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.