XK0-005 CompTIA Linux+ Exam Questions and Answers

The user1 password is expired. This can be inferred from the output of the chage -l user1 command, which shows the password expiration information for user1. The output shows that the password expired on 2020-10-01, and the account expired on 2020-10-08. This means that user1 cannot log in to the server unless the password and account are reactivated by the system administrator.

The other options are not correct based on the outputs above. User1 does not need to set a long password, because the output of the passwd -S user1 command shows that the password has a minimum length of 5 characters, which is met by user1’s password. User1 is not in the incorrect group, because the output of the groups user1 command shows that user1 belongs to the app group, which is presumably the correct group for accessing the server. The user1 shell assignment is not incorrect, because the output of the grep user1 /etc/passwd command shows that user1 has /bin/bash as the default shell, which is a valid and common shell for Linux users.

These commands will unmask the mariadb service, which is currently prevented from starting, and then start it normally. The other commands are either not relevant, not valid, or not sufficient for this task. For more information on how to manage masked services with systemctl, you can refer to the web search result 1.

The RPM option -e should be used to remove software from the server. The rpm command is a tool for managing software packages on RPM-based Linux distributions. The -e option stands for erase and removes the specified package from the system. This is the correct option to use to accomplish the task. The other options are incorrect because they either do not exist (-s or -d) or do not remove software (-q stands for query and displays information about the package). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Managing Software, page 489.

To prevent certain files from being tracked by Git, the administrator can use a .gitignore file (B) in the repository. The .gitignore file can specify patterns of files or directories that Git should ignore. This way, the Terraform state files will not appear in the main branch or any other branch. The other commands are not related to this requirement. References:

• [CompTIA Linux+ Study Guide], Chapter 10: Working with Git, Section: Ignoring Files with .gitignore
• [How to Use .gitignore File]

Based on the output of the image sent by the user, the system requires more swap space to allow for spikes in usage during peak hours and prevent the Java process from stopping due to a lack of memory. The output shows that there is only 0 MB of swap space available on the system, which means that there is no room for swapping out memory pages when physical memory is full or low. The output also shows that there is only 793 MB of available memory on the system, which may not be enough to handle high-demand applications such as Java. This may cause Java to stop working due to insufficient memory or trigger an OutOfMemoryError exception. Configuring more swap space on the system would help to alleviate this issue by providing more virtual memory for applications and improving performance. Configuring memory allocation policies during business hours will not help to solve this issue, as it will not increase the amount of available memory or swap space on the system. Configuring a different nice value for Java process will not help to solve this issue, as it will only affect its scheduling priority, not its memory consumption or allocation. Configuring more CPU cores will not help to solve this issue, as it will only increase processing power, not memory capacity or availability. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 15: Managing Memory and Process Execution, page 468.

The required changes need to be made to the /etc/login.defs configuration file. The /etc/login.defs file defines the default values for user and group IDs, passwords, shells, and other parameters for user and group creation. The file contains the directives UID_MIN, UID_MAX, GID_MIN, and GID_MAX, which set the minimum and maximum values for automatic user and group ID selection. The administrator can edit this file and change the values to match the organization’s new cybersecurity policies. This is the correct file to modify to accomplish the task. The other options are incorrect because they either do not affect the user and group IDs (/etc/security/limits.conf or /etc/profile) or do not set the default values (/etc/default/useradd). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 15: Managing Users and Groups, page 463.

The file /etc/ssh/sshd_config contains the configuration settings for the SSH daemon, which handles the secure remote login. To change the port number, the engineer should edit this file and modify the line that says Port 22 to Port 49000. The other files are not related to the SSH service. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 13: Managing Network Services, page 411.

To enable LUKS on a USB storage device with an ext4 filesystem format, the administrator needs to perform the following steps:

• Unmount the device if it is mounted using umount /dev/sdc (D)
• Create a partition table on the device using fdisk /dev/sdc (E)
• Format the partition with LUKS encryption using cryptsetup luksFormat /dev/sdc1 (H)
• Open the encrypted partition using cryptsetup luksOpen /dev/sdc1 LUKS0001
• Create an ext4 filesystem on the encrypted partition using mkfs.ext4 /dev/mapper/LUKS0001 ©
• Mount the encrypted partition using mount /dev/mapper/LUKS0001 /mnt References:
• [CompTIA Linux+ Study Guide], Chapter 9: Securing Linux, Section: Encrypting Disks
• [How to Encrypt USB Drive on Ubuntu 18.04]

The command ip route add 10.0.213.5/32 via 10.0.5.1 dev eth0 adds a static route to the routing table that sends packets destined for 10.0.213.5/32 (a single host) through the gateway 10.0.5.1 on the interface eth0. This is the correct way to achieve the goal. The other options are incorrect because they either use the wrong syntax (route -i etho -p add), the wrong command (route modify), or the wrong file (/proc/net/route). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 12: Managing Network Connections, page 379.

This command will create a local port forwarding, which means that connections from the SSH client are forwarded via the SSH server, then to a destination server. In this case, the destination server is the same as the SSH server (localhost), and the destination port is 80. The SSH client will listen on port 8080 on the local machine, and any connection to that port will be forwarded to port 80 on the server. This way, the administrator can securely access the web service running on port 80 on the server by using http://localhost:8080 on the local machine.

The other options are incorrect because:

B. ssh -R 8080:localhost:80 admin@server

This command will create a remote port forwarding, which means that connections from the SSH server are forwarded via the SSH client, then to a destination server. In this case, the destination server is the same as the SSH client (localhost), and the destination port is 80. The SSH server will listen on port 8080 on the remote machine, and any connection to that port will be forwarded to port 80 on the client. This is not what the administrator wants to do.

C. ssh -L 80:localhost:8080 admin@server

This command will also create a local port forwarding, but it will use port 80 on the local machine and port 8080 on the server. This is not what the administrator wants to do, and it may also fail if port 80 is already in use by another service on the local machine.

D. ssh -R admin@server

This command is incomplete and invalid. It does not specify any port numbers or destination addresses for the remote port forwarding. It will also fail if the SSH server does not allow remote port forwarding.

References:

• CompTIA Linux+ Certification Exam Objectives
• How to Set up SSH Tunneling (Port Forwarding)

The correct answer is D. The administrator should run “echo .DS STORE >> .gitignore” from the root of the local repository before the next commit to ensure the file is not uploaded again in future commits.

This command will append the file name .DS STORE to the end of the .gitignore file, which is a special file that tells Git to ignore certain files or directories that should not be tracked or uploaded to the repository. By adding .DS STORE to the .gitignore file, the administrator will prevent Git from staging, committing, or pushing this file in the future.

The other options are incorrect because:

A. rm -f .DS STORE && git push

This command will delete the file .DS STORE from the local repository and then push the changes to the remote repository. However, this does not prevent the file from being uploaded again in future commits, if it is recreated or copied to the local repository.

B. git fetch && git checkout .DS STORE

This command will fetch the latest changes from the remote repository and then restore the file .DS STORE from the remote repository to the local repository. This is not what the administrator wants to do, as this will undo the deletion of the file from the online repository.

C. rm -f .DS STORE && git rebase origin main

This command will delete the file .DS STORE from the local repository and then rebase the local branch onto the main branch of the remote repository. This will rewrite the commit history of the local branch and may cause conflicts or errors. This is not what the administrator wants to do, as this is a risky and unnecessary operation.

