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Goals of Finit

The intent of finit is to monitor not just processes, but to supervise an entire system and the behavior of certain processes that declare themselves to be finit compliant. Similar to launchd, the goal of finit is to be a replacement for:

  • init
  • inetd
  • crond
  • watchdogd

A small and simple replacement, primarily for embedded systems, with a very low dependency on external packages.

General

  • Add compile-time support for running /bin/sh instead of getty

  • Add ! or [wait <pidfile>] to service directive to let finit pause and wait for a pidfile before starting processes -- both at boot and when starting processes in a runlevel.

  • Allow custom reload for processes like libreSwan's pluto

      service [2345] <!gw,if:eth0,reload:'starter reload'> /sbin/pluto

  • Allow process callbacks to be scripts.

  • Add support for a pipe/popen where we can listen for STOP, START and RELOAD on STDOUT from a script ... call it for example .monitor= in svc_t ... the script named as the basename of the service it monitors + .sh.

  • Add support for /etc/sysctl.d

  • Implement initctl stop|start|restart|reload|status <SVC> and service <SVC> stop|start|restart|reload|status on top

  • Add PRE and POST hooks for when switching between runlevels

  • Make sure to install queue.h to $(PREFIX)/include/finit/queue.h

  • Move finit.conf "check" command to plugin which checks /etc/fstab instead. This is the de-facto practice. But keep the check command for really low-end systems w/o /etc/fstab.

  • Add support for generic events (strings or ubus events) that are passed verbatim (?) to the service stanza definitions.

Init

Finit in itself is not SysV Init compatible, it doesn't use /etc/rc.d and /etc/inet.d scripts to boot the system. However, a plausible way to achieve compatibility would be to add a plugin to finit which reads /etc/inittab to be able to start standard Linux systems.

Inetd

Optimize interface filtering by using socket filter. The functions inet_*_peek() and inetd_is_allowed() used for interace filtering should be possible to rewrite as socket filters.

Crond

Requirements are quite rudimentary, basic cron functionality, mainly system-level timed periodic tasks:

  • Periodically run a task, in a matching runlevel
  • Optionally run as non-root (crontab -e as operator)

Proposed syntax:

# Crontab
cron @YY-mm-ddTHH:MM [LVLS] /path/to/cmd [ARGS] -- Optional descr

# One-shot 'at' command
at @YY-mm-ddTHH:MM [LVLS] /path/to/cmd [ARGS] -- Optional descr

Notice the ISO date in notation. The runlevels is extra filtering sugar. E.g., if cron service is only allowed in runlevels two or three it will not start if system currently is in runlevel four.

To run a command as another user the .conf file must have a that owner. E.g., /etc/finit.d/extra.conf may be owned by operator and only hold cron ... lines.

What would be extremely useful is if initctl, or a homegrown at, could support the basic functionality of the at command directly from the shell -- that way setting up one-time jobs would not entail re-reading /etc/finit.conf

Watchdog

Support for monitoring the health of the system and its processes.

  • Add support for a /dev/watchdog built-in to replace both the BusyBox watchdogd and my own refreshed uClinux-dist adaptation, watchdogd
  • Add a system supervisor (pmon) to optionally reboot the system when a process stops responding, or when a respawn limit has been reached, as well as when system load gets too high. For details on UNIX loadavg, see http://stackoverflow.com/questions/11987495/linux-proc-loadavg
    • Default to 0.7 as MAX recommended load before warning and 0.9 reboot
  • API for processes to register with the watchdog, libwdt
    • Deeper monitoring of a process' main loop by instrumenting
    • If a process is not heard from within its subscribed period time reboot system or restart process.
    • Add client libwdt library, inspired by old Westermo API and the libwdt API published in the Fritz!Box source dump, take for instance the fritzbox7170-source-files-04.87-tar.gz drop and see the GPL-release_kernel.tgz in drivers/char/avm_new/ for the kernel driver, and the LGPL-GPL-release_target_tools.tgz in wdt/ for the userland API.
    • When a client process (a standard app/daemon instrumented with libwdt calls in its main loop) registers with the watchdog, we raise the RT priority to 98 (just below the kernel watchdog in prio). This to ensure that system monitoring goes before anything else in the system.
    • Use UNIX domain sockets for communication between daemon and clients
  • Separate /etc/watchdog.conf configuration file, or a perhaps support for a more generic /etc/finit.d/PLUGIN.conf?
  • Support enable/disable watchdog features:
    • Supervise processes,
    • CPU loadavg,
    • Watch for file descriptor leaks,
    • etc.

Documentation

  • Write man pages for finit and finit.conf, steal from the excellent pimd man pages ...
  • Update Debian finit.conf example with runlevels, tty/console and dependency handling for Debian 8 (the dreaded systemd release).

Investigation