mirror of
https://github.com/troglobit/finit.git
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Tobias Waldekranz
b62c975dc4
Add a plugin that will allow the user to trigger the execution of scripts from plugin hook points. This is particularly useful for early boot debugging that needs to take place before regular services are available. For example, let's say that you want to enable some kernel tracing before modules are loaded. With hook-scripts, you can just drop in a shell script in /libexec/finit/hook/mount/all/ that will poke the right control files in tracefs.
129 lines
4.9 KiB
Markdown
129 lines
4.9 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/` for modules to load
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using `modprobe`. Each file in this directory can contain multiple
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lines with the name of the module to load. Any line starting with
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the standard UNIX comment character, `#`, is skipped.
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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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