The issue is that the administrator did not set the default target to graphical.target. A target is a unit of systemd that groups together other units by a common purpose or state. The graphical.target is a target that starts the graphical user interface (GUI) along with other services. The administrator used the command systemct1 isolate graphical.target to switch to this target temporarily, but this does not change the default target that is activated at boot time. To make this change permanent, the administrator should have used the command systemct1 set-default graphical.target, which creates a symbolic link from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.

The other options are not correct explanations for the issue. The administrator did reboot the server properly by using systemct1 reboot, which shuts down and restarts the system cleanly. The administrator did not need to set the default target to basic.target, which is a minimal target that only starts essential services. The administrator did not shut down the server improperly, which could have caused file system corruption or data loss, but not affect the default target. References: systemct1(1) - Linux manual page; How to Change Runlevels (targets) in SystemD

The sshd is the Secure Shell Daemon, which is a service that allows remote login to a Linux system using the SSH protocol. The output shows that the sshd is running on port 2222, which is a non-standard port for SSH. The default port for SSH is 22, which is what the user is trying to use. Therefore, the statement B is most likely causing the issue. The statements A, C, and D are incorrect because they do not explain why the user cannot log on using port 22. References: [How to Change SSH Port in Linux]

The rpm -qf /etc/httpd/conf/httpd.conf command will identify the RPM package that installed the configuration file. This command will query the database of installed packages and display the name of the package that owns the specified file. The rpm -ql /etc/httpd/conf/httpd.conf command is invalid, as -ql is not a valid option for rpm. The rpm --query /etc/httpd/conf/httpd.conf command is incorrect, as --query requires a package name, not a file name. The rpm -q /etc/httpd/conf/httpd.conf command is incorrect, as -q requires a package name, not a file name. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Packages and Software, page 560.

The firewall-cmd command is used to manage firewalld, which is a firewall service for Linux systems that provides dynamic and persistent configuration of firewall rules. Firewalld uses zones and services to define different levels of trust and access for network connections.

To permit access temporarily to an application running on port 1234/TCP on a Linux server, the systems administrator can use the firewall-cmd --add-port=1234/tcp command. This command will add a rule to the default zone (usually public) that allows incoming traffic on port 1234/TCP. The rule will only be effective until the next reload or restart of firewalld. To make the rule permanent, the administrator can add the --permanent option to the command. The statement C is correct.

The statements A, B, and D are incorrect because they do not permit access to port 1234/TCP. The firewall-cmd --new-service=1234/tcp command does not exist. The firewall-cmd --service=1234 --protocol=tcp command does not work because 1234 is not a predefined service name in firewalld. The firewall-cmd --add-whitelist-uid=1234 command does not exist. References: [How to Use FirewallD to Manage Firewall in Linux]

To allow the same Kubernetes container configurations to be deployed in different environments without statically configuring custom locations, the engineer can use an ambassador container (D). An ambassador container is a proxy container that handles communication between containers and external services. It can dynamically configure locations based on environment variables or other methods. The other options are not related to this requirement. References:

• [CompTIA Linux+ Study Guide], Chapter 11: Working with Containers, Section: Using Ambassador Containers
• [How to Use Ambassador Containers]

The administrator should do the following two actions to resolve the issue:

• Boot the system on a LiveCD/ISO. This is necessary to access the system and repair the boot loader. A LiveCD/ISO is a bootable media that contains a Linux distribution that can run without installation. The administrator can boot the system from the LiveCD/ISO and mount the root partition of the system to a temporary directory, such as /mnt.
• Execute grub-install /dev/sdX and reboot. This will reinstall the GRUB boot loader to the disk device, where sdX is the device name of the disk, such as sda or sdb. The GRUB boot loader is a program that runs when the system is powered on and allows the user to choose which operating system or kernel to boot. The issue is caused by a corrupted or missing GRUB boot loader, which prevents the system from booting. The command grub-install will restore the GRUB boot loader and fix the issue.

The other options are incorrect because they either do not fix the boot loader (interrupt the boot process in the GRUB menu or fix the partition modifying /etc/default/grub) or do not use the correct syntax (grub-install --root-directory=/mnt instead of grub-install /dev/sdX or rescue or single instead of recovery in the GRUB menu). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 8: Managing the Linux Boot Process, pages 265-266.

The ping command shows that the Linux system can reach the DNS server at 192.168.2.2, so the DNS host is not down. The dig and nc commands show that the Linux system cannot connect to the DNS server on port 53, which is the standard port for DNS queries. This means that either the DNS service is not running on the DNS server, or there is a firewall or network device blocking the port 53 traffic. Therefore, the DNS service is currently not available or the corresponding port is blocked.References1: How To Troubleshoot DNS Client Issues in Linux - RootUsers2: 6 Best Tools to Troubleshoot DNS Issues in Linux - Tecmint3: How To Troubleshoot DNS in Linux - OrcaCore4: Fixing DNS Issues in Ubuntu 20.04 | DeviceTests

This command will allow the systems administrator to change the password of another user account in the system. The sudo prefix will grant the administrator the necessary privileges to perform this action, and the passwd command will prompt for the new password for the specified user. For example, if the administrator wants to change the password of a user named tom, the command will look like this:

sudo passwd tom

The other options are incorrect because:

B. sudo userdel

This command will delete a user account from the system, not change its credentials. The userdel command removes the user’s entry from the /etc/passwd and /etc/shadow files, as well as deletes the user’s home directory and mail spool. This is not what the request asked for.

C. sudo chage

This command will change the password expiration and aging information for a user account, not its credentials. The chage command can be used to set or modify various parameters related to password aging, such as the minimum and maximum number of days between password changes, the number of days before password expiration to issue a warning, and so on. This is not what the request asked for.

D. sudo usermod

This command will modify various attributes of a user account, such as its login name, home directory, default shell, primary group, and so on. However, it cannot change the user’s password directly. To do that, the usermod command requires the -p option followed by an encrypted password string, which is not easy to generate manually. Therefore, this is not a practical way to change a user’s credentials.

References:

• How to Change Account Passwords on Linux
• How to Change a Password in Linux for Root and Other Users
• CompTIA Linux+ Certification Exam Objectives

To mirror the website files on the primary web server, www1, to the backup web server, www2, the administrator can use the command rsync -a -e ssh /var/www/html/ user1@www2:/var/www/html (A). This will synchronize all files and directories under /var/www/html/ on www1 to /var/www/html on www2 using ssh as the remote shell. The -a option will preserve all attributes and permissions of the files. The other commands will not mirror the website files, but either copy them once, download them from a web server, or archive them. References:

• [CompTIA Linux+ Study Guide], Chapter 12: Troubleshooting Linux Systems, Section: Synchronizing Files with rsync
• [How to Use rsync Command in Linux]

The configuration file shown in the image is written in YAML format, so the syntax formatter should support YAML to correct any issues with the file. YAML stands for YAML Ain’t Markup Language, and it is a human-readable data serialization language that uses indentation and colons to define key-value pairs. YAML supports various data types, such as scalars, sequences, mappings, anchors, aliases, and tags. The configuration file follows the rules and syntax of YAML, while the other options do not. Markdown is a lightweight markup language that uses plain text formatting to create rich text documents. XML is a markup language that uses tags to enclose elements and attributes. JSON is a data interchange format that uses curly braces to enclose objects and square brackets to enclose arrays. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 21: Automating Tasks with Ansible, page 591.

This command will use the chsh tool to change the login shell of the users www-data and db to /bin/false, which means they will not be able to log in to the system1. This will prevent unauthorized access attempts and improve security.

