RH033 Red Hat Linux Essentials Questions and Answers

The du command is used to summarize disk usage. The du command displays the number of blocks used for files. If the File parameter specified is actually a directory, the disk usage of all files within the directory are summarized. If no

File parameter is provided, the du command uses the files in the current directory.

Answer option C is incorrect. The df command reports information about space on file systems.

Answer option B is incorrect. The fsck command checks file system consistency and interactively repairs the file system.

Answer option D is incorrect. The dfsck command checks and repairs two file systems simultaneously on different drives.

Pidgin (formerly named Gaim) is a multi-platform instant messaging client, based on a library named

libpurple. Libpurple has support for many commonly used instant messaging protocols, allowing a user to log into various different services from one application.

What is Pidgin?

Pidgin is a multi-protocol Instant Messaging client that allows a user to use all of his IM accounts at once. It is a free software that can work with AIM ,Gadu-Gadu, Jabber, ICQ ,IRC, MSN, SILC, XMPP, Yahoo!, and Zephyr Network. Anyone is free to use it and modify it, but if a user distributes his modifications, he must distribute the modified source code as well.

The license of this communication software is Freeware, i.e. anyone can freely download and use this communication software.

Answer options A and D are incorrect. Evolution and Thunderbird are Graphical mail clients in Linux.

It is not an Instant Messenger.

What is Evolution?

Evolution is a full-featured personal and workgroup information management tool for Linux systems, and is the default email client for Red Hat Enterprise Linux. It provides all of the standard email client features, including powerful mailbox management, user-defined filters, and quick searches. Its additional feature is a flexible calendar/scheduler, which allows users to create and confirm group meetings and special events online.

What is Thunderbird?

Mozilla Thunderbird is a free, open source, cross-platform e-mail and news client developed by the

Mozilla Foundation.

Thunderbird can manage multiple e-mail, newsgroup and RSS accounts and supports multiple identities within accounts.

Thunderbird incorporates a Bayesian spam filter, a white list based on the included address book, and can also understand classifications by server-based filters such as SpamAssassin. Thunderbird provides enterprise and government-grade security features such as SSL/TLS connections to IMAP and SMTP servers. It also offers native

support for S/MIME secure email (digital signing and message encryption using certificates).

Answer option B is incorrect. mutt is an email client that manages emails within a text-only environment. It is not an Instant Messenger.

What is mutt? mutt is a powerful tool for managing email within a text-only environment. This tool is very important to access email even when a graphical interface is not available. Some of its strengths are handling of message threads and flexibility. When mutt sees a series of related messages, it displays each reply under the parent. mutt supports sending of attachments through a mail. The following example describes how a file can be attached to a mail: echo "Sending an attachment." | mutt -a backup.zip -s "attachment" local@domain.com

This command will send a mail to local@domain.com with the subject (-s) "attachment", the body text "Sending an

attachment.", containing the attachment (-a) backup.zip.

The lpc command can be used to rearrange jobs awaiting printing, as well as to disable/enable a

printer or queue and find the status of printers.

Answer option D is incorrect. The lpr sends a job to the queue to be printed.

Answer option A is incorrect. The lpq views the contents of the queue.

Answer option C is incorrect. The lprm removes a job from the queue.

According to the question's requirement, the following time specifications can be set for the cron

job:

30 17 * * 5

30 17 * * FRI

In this time specification, you can define five parameters. The first two parameters define minutes and hours of the day. The last or the fifth parameter shows the day of the week. It can be the name or the number of a day. Numbers 0 and 7 are for Sunday, whereas from Monday to

Saturday, the numbers are from 1 to 6.

According to the scenario, John will use the chgrp bar foo command to accomplish the task. The chgrp (from change group) command is used by unprivileged users to change the group associated with a file. Unlike the chown command, chgrp allows regular users to change groups, but only to one of which they are a member. The general syntax of the chgrp command is as follows:

chgrp group target1 [target2 ..]

The group parameter indicates the new group with which the targets should be associated.

The target1 parameter indicates the files or directories for which the change should be made.

The target2 parameter indicates the optional additional files or directories for which the change should be made.

For example:

The above command changes the group associated with ttt to 'system', provided the executing user is a member of that group.

Answer option A is incorrect. In the chgrp command, first we write the group name and after that, we write the file name. But here just the opposite is written, so this command will not give the desired result.

