OpenWRT procd

What is procd

https://wiki.openwrt.org/doc/techref/procd

Table of Contents

• What is procd?
• Help with the development of procd
• Buttons with procd
• Init scripts with procd
• Why do we want procd?
• OpenWrt – operating system architecture
  • Dependencies of LuCI2
  • What's the difference between ubus and dbus?
• History

What is procd?

procd is the new OpenWrt process management daemon written in C. It keeps track of processes started from init scripts (via ubus calls), and can suppress redundant service start/restart requests when the config/environment has not changed.

procd has replaced … , e.g.

• hotplug2, a dynamic device management subsystem for embedded systems. Hotplug2 is a trivial replacement of some of the UDev functionality in a tiny pack, intended for Linux early userspace: Init RAM FS and InitRD.
• busybox-klogd and busybox-syslogd
• busybox-watchdog

procd is intended to stay compatible with the existing format of /etc/config/; exceptions …

Help with the development of procd

1. test what has been ported
2. review of the code

Buttons with procd

see commit in https://dev.openwrt.org/log/trunk/package/base-files/files/etc/rc.button

see use case hardware.button

Init scripts with procd

see procd-init-scripts

Why do we want procd?

One thing that procd does much better then …

It boils down to the fact that the current … are rather constrained and inflexible:

• …
• …
• …

procd will be able to … - and of course all that without adding unnecessary bloat. AFAIK there are no alternatives to procd.

Under Construction! This page is currently under construction. You can edit the article to help completing it.

 

procd (process management daemon) – Technical Reference

• Project's git
• procd is available in OpenWrt since r34865 (trunk). It consists of files under GPLv2, LGPLv2.1 and ISC licenses.
• commits to OpenWrt trunk regarding procd

OpenWrt – operating system architecture

 

Whereas desktop distributions use glib and dbus (and udev) OpenWrt uses libubox and ubus (and hotplug2). This provides some pretty awesome functionality without requiring huge libraries with huge dependencies (*cough* glib).

	Desktop Distributions		OpenWrt		Android	Replicant	mer-based
Typical main memory size	128 MiB to 16 GiB (or more)		32 MiB to 512 MiB1)		min 92 MiB for Android 2.1 min 340 MiB for Android 4.0		?
Supported instruction sets	almost anything		almost anything		x86, 86-64, ARM, MIPS32
non-volatile storage space	100 MiB		8 MiB2)		150MiB for Android 2.1 512MiB for Android 4.0		?
kernel	Linux kernel
	FOSS and binary drivers		FOSS drivers: e.g. 802.11; Iaccess		Android binary drivers
C standard library	glibc		uClibc		bionic	glibc + libhybris	eglibc 2.15
init	init Upstart Initng	systemd	busybox-initd	procd	Android init-fork		systemd
	rsyslog / syslog-ng		busybox-klogd, busybox-syslogd
	watchdog		busybox-watchdog
	udev		hotplug2	ubox?
	cron		busybox-crond
	atd		na
	D-Bus		ubus		Binder	?	D-Bus
network configuration	NetworkManager + GUI		netifd		ConnectivityManager (not ConnMan = ConnectionManager!)	?	ConnMan
	GLib (GObject, Glib, GModule, GThread, GIO)		libubox		?	?	Qt-based?
	PulseAudio		PulseAudio (optional)		PulseAudio	PulseAudio	PulseAudio
Package management system	dpkg/APT RPM/yum portage pacman …		opkg		apk	?	RPM

Dependencies of LuCI2

The idea for LuCI2 and its different components started a long time ago: http://luci.subsignal.org/trac/browser/luci2; Code is being developed here;

• libubox (~ 12KiB) is a general purpose library which provides things like an event loop, binary blob message formatting and handling, the Linux linked list implementation, and some JSON helpers. The functions in libubox are used to write the other software in LuCI2
• ubus (~ 13KiB) is an RPC daemon similar to D-Bus but with a much friendlier C API

• ubox
• mountd
• rpcd

• PulseAudio does not depend on GLib and does not seem to depends on D-Bus neither: LFS
• FOSDEM2013: Can Linux network configuration suck less?

What's the difference between ubus and dbus?

dbus is bloated, its C API is very annoying to use and requires writing large amounts of boilerplate code. In fact, the pure C API is so annoying that its own API documentation states: "If you use this low-level API directly, you're signing up for some pain."

ubus is tiny and has the advantage of being easy to use from regular C code, as well as automatically making all exported API functionality also available to shell scripts with no extra effort.

"Of course, NetworkManager should be renamed to "unetwork", dbus to "ubus", PulseAudio to "usound", and X.Org-Server/Wayland-Compositor to "udisplay"; and then indescribable happiness would come down to all people of this world." – Lennart Poettering

---

• → OpenWrt Buildroot – About
• → OpenWrt Buildroot – Installation
• → OpenWrt Buildroot – Usage
• → OpenWrt Buildroot – Patches

---

• → file_system / flash.layout
• → internal.layout
• → preinit_mount/ process.boot/ requirements.boot.process

 

History

Package history is available at:

• current history: https://dev.openwrt.org/log/trunk/package/system/procd
• old history pre r37007 https://dev.openwrt.org/log/trunk/package/procd/Makefile?rev=36995

• r34865: procd: add initial implementation
• r34866: base-files: add basic procd integration, let procd start (and restart) ubus instead of having an ubus init script
• r34867: dropbear: convert init script to procd
• r36003: base-files: make basefiles aware of procd
• r36005: busybox: make init and logread depend on !PROCD_INIT
• r36446: hotplug2: make it depend on !PROCD_INIT
• r36896: procd: make the preinit rules wildcard all buttons for failsafe
• r36987: hotplug2: procd does the hotplugging now
• r36998: base-files: procd is now the init process
• r36999: base-files: diag does not need to insmod any drivers, procd already did it for us
• r37000: base-files: input/button drivers get loaded before preinit by procd
• r37002: base-files: /etc/init.d/rcS is no longer needed, procd handles this for us now
• r37039: busybox: disable syslogd/klogd by default, procd replaces them
• r37106: busybox: disable the watchdog utility by default (procd handles watchdog devices)
• r37242, 37243, 37244: busybox: convert telnet, crond and sysntpd init scripts to procd
• r37245: dropbear: register a config.change trigger: procd_add_config_trigger "dropbear" "/etc/init.d/dropbear" "restart"
• r37429: procd: add proto and trigger support to the /etc/init.d/log
• r37336: procd: make old button hotplug rules work until all packages are migrated

¹⁾ yes, heavily stripped OpenWrt can run on 16 or even 8MiB

²⁾ yes, 4MiB and 2MiB possible

doc/techref/procd.txt · Last modified: 2016/02/19 12:19 by karlp