Linux Essentials

Question 1

What is the file descriptor number for STDIN?

Answer 1

the file descriptor number for STDIN is zero (0)

Question 2

How is the file descriptor number for STDIN used in redirection?

Answer 2

< (same as 0<)
Redirects STDIN.

Question 3

What is the file descriptor number for STOUT?

Answer 3

the file descriptor number for STOUT is one (1)

Question 4

How is the file descriptor number for STOUT used in redirection?

Answer 4

> (same as 1>)
Redirects STDOUT. If redirection is to a file, the current contents of that file are overwritten.
—
> (same as 1»)
Redirects STDOUT in append mode. If output is written to a file, the output is appended to that file.

Question 5

What is the file descriptor number for STERR?

Answer 5

the file descriptor number for STERR is two (2)

Question 6

How is the file descriptor number for STERR used in redirection?

Answer 6

2>
Redirects STDERR.

2>&1
Redirects STDERR to the same destination as STDOUT.

Notice that this has to be used in combination with normal output redirection, as in ‘‘ls whuhiu > errout 2>&1.’’

Question 7

In the Linux Filesystem Hierarchy Standard (FHS) what does / contain?

Answer 7

The / specifies the root directory. This is where the file system tree starts.

Question 8

In the Linux Filesystem Hierarchy Standard (FHS) what does /boot contain?

Answer 8

/boot contains all files and directories that are needed to boot the Linux kernel.

Question 9

In the Linux Filesystem Hierarchy Standard (FHS) what does /boot/EFI contain?

Answer 9

/boot/EFI contains all files and directories that are needed to boot the Linux kernel.

Question 10

In the Linux Filesystem Hierarchy Standard (FHS) what does /dev contain?

Answer 10

/dev contains device files that are used for accessing physical devices. This directory is essential during boot.

Question 11

In the Linux Filesystem Hierarchy Standard (FHS) what does /etc contain?

Answer 11

/etc contains configuration files that are used by programs and services on your server. This directory is essential during boot.

Question 12

In the Linux Filesystem Hierarchy Standard (FHS) what does /home contain?

Answer 12

/home contains local user home directories.

Question 13

In the Linux Filesystem Hierarchy Standard (FHS) what do /media and /mnt contain?

Answer 13

/media and /mnt contain directories that are used for mounting devices in the file system tree.

Question 14

In the Linux Filesystem Hierarchy Standard (FHS) what does /opt contain?

Answer 14

/opt contains optional packages that may be installed on your server.

Question 15

In the Linux Filesystem Hierarchy Standard (FHS) what does /proc contain?

Answer 15

/proc is used by the proc file system. This is a file system structure that gives access to kernel information.

Question 16

In the Linux Filesystem Hierarchy Standard (FHS) what does /root contain?

Answer 16

/root is the home directory of the root user.

Question 17

In the Linux Filesystem Hierarchy Standard (FHS) what does /run contain?

Answer 17

/run contains process and user-specific information that has been created since the last boot.

Question 18

In the Linux Filesystem Hierarchy Standard (FHS) what does /srv contain?

Answer 18

/srv may be used for data by services like NFS, FTP, and HTTP.

Question 19

In the Linux Filesystem Hierarchy Standard (FHS) what is /sys used for?

Answer 19

/sys is used as an interface to different hardware devices that are managed by the Linux kernel and associated processes.

Question 20

In the Linux Filesystem Hierarchy Standard (FHS) what does / represent?

Answer 20

The / specifies the root directory. This is where the file system tree starts.

Question 21

In the Linux Filesystem Hierarchy Standard (FHS) what does /usr contain?

Answer 21

/usr contains subdirectories with program files, libraries for these program files, and documentation about them.

Question 22

In the Linux Filesystem Hierarchy Standard (FHS) what does /var contain?

Answer 22

/var contains files that may change in size dynamically, such as log files, mail boxes, and spool files.

Question 23

Regular Expressions

What does the regex ^text do?

Answer 23

The regex ^text matches line that starts with specified text.

Question 24

Regular Expressions

What does the regex text$ do?

Answer 24

The regex text$ matches line that ends with specified text.

Question 25

# Regular Expressions What does the regex **.** do?

Answer 25

The regex **.** matches any single character (wildcard).

Question 26

# Regular Expressions What does the regex **[abc]** do?

Answer 26

The regex **[abc]** matches a, b, or c.

Question 27

# Regular Expressions What does the regex **?** do?

Answer 27

The regex **?** is an extended regular expression that matches zero or one of the preceding character.

Question 28

# Regular Expressions What does the regex **+** do?

Answer 28

The regex **+** is an extended regular expression that matches one or more of the preceding character.

Question 29

# Regular Expressions What does the regex **`*`** do?

Answer 29

The regex **`*`** matches zero to an infinite number of the previous character..