References: 1: Replacing /bin/bash with /bin/false in /etc/passwd file

The file that holds the system configuration for journal when running systemd is /etc/systemd/journald.conf. This file contains various settings that control the behavior of the journald daemon, which is responsible for collecting and storing log messages from various sources. The journald.conf file can be edited to change the default values of these settings, such as the storage location, size limits, compression, and forwarding options of the journal files. The file also supports a drop-in directory /etc/systemd/journald.conf.d/ where additional configuration files can be placed to override or extend the main file. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Automating Tasks; journald.conf(5) - Linux manual page

LDAP stands for Lightweight Directory Access Protocol, which is a protocol for accessing and managing a central directory of users and groups. LDAP can be used as a central repository of Linux users and groups, allowing for centralized authentication and authorization across multiple Linux systems. MFA, SSO, and PAM are not technologies that can be used as a central repository of Linux users and groups. MFA stands for Multi-Factor Authentication, which is a method of verifying a user’s identity using more than one factor, such as a password, a token, or a biometric. SSO stands for Single Sign-On, which is a feature that allows a user to log in once and access multiple applications or systems without having to re-enter credentials. PAM stands for Pluggable Authentication Modules, which is a framework that allows Linux to use different authentication methods, such as passwords, tokens, or biometrics. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 8: Managing Users and Groups

The command that will accomplish this task is sudo useradd -e 2021-09-30 Project_user. This command will create a new user account named Project_user with an expiration date of 2021-09-30. The -e option of useradd specifies the date on which the user account will be disabled in YYYY-MM-DD format.

The other options are not correct commands for creating a user account with an expiration date. The sudo useradd -c 2021-09-30 Project_user command will create a new user account named Project_user with a comment of 2021-09-30. The -c option of useradd specifies a comment or description for the user account, not an expiration date. The sudo modinfo -F 2021-09-30 Project_user command is invalid because modinfo is not a command for managing user accounts, but a command for displaying information about kernel modules. The -F option of modinfo specifies a field name to show, not an expiration date. The sudo useradd -m -d 2021-09-30 Project_user command will create a new user account named Project_user with a home directory of 2021-09-30. The -m option of useradd specifies that the home directory should be created if it does not exist, and the -d option specifies the home directory name, not an expiration date. References: useradd(8) - Linux manual page; modinfo(8) - Linux manual page

File attributes are preventing file modification, which is causing the error message. The output of lsattr /home/user/data.txt shows that the file has the immutable attribute (i) set, which means that the file cannot be changed, deleted, or renamed. The command setfacl -b /home/user/data.txt tries to remove the ACL from the file, but fails because of the immutable attribute. The administrator needs to remove the immutable attribute first by using the command chattr -i /home/user/data.txt and then try to remove the ACL again. The other options are incorrect because they are not supported by the outputs. The administrator is using a highly privileged account, as shown by the # prompt. The filesystem is mounted with the correct options, as shown by the output of mount | grep /home. SELinux file context is not denying the ACL changes, as shown by the output of ls -Z /home/user/data.txt. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11: Managing Files and Directories, pages 357-358.

The error indicates that the application requires an X11 display, but the SSH session does not forward the X11 connection. To enable X11 forwarding, the administrator needs to use the ssh -X option, which requests X11 forwarding with authentication spoofing. This will set the DISPLAY environment variable on the remote host and allow the application to open a window on the local display.

References

• CompTIA Linux+ (XK0-005) Certification Study Guide, page 314
• Open a window on a remote X display (why “Cannot open display”)?, answer by Gilles ‘SO- stop being evil’

The command that will allow the technician to execute the services and continue deploying other microservices within the same terminal session is bg %1 job name. This command will send the job with ID 1 and name job name to the background, where it will run without occupying the terminal. The other options are incorrect because:

• gedit & disown will launch a graphical text editor in the background and detach it from the terminal, but it will not execute any service.
• kill 9 %1 will terminate the job with ID 1 using a SIGKILL signal, which cannot be ignored or handled by the process.
• fg %1 will bring the job with ID 1 to the foreground, where it will occupy the terminal until it finishes or is stopped. References: CompTIA Linux+ Study Guide, Fourth Edition, page 181-182.

The mount unit file name and the Where entry must be escaped to handle spaces in the path.ReferencesThe mount unit file name must be named after the mount point directory, with spaces replaced by \x20. See How to escape spaces in systemd unit files? and systemd.mount.The Where entry must use \x20 to escape spaces in the path. See systemd.mount and The workaround is to use /usr/bin/env followed by the path in quotes..

The Linux administrator should request the following types of DNS records from the DNS team:

• A: This record type is used to map a hostname to an IPv4 address. The administrator needs four A records for devel.comptia.org, one for each IP address (5.5.5.1, 5.5.5.2, 5.5.5.3, 5.5.5.4). This will allow users to access the web servers by using the hostname devel.comptia.org instead of the IP addresses1.
• CNAME: This record type is used to create an alias for another hostname. The administrator needs two CNAME records, one for dev.comptia.org and one for development.comptia.org, both pointing to devel.comptia.org. This will allow users to access the web servers by using any of these three hostnames interchangeably1.
• NS: This record type is used to delegate a domain or a subdomain to another name server. The administrator needs one NS record for comptia.org, pointing to 5.5.5.254, which is the name server that hosts the records for the subdomain devel.comptia.org2. This will allow users to resolve the hostnames under comptia.org by querying the name server 5.5.5.2542.

The other record types are not relevant for the administrator’s task:

• MX: This record type is used to specify the mail exchange server for a domain or a subdomain1. The administrator does not need this record type because the web servers are not intended to handle email traffic.
• PTR: This record type is used to map an IP address to a hostname, which is the reverse of an A record1. The administrator does not need this record type because the web servers are not expected to be accessed by their IP addresses.
• RRSIG: This record type is used to provide digital signatures for DNSSEC, which is a security extension for DNS that verifies the authenticity and integrity of DNS responses3. The administrator does not need this record type because it is not mentioned in the task requirements.
• SOA: This record type is used to provide information about the authoritative name server and other parameters for a domain or a subdomain1. The administrator does not need this record type because it is usually created automatically by the name server software when a new zone file is created4.
• TXT: This record type is used to store arbitrary text data that can be used for various purposes, such as SPF, DKIM, DMARC, etc1. The administrator does not need this record type because it is not related to the web server functionality.
• SRV: This record type is used to specify the location and port number of a service that runs on a domain or a subdomain1. The administrator does not need this record type because the web servers use the standard HTTP port 80, which does not require an SRV record.

References: 1: DNS Record Types – CompTIA Network+ N10-007 – 1.8 2: NS Record - DNSimple Help 3: DNSSEC - Wikipedia 4: SOA Record - DNSimple Help

The custom.conf file grants sudo privileges to user1 and webadmin for managing the Apache web service, but it uses different commands for each of them. User1 is allowed to use systemctl to start and stop the httpd service, while webadmin is allowed to use init.d, service, or apache2ctl to restart the httpd service. However, the user1 is unable to restart the service, only start and stop it. To fix this, user1 should be able to use the same commands as webadmin, which can be achieved by listing webadmin as a group in the custom.conf file, using the syntax %groupname. This way, user1 will inherit the sudo privileges of the webadmin group, and be able to restart the Apache web service without compromising the least privilege security model.

