2 - Raspberry PI Community Projects

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Working with several groups
Each user may be a member of many groups; one of them is their “main group”.
A user's main group is, by default, created during initial user configuration. By
default, each file that a user creates belongs to them, as well as to their main
group. This is not always desirable; for example, when the user needs to work
in a directory shared by a group other than their main group. In this case, the
user needs to change their main group using one of the following commands:
newgrp, which starts a new shell, or sg, which simply executes a command
using the supplied alternate group. These commands also allow the user to
join a group to which they do not belong. If the group is password protected,
they will need to supply the appropriate password before the command is
executed.
Alternatively, the user can set the setgid bit on the directory, which causes
files created in that directory to automatically belong to the correct group.
For more details, see sidebar “setgid directory and sticky bit” (page 196).
The id command displays the current state of a user, with their personal identifier
(uid variable), current main group (gid variable), and the list of groups
to which they belong (groups variable).
The groupadd and groupdel commands add or delete a group, respectively. The groupmod command
modifies a group's information (its gid or identifier). The command passwd -g group
changes the password for the group, while the passwd -r -g group command deletes it.
TIP
getent
The getent (get entries) command checks the system databases the standard
way, using the appropriate library functions, which in turn call the NSS modules
configured in the /etc/nsswitch.conf file. The command takes one or
two arguments: the name of the database to check, and a possible search key.
Thus, the command getent passwd rhertzog will give the information from
the user database regarding the user rhertzog.
8.5. Creating Accounts
One of the first actions an administrator needs to do when setting up a new machine is to create
user accounts. This is typically done using the adduser command which takes a user-name for
the new user to be created, as an argument.
The adduser command asks a few questions before creating the account, but its usage is fairly
straightforward. Its configuration file, /etc/adduser.conf, includes all the interesting settings:
it can be used to automatically set a quota for each new user by creating a user template,
or to change the location of user accounts; the latter is rarely useful, but it comes in handy
when you have a large number of users and want to divide their accounts over several disks, for
instance. You can also choose a different default shell.
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ota
The term “quota” refers to a limit on machine resources that a user is allowed
to use. This frequently refers to disk space.
Chapter 8 — Basic Configuration: Network, Accounts, Printing…
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