RH033 Red Hat Linux Essentials Questions and Answers

According to the scenario, the S status message shows that the process id 24224 is in sleeping status.

The ps -aux command reports the status of processes currently running on a Linux computer. It shows the following status messages:

In order to accomplish the task, you will have to kill the process and rerun it by using the nice command to lower the priority of the process.

You will have to run the following command: kill < process Id > : nice < process name > -n 19

The nice command is used to run a process with the desired priority level. The priority level varies from 1 to 19. Level 1 is for the highest priority and level 19 is for the lowest. By default, every process runs with the priority level 10.

Answer option C is incorrect. The fg command is used to run a process in the foreground.

Answer option D is incorrect. The bg command is used to run a process in the background.

Answer option A is incorrect. The -n 1 switch will provide the process the top priority.

The lprm - and lprm -a all commands can be used to delete all jobs queued in a printer. The lprm command is used to remove the print jobs that have been queued for printing. If no arguments are supplied, the current job on the default destination is cancelled. The command syntax for the lprm command is as follows:

lprm [-E] [-U username] [-h server[:port]] [-P destination[/instance]] [-] [job ID(s)]

where,

Answer options B and C are incorrect. These are not valid lprm command syntaxes.

This command will prompt you to remove Joe ' s tmp files that are 3 days older. When the -ok option is used with the find command it causes find to execute the rm command once for each /tmp file that is 3 days older. {} can be used as a filename placeholder.

The -ok option with the find command is used to execute a command once for each file that matches the given criteria. This is commonly used in situations such as removing files or renaming files to have a certain extension. The -ok option causes find to ask for each file before removing it.

What is the find command?

The find command is a versatile method for locating files on a file system. The syntax for this command is as follows:

find < start directory > - < criteria >

Some of the important criteria are described in the table below:

What are some numeric criteria that the find command uses?

The find command can search your system for files that comply with certain numeric criteria. For

example, -ctime, -atime, -

cmin, -amin, etc. The -ctime and -atime are measured in days and the -cmin and -amin are measures in minutes.

For example:

find /tmp -ctime +10

This command searches for files that are more than 10 days older.

find /tmp -cmin +10

This command searches for files that are more than 10 minutes older.

What is the purpose of using \; at the end of the find command?

The purpose of using \; at the end of the find command is that when find is used with -exec and –ok the find command uses ; as the delimiting character. Unfortunately ; is also a delimiting character for the bash shell so we must prevent bash from interpreting it. When a character is preceded with a backslash (\), bash instructs it literally, so typing \; at the bash command prompt will send ; to find command after bash has done its interpretation.

Answer option A is incorrect. This command will prompt you to remove Joe ' s tmp files that are 3 minutes older.

Answer options D and B are incorrect. These are the incorrect command syntaxes.

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 overwrites that file.

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.

The read permission has been assigned to the owner of the file and the read permission has also been assigned to members of its owing group.

The first field - represents the type of a file and the next three characters (rwx) represent the permission given to the owner of the file then the next three characters (r--) represent the permission given to the group to which the file belongs and the last three characters (---) represent the permission given to others.

Answer option C is incorrect. No permission has been assigned to others users.

In order to run the script, you are required to add the execute permission to the script file. The permission can be assigned through the chmod command.

What is the chmod command?

The chmod command is used to change file access permissions in Linux.

Syntax:

chmod [option] [mode] < file1, file2, ... >

Option: The following is a list of some important options that can be provided with the command:

Mode: Mode is written in the following format:

[ugoa] [+-=] [rwxXstugo]

The combination of ugoa specifies the users for whom the file access permissions will be changed. In ugoa, u is for the user who owns the file, g is for other users in the file group, o is for other users not in the file group, and a is for all users.

The operator + adds the specified permissions to the existing permissions of each file. The - operator removes, and the = character specifies that the specified permissions are the only permissions for that file.

The combination of rwxXstugo is permission type. In rwxXstugo, r is for read, w is for write, x is for execute, X is to execute only if the file is a directory or already has execute permission for some user, s is to set user or group

ID on execution, t is to save program text on swap device, u are the permissions that the user who owns the file currently has for it, g are the permissions that other users in the file group have for the file, and o are the permissions that other users not in the file group have for the file.

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 chmod command is used to change or edit file/folder permissions in Linux. In order to accomplish the task, you will have to run the following command:

chmod 754 report

This will provide Read, Write, and Execute permissions to the owner (in this case, David), Read and

Execute permissions to the members of the JAdmin group, and only Read permission to other users.

