Hardware Reference
In-Depth Information
Users and Groups
In Linux, each user has three main attributes: their
User ID (UID),
their
Group ID (GID)
and a
list of supplementary group memberships. A user can be a member of as many groups as
he or she pleases, although only one of these can be the user's primary group. This is usu-
ally a self-named group matching the user name.
Group membership is important. While users can be granted direct access to iles and
devices on the system, it's more common for a user to receive access to these via group
membership. The group
audio
, for example, grants all members the ability to access the
Pi's sound playback hardware. Without that membership, the user won't be listening to any
music.
To see a user's group memberships, type
groups
username
at the terminal. If you use
this on the default user
pi
, you'll see the list of groups any new member should join to make
use of the Pi. This is where the information used in step 2 of the preceding procedure was
found.
File System Layout
he content of the SD card is known as its
ile system
, and is split into multiple sections each
with a particular purpose. Although it's not necessary for you to understand what each sec-
tion does in order to use the Raspberry Pi, it can be helpful background knowledge should
anything go wrong.
Logical Layout
he way Linux deals with drives, iles, folders and devices is somewhat diferent to other
operating systems. Instead of having multiple drives labelled with a letter, everything appears
as a branch beneath what is known as the
root ile system
.
If you log in to the Pi and type
ls /
you'll see various directories displayed (see Figure 2-3).
Some of these are areas of the SD card for storing iles, while others are
virtual directories
for
accessing diferent portions of the operating system or hardware.
