Linux Groups and the /etc/group File

Question 1

A group is just an …?

Answer 1

integer group id (gid).

Question 2

Every process that runs on the system runs under a…?

Answer 2

collection of groups (gids)

Question 3

The /etc/group file maps gids to…?

Answer 3

group names and group memberships.

Question 4

Every file in the filesystem is owned by…?

Answer 4

a single gid.

Question 5

Users have a single primary group defined in…?

Answer 5

the /etc/passwd file

Question 6

Users may be members of multiple …?

Answer 6

secondary groups, defined in the /etc/groups file.

Question 7

Group memberships allow system administrators to…?

Answer 7

efficiently manage collections of users with similar objectives.

Question 8

Every user is a member of…?

Answer 8

one primary group.

Question 9

Users can be a member of zero or more…?

Answer 9

secondary groups.

Question 10

To the Linux kernel, a group is referenced using a…?

Answer 10

32 bit integer group id (GID).

Question 11

The /etc/group file associates group names with..?

Answer 11

GIDs (for humans), and defines which users belong to which groups.

Question 12

The /etc/group file plays a similar role for groups as the…?

Answer 12

/etc/passwd file plays for users, has a similar structure, and more reasonable name. It is a line based configuration file, with each consisting of colon separated fields.

Question 13

/etc/group file fields:

Field 1…?

Answer 13

Group names, the group name is used to give a human readable name to the group.

Question 14

/etc/group file fields:

Field 2…?

Answer 14

Group Password, Groups can be supplied with a group password, though this is rarely done.

Question 15

/etc/group file fields:

Field 3…?

Answer 15

Group ID (GID), The integer group id.

Question 16

/etc/group file fields:

Field 4…?

Answer 16

Group members, A comma separated list of usernames defining the group members.

Question 17

Group memberships are most often used to determine who has…?

Answer 17

access to what in the filesystem.

Question 18

Every file on the system is owned by…?

Answer 18

is owned by a user and also owned by a group, which is referred to as the “group owner” of the file.

Question 19

Because every file must have a group owner, there must be a …?

Answer 19

default group associated with each user. This default group becomes the group owner of newly created files. This group is known as a user’s primary group.

Question 20

A user’s primary group is defined in the…?

Answer 20

fourth field of a user’s /etc/passwd entry.

Question 21

In addition to a primary group, users may optionally belong to…?

Answer 21

other groups as well. These groups are termed secondary groups, and are defined (coincidentally) in the fourth field of the /etc/group file.

Question 22

A user’s secondary groups are defined by…?

Answer 22

adding the username to the fourth field of the appropriate lines in the /etc/group file.

Question 23

Standard users do not have….?

Answer 23

permission to edit the /etc/passwd file or the /etc/group file, and therefore cannot change their group memberships. Instead, only the administrative user, root, may change group memberships.

Question 24

If you access to a machine as root, group memberships may be modified using the…?

Answer 24

usermod and groupmod command line utilities, or the system-config-users graphical utility.