CompTIA XK0-005 - CompTIA Linux+ Exam

To unlock an account that has been locked due to login failures, the administrator can use the command pam_tally2 --user=dev2 --reset (D). This will reset the failure counter for the user “dev2” and allow the user to log in again. The other commands will not unlock the account, but either display or increase the failure count. References:

[CompTIA Linux+ Study Guide], Chapter 4: Managing Users and Groups, Section: Locking Accounts with pam_tally2

[How to Lock and Unlock User Account in Linux]

The command that would allow a user to choose a stronger password and set it on the existing SSH key file is ssh-keygen -p -f . This command uses the ssh-keygen tool, which is used to generate, manage, and convert authentication keys for SSH. The -p option stands for passphrase, and it allows the user to change or remove the passphrase of an existing private key file. The -f option specifies the filename of the key file. The command will prompt the user for the old passphrase, and then for the new passphrase twice.

The other options are not correct commands for changing the password of an SSH key file. The passwd command is used to change the password of a user account on a Linux system, not an SSH key file. The ssh command is used to log in to a remote system using SSH, not to change the password of an SSH key file. The pwgen command is used to generate random passwords, not to change the password of an SSH key file.

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 push action is used to publish the changes made in a local branch to a remote branch of a Git repository. This action will update the remote branch with the commits made in the local branch and synchronize the two branches. The rebase action is used to reapply commits from one branch onto another branch, creating a linear history of commits. This action does not publish any changes to a remote repository. The tag action is used to create an annotated reference to a specific commit in a Git repository. This action does not publish any changes to a remote repository. The commit action is used to record changes made in the local repository and create a new snapshot of the project state. This action does not publish any changes to a remote repository. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 20: Writing and Executing Bash Shell Scripts, page 579.

The mv /home/tmp/tempa /home/tmp/temp command will fix the issue of the misnamed directory. This command will rename the directory /home/tmp/tempa to /home/tmp/temp, which is the expected path for users to save their documents. The cp /home/tmp/tempa /home/tmp/temp command will not fix the issue, as it will copy the contents of /home/tmp/tempa to a new file named /home/tmp/temp, not a directory. The cd /temp/tmp/tempa command will not fix the issue, as it will change the current working directory to /temp/tmp/tempa, which does not exist. The ls /home/tmp/tempa command will not fix the issue, as it will list the contents of /home/tmp/tempa, not rename it. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 12: Managing Files and Directories, page 413.

The systemct1 reload sshd command can be used to apply the configuration changes of the SSH server daemon without restarting it. This is useful to avoid interrupting existing connections. The systemct1 stop sshd command would stop the SSH server daemon, not apply the changes. The systemct1 mask sshd command would prevent the SSH server daemon from being started, not apply the changes. The systemct1 start sshd command would start the SSH server daemon if it is not running, but it would not apply the changes if it is already running. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 12: Secure Shell (SSH), page 415.

The free -h command can be used to check the amount of free and used memory in the system in a human-readable format. This can help to troubleshoot the issue of mysqld being killed due to out of memory. The vmstat -a 1 4 command can be used to monitor the system’s virtual memory statistics, such as swap usage, paging activity, and memory faults, every one second for four times. This can help to identify any memory pressure or performance issues that may cause out of memory errors. The nc -v 127.0.0.1 3306 command would attempt to connect to the MySQL server on port 3306 and display any diagnostic messages, but this would not help to troubleshoot the memory issue. The renice -15 $( pidof mysql ) command would change the priority of the mysql process to -15, but this would not prevent it from being killed due to out of memory. The lsblk command would display information about block devices, not memory usage. The killall -15 command would send a SIGTERM signal to all processes with a matching name, but this would not help to troubleshoot the memory issue. References: [CompTIA Linux+ (XK0-005) Certification Study Guide], Chapter 15: Managing Memory and Process Execution, pages 468-469.

After installing a new version of a package that includes a configuration file that already exists on the system, such as /etc/httpd/conf/httpd.conf, RPM will create a new file with the .rpmnew extension instead of overwriting the existing file. This allows the administrator to review the default configuration that shipped with this version and compare it with the current configuration before deciding whether to merge or replace the files. The /etc/named.conf.rpmsave file is created by RPM when a package is uninstalled and it contains a configuration file that was modified by the administrator. This allows the administrator to restore the configuration file if needed. The /etc/named.conf file is the main configuration file for the BIND name server, not the httpd web server. The /etc/bind/bind.conf file does not exist by default in Linux systems. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Packages and Software, page 561.

The command ssh -i "ABC-key.pem" root@10.0.0.1 would allow the administrator to connect securely to the remote server in order to install application software. The ssh command is a tool for establishing secure and encrypted connections between remote systems. The -i option specifies the identity file that contains the private key for key-based authentication. The "ABC-key.pem" is the name of the identity file that contains the private key. The root@10.0.0.1 is the username and the IP address of the remote server. The command ssh -i "ABC-key.pem" root@10.0.0.1 will connect to the remote server using the private key and allow the administrator to install application software. This is the correct command to use to connect securely to the remote server. The other options are incorrect because they either do not use key-based authentication (sftp root@10.0.0.1 or telnet 10.0.0.1 80) or do not use the correct syntax for the command (scp "ABC-key.pem" root@10.0.0.1 instead of scp -i "ABC-key.pem" root@10.0.0.1 or sftp "ABC-key.pem" root@10.0.0.1 instead of sftp -i "ABC-key.pem" root@10.0.0.1). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 17: Implementing Basic Security, page 513.

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]