References

• Sudo and Sudoers Configuration | Servers for Hackers, section “Groups”
• Chapter 12. Managing sudo access - Red Hat Customer Portal, section “12.1. Configuring sudo access for users and groups”

The command find . -type f -print | xargs grep -li denied will accomplish the task of identifying files that contain any occurrence of the word denied. The find command is a tool for searching for files and directories on Linux systems. The . is the starting point of the search, which means the current directory. The -type f option specifies the type of the file, which means regular file. The -print option prints the full file name on the standard output. The | is a pipe symbol that redirects the output of one command to the input of another command. The xargs command is a tool for building and executing commands from standard input. The grep command is a tool for searching for patterns in files or input. The -li option specifies the flags that the grep command should apply. The -l flag shows only the file names that match the pattern, instead of the matching lines. The -i flag ignores the case of the pattern, which means it matches both uppercase and lowercase letters. The denied is the pattern that the grep command should search for. The command find . -type f -print | xargs grep -li denied will find all the regular files in the current directory and its subdirectories, and then search for any occurrence of the word denied in those files, ignoring the case, and print only the file names that match the pattern. This will allow the administrator to identify files that contain any occurrence of the word denied. This is the correct command to use to accomplish the task. The other options are incorrect because they either do not ignore the case of the pattern (find . -type f -print | xargs grep -ln denied or find . -type f -print | xargs grep -wL denied) or do not show the file names that match the pattern (find . -type f -print | xargs grep -nv denied). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Managing Logging and Monitoring, page 489.

The xfs repair command is used to check and repair an XFS filesystem, which is the type of filesystem used for the /data partition, as shown in the output. The administrator needs to unmount the /data partition before running the xfs repair command on it, and then mount it back after the repair is done. For example: umount /data; xfs_repair /dev/sdcl; mount /data. The mkfs.xfs command is used to create a new XFS filesystem, which would erase all the data on the partition. The fsck command is used to check and repair other types of filesystems, such as ext4, but not XFS. The pvs command is used to display information about physical volumes in a logical volume manager (LVM) setup, which is not relevant for this issue.

The /sbin/nologin shell is a special shell that prevents the user from logging into an interactive session. It is commonly used for system accounts that are not meant to be accessed by users, such as daemon or service accounts. When a user tries to log in with this shell, they will see a message like “This account is currently not available” and the login will fail.

References:

• The /sbin/nologin shell is listed as one of the valid shells in the /etc/shells file1.
• The CompTIA Linux+ Certification Exam Objectives mention that the candidate should be able to “configure and manage system accounts and groups, including password aging and restricted shells” as part of the Hardware and System Configuration domain2.
• The usermod command can be used to change the user’s login shell with the -s or --shell option3. For example, to change the shell of a user named daemon to /sbin/nologin, the command would be: sudo usermod -s /sbin/nologin daemon

The fastest way to boot the Linux system to normal mode is to comment out the /opt/app filesystem in /etc/fstab and reboot. This will prevent the system from trying to mount the /opt/app filesystem at boot time, which causes an error because the filesystem does not exist or is corrupted. Commenting out a line in /etc/fstab can be done by adding a # symbol at the beginning of the line. Rebooting the system will apply the changes and allow the system to boot normally. Reformatting the /opt/app filesystem will not help to boot the system, as it will erase any data on the filesystem and require manual intervention to create a new filesystem. Performing filesystem checks on local filesystems will not help to boot the system, as it will not fix the missing or corrupted /opt/app filesystem. Triggering a filesystem relabel will not help to boot the system, as it will only change the security context of files and directories according to SELinux policy. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 14: Managing Disk Storage, page 456.

The main objective when using Application Control is to ensure the security and privacy of information. Application Control is a security practice that blocks or restricts unauthorized applications from executing in ways that put data at risk. The control functions vary based on the business purpose of the specific application, but the main objective is to help ensure the privacy and security of data used by and transmitted between applications1. Application Control can also prevent malware, untrusted, or unwanted applications from running on the network, reducing the risks and costs associated with data breaches1. Application Control can also improve the overall network stability and performance by eliminating unnecessary or harmful applications1.

Application Control is not mainly used to filter out specific content, although it can be combined with other technologies such as URL filtering or content filtering to achieve that goal. Application Control is not mainly used to assist the firewall blade with handling traffic, although it can be integrated with firewall policies to enforce granular access rules based on applications. Application Control is not mainly used to see what users are doing, although it can provide visibility and reporting on application usage and activity.

To change the swappiness parameter to 0 and make it persistent across reboots and applied immediately, the administrator can perform the following steps:

• Append the line vm.swappiness=0 to the file /etc/sysctl.conf using echo "vm.swappiness=0" >> /etc/sysctl.conf (A). This will set the swappiness parameter to 0 for future boots.
• Reload the sysctl configuration using sysctl -p (A). This will apply the changes to the current system without rebooting. The other commands will not achieve this task, but either write to a wrong file, use a wrong option, or have a syntax error. References:
• [CompTIA Linux+ Study Guide], Chapter 8: Optimizing Linux Performance, Section: Tuning Kernel Parameters with sysctl
• [How to Change Swappiness in Linux]

The best command to use to confirm on which server the HBA card was installed is A. lspci | egrep ‘hba| fibr’. This command will list all the PCI devices on the server and filter the output for those that match the pattern ‘hba’ or ‘fibr’, which are likely to be related to the HBA card. The egrep command is a variant of grep that supports extended regular expressions, which allow the use of the ‘|’ operator for alternation. The other commands are either invalid or will not produce the desired output. For example:

• B. lspci | zgrep ‘hba | fibr’ will try to use zgrep, which is a command for searching compressed files, not standard output.
• C. lspci | pgrep ‘hba| fibr’ will try to use pgrep, which is a command for finding processes by name or other attributes, not text patterns.
• D. lspci | ‘hba | fibr’ will try to use ‘hba | fibr’ as a command, which is not valid and will cause an error.

The command semanage port -a -t http_port_t -p tcp 6379 adds a new port definition to the SELinux policy and assigns the type http_port_t to the port 6379/tcp. This allows the web application to run on this port and accept connections from users. This is the correct way to resolve the issue. The other options are incorrect because they either delete a port definition (-d), use the wrong protocol (top instead of tcp), or list the existing port definitions (-l). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Securing Linux Systems, page 535.

The command that will accomplish the task of running a container with the httpd server inside and exposing it at port 443 of the Linux host machine while it internally listens on port 8443 is podman run -d -p 443:8443 httpd. This command uses the podman tool, which is a daemonless container engine that can run and manage containers on Linux systems. The -d option runs the container in detached mode, meaning that it runs in the background without blocking the terminal. The -p option maps a port on the host machine to a port inside the container, using the format host_port:container_port. In this case, port 443 on the host machine is mapped to port 8443 inside the container, allowing external access to the httpd server. The httpd argument specifies the name of the image to run as a container, which in this case is an image that contains the Apache HTTP Server software. The other options are not correct commands for accomplishing the task. Podman run -d -p 8443:443 httpd maps port 8443 on the host machine to port 443 inside the container, which does not match the requirement. Podman run –d -e 443:8443 httpd uses the -e option instead of the -p option, which sets an environment variable inside the container instead of mapping a port. Podman exec -p 8443:443 httpd uses the podman exec command instead of the podman run command, which executes a command inside an existing container instead of creating a new one. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Automating Tasks

The command tail -n 20 will display the last 20 lines of a file. The -n option specifies the number of lines to show. This is the correct command to execute the task. The other options are incorrect because they either use the wrong options (-v, -c, or -l) or have the wrong arguments (20 instead of 20 filename). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 11: Managing Files and Directories, page 352.

