finit/TODO.md

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 supoprt for running /bin/sh instead of getty
• Add support for init <q | reload-configuration> and SIGHUP to have finit reload its finit.conf, but also
• Add support for inotify to automatically reload finit.conf
• 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
• Add support for init -v,--version | version
• Cleanup move sources from top-level directory to src/ and include/
• 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.
• Fix restart_any_lost_procs(), currently it restarts task/run when called -- must check SVC_CMD_SERVICE, like svc_monitor() does.
• Use /etc/hostname with fallback to hostname from /etc/finit.conf
• Set hostname early, so boostrap processes, e.g., syslog can use it.

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

Simple way of running Internet services on demand, like the old inetd:

inetd PORT/PROTO <wait|nowait> [@USER[:GROUP]] /path/to/daemon args -- desc

Examples:

# Inetd services, launched on demand
inetd ssh/tcp nowait [2345] @root:root /usr/sbin/sshd -i -- SSH daemon

In keeping with the finit tradition, an optional callback can be setup to each inetd service. When a client connects the finit will call the callback with a struct in_pktinfo argument which the callback then can allowed or deny.

Alternatively, borrowing from TCP wrappers by Wietse Venema, a set of allow and deny directives can be added to finit.conf to control inetd services. It could be what IP addreses, networks or interfaces are allowed to connect to the given inetd services. To start with the easiest (and what we need for WeOS at Westermo) is allow/deny per iface.

# Disable access to SSH
deny  ssh all
# Allow SSH connections originating from eth0
allow ssh eth0

Another option, to further extend the Inetd capabilities, is a separate finetd.conf to list services. This would be beneficial when running an SSH service on different ports on different interfaces:

# Run SSH on port 22 on all interfaces except upstream
tcp ssh {
   listen = *, !wan0
   exec   = dropbear -i
}

# Run SSH on non-standard port 222 for upstream interface
tcp 222 {
   listen = wan0
   exec   = dropbear -i
   wait   = yes
}

# Run TFTP service on all interfaces except upstream interface
udp tftp {
   listen = *, !wan0
   exec   = uftpd -i -t
   user   = root
}

Syntax very similar to xinetd

Internal inetd services

There are a few standard services that inetd usually had built-in:

• time
• echo
• chargen
• discard

At least 'time' will be implemented in finit, as a plugin, to serve as a simple means of testing inetd functionality stand-alone, but also as a very rudimentary time server for rdate clients.

Example:

# Built-in inetd time service, launched on demand
inetd time/udp wait [2345] @root:root internal

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 plugin to replace watchdogd
• Integrate system supervisor 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.
• API for processes to register with the watchdog.
  • Deeper monitoring of a process' main loop
  • If a process is not heard from within its subscribed period time reboot system or restart process.
• Separate /etc/watchdog.conf configuration file, or a perhaps support for /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

• FHS changes affecting runtime status, plugins, etc.