Answer option D is incorrect. This will provide Read, Write, and Execute permissions to David, to the members of the JAdmin group, and to other users.

Answer option A is incorrect. This will provide Read and Execute permissions to David, to the members of the JAdmin group, and to other users.

Answer option C is incorrect. The chown command is used to change the ownership on files or folders.

Using the -f option causes tail to continue to display the file in real time, showing added lines to the end of the file as they occur.

What is the tail -f command?

The tail command is used to display the last few lines of a text file or piped data. It has a special command line option –f (follow) that allows a file to be monitored. Instead of displaying the last few lines and exiting, tail displays the lines and then monitors the file. As new lines are added to the file by another process, tail updates the display.

This is particularly useful for monitoring log files. The following command will display the last 10 lines of messages and append new lines to the display as new lines are added to messages: tail -f /var/adm/messages

Answer option C is incorrect. The cat command simply shows the content of the file when it was last opened, cat does not continue to show updates of the file.

Answer option D is incorrect. The tail -n 3 /var/adm/messages command is used to show most recent entries in log file but it will not continue to show updates of the log file.

Answer option B is incorrect. The tail command will show the last few lines of the log file, but it will not continue to show updates of the log file.

You can view all running processes with the help of the ps -aux command. Hence, any of the ps –aux commands (i.e., ps -aux | grep cc, ps -aux

| more, or ps -aux) can be used to check whether the cc process is running on the computer.

Answer option B is incorrect. The tail command is used to display the last few lines of a text file or piped data. It has a special command line option -f (follow) that allows a file to be monitored. Instead of displaying the last few lines and exiting, tail displays the lines and then monitors the file. As new lines are added to the file by another process, tail updates the display. This is particularly useful for monitoring log files. The following command will display the last 10 lines of messages and append new lines to the display as new lines are added to messages: tail -f /var/adm/messages

The evince utility is used to view PDF files on the Linux operating system.

What is the evince command?

The evince command is a document viewer capable of displaying multiple and single page document formats such as PDF and Postscript.

Syntax:

evince [Options] [Filename]

Answer options B and D are incorrect. These commands are used to convert a text to PostScript and send it to a file or the print queue.

What is PostScript?

PostScript is a language developed by Adobe Systems for printing documents on laser printers. It can also be adapted to produce images on other types of devices. It is the standard for desktop publishing. Every PostScript printer contains a built-in interpreter that executes PostScript instructions. Level 1, Level 2, and PostScript 3 are three basic versions of PostScript language.

Answer option A is incorrect. The ps2pdf utility is used to create PDF files.

find /etc -name *.txt command is used to search for files anywhere on the system that end in .txt.

What is the find command?

The find command can perform a search based on a variety of search limitations. It searches through one or more directory tree(s) of a filesystem, locating files based on some user-specified criteria. By default, find returns all files in the current working directory. Further, find allows a user to specify an action to be taken on each matched file.

Thus, it is an extremely powerful command for applying actions to many files.

The find command can be used with a wild card (*), but it works best when we know the name of the file or directory we are looking for.

The find command can search your system for files that comply with certain numeric criteria, such as the size of the file (- size), the number of links to the file (-links), the date of the last change to the files data (-mtime), or the date of the last time the file was read (-atime). All these criteria accept a numeric value. When a numeric value is provided to find, it looks for an exact match, more than the number, or less than the number.

Answer options D, B, and C are incorrect. There is no such commands in the Linux.

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 service and chkconfig commands are used to start and stop a service, and to ensure persistence across reboots. The service command is used to abstract the management of services provided by the system. It can be used to start and stop services, as well as to determine the status of services. To execute a given command for a given service, it uses the start, stop, restart, and reload arguments. Some important options used with the service command are as follows:

The chkconfig tool is used to update and query runlevel information for system services.

Answer option D is incorrect. The yum command automatically attempts to check all configured repositories to resolve all package dependencies during an installation/upgrade.

Answer option B is incorrect. The tape archive (tar) command combines a large number of files into a single file for archival purposes.

You can use the tr command to convert all lowercase letters of a text file to uppercase. The tr

command is used to translate, squeeze, and/or delete characters from standard input, writing to standard output. If you want to change all lowercase letters to uppercase, you will use the tr

[a-z] [A-Z] command.

Answer options B, A, and D are incorrect. The cat, tac, and less commands are used to display the output of the text file on the screen. These commands cannot translate the text from one form to another.