Answer options D and B are incorrect. There is no such command as chgroup in Linux.

The VI is a visual interactive text editor that allows a user to create, modify, and store files on a Linux computer. It works in the following modes:

Command: This is the default mode of the command. Various commands can be used in this mode to manipulate the opened text.

Input: In this mode, a user can insert text directly in the text screen area.

Answer option D is incorrect. The GNU zip (GZIP) utility is a compression utility that is used to compress files for saving space. It creates files with the .gz extension. It can also compress tar files. In order to unzip files with the .gz extension, the

GUNZIP command is used.

Answer option B is incorrect. The nmap utility, also commonly known as port scanner, is used to view the open ports on a Linux computer. It is used by administrators to determine which services are available for external users. This utility helps administrators in deciding whether to disable the services that are not being used in order to minimize any security risk.

Answer option C is incorrect. MS Word is a Windows-based utility. Hence, it cannot be used in Linux.

You will use the ssh command to remotely login to the host York and then remotely execute the command 'df -h' to check the disk space usage on the remote system.

According to the scenario, since John wants to copy all files with the .dat extension from /home/john

to /home/maria while preserving the file

attributes such as timestamps, mode, and ownership, he will use the cp -p /home/john/*.dat

/home/maria command to accomplish the task. The cp -p command copies files from source to destination while preserving the file attributes, such as timestamps, mode, and ownership.

Answer option B is incorrect. The cp -R /home/john/*.dat /home/maria command will recursively copy all .dat files from source to destination; however, it will not preserve the file attributes.

Answer option D is incorrect. The cp -l /home/john/*.dat /home/maria command will link all .dat

files from /home/john to /home/maria instead of copying them.

Answer option C is incorrect. The cp -l /home/maria/*.dat /home/john command will link all .dat

files from /home/maria to /home/john instead of copying them.

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.

smbclient is a command-line tool that provides access to SMB/CIFS shares.

What is the smbclient command?

smbclient is a command-line tool that provides access to SMB/CIFS shares. smbclient is a samba client with an "ftp like" interface. It is a useful tool to test connectivity to a Windows share. It can be used to transfer files, or to look at share names. In addition, it has the ability to backup and restore files from a server to a client and visa versa.

Example:

#smbclient -L server1

The above command will list all shares on server1.

Some useful options are as follows:

Answer option C is incorrect. scp copies files between hosts on the Linux network.

Answer option A is incorrect. rsync is a fast and extraordinarily versatile file copying tool. It can copy locally, to/from another host over any remote shell or to/from a remote rsync daemon.

What is rsync?

In computing, rsync is a software application for Unix systems. It synchronizes files and directories from one location to another while minimizing data transfer using delta encoding. It can copy or display directory contents and copy files, optionally using compression and recursion.

In daemon mode, rsync listens to the default TCP port of 873, serving files in the native rsync protocol or via a remote shell such as RSH or SSH. In the latter case, the rsync client executable must be installed on both the local and remote hosts.

Answer option B is incorrect. mutt is a small but very powerful text based program for reading electronic mail under Linux operating systems.

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 default tool for email and groupware in Red Hat Enterprise Linux is called Evolution. Evolution provides not only the email access, but also the ability to maintain a calendar, tasklist and contacts database.

What is Evolution?

Evolution is a full-featured personal and workgroup information management tool for Linux systems, and is the default email client for Red Hat Enterprise Linux. It provides all of the standard email client features, including powerful mailbox management, user-defined filters, and quick searches. Its additional feature is a flexible calendar/scheduler, which allows users to create and confirm group meetings and special events online.

Answer option C is incorrect. Thunderbird is a graphical mail client that offers email, Usenet and rss support but it does not support groupware features. Thunderbird is provided along with Firefox and others as part of the Mozilla suit of application.

What is groupware?

Groupware refers to programs that help users work together collectively while located remotely from each other.

Groupware services can include the sharing of calendars, collective writing, e-mail handling, shared database access, electronic meetings with each user able to see and display information to others, and other activities. Sometimes called collaborative software, groupware is an integral component of a field of study known as Computer-

Supported Cooperative Work or CSCW.

Answer options A and D are incorrect. The mutt and pidgin are Non-GUI mail clients.

