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

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.

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procd (process management daemon) – Technical Reference

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 intruction 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

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



1) yes, heavily stripped OpenWrt can run on 16 or even 8MiB
2) yes, 4MiB and 2MiB possible
1) yes, heavily stripped OpenWrt can run on 16 or even 8MiB
2) yes, 4MiB and 2MiB possible

History

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doc/techref/procd.txt · Last modified: 2013/12/22 20:45 by valentt