mirror of
https://github.com/troglobit/finit.git
synced 2026-10-15 10:29:35 +00:00
Joachim Nilsson
eeb59eb22b
This patch adopts the BusyBox init signals for handling halt, reboot, and poweroff. The SIGINT and SIGPWR signals still behave the same as before, even though they likely will become configurable in a future release. Note: the disabling of Ctrl-Alt-Delete (SIGINT) is also removed! Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
162 lines
6.3 KiB
Markdown
162 lines
6.3 KiB
Markdown
Goals of Finit
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==============
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The intent of finit is to monitor not just processes, but to supervise
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an entire system and the behavior of certain processes that declare
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themselves to be finit compliant. Similar to launchd, the goal of
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finit is to be a replacement for:
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* init
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* inetd
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* crond
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* watchdogd
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A small and simple replacement, primarily for embedded systems, with a
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very low dependency on external packages.
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General
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-------
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* Add halt/poweroff/shutdown symlinks to finit and convert reboot, but
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only install symlinks if these tools don't already exist.
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* Add reboot, halt, poweroff commands to `initctl` tool
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* SysV init and systemd use SIGUSR1 to restart their FIFO/D-Bus. Add
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API restart to SIGHUP callback for the same functionality in Finit.
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* Add `finit.conf` support for UPS notification (SIGPWR) to start a task
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using, e.g. <sys/power/{ok,fail,low}> conditions. More info in sig.c
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* Add `finit.conf` support for ctrl-alt-delete (SIGINT) and kbrequest,
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i.e. KeyboardSignal, (SIGWINCH) behavior. Using conditions to a task,
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e.g, <sys/key/ctrlaltdel> and <sys/key/signal> like SIGPWR handling.
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* Add `IFF_RUNNING` support to netlink plugin along `IFF_IUP`
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* Add compile-time support for running `/bin/sh` instead of `getty`
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* Add `!` or `[wait <pidfile>]` to service directive to let finit pause
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and wait for a pidfile before starting processes -- both at boot and
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when starting processes in a runlevel.
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* Allow process callbacks to be scripts.
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* Add support for a pipe/popen where we can listen for `STOP`, `START`
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and `RELOAD` on `STDOUT` from a script ... call it for example
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`.monitor=` in `svc_t` ... the script named as the basename of the
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service it monitors + `.sh`.
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* Add support for `/etc/sysctl.d`
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* Implement `initctl stop|start|restart|reload|status <SVC>` and
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`service <SVC> stop|start|restart|reload|status` on top
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* Add support for JSON output, or similar, from `initctl show`, e.g.
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`initctl show --json`
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* Add PRE and POST hooks for when switching between runlevels
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* Make sure to install `queue.h` to `$(PREFIX)/include/finit/queue.h`
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* Move `finit.conf` "check" command to plugin which checks `/etc/fstab`
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instead. This is the de-facto practice. But keep the check command
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for really low-end systems w/o `/etc/fstab`.
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* Add support for generic events (strings or ubus events) that are passed
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verbatim (?) to the service stanza definitions.
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Init
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----
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Finit in itself is not SysV Init compatible, it doesn't use `/etc/rc.d`
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and `/etc/inet.d` scripts to boot the system. However, a plausible way
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to achieve compatibility would be to add a plugin to finit which reads
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`/etc/inittab` to be able to start standard Linux systems.
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Inetd
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-----
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Add support for throttling connections.
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Optimize interface filtering by using socket filter. The functions
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`inet_*_peek()` and `inetd_is_allowed()` used for interace filtering
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should be possible to rewrite as socket filters.
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Crond
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-----
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Requirements are quite rudimentary, basic cron functionality, mainly
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system-level timed periodic tasks:
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* Periodically run a task, in a matching runlevel
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* Optionally run as non-root (`crontab -e` as operator)
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Proposed syntax:
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# Crontab
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cron @YY-mm-ddTHH:MM [LVLS] /path/to/cmd [ARGS] -- Optional descr
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# One-shot 'at' command
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at @YY-mm-ddTHH:MM [LVLS] /path/to/cmd [ARGS] -- Optional descr
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Notice the ISO date in notation. The runlevels is extra filtering
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sugar. E.g., if cron service is only allowed in runlevels two or three
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it will not start if system currently is in runlevel four.
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To run a command as another user the `.conf` file must have a that
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owner. E.g., `/etc/finit.d/extra.conf` may be owned by operator and
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only hold `cron ...` lines.
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What would be extremely useful is if `initctl`, or a homegrown `at`,
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could support the basic functionality of the `at` command directly from
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the shell -- that way setting up one-time jobs would not entail
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re-reading `/etc/finit.conf`
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Watchdog
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--------
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Support for monitoring the health of the system and its processes.
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* Add support for a `/dev/watchdog` built-in to replace both the BusyBox
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watchdogd and my own refreshed uClinux-dist adaptation,
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[watchdogd](https://github.com/troglobit/watchdogd)
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* Add a system supervisor (pmon) to optionally reboot the system when a
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process stops responding, or when a respawn limit has been reached, as
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well as when system load gets too high. For details on UNIX loadavg,
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see http://stackoverflow.com/questions/11987495/linux-proc-loadavg
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- Default to 0.7 as MAX recommended load before warning and 0.9 reboot
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* API for processes to register with the watchdog, libwdt
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- Deeper monitoring of a process' main loop by instrumenting
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- If a process is not heard from within its subscribed period time
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reboot system or restart process.
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- Add client libwdt library, inspired by old Westermo API and the
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[libwdt] API published in the [Fritz!Box source dump], take for
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instance the `fritzbox7170-source-files-04.87-tar.gz` drop and see
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the `GPL-release_kernel.tgz` in `drivers/char/avm_new/` for the
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kernel driver, and the `LGPL-GPL-release_target_tools.tgz` in `wdt/`
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for the userland API.
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- When a client process (a standard app/daemon instrumented with
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libwdt calls in its main loop) registers with the watchdog, we raise
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the RT priority to 98 (just below the kernel watchdog in prio).
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This to ensure that system monitoring goes before anything else in
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the system.
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- Use UNIX domain sockets for communication between daemon and clients
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* Separate `/etc/watchdog.conf` configuration file, or a perhaps
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support for a more generic `/etc/finit.d/PLUGIN.conf`?
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* Support enable/disable watchdog features:
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- Supervise processes,
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- CPU loadavg,
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- Watch for file descriptor leaks,
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- etc.
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Documentation
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-------------
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* Write man pages for finit and `finit.conf`, steal from the excellent
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`pimd` man pages ...
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* Update Debian `finit.conf` example with runlevels, `tty/console` and
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dependency handling for Debian 8 (the dreaded systemd release).
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* Add simple, *very* simple, `finit-simple.conf` example. To illustrate
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how close Finit3 still is to the original easy-to-use Finit0 :)
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[libwdt]: http://www.wehavemorefun.de/fritzbox/Libwdt.so
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[Fritz!Box source dump]: ftp://ftp.avm.de/fritz.box/fritzbox.fon_wlan_7170/x_misc/opensrc/
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