, e.g.,
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UTMP (tracks logins at boot). This plugin is central to get a working
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system and runs at `HOOK_BASEFS_UP`. The `/var`, `/run`, and `/dev`
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file systems must be writable for this plugin to work.
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Note: On an embedded system both `/var` and `/run` can be `tmpfs` RAM
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disks and `/dev` is usually a `devtmpfs`. This must be defined in the
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`/etc/fstab` file and in the Linux kernel config.
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* *dbus.so*: Setup and start system message bus, D-Bus, at boot.
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_Optional plugin._
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* *hook-scripts.so*: Trigger the execution of scripts from plugin hook
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points (see [Hooks](#hooks)). Scripts are located in
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`/libexec/finit/hook` by default, this can be build-time customized
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by using the `--with-hook-scripts-path=PATH` argument to
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`configure`. _Optional plugin._
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* *hotplug.so*: Setup and start either udev or mdev hotplug daemon, if
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available. Enabled by default.
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* *rtc.so*: Restore and save system clock from/to RTC on boot/halt.
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Enabled by default.
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* *modules-load.so*: Scans `/etc/modules-load.d/*.conf` for modules to
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load using `modprobe`. Each file can contain multiple lines with the
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name of the module to load. Any line starting with the standard UNIX
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comment character, `#`, is skipped.
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Modules are loaded when entering runlevel `[2345]` using the `task`
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stanza. Each module gets a unique `name:modprobe.foo`, and
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optional`:ID`. The `:ID` is a globally incremented index, which can
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be disabled per file (anywhere) using the following config line:
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set noindex
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**Note:** unlike the traditional .conf `module` directive, which load
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any listed module immediately, this plugin creates standard `taks`
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directives which load the module(s) in the background. As long as
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the `modprobe` program is found in the path, these tasks will always
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return `[ OK ]` at boot. Check the actual status using `initctl`.
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* *netlink.so*: Listens to Linux kernel Netlink events for gateway and
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interfaces. These events are then sent to the Finit service monitor
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for services that may want to be SIGHUP'ed on new default route or
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interfaces going up/down. Enabled by default.
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* *resolvconf.so*: Setup necessary files for `resolvconf` at startup.
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_Optional plugin._
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* *tty.so*: Watches `/dev`, using inotify, for new device nodes (TTY's)
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to start/stop getty consoles on them on demand. Useful when plugging
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in a usb2serial converter to login to your embedded device. Enabled
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by default.
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* *urandom.so*: Setup random seed at startup. Enabled by default.
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* *x11-common.so*: Setup necessary files for X-Window. _Optional plugin._
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Usually you want to hook into the boot process once, simple hook plugins
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like `bootmisc.so` are great for that purpose. They are called at each
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hook point in the boot process, useful to insert some pre-bootstrap
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mechanisms, like generating configuration files, restoring HW device
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state, etc. Available hook points are:
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Hooks
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-----
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### Bootstrap Hooks
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* `HOOK_BANNER`: The very first point at which a plugin can run.
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Intended to be used as a banner replacement. Essentially this runs
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just before entering runlevel S. Assume nothing is available, so
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be prepared to use absolute paths, etc.
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* `HOOK_ROOTFS_UP`: When `finit.conf` has been read and `/` has is
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mounted — very early
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* `HOOK_BASEFS_UP`: All of `/etc/fstab` is mounted, swap is available
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and default init signals are setup
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* `HOOK_NETWORK_UP`: System bootstrap, runlevel S, has completed and
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networking is up (`lo` is up and the `network` script has run)
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* `HOOK_SVC_UP`: All services in the active runlevel has been launched
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* `HOOK_SYSTEM_UP`: All services *and* everything in `/etc/finit.d`
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has been launched
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### Runtime Hooks
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* `HOOK_SVC_RECONF`: Called when the user has changed something in the
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`/etc/finit.d` directory and issued `SIGHUP`. The hook is called when
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all modified/removed services have been stopped. When the hook has
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completed, Finit continues to start all modified and new services.
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* `HOOK_RUNLEVEL_CHANGE`: Called when the user has issued a runlevel
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change. The hook is called when services not matching the new
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runlevel have been been stopped. When the hook has completed, Finit
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continues to start all services in the new runlevel.
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### Shutdown Hooks
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* `HOOK_SHUTDOWN`: Called at shutdown/reboot, right before all
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services are sent `SIGTERM`
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Plugins like `tty.so` extend finit by acting on events, they are called
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I/O plugins and are called from the finit main loop when `poll()`
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detects an event. See the source code for `plugins/*.c` for more help
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and ideas.
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