2 - Raspberry PI Community Projects

which are stored in /etc/init.d/. The administrator can fine tune the services available in
each runlevel by re-running update-rc.d with adjusted parameters. The update-rc.d(1) manual
page describes the syntax in detail. Please note that removing all symbolic links (with the
remove parameter) is not a good method to disable a service. Instead you should simply configure
it to not start in the desired runlevel (while preserving the corresponding calls to stop it in
the event that the service runs in the previous runlevel). Since update-rc.d has a somewhat
convoluted interface, you may prefer using rcconf (from the rcconf package) which provides a
more user-friendly interface.
DEBIAN POLICY
Restarting services
The maintainer scripts for Debian packages will sometimes restart certain
services to ensure their availability or get them to take certain options into
account. The command that controls a service — /etc/init.d/service
operation — doesn't take runlevel into consideration, assumes (wrongly) that
the service is currently being used, and may thus initiate incorrect operations
(starting a service that was deliberately stopped, or stopping a service that is
already stopped, etc.). Debian therefore introduced the invoke-rc.d program:
this program must be used by maintainer scripts to run services initialization
scripts and it will only execute the necessary commands. Note that, contrary
to common usage, the .d suffix is used here in a program name, and not in a
directory.
Finally, init starts control programs for various virtual consoles (getty). It displays a prompt,
waiting for a username, then executes login user to initiate a session.
VOCABULARY
Console and terminal
The first computers were usually separated into several, very large parts: the
storage enclosure and the central processing unit were separate from the peripheral
devices used by the operators to control them. These were part of
a separate furniture, the “console”. This term was retained, but its meaning
has changed. It has become more or less synonymous with “terminal”, being
a keyboard and a screen.
With the development of computers, operating systems have offered several
virtual consoles to allow for several independent sessions at the same time,
even if there is only one keyboard and screen. Most GNU/Linux systems offer
six virtual consoles (in text mode), accessible by typing the key combinations
Control+Alt+F1 through Control+Alt+F6.
By extension, the terms “console” and “terminal” can also refer to a terminal
emulator in a graphical X11 session (such as xterm, gnome-terminal or kons
ole).
9.2. Remote Login
It is essential for an administrator to be able to connect to a computer remotely. Servers, confined
in their own room, are rarely equipped with permanent keyboards and monitors — but
they are connected to the network.
188 The Debian Administrator's Handbook