The code snippet is written in Terraform language, which is a tool for building, changing, and versioning infrastructure as code. Terraform uses a declarative syntax to describe the desired state of the infrastructure and applies the changes accordingly. The code defines a resource of type aws_instance, which creates an AWS EC2 instance, and sets the attributes such as the AMI ID, instance type, security group IDs, and key name. The code also uses a count parameter to create three identical instances and assigns them different names using the count.index variable. This is the correct technology that the administrator is using. The other options are incorrect because they use different languages and syntaxes for infrastructure as code. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Cloud and Virtualization Technologies, page 559.

Ctrl+Z suspended the process, and "fg" will bring it back into the foreground of the shell

A Comprehensive and Detailed Explanation: To go back to a program that was suspended by pressing Ctrl+Z in the command line, the command that can be used is fg. The fg command stands for foreground, and it resumes the job that is next in the queue and brings it to the foreground. Alternatively, if there are more than one suspended jobs, fg can be followed by a job number to resume a specific job. The other commands are incorrect because they either do not resume a suspended job, or they have different functions such as switching user (su), pushing a job to the background (bg), or editing a file (ed). References: CompTIA Linux+ Study Guide, Fourth Edition, page 181-182.

The su command is used to switch to another user account on Linux systems. The - option makes the shell a login shell, which means that it will read the profile and environment variables of the target user. Without this option, the shell will retain the environment variables of the original user. This can cause confusion when issuing commands that depend on these variables, such as ls, which uses the $HOME variable to determine the home directory. Therefore, Ann should have issued su - Joe to list Joe’s files instead of her own. References: [How to Use su Command in Linux with Examples]

The systems administrator used Terraform to create a cloud-based server with a public IP address. Terraform is a tool for building, changing, and versioning infrastructure as code. Terraform can create and manage resources on different cloud platforms, such as AWS, Azure, or Google Cloud. Terraform uses a declarative syntax to describe the desired state of the infrastructure and applies the changes accordingly. Terraform can also assign a public IP address to a cloud server by using the appropriate resource attributes. This is the correct technology that the systems administrator used to complete the task. The other options are incorrect because they are either not designed for creating cloud servers (Puppet or Git) or not capable of assigning public IP addresses (Ansible). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Cloud and Virtualization Technologies, page 559.

This file prevents any non-root user from logging in to the system, regardless of the authentication method. The contents of the file are displayed to the user before the login is terminated. This can be useful for system maintenance or security reasons12.

References: 1: Creating the /etc/nologin File - Oracle 2: How to Restrict Log In Capabilities of Users on Ubuntu

The command systemct1 mask nginx disables the nginx service from the environment and prevents it from being automatically and manually started. This command creates a symbolic link from the service unit file to /dev/null, which makes the service impossible to start. This is the correct way to accomplish the task. The other options are incorrect because they either do not exist (systemct1 cancel nginx), do not prevent manual start (systemct1 disable nginx), or do not prevent automatic start (systemct1 stop nginx). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 14: Managing Processes and Scheduling Tasks, page 429.

The correct order of Git commands to add a new configuration file to a Git repository is pull -> add -> commit -> push. The pull command will fetch and merge the changes from the remote repository to the local repository, ensuring that the local repository is up to date. The add command will stage the new configuration file for the next commit, marking it as a new file to be tracked by Git. The commit command will create a new snapshot of the project state with the new configuration file and a descriptive message. The push command will publish the commit to the remote repository, updating the remote branch with the new configuration file. The pull -> push -> add -> checkout order is incorrect, as it will not create a commit for the new configuration file, and it will switch to a different branch without pushing the changes. The checkout -> push -> add -> pull order is incorrect, as it will switch to a different branch before adding the new configuration file, and it will overwrite the local changes with the remote changes without creating a commit. The pull -> add -> push -> commit order is incorrect, as it will not create a commit before pushing the changes, and it will create a commit that is not synchronized with the remote branch. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 20: Writing and Executing Bash Shell Scripts, page 579.

These commands can display all the firewall rules applied to the Linux servers, depending on which firewall service is being used.

• The firewall-cmd command is a utility for managing firewalld, which is a dynamic firewall service that supports zones and services. The --list-all option will show all the settings and rules for the default zone, or for a specific zone if specified. For example, firewall-cmd --list-all --zone=public will show the rules for the public zone1.
• The ufw command is a frontend for iptables, which is a low-level tool for manipulating netfilter, the Linux kernel’s packet filtering framework. The status option will show the status of ufw and the active rules, or the numbered rules if verbose is specified. For example, ufw status verbose will show the numbered rules and other information2.

The other options are incorrect because:

A. ufw limit

This command will limit the connection attempts to a service or port using iptables’ recent module. It does not display any firewall rules2.

B. iptables -F

This command will flush (delete) all the rules in the selected chain, or all chains if none is given. It does not display any firewall rules3.

C. systemctl status firewalld

This command will show the status of the firewalld service, including whether it is active or not, but it does not show the firewall rules4.

F. iptables -A

This command will append one or more rules to the end of the selected chain. It does not display any firewall rules3.

The command git clone https://git.company.com/admin/project.git  will achieve the goal of downloading a Git repository from the given URL. The git command is a tool for managing version control systems. The clone option creates a copy of an existing repository. The URL specifies the location of the repository to clone, in this case https://git.company.com/admin/project.git. The command  git clone https://git.company.com/admin/project.git  will download the repository and create a directory named project in the current working directory. This is the correct command to use to accomplish the goal. The other options are incorrect because they either do not download the repository (git checkout, git pull, or git branch) or do not use the correct syntax (git checkout https://git.company.com/admin/project.git  instead of git checkout -b project https://git.company.com/admin/project.git  or git branch https://git.company.com/admin/project.git  instead of git branch project https://git.company.com/admin/project.git ). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Cloud and Virtualization Technologies, page 571.

The chmod command is used to change the permissions of files and directories on Linux systems. The g+s option sets the setgid bit on a directory, which means that all files and folders created inside that directory will inherit the group name of the parent directory. This command can help the developer ensure that all files and folders created inside the /GroupOODEV directory have the same group name as /GroupOODEV. References: [How to Use chmod Command in Linux with Examples]

The correct answer is A. systemctl isolate multi-user.target sh script.sh systemctl isolate graphical.target

This sequence will allow the administrator to switch from the graphical mode to the console mode, run the script, and then switch back to the graphical mode.

The systemctl command is used to control the systemd system and service manager, which manages the boot targets and services on Linux systems. The isolate subcommand starts the unit specified on the command line and its dependencies and stops all others. The multi-user.target is a boot target that provides a text-based console login, while the graphical.target is a boot target that provides a graphical user interface. By using systemctl isolate, the administrator can change the boot target on the fly without rebooting the system.

The sh command is used to run a shell script, which is a file that contains a series of commands that can be executed by the shell. The script.sh is the name of the script that contains the application change that the administrator needs to make. By running sh script.sh, the administrator can execute the script in the console mode.

The other options are incorrect because:

B. systemctl isolate graphical.target sh script.sh systemctl isolate multi-user.target

This sequence will switch from the console mode to the graphical mode, run the script, and then switch back to the console mode. This is not what the administrator wants to do, as the script must be run only in console mode.

C. sh script.sh systemctl isolate multi-user.target systemctl isolate graphical.target

This sequence will run the script in the current mode, which may or may not be console mode, and then switch to console mode and back to graphical mode. This is not what the administrator wants to do, as the script must be run only in console mode.

D. systemctl isolate multi-user.target systemctl isolate graphical.target sh script.sh

This sequence will switch from graphical mode to console mode and then back to graphical mode, without running the script at all. This is not what the administrator wants to do, as the script must be run only in console mode.

