Directory Ownerships and Permissions

Question 1

Because directories are also files, they have a…?

Answer 1

user owner, a group owner, and a set of permissions.

Question 2

Read permissions allow a user to…?

Answer 2

list the contents of a directory.

Question 3

Write permissions allow a user to…?

Answer 3

access a file within the directory.

Question 4

Execute permissions allow a user to …?

Answer 4

access a file within the directory.

Question 5

Directory permissions are…?

Answer 5

modified with chmod command.

Question 6

When someone is using a file within Linux, they are generally either…?

Answer 6

reading its information, modifying its information, or trying to execute the file as a script or application. (Therefore the permission types are already discussed, namely (r)ead, (w)rite, and e(x)ecute have a very natural interpretations).

Question 7

To Linux, a directory is just a special type of file, therefore it also has the same types of….?

Answer 7

permissions ((r)ead, (w)rite, and e(x)ecute), a user owner, a group owner, and the same classes of access ((u)ser, (g)roup, and (o)ther. However, directories are obviously used differently.

Question 8

Would it be meaningful to open a directory in an editor, such as nano/home/elvis?

Answer 8

Because people use directories differently, directory permissions have different interpretations.

Question 9

What do people do with directories…?

Answer 9

They list their contents with the ls command. They remove files from them, create new files within them, and move files from one directory to another.

Question 10

Directory permissions should allow a directory owner to control…?

Answer 10

who can perform which of these operations.

Question 11

Linux considers listing a directory’s contents (as with the ls command) analogous to..?

Answer 11

“read”ing a directory, and therefore someone must have (r)ead permissions to list its contents.

Question 12

Adding or removing a file from a directory is considered…?

Answer 12

“write”ing to the directory, and therefore someone must have (w)rite permissions in order to shuffle files within the directory.

Question 13

There is no reasonable analogy to “execute”ing a directory, so Linux doesn’t try to define a similar behavior. Instead, the e(x)cute permission controls…?

Answer 13

a behavior for directories which has nothing to do with the command execution. In order to access any file within a directory, a user must have e(x)cute permission. This permission is known as the “search” permission, but the third permission was already called “execute” for regular files. the same word (and letter) is used for directories as well. In order to refer to any file within a directory (including subdirectories!), a user must have e(x)ecute permissions.

Question 14

What (r)ead, (w)rite and e(x)ecute permissions mean to a regular file..?

Answer 14

(r)ead = view the file
(w)rite = modify the file
e(x)ecute = use the file as a command

Question 15

What (r)ead, (w)rite, e(x)ecute permissions mean to a directory…?

Answer 15

(r)ead = list directory contents
(w)rite = add or remove files
e(x)ecute = “search” for a known file within the directory.

Question 16

Newly created regular files are …?

Answer 16

readable by everybody, but can only be modified by the user and group owner of the file.

Question 17

How are newly created directories handled…?

Answer 17

The default permissions for newly created directories are rwxrwxr-x. These permissions have the following implications:

1. Anyone can search files within the directory.
2. Anyone can list the files within the directory.
3. Only the directory owner (or members of the group owner) can add or remove files from within the directory.

Question 18

In Red Hat Enterprise Linux, a user’s home directory does not…?

Answer 18

fallow the default permissions.

Question 19

In Red Hat Enterprise Linux, home directories are…?

Answer 19

“protected”. By default, the only the user that owns a home directory has search permissions.

Question 20

In Red Hat Enterprise Linux, there are generally only two places where users can create files…?

Answer 20

the /tmp directory and ~ (the user’s home directory.)

Question 21

In Red Hat Enterprise Linux, the /tmp directory is “swept.” If a file within the /tmp is not accessed for 10 days, it is…?

Answer 21

removed from the system.

Question 22

”.” always refers to the…?

Answer 22

current directory, in this case /home/nero/pub.

Question 23

”..” always refers to…?

Answer 23

the current directory’s parents, in this case /home/nero.

Question 24

In order to create a publicly accessible directory within a home directory, a user must…?

Answer 24

allow people to search their home directory.

Question 25

Often, users elect to allow other users to have access to their home directories (consider, for example, the previous example). By allowing others e(x)ecute, but not (r)ead, permissions to their home directory, other users…?

Answer 25

must know that a directory exists within the home directory in order to access it. Because other users may not use the ls command to discover the contents of their home directory, users home directories remain private, and only the parts they choose to expose are available to other users.

Question 26

While not adding (r)ead permissions to a home directory provides some protection against the browsing of the other users, it is not…?

Answer 26

foolproof. Other users can still “guess” all the contents of a directory to which they have e(x)ecute but not (r)ead permissions. For example, users commonly create a directory called ~/mail, for storing mail messages.