You can use the file command to display the file types of all the files in a directory at a time. In order to accomplish the task, you will have to issue the following command:

file *

What is the file command?

The file command is used to analyze the files specified in the argument.

Syntax:

file [] [] ...

By providing the name of a file as an argument, the file command analyzes the file. The file command supports multiple arguments. The asterix (*) metacharacter can also be used with the file command.

Answer option C is incorrect. In Linux, the mount command is used to mount and display disks, partitions, and file systems. Mounting refers to the process in which the operating system prepares the media to be read.

Answer option A is incorrect. The File System Check (fsck) command is used to scan all disks and partitions, and it repairs them if required. The fsck command should be run only on an unmounted file system.

Answer option D is incorrect. The init command is used to switch a Linux computer to different run levels.

Mail delivery is most typically done through one of the SMTP family of protocols, either SMTP or

ESMTP.

What is the ESMTP protocol?

ESMTP (Extended Simple Mail Transfer Protocol) specifies extensions to the original protocol for sending e-mail that supports graphics, audio and video files, and text in different national languages. The original

Internet protocols for sending e-mail are described in Request for Comments (RFC) 822, Standard for the Format of ARPA

Internet Text Messages, and in RFC 821, Simple Mail Transfer Protocol (SMTP). As users demanded to attach various kinds of files to email, the need for additional facilities arose and resulted in RFC 1869, Extended Simple Mail Transfer Protocol. ESMTP provides the facility for a client e-mail program to ask a server e-mail program which facilities it supports and then communicate accordingly.

Answer options A and D are incorrect. IMAPS and POP3S are used for mail pickup.

What is the POP3S protocol?

Post Office Protocol version 3 (POP3) is the protocol that clients use to pick up mail from servers.

Users of POP3 generally store their mail locally on their system and configure their mail client to pick up new mail periodically.

POP3 servers need clients to authenticate with a username and password. This ensures that only authenticated clients can pick up the user's email. Unfortunately, POP3 is an unencrypted protocol, so the username and password travel in cleartext.

POP3S, on the other hand, is POP3 over Secure Sockets Layer. It provides an encrypted connection for the Post Office Protocol. More significantly, it provides an encrypted connection over which the username and password may be transmitted for authentication purposes.

The departmental mail server provides POP3 (internally) and POP3S (internally and externally).

Ultimately, POP3 support will be turned off in favor of IMAPS, which is a more modern protocol that can do everything POP3 can.

The scp command copies files between hosts on a network. It uses ssh for data transfer, and uses the same authentication and provides the same security as ssh. Unlike rcp, scp will ask for passwords or passphrases if they are needed for authentication. Any file name may contain a host and user specification to indicate that the file is to be copied to/from that host.

Copies between two remote hosts are permitted.

The /etc/X11/xdm/xdm-config file is the default configuration file of XDM. The X Window Display

Manager (XDM) is the default display manager for the X Window System. XDM is distributed as part of XFree86 and is configured by a series of files located in /etc/X11/XDM. Some of the important files of XDM are given below in the list:

Xaccess: It is used to control inbound requests from remote hosts.

Xresources: This file holds configuration information for XDM resources and the graphical login screen. It can be edited to modify the appearance of the XDM login screen. Xservers: This file is used to associate the X display names with either the local X server software or a foreign display such as an X terminal.

Xsession: This file contains the script XDM launches after a successful login.

Xsetup_0: This file defines how XDM will open. It is a script started before the graphical login screen.

It often includes commands to set colors, display graphics, or run other programs. This script is executed as root.

XDM-config: This file is used to configure XDM configuration resources.

Answer option B is incorrect. $HOME/.Xauthority is the user authorization file where XDM stores keys for clients to read.

Answer option D is incorrect. The /usr/bin/xterm file is the default session program of XDM.

Answer option C is incorrect. It is not a valid XDM configuration file.

When a user types alias c= 'clear' on the command prompt and presses Enter this will create an alias for the clear command. After creating the alias whenever a user wants to clear the screen, he just needs to type c and then press Enter.