References:

• systemctl(1) - Linux manual page
• How to switch between the CLI and GUI on a Linux server
• How to PROPERLY boot into single user mode in RHEL/CentOS 7/8
• Changing Systemd Boot Target in Linux
• Exit Desktop to Terminal in Ubuntu 19.10

The ss command is used to display information about socket connections, such as the port number, state, and process ID. The error message indicates that the port 80 is already in use by another process, which prevents the Apache web server from binding to it. By using the ss command with the -l and -n options, the administrator can list all the listening sockets and their port numbers in numeric form, and identify which process is using the port 80. For example: ss -ln | grep :80. The ip, dig, and nc commands are not relevant for this issue, as they are used for different purposes, such as configuring network interfaces, querying DNS records, and testing network connectivity.

The command hostnamectl set-hostname Comptia-WebNode -H root@192.168.2.14 sets the hostname of the web server to Comptia-WebNode and connects to the server using the SSH protocol and the root user. This is the correct way to complete the requirement. The other options are incorrect because they either display the current hostname status (hostnamectl status), set an invalid hostname (hostnamectl set-hostname "$(perl -le "print" "A" x 86)"), or set a transient hostname that is not persistent (hostnamectl set-hostname Comptia-WebNode --transient). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 9: Managing System Components, page 291.

Option C is the only data structure that is written in JSON format. JSON stands for JavaScript Object Notation, and it is a lightweight and human-readable data interchange format. JSON uses curly braces to enclose objects, which consist of key-value pairs separated by commas. JSON uses square brackets to enclose arrays, which consist of values separated by commas. JSON supports six data types: strings, numbers, booleans, null, objects, and arrays. Option C follows these rules and syntax of JSON, while the other options do not. Option A is written in XML format, which uses tags to enclose elements and attributes. Option B is written in YAML format, which uses indentation and colons to define key-value pairs. Option D is written in INI format, which uses sections and equal signs to define key-value pairs. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 21: Automating Tasks with Ansible, page 591.

The ssh-copy-id command is used to copy a public SSH key from a local machine to a remote server and add it to the authorized_keys file, which allows passwordless authentication between the machines. The administrator can use this command to copy the root user’s public key from nodea to nodeb, and vice versa, to enable SSH access between the nodes without entering a password every time. For example: [root@nodea ssh-copy-id -i ~/.ssh/id_rsa root@nodeb]. The ssh command is used to initiate an SSH connection to a remote server, but it does not copy any keys. The scp command is used to copy files securely between machines using SSH, but it does not add any keys to the authorized_keys file. The ssh-add command is used to add private keys to the SSH agent, which manages them for SSH authentication, but it does not copy any keys to a remote server.

The command that can be used to check if a partition table is on a disk is fdisk. The fdisk command can display, create, delete, and modify partitions on a disk. To show the partition table of a disk, the administrator can use fdisk -l /dev/sdd (B). References:

• [CompTIA Linux+ Study Guide], Chapter 5: Managing Filesystems and Logical Volumes, Section: Partitioning Disks
• [How to Use Fdisk Command in Linux]

SSH, or Secure Shell, is a protocol that allows you to access a remote terminal or virtual machine securely over an encrypted connection. You can use SSH to run commands, transfer files, or tunnel network traffic on a remote system. To use SSH, you need an SSH client program on your local system and an SSH server program on the remote system. You also need to authenticate yourself using a username and password or a public/private key pair. SSH is widely used by system administrators, developers, and engineers to remotely manage Linux servers and other devices.

The other options are not correct answers. TFTP, or Trivial File Transfer Protocol, is a simple protocol that allows you to transfer files between systems, but it does not provide any security or encryption features. SCP, or Secure Copy Protocol, is a protocol that uses SSH to securely copy files between systems, but it does not provide a remote terminal access. FTP, or File Transfer Protocol, is another protocol that allows you to transfer files between systems, but it also does not provide any security or encryption features.

The command useradd -d /comptia/projects user02 will accomplish the task of creating a new user named user02 with a different home directory. The useradd command is a tool for creating new user accounts on Linux systems. The -d option specifies the home directory for the new user, which is the directory where the user’s personal files and settings are stored. The /comptia/projects is the path of the home directory for the new user, which is different from the default location of /home/user02. The user02 is the name of the new user. The command useradd -d /comptia/projects user02 will create a new user named user02 with a home directory under /comptia/projects. This is the correct command to use to accomplish the task. The other options are incorrect because they either do not specify the home directory for the new user (useradd -m /comptia/projects user02 or useradd -s /comptia/projects user02) or do not use the correct option for the home directory (useradd -b /comptia/projects user02 instead of useradd -d /comptia/projects user02). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 13: Managing Users and Groups, page 403.

The Linux administrator should configure /etc/yum.repos.d/db.repo so that the requested packages can be installed. This file defines a custom repository for yum, which is a package manager for RPM-based systems. The file should contain information such as the name, baseurl, gpgcheck, and enabled options for the repository. By creating this file and enabling the repository, the administrator can use yum to install packages from the custom repository. The /etc/yum.conf file is the main configuration file for yum, but it does not define repositories. The /etc/ssh/sshd.conf file is the configuration file for sshd, which is a daemon that provides secure shell access to remote systems. The /etc/resolv.conf file is the configuration file for DNS resolution, which maps domain names to IP addresses. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Packages and Software, page 559.

The file command is used to determine the type of a file by examining its contents. It can recognize many different formats, such as text, binary, executable, compressed, image, audio, video, etc. It can also display some additional information about the file, such as encoding, size, dimensions, etc12

References: 1: file(1) - Linux manual page 2: How to use the file command in Linux

RAID stands for Redundant Array of Independent Disks, which is a technology that combines multiple physical disks into a logical unit that provides improved performance, reliability, or both. RAID can significantly help to reduce data loss if more than one drive fails at the same time, depending on the RAID level used. For example, RAID 1 (mirroring) duplicates the data on two or more disks, so that if one disk fails, the data can be recovered from another disk. RAID 5 (striping with parity) distributes the data and parity information across three or more disks, so that if one disk fails, the data can be reconstructed from the remaining disks. RAID 6 (striping with double parity) extends RAID 5 by adding another parity block, so that if two disks fail, the data can still be recovered from the remaining disks. References: [What is RAID?]

Terraform is a tool for building, changing, and managing infrastructure as code in a cloud-based environment. Terraform uses configuration files to describe the desired state of the infrastructure and applies changes accordingly. Terraform supports various cloud providers, such as AWS, Azure, Google Cloud Platform, and more.

To validate changes before they are applied to the cloud-based environment, the administrator can use the terraform plan command. This command will compare the current state of the infrastructure with the desired state defined in the configuration files and show what actions will be performed to achieve the desired state. This command will not make any changes to the infrastructure but only show a plan of changes. The statement D is correct.

The statements A, B, and C are incorrect because they do not validate changes before they are applied to the cloud-based environment. Ansible is another tool for automating infrastructure management, but it does not have a plan command. Git clone and git pull are commands for working with git repositories, which are used for version control of code. References: [How to Use Terraform to Manage Cloud Infrastructure]

The vi text editor is a popular and powerful tool for editing text files on Linux systems. The vi editor has two modes: command mode and insert mode. In command mode, the user can issue commands to manipulate the text, such as moving the cursor, deleting, copying, pasting, searching, replacing, and saving. In insert mode, the user can type text into the file. To switch from command mode to insert mode, the user can press various keys, such as i, a, o, I, A, or O. To switch from insert mode to command mode, the user can press the Esc key.