Question 30

# Regular Expressions What does the regex **`\{2\}`** do?

Answer 30

The regex **`\{2\}`** matches exactly two of the previous character.

Question 31

# Regular Expressions What does the regex **`\{1,3\}`** do?

Answer 31

The regex **`\{1,3\}`** matches a minimum of one and a maximum of three of the previous character.

Question 32

# Regular Expressions What does the regex **`colou?r`** do?

Answer 32

The regex **`colou?r`** matches zero or one of the previous character. This makes the previous character optional, which in this example would match both color and colour.

Question 33

# Regular Expressions What does the regex **`(…)`** do?

Answer 33

The regex **`(…)`** is used to group multiple characters so that the regular expression can be applied to the group.

Question 34

What command can be used to force a reset of a Linux machine?

Answer 34

To force a machine to reset, from a root shell you can type **echo b > /proc/sysrq-trigger**. This command immediately resets the machine without saving anything. Notice that this command should be used only if there are no other options!

Question 35

You want to set a local variable that will be available for every user in every shell. Which of the following files should you use?

Answer 35

**/etc/bashrc** is processed when a subshell is started, and it is included while starting a login shell as well.

Question 36

What file is used to display a message to a user during (before) logon?

Answer 36

**/etc/issue**

Question 37

What file is used to display a message to a user upon (after) logon?

Answer 37

**/etc/motd**

Question 38

You are using man -k user, but you get the message “nothing appropriate.” Which of the following solutions is most likely to fix this for you?

Answer 38

**sudo mandb**

Question 39

What is the name of the file where Bash stores its history?

Answer 39

**~/.bash_history**

Question 40

What command can be used to show to first 10 lines of a text file?

Answer 40

**head**

Question 41

What command can be used to show to last 10 lines of a text file?

Answer 41

**tail**

Question 42

What is **less** command used for?

Answer 42

**less** opens the text file in a pager, which allows for easy reading

Question 43

What is the **grep** option **-i** used for?

Answer 43

-i matches upper- and lowercase letters (i.e., not case sensitive).

Question 44

What is the **grep** option **-v** used for?

Answer 44

-v shows only lines that do not contain the regular expression.

Question 45

What is the **grep** option **-r** used for?

Answer 45

-r searches files in the current directory and all subdirectories.

Question 46

What is the **grep** option **-e** used for?

Answer 46

-e searches for lines matching more than one regular expression. Use -e before each regular expression you want to use.

Question 47

What is the **grep** option **-E** used for?

Answer 47

-E interprets the search pattern as an extended regular expression.

Question 48

What is the **grep** option **-A ``** used for?

Answer 48

**-A ``** shows `` of lines after the matching regular expression.

Question 49

What is the **grep** option **-B ``** used for?

Answer 49

**-A ``** shows `` of lines before the matching regular expression.

Question 50

What is the **rync** option **-r** used for?

Answer 50

**-r** synchronizes the entire directory tree

Question 51

What is the **rync** option **-l** used for?

Answer 51

**-l** copies symbolic links as symbolic links

Question 52

What is the **rync** option **-p** used for?

Answer 52

**-p** preserves permissions

Question 53

What is the **rync** option **-n** used for?

Answer 53

**-n** performs only a dry run, not actually synchronizing anything

Question 54

What is the **rync** option **-a** used for?

Answer 54

**-a** uses archive mode, thus ensuring that entire subdirectory trees and all file properties will be synchronized

Question 55

What is the **rync** option **-A** used for?

Answer 55

**-A** uses archive mode, and in addition synchronizes ACLs

Question 56

What is the **rync** option **-X** used for?

Answer 56

**-X** synchronizes SELinux context as well

Question 57

What is **su**?

Answer 57

The **su** command opens a subshell as a different user, with the advantage that commands are executed as root only in the subshell

Question 58

What is **sudo**?

Answer 58

The sudo command allows authorized users to work with administrator privileges.

Question 59

What is PolicyKit (**Polkit**) used for?

Answer 59

PolicyKit (Polkit) enables you to set up graphical utilities to run with administrative privileges

Question 60

What can a **user** with **read permissions** do at a **file** and **directory** level?

Answer 60

**Files:** View file content **Directory:** List contents of directory

Question 61

What can a **user** with **write permissions** do at a **file** and **directory** level?

Answer 61

**Files:** Change contents of a file **Directory:** Create and delete files

Question 62

What can a **user** with **execute permissions** do at a **file** and **directory** level?

Answer 62

**Files:** Run a program file **Directory:** Change to the directory

Question 63

What is the **numeric representation** of the **read permission**?

Answer 63

4

Question 64

What is the **numeric representation** of the **write permission**?

Answer 64

2

Question 65

What is the **numeric representation** of the **execute permission**?

Answer 65

1