mirror of
https://github.com/troglobit/finit.git
synced 2026-10-12 10:12:32 +00:00
Joachim Nilsson
6e07dd8dec
This commit adds support for event based services to Finit. Along with
the previously added support for multiple instances of the same process,
the feature scope for Finit v2.0 has been reached!
As of now a service can be declared in /etc/finit.conf or /etc/finit.d/
like this:
service :1 [2345] <!IFUP:eth0,GW> /sbin/dropbear -R -F -p 22 -- SSH daemon
Here the first instance `:1` of dropbear is declared to run in runlevels
2-5, but only if eth0 `IFUP:eth0` is up and a gateway `GW` is set. When
the configuration changes, a new gateway is set, or somehow a new `IFUP`
event for eth0 is received, then dropbear is not SIGHUP'ed, but instead
stop-started `<!>`. The latter trick applies to all services, even
those that do not define any events.
Currently inetd services are not supported for event based starting, but
it could easily be added. Likely scenario is to deny incoming requests
on, e.g., eth0 if there is no gateway.
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
155 lines
5.6 KiB
Markdown
155 lines
5.6 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 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 custom reload for processes like libreSwan's pluto
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service [2345] <!gw,if:eth0,reload:'starter reload'> /sbin/pluto
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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 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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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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Investigation
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-------------
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* [FHS changes](http://askubuntu.com/questions/57297/why-has-var-run-been-migrated-to-run)
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affecting runtime status, plugins, etc.
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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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