To insert a character at the end of the current line in the vi editor, the user can press the A key in command mode. This will move the cursor to the end of the line and switch to insert mode. Then, the user can type the desired character and press Esc to return to command mode. The statement D is correct.

The statements A, B, C, and E are incorrect because they do not perform the desired task. The p key in command mode will paste the previously copied or deleted text after the cursor. The r key in command mode will replace the character under the cursor with another character. The bb key in command mode will move the cursor back two words. The i key in command mode will switch to insert mode before the cursor. References: [How to Use vi Text Editor in Linux]

The docker exec ls command can be used to verify whether the built container has the app.go file in its root directory. This command will run the ls command inside the specified container and list the files and directories in its root directory. If the app.go file is present, it will be displayed in the output. The docker image inspect command will display information about an image, not a container, and it will not list the files inside the image. The docker container inspect command will display information about a container, not its files. The docker ps command is invalid, as ps does not accept a container name as an argument. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Virtualization and Cloud Technologies, page 499.

The command if [ -f "$filename" ]; then checks if the variable $filename refers to a regular file that exists. The -f option is used to test for files. If the condition is true, the commands after then are executed. This is the correct way to replace the  string. The other options are incorrect because they either use the wrong option (-d tests for directories), the wrong syntax (missing a semicolon after the condition), or the wrong keyword (while is used for loops, not conditions). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Writing and Executing Bash Shell Scripts, page 493.

This command will remove all containers, regardless of their state, by passing the IDs of all containers to the docker rm command. The docker ps -aq command will list the IDs of all containers, including the ones in an exited state, and the $ ( ) syntax will substitute the output of the command as an argument for the docker rm command. This is a quick and easy way to clean up all containers, but it may also remove containers that are still needed or running.

References

• docker rm | Docker Docs - Docker Documentation, section “Remove all containers”
• Docker Remove Exited Containers | Easy methods. - Bobcares, section “For removing all exited containers”

The filesystem that system logs are commonly stored in is /var. The /var filesystem is a directory that contains variable data files on Linux systems. Variable data files are files that are expected to grow in size over time, such as logs, caches, spools, and temporary files. The /var filesystem is separate from the / filesystem, which contains the essential system files, to prevent the / filesystem from being filled up by the variable data files. The system logs are files that record the events and activities of the system and its components, such as the kernel, the services, the applications, and the users. The system logs are useful for monitoring, troubleshooting, and auditing the system. The system logs are commonly stored in the /var/log directory, which is a subdirectory of the /var filesystem. The /var/log directory contains various log files, such as syslog, messages, dmesg, auth.log, and kern.log. The filesystem that system logs are commonly stored in is /var. This is the correct answer to the question. The other options are incorrect because they are not the filesystems that system logs are commonly stored in (/tmp, /etc, or /opt). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 16: Managing Logging and Monitoring, page 487.

The server’s firewall is preventing connections from being made, which is causing the connectivity issue. The output of iptables -L -n shows that the firewall is blocking all incoming traffic on port 22, which is the default port for SSH. The output of ssh -v user@104.21.75.76 shows that the connection is refused by the server. To resolve the issue, the administrator needs to allow port 22 on the firewall. The other options are incorrect because they are not supported by the outputs. The workstation has the correct IP settings, as shown by the output of ip addr show. The sshd service is enabled and running, as shown by the output of systemct1 status sshd. The server has the correct default gateway configuration, as shown by the output of ip route show. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 13: Managing Network Services, pages 406-407.

The cause of the issue based on the output above is C. The inodes is at full capacity and would affect file creation for users.

An inode is a data structure that stores information about a file or directory, such as its name, size, permissions, owner, timestamps, and location on the disk. Each file or directory has a unique inode number that identifies it. The number of inodes on a filesystem is fixed when the filesystem is created, and it determines how many files and directories can be created on that filesystem. If the inodes are exhausted, no new files or directories can be created, even if there is enough disk space available.

The output for the second command shows that the /ftpusers/ filesystem has 0% of inodes available, which means that all the inodes have been used up. This would prevent users from creating new files on the FTP server. The administrator should either delete some unused files or directories to free up some inodes, or resize the filesystem to increase the number of inodes.

The other options are incorrect because:

A. The users do not have the correct permissions to create files on the FTP server.

This is not true, because the output for the first command shows that the /ftpusers/ filesystem has 26% of disk space available, which means that there is enough space for users to create files. The permissions of the files and directories are not shown in the output, but they are not relevant to the issue of inode exhaustion.

B. The ftpusers filesystem does not have enough space.

This is not true, because the output for the first command shows that the /ftpusers/ filesystem has 26% of disk space available, which means that there is enough space for users to create files. The issue is not related to disk space, but to inode capacity.

D. ftpusers is mounted as read only.

This is not true, because the output for the first command does not show any indication that the /ftpusers/ filesystem is mounted as read only. If it was, it would have an (ro) flag next to the mounted on column. A read only filesystem would prevent users from creating or modifying files on the FTP server, but it would not affect the inode usage.

The renice command is used to change the priority of a running process by specifying its PID and the new nice value. The -n flag indicates the amount of change in the nice value, which can be positive or negative. A lower nice value means a higher priority, so -15 will increase the priority of the process with PID 2274. The administrator needs to have root privileges to do this.

References:

• The renice command is listed as one of the commands to manipulate process priority in the web search result 1.
• The renice command is also explained with examples in the web search result 2.
• The CompTIA Linux+ Certification Exam Objectives mention that the candidate should be able to “manage process execution priorities” as part of the System Operation and Maintenance domain1.

The users who have root-level command-line access are those who have either the same user ID (UID) as root, which is 0, or the ability to run commands as root using sudo. Based on the /etc/passwd and /etc/sudoers files, the users who meet these criteria are:

• Carl: Carl has the same UID as root, which is 0, as shown in the /etc/passwd file. This means that Carl can log in as root and execute any command with root privileges1
• Mallory: Mallory has the ability to run commands as root using sudo, as shown in the /etc/sudoers file. The line ALL = (ALL) ALL means that any user can run any command as any other user, including root, by using sudo. Mallory can also use the root shell /bin/bash as her login shell, as shown in the /etc/passwd file2

Therefore, the correct answer is A and C. Lee, Eve, Bob, and Alice do not have root-level command-line access because they have different UIDs from root and they cannot use sudo to run commands as root. Lee can only use sudo to run the commands listed in the Cmnd_Alias SHELLS, which are /bin/tcsh, /bin/sh, and /bin/bash. Eve cannot log in at all because her login shell is /bin/nologin. Bob and Alice can only use sudo to run the command /usr/sbin/tcpdump without a password, as specified by the Cmnd_Alias SYSADMIN and the line ALL = NOPASSWD: SYSADMIN2

The command that would ensure the server is set to runlevel 5 is systemct1 isolate graphical.target. This command will change the current target (or runlevel) of systemd to graphical.target, which is equivalent to runlevel 5 in SysV init systems. Graphical.target means that the system will start with a graphical user interface (GUI) and all services required for it.