This action will clear the screen. This alias will be lost if a user logs out and logs in again.

What is the alias command?

The alias command is a shortcut name for longer commands. If a command is run often, but it takes a considerable amount of time in typing that command, the time can be reduced by using the alias command.

For example: # alias list= 'ls-la'

This will create an alias called list, which will use the ls command to print a long-style listing of all files in the current directory (the -l gives a long-style list, and the -a shows all files -including hidden files).

Answer options B, C, and A are incorrect. These are incorrect commands and will show error messages on the command prompt.

The second column in the listing shows the number of hard links created for the file.

The cat command concatenates both files foo.txt and student.txt together and | (pipe) will send the standard output of the cat command to the standard input of the less command, and this will show the output of both files on one screen at a time.

From the above output, it is clear that 245 words are present in the file file.txt, as the second column represents the number of words present in a file.

A file can be viewed in two windows in a single vim screen by issuing Ctrl-w, s and Ctrl-w, v. The Keycombination

Ctrl-w, s splits the vim screen horizontally. The key-combination Ctrl-w, v splits the screen vertically.

Answer option C is incorrect. The Key-combination :wq is used to save a file and quit from the file in a vim text-editor.

Answer option D is incorrect. The key combination :q! is used to quit from a file without saving its contents.

What is vim?

Vim is an advanced text editor that seeks to provide the power of the Unix editor vi with a more complete feature set. Vim is useful whether a user is already using vi or using a different editor. Vim is a highly configurable text editor built to enable efficient text editing. It is an improved version of the vi editor distributed with most Unix systems. It is perfect for all kinds of text editing, from composing email to editing configuration files.

The ps2pdf utility is used to create PDF files. Therefore, in the above scenario, you will use ps2pdf command to accomplish the task.

Answer option C is incorrect. The pdf2ps utility converts PDF files to PostScript.

Answer options B and D are incorrect. enscript and a2ps commands convert text to PostScript and send it to the print queue.

This command will search for files with a size of over 50 megabytes. The -size option tells find to search files according to the size of files, and

+50M will tell the find command to search files over 50 megabytes.

Answer option C is incorrect. This command will search for files with a size of exactly 50 megabytes.

Answer option B is incorrect. This command will search for files with a size of less than 50 megabytes.

Answer option D is incorrect. - must be prefixed with size, otherwise shell will not recognize this command, and display an error message.

pgrep looks through the currently running processes and lists the process IDs that match the selection criteria to stdout. All the criteria have to match. pkill is a tool that looks up or signals processes based on name and other attributes. Pkill will send the specified signal (by default SIGTERM) to each process instead of listing them on stdout.

Answer option A is incorrect. The top command is used to produce a frequently-updated list of processes. By default, the processes are ordered by percentage of CPU usage, with only the "top" CPU consumers shown. This command shows how much processing power and memory are being used, as well as other information about the running processes. The following figure demonstrates the output of the top command:

Answer option C is incorrect. The sort command is used to print the lines of its input or concatenation of all files listed in its argument list in sorted order. Sorting is done based on one or more sort keys extracted from each line of input. By default, the entire input is taken as the sort key. The blank space is taken used as the default field separator in the output of the sort command.

The -r flag, however, reverses the sort order. For example, the ls -s | sort -nr command will sort the directories of the root directory in reverse order of size.

The cal 7 2010 command will display the calendar of July 2010.

What is the cal command?

The cal command prints an ASCII calendar of the current month.

Syntax: cal [month] [year]

Given a month and year as arguments, cal displays the calendar for that particular month of the given year.

When a single numeric argument (such as 2005) is given, cal will display a calendar for the given year. Always use a fourdigit year. For example, the command cal 05 will display the calendar for the year 05, not the year

2005.

Answer option B is incorrect. The cal 20 July command will display only the month and year, and not the date.

Answer option A is incorrect. The cal command will display the calendar of the current month.

Answer option D is incorrect. The date command will display the current date and time of the system.

This command looks for files on the system whose data has been changed exactly five days ago.