The lpc command is used to check the status of printers, enable and disable printers, and change the arrangement of jobs in the print queue.

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

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

Answer option B is incorrect. The lprm command removes a job from the print queue.

The date command with the %M specifier prints the current time (Minutes). Since the output is redirected towards the date.txt file, the current time (Minutes) will be printed in the date.txt file.

You will use find ~ -perm -002 -exec chmod o-w {} \; command to fix other writable files in your home directory.

Answer option B is incorrect. The find /home -type d -ls command is used to do an ls -l style listing of all directories in /home/.

Answer options A and D are incorrect. There are no such commands in Linux.

All these information are stored in the /etc/passwd file.

What is the /etc/passwd file?

In Linux operating systems, the /etc/passwd file lists information about each of the users that may login to the system. The file is so named because originally it also contained the data used to verify passwords. However, on

modern Unix systems, the security-sensitive password information is instead often stored in a different file using shadow passwords.

The /etc/passwd file typically has world-readable permissions, though it may only be edited by the

superuser or by using a few special purpose commands.

The first field is the user name. Each record in the file must have a unique user name field.

The second field stores information used to confirm a user ' s password; however, in most modern uses, this field is usually set to " x " (or some other indicator) with the actual password information being stored in a separate shadow password file.

The third field is the user identifier, the number that the operating system uses for internal purposes. It does not have to be unique.

The fourth field is the group identifier. This number identifies the primary group of the user; all files that are created by this user will initially belong to this group.

Reserved gecos ID (Typically, this is a set of comma-separated values including the user ' s full name

and contact details).

The sixth field is the path to the user ' s home directory.

The seventh field is the shell program that is started every time the user logs into the system.

Answer option C is incorrect. The shadow password is stored in the /etc/shadow file.

What is /etc/shadow file?

The /etc/shadow file stores the account information in the following format:

The history !! command shows the previously entered command in the bash shell. In the bash shell, the history command is used to view the recently executed commands. History is on by default. A user can turn off history using the command set +o history and turn it on using set –o history. An environment variable HISTSIZE is used to inform bash about how many history lines should be kept. The following commands are frequently used to view and manipulate history:

Answer option A is incorrect. The history !# command shows the entire command line typed.

Answer option D is incorrect. The history !n command shows the nth command typed. Since n is equal to 1 in this command, the first command will be shown.

Answer option C is incorrect. It is not a valid command.

The cp -u command copies only when the source file is newer than the destination file or when the destination file is missing.

Answer option C is incorrect. The cp -p command copies the files from source to destination with preserving file attributes, such as timestamps, mode, and ownership.

Answer option B is incorrect. The cp -l command links files from source to destination instead of copying.

Answer option D is incorrect. The cp -s command makes symbolic links instead of copying.

The ls -l command shows the permissions on a specified file.

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

Answer option D is incorrect. No such command exists in Linux.

Answer option A is incorrect. The cat command shows the contents of a file.

The rm -rf commarecursively removes directories and its contents, ignoring warnings about removing write-protected files and directories.

Answer option B is incorrect. rm -f removes only files forcibly not a directory. To remove a directory and its contents forcibly, use -r in combination with -f with the rm command.

Answer option C is incorrect. The rmdir command is use to remove an empty directory.

Answer option D is incorrect. rm with no arguments deletes files.

The $! environmental variable represents the PID value of the last child process.

Answer option D is incorrect. The $$ environmental variable represents the PID of the running shell.

Answer option A is incorrect. The $? environmental variable results in the value zero if the last command was executed successfully, otherwise it displays the value one.

Answer option C is incorrect. It is an invalid Linux standard environmental variable.

This is the correct syntax for granting ownership of foofile to John.

What is the chown command?

The chown command is used to change the ownership of a file. Only root can change the ownership of a file. The chown command can be used with the -R option to recursively change the ownership of an entire directory tree.

Syntax:

chown [-R] newowner filename

Answer option B is incorrect. The chmod command is used to change access mode for files and directories.

Answer option D is incorrect. The syntax of this command is not correct. With chown, first write the name of the user whom you want to give ownership, then write the filename of the file whose ownership you want to change.

Answer option C is incorrect. The chgrp command is used to change Group-ownership not file ownership.