The other options are not correct commands for setting the server to runlevel 5. The systemct1 isolate multi-user.target command will change the current target to multi-user.target, which is equivalent to runlevel 3 in SysV init systems. Multi-user.target means that the system will start with multiple user logins and networking, but without a GUI. The systemct1 isolate network.target command will change the current target to network.target, which is not a real runlevel but a synchronization point for network-related services. Network.target means that network functionality should be available, but does not specify whether it should be started before or after it. The systemct1 isolate basic.target command will change the current target to basic.target, which is also not a real runlevel but a synchronization point for basic system services. Basic.target means that all essential services should be started, but does not specify whether it should be started before or after it. References: systemd System and Service Manager; systemd.special(7) - Linux manual page

The best command sequence to rebuild a kernel module from source code is A. ./configure make make install. This is the standard way to compile and install a Linux kernel module, as explained in the web search result 5. The other commands are either not relevant, not valid, or not sufficient for this task. For example:

• B. wget gcc cp will try to download, compile, and copy a file, but it does not specify the source code, the module name, or the destination directory.
• C. tar xvzf build cp will try to extract, build, and copy a compressed file, but it does not specify the file name, the module name, or the destination directory.
• D. build install configure will try to run three commands that are not defined or recognized by the Linux shell.

The command restorecon -R -v /var/www/html will best resolve the issue. The issue is caused by the incorrect SELinux context of the web server files under the /var/www/html directory. The output of ls -Z /var/www/html shows that the files have the type user_home_t, which is not allowed for web content. The command restorecon restores the default SELinux context of files based on the policy rules. The options -R and -v are used to apply the command recursively and verbosely. This command will change the type of the files to httpd_sys_content_t, which is the correct type for web content. This will allow the web server to access the files and serve the pages to the browser. The other options are incorrect because they either disable SELinux entirely (sed -i 's/SELINUX=enforcing/SELINUX=disabled/' /etc/selinux/config or setenforce 0), which is not a good security practice, or enable an unnecessary boolean (setsebool -P httpd_can_network_connect_db on), which is not related to the issue. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Securing Linux Systems, page 535.

The correct command to block the IP address 192.168.10.50 from accessing a Linux server is iptables -A INPUT -s 192.168.10.50 -j DROP. This command appends a rule to the INPUT chain that matches the source address 192.168.10.50 and jumps to the DROP target, which discards the packet. The other commands are incorrect because they either have invalid syntax, wrong parameters, or wrong order of arguments. References: CompTIA Linux+ Study Guide, Fourth Edition, page 457-458.

The docker image tag test test:v1 command can be used to assign the v1 version to the image called test. This command creates a new tag for the existing image, without changing the original image. The docker image save test test:v1 command would save the image to a file, not assign a version. The docker image build test:vl command is invalid, as vl is not a valid version number. The docker image version test:v1 command does not exist. References: [CompTIA Linux+ (XK0-005) Certification Study Guide], Chapter 16: Virtualization and Cloud Technologies, page 500.

The ~/.ssh/config file can be used to set various options for SSH connections, including the port number, for specific hosts or groups of hosts. This file is located in the user’s home directory and affects only the current user. The /etc/ssh/sshd_config file is used to configure the SSH server daemon, not the client. The /etc/ssh/moduli file contains parameters for Diffie-Hellman key exchange, not port settings. The ~/.ssh/authorized_keys file contains public keys for authentication, not port settings. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 12: Secure Shell (SSH), page 414.

As the web search results show, processes in state Z are defunct or zombie processes, which means they have terminated but their parent process has not reaped them properly. They do not consume any resources, but they occupy a slot in the process table. To remove them from the process list, the administrator needs to kill the parent process of the zombies, which will cause them to be reaped by the init process (PID 1). Killing the zombies themselves or the init process will not have any effect, as they are already dead. Rebooting the server may work, but it is not a safe or efficient option, as it may cause unnecessary downtime or data loss for a mission-critical server.

References

• Processes in a Zombie (Z) or Defunct State | Support | SUSE, paragraph 3
• linux - Zombie vs Defunct processes? - Stack Overflow, answer by admirableadmin
• How To Kill Zombie Processes on Linux | Linux Journal, paragraph 4

The issue is caused by the server 192.168.168.53 being unreachable. This server is the DNS server configured in the /etc/resolv.conf file, which is used to resolve domain names to IP addresses. The ping command shows that the server cannot be reached, and the nslookup command shows that the name www.comptia.org cannot be resolved using this server. The other options are incorrect because:

• The name www.comptia.org does point to a valid IP address, as shown by the nslookup command using another DNS server (8.8.8.8).
• The default route is set on the server, as shown by the ip route command, which shows a default gateway of 192.168.168.1.
• The network interface eth0 is connected, as shown by the ip link command, which shows a state of UP for eth0. References: CompTIA Linux+ Study Guide, Fourth Edition, page 457-458, 461-462.

To create a symlink for /usr/local/bin/app-a, which was installed in /usr/local/share/app-a, the administrator can use the command ln -s /usr/local/share/app-a /usr/local/bin/app-a (A). This will create a symbolic link named /usr/local/bin/app-a that points to the original file /usr/local/share/app-a. The other commands will not create a symlink, but either move, copy, or synchronize the file. References:

• [CompTIA Linux+ Study Guide], Chapter 3: Working with Files, Section: Creating Links
• [How to Create Symbolic Links in Linux]

After fixing issues in the code, the next step is to merge these changes into the main branch. This is typically done by creating a pull request78.

References:7(https://zeet.co/blog/deploy-to-production) 8(https://stackoverflow.com/questions/11833511/git-deploy-to-production)

The correct answer is A. semanage port -a -t ssh_port_t -p tcp 2222

This command will allow the SSH server to bind to port 2222 by adding it to the SELinux policy. The semanage command is a utility for managing SELinux policies. The port subcommand is used to manage network port definitions. The -a option is used to add a new record, the -t option is used to specify the SELinux type, the -p option is used to specify the protocol, and the tcp 2222 argument is used to specify the port number. The ssh_port_t type is the default type for SSH ports in SELinux.

The other options are incorrect because:

B. chcon system_u:object_r:ssh_home_t /etc/ssh/*

This command will change the SELinux context of all files under /etc/ssh/ to system_u:object_r:ssh_home_t, which is not correct. The ssh_home_t type is used for user home directories that are accessed by SSH, not for SSH configuration files. The correct type for SSH configuration files is sshd_config_t.

C. iptables -A INPUT -p tcp --dport 2222 -j ACCEPT

This command will add a rule to the iptables firewall to accept incoming TCP connections on port 2222. However, this is not enough to fix the issue, as SELinux will still block the SSH server from binding to that port. Moreover, iptables may not be the default firewall service on some Linux distributions, such as Fedora or CentOS, which use firewalld instead.

D. firewall-cmd --zone=public --add-port=2222/tcp

This command will add a rule to the firewalld firewall to allow incoming TCP connections on port 2222 in the public zone. However, this is not enough to fix the issue, as SELinux will still block the SSH server from binding to that port. Moreover, firewalld may not be installed or enabled on some Linux distributions, such as Ubuntu or Debian, which use iptables instead.

References:

• How to configure SSH to use a non-standard port with SELinux set to enforcing
• Change SSH Port on CentOS/RHEL/Fedora With SELinux Enforcing
• How to change SSH port when SELinux policy is enabled

To troubleshoot a storage capacity issue on a server without a specific mount point or directory, two commands that would be most helpful are df and du. The df command displays information about disk space usage on all mounted filesystems, including their size, used space, available space, and percentage of usage. The du command displays disk space usage by files and directories in a given path, which can help identify large files or directories that may be taking up too much space. The other commands are incorrect because they either do not show disk space usage, or they are used for other purposes such as partitioning, formatting, checking, mounting, copying, or listing files. References: CompTIA Linux+ Study Guide, Fourth Edition, page 417-419.