Raspberry Pi A, User Manual, Page: 68 / 314

P A R T I
C O N N E C T I N G T H E B O A R D
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2. Type the following as a single line with no spaces after any of the commas:
sudo useradd -m -G adm,dialout,cdrom,audio,plugdev,users,
↵
lpadmin,sambashare,vchiq,powerdev username
This creates a new, blank user account.
3. To set a password on the new account, type
sudo passwd username
followed by
the new password when prompted.
To explain what just happened: the command
sudo
tells the operating system that the com-
mand you’re typing should be run as if you were logged in as the root account. The
useradd
command says you want to create a new user account. The
-m
section—known as a flag or an
option —tells the
useradd
program to create a home directory where the new user can store
his or her files. The big list following the
-G
flag is the list of groups of which the user should
be a member.
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 files 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
The content of the SD card is known as its file 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.