[systemd-devel] draft systemd wiki intro section.

[David Farning]

I took a stab at a draft intro section for the fd.o wiki.

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Systemd manages system startup and UNIX services. In recent years,
computers have become more dynamic. Servers are turned on and off to
balance performance and resource usage. Desktop hardware is attached
and detached as necessary. Appliances must be available instantly.

Systemd launches and supervises services on demand. This brings three
advantages:
1. Hot plugging. Close coordination between udev, the device manager,
and systemd enables the system to rapidly adapt to changing hardware
configurations.
2. Rapid boot times. Rather than waiting for services to start one at
a time, services start in parallel.
3. Greater control over services. Close coordination between the
kernel and systemd provide administrators greater control over
services.

Systemd accomplishes this by providing a framework for communication
between services. Traditional systems encouraged individual services
to setup and manage interprocess communication on their own. This
requires a set of complex start-up scripts. Systemd provides:
1. Sockets. Consumers don't need to know if providers are present or
running before starting as long as systemd sets up and monitors a pair
socket between them
2. D-bus. Once started, systemd provides a policy for services to
communicate via D
3. Cgroups. Systemd uses cgroups to isolate process for greater control.

Systemd is reverse compatible SystemV init scrips and other process
management utilities such as cron and at.

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This blurb starts with the problems systemd solves. Then it sumarizes
the technologies uses to solve those. Project developers by nature
tend to go into to much detail too early. This blurb removes
references to developers blogs in order to centralize information at
fd.o.

>From a communication point of view the first couple of paragraphs on
the blog are crucial because many people who writes or talk about the
project begin by quoting the wiki.