SELinux is an operating system based on Linux which includes Mandatory Access Control. The

SELinux provides Kernel-level security for Red Hat Enterprise Linux.

Answer options C, B, and A are incorrect. These are the features of SELinux.

What are the features of SELinux?

The features of SELinux are as follows:

SELinux provides Kernal-level security.

SELinux implements Mandatory access control (MAC) security in Red Hat Enterprise Linux.

SELinux assigns every file and process on the system a context, identifying its type and purpose.

SELinux enforces a policy that dictates which actions a given type of process may take on a given type of file

SELinux applies to all users, including root.

aspell is a utility that can function as an ispell -a replacement, as an independent spell checker, as a test utility to test out Aspell features, and as a utility for managing dictionaries.

Syntax:

aspell [options]

Some important options used with aspell are as follows:

The following options may be used with the aspell command to control which dictionaries to use and how they behave:

Answer option A is incorrect. The tee command is used to split the output of a program so that it can be seen on the display and also be saved in a file. It can also be used to capture intermediate output before the data is altered by another command or program. The tee command reads standard input, then writes its content to standard output, and simultaneously copies it into the specified file(s) or variables.

The syntax of the tee command is as follows: tee [-a] [-i] [File] where, the -a option appends the output to the end of File instead of writing over it and the -i option is used to ignore interrupts.

Answer option B is incorrect. The concatenate (cat) command is used to display or print the contents of a file.

Syntax:

cat filename

For example, the following command will display the contents of the /var/log/dmesg file:

cat /var/log/dmesg

Note: The more command is used in conjunction with the cat command to prevent scrolling of the screen while displaying the contents of a file.

Answer option D is incorrect. There is no such utility as dict in Linux.

The /etc/group file contains group information. This file shows which users are members of which groups.

The ls -al /root command lists all the files and directories, including hidden files in the /root

directory, in long listing format. /root is the root

user's home directory.

What is the ls command?

The ls command is used to list files on a Linux computer. The syntax of the ls command is as follows:

ls [option] [directory name]

Several options are used with the ls command. Following is a list of some important options:

For example, the following command displays all the files (including hidden files) in the /home

directory and the contents in

the subdirectories:

ls -aR /home

Answer option B is incorrect. The ls command without arguments lists the file and directory names

in the current directory.

Answer option C is incorrect. The ls -s /root command shows the size of all files and directories (in blocks, not bytes) that reside in the /root directory.

Answer option D is incorrect. The ls -h /root command shows the size of files and directories in

"human readable format" (i.e. 19M, 3G, etc).

Answer option C is incorrect. The pdf2ps utility is used to convert a PDF file to a PostScript.

The Unix utility sed (stream editor) is a text editing tool that can be used to edit text files without having to open them. This utility parses text files and implements a programming language which can apply textual transformations to such files.

It reads input files line by line

(sequentially), applying the operation which has been specified via the command line (or a sed script), and then outputs the line.

Answer option D is incorrect. The more command is used to view (but not modify) the contents of a text file on the terminal screen at a time.

The syntax of the more command is as follows: more [options] file_name

Where,

Answer option A is incorrect. The less command is used to view (but not change) the contents of a text file, one screen at a time. It is similar to the more command. However, it has the extended capability of allowing both forward and backward navigation through the file. Unlike most Unix text editors/viewers, less does not need to read the entire file before starting; therefore, it has faster load times with large files.

The command syntax of the less command is as follows: less [options] file_name

Where,

Answer option C is incorrect. The vi editor is an interactive, cryptic, and screen-based text editor used to create and edit a file. It operates in either Input mode or Command mode. In Input mode, the vi editor accepts a keystroke as text and displays it on the screen, whereas in Command mode, it interprets keystrokes as commands. As the vi editor is case sensitive, it interprets the same character or characters as different commands, depending upon whether the user enters a lowercase or uppercase character.

When a user starts a new session with vi, he must put the editor in Input mode by pressing the "I" key. If he is not able to see the entered text on the vi editor's screen, it means that he has not put the editor in Insert mode. The user must change the editor to Input mode before entering any text so that he can see the text he has entered.