What is mutt? mutt is a powerful tool for managing email within a text-only environment. This tool is very important to access email even when a graphical interface is not available. Some of its strengths are handling of message threads and flexibility. When mutt sees a series of related messages, it displays each reply under the parent. mutt supports sending of attachments through a mail. The following example describes how a file can be attached to a mail: echo "Sending an attachment." | mutt -a backup.zip -s "attachment" local@domain.com

This command will send a mail to local@domain.com with the subject (-s) "attachment", the body text "Sending an

attachment.", containing the attachment (-a) backup.zip.

What is Pidgin?

Pidgin is a multi-protocol Instant Messaging client that allows a user to use all of his IM accounts at once. It is a free software that can work with AIM ,Gadu-Gadu, Jabber, ICQ ,IRC, MSN, SILC, XMPP, Yahoo!, and Zephyr Network. Anyone is

free to use it and modify it, but if a user distributes his modifications, he must distribute the modified source code as well.

The license of this communication software is Freeware, i.e. anyone can freely download and use this communication software.

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 locate command queries a database for all pathnames that match the specified pattern. The specificity of locate can be increased by using it together with wildcards or other regular expressions. This command uses the star wildcard to display all files on the system that have the .xml filename extension.

What is a regular expression?

A regular expression is a way of describing a string of text using metacharacters or wildcard symbols.

For example, "*.xml" is a regular expression that refers to all files having the extension .xml.

What is a wildcard?

The specificity of LOCATE can be increased by using it together with wildcards or other regular expressions. Wildcards are characters that can be used to substitute for any other character or characters. For example, the star character (*) is a wildcard that can represent any single character or any string containing any number of characters.

Answer option A is incorrect. This is an incorrect syntax and an error messages will be displayed.

Answer option D is incorrect. The cat command displays the content of the specified file.

Answer option B is incorrect. This is an incorrect command, when you type this command an error message will be displayed.

The Interface configuration files are read by system-config-network, ifup, ifdown, and other tools that bring network interfaces up and down.

Answer option B is incorrect. The system-config-services tool is used to manage services in Linux.

The ps command reports the status of processes that are currently running on a Linux computer.

What is >> command?

The >> command is used for storing the output generated by different commands. It creates a file specified to store the output. If the specified file already exists, it appends that file.

This command will run sort on the file marketing.txt and sort the file in the reverse alphabetical order.

Answer option B is incorrect. sort with no options is used to sort file alphabetically. It will not sort the file in the reverse alphabetical order.

Answer option C is incorrect. The -n option used with the sort command sorts the text numerically, instead of by characters.

Answer option A is incorrect. The -u option with sort removes duplicate lines from the output.

In order to accomplish the task, you will use the at command. The at command is used to set a specific command or batch file to execute at a certain time.

Syntax:

at [option] schedule time

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

The atd daemon monitors the queue of the at commands and executes them at a specified time.

Example:

The following command will create a list of jobs to be executed at 8:00 AM on 22nd August 2004.

at 08:00 22.08.2004

at> ls

at> pwd

+

The + key combination is used to end the list of commands.

The jobs can be removed from an at queue by using the atrm command.

Note: The at command cannot schedule recurring jobs.

Answer option C is incorrect. You will not run the crontab command, since it runs a program repeatedly. The crontab command is used to view and edit the crontab files, which are used to organize the cron facility. Each user has access to the

cron facility through a crontab file. Some of the frequently used crontab command options are as follows:

Answer option A is incorrect. In computing, rsync is a software application for Unix systems. It synchronizes files and directories from one location to another while minimizing data transfer using delta encoding. It can copy or display directory contents and copy files, optionally using compression and recursion.

In daemon mode, rsync listens to the default TCP port of 873, serving files in the native rsync protocol or via a remote shell such as RSH or

SSH. In the latter case, the rsync client executable must be installed on both the local and remote hosts.

Answer option D is incorrect. The sync command is used to flush filesystem buffers. It ensures that all disk writes have been completed before the processor is halted or rebooted. Generally, it is preferable to use reboot or halt to shut down a system, as they may perform additional actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync.

xinit is a program that allows a user to manually start an X server. The startx script is a front-end for xinit. By default, xinit and

startx start an X server on display :0 and then start an xterm on it. When the xterm terminates, xinit and startx kill the X server. In general,

xinit and startx can start an arbitrary server and run an arbitrary script. Typically, this script runs a number of programs and a window manager. Arguments immediately following the startx command are used to start a client in the same manner as xinit. For example the startx -

- -dpi 100 command starts the xsession with 100 dpi.