In order to replace all the occurrences of " net " with " Net " in the first fifty lines of the file, you will have to execute the following command: :1,50 s/net/Net/g

This command is issued in the command mode of the VI utility. 1,50 defines the initial and final line numbers of the current document where the command will execute. The s/ switch with the net/Net/g option will globally replace all the occurrences of " net " with " Net " .

Answer option A is incorrect. This command will replace " net " with " Net " all over the current document.

Answer option B is incorrect. Since this command executes on the first 100 lines of a document, it will replace " net " with " Net " in all the 100 lines of the current document.

Answer option D is incorrect. This command will replace " net " with " Net " in the current line of the current document.

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.

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.

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 < enter >

at > pwd < enter >

< ctrl > + < d >

The < ctrl > + < d > 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.

If no path is given, find looks in the current directory and its subdirectories. Using the -i option tells the find command to perform caseinsensitive search for files named snow.html. It will show all files named snow.html, Snow.html,

SNOW.html in the current directory.

Answer option B is incorrect. This command will only search for files named snow.html in the current directory with case-sensitiveness. It will not search for those files named Snow.html, SNOW.html.

Answer option C is incorrect. This is an incorrect command; it will show an error message.

Answer option D is incorrect. This is also an incorrect command, there should be a name after -i in the command.

According to the scenario, John can use the set +o history command to disable history.

Answer option D is incorrect. John cannot use the set -o history command to accomplish his task.

This command is used to enable disabled history.

Answer option A is incorrect. John cannot use the history !! command to accomplish his task. This command is used to see the most recently typed command.

Answer option C is incorrect. John cannot use the history !N command to accomplish his task. This command is used to display the Nth history command.

What is the history command?

In the bash shell, the history command is used to view the recently executed commands. History is on by default. A user can turn off history using the command set +o history and turn it on using set -o history. An environment variable

HISTSIZE is used to inform bash about how many history lines should be kept. The following commands are frequently used to view and manipulate history:

The useradd or adduser command is used to add a user on the Linux operating system.

The bg utility resumes suspended jobs from the current environment by running them as background jobs if job control is enabled. If the job specified by job_id is already a running background job, the bg utility will have no effect and shall exit successfully. Using bg to place a job into the background will cause its process ID to become " known in the current shell execution environment " , as if it had been started as an asynchronous list.

Answer option D is incorrect. The fg utility continues a stopped job by running it in the foreground, some shells are not able to run this command.

Syntax:

fg [%job] Where %job specifies the job that a user wants to run in the foreground.

Answer option A is incorrect. The jobs command lists the jobs that are running in the background and in the foreground. If the prompt is returned with no information, no jobs are present.

Syntax: jobs [-p | -l] [-n] [-p] [-x] [job id]

Some important options used with jobs command are as follows:

Answer option C 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:

When you will execute find -name " *.conf " -exec cp {} {} .orig \ ; command on the terminal, it will back up configuration files from the current directory and a .orig extension.

What is the find command?

The find command can perform a search based on a variety of search limitations. It searches through one or more directory tree(s) of a filesystem, locating files based on some user-specified criteria. By default, find returns all files in the current working directory. Further, find allows a user to specify an action to be taken on each matched file.

Thus, it is an extremely powerful command for applying actions to many files.

The find command can be used with a wild card (*), but it works best when we know the name of the file or directory we are looking for.

The find command can search your system for files that comply with certain numeric criteria, such as the size of the file (- size), the number of links to the file (-links), the date of the last change to the files data (-mtime), or the date of the last time the file was read (-atime). All these criteria accept a numeric value. When a numeric value is provided to find, it looks for an exact match, more than the number, or less than the number.

Answer options B and A are incorrect. These options are invalid.

Answer option D is incorrect. To fix other-writable files in your home directory, you will run find ~ - perm -002 -exec chmod o-w {} \;.

According to the scenario, John wants to change the modified date and time of the file private.txt to a desired date and time. For this, he can use either the touch -t or touch -d command. The difference between these two commands is that the touch -d command is more flexible, while the touch -t command takes the date and time in the format MMDDhhmm.ss.

The shutdown -h now, halt -h, and poweroff -h commands can be used to shut down the Red Hat operating system immediately.

Answer option B is incorrect. This is an invalid answer and hence cannot be used to shut down the system.

The following directories cannot be separated from the root filesystem:

/lib

/dev

/etc

/sbin

/bin

Answer option D is incorrect. /var can be separated from the root filesystem. Such filesystems are known as optional filesystems. Some of the optional filesystems are as follows:

/var

/usr

/opt

/home

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

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.

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.