Explanation
The command docker images prune -a will help to remove all dangling images and delete all the images that do not have an associated container. The docker command is a tool for managing Docker containers and images. The images subcommand operates on images. The prune option removes unused images.
The -a option removes all images, not just dangling ones. A dangling image is an image that is not tagged and is not referenced by any container. This command will accomplish the task of cleaning up the unused images.
The other options are incorrect because they either do not exist (docker push images -a or docker images rmi
--all) or do not remove images (docker rmi -a images only removes images that match the name or ID of
"images"). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 19: Managing Cloud and Virtualization Technologies, page 567.

Explanation
This answer allows the accounting user to run the /opt/acc/report command as root on any host without entering a password. The % sign indicates that accounting is a group name, not a user name. The ALL keyword means any host, any user, and any command, depending on the context. The NOPASSWD tag overrides the default behavior of sudo, which is to ask for the user's password.
The other answers are incorrect for the following reasons:
A: accounting localhost=/opt/acc/report
This answer only allows the accounting user to run the command on the localhost, not on any host.
This answer also requires the accounting user to enter their password, which is not specified in the question.
B: accounting ALL=/opt/acc/report
This answer only allows the accounting user to run the command as themselves, not as root.
This answer also requires the accounting user to enter their password, which is not specified in the question.
D: accounting /opt/acc/report= (ALL) NOPASSWD: ALL
This answer has an invalid syntax, as there should be no space between the equal sign and the parentheses.
This answer also grants too much privilege to the accounting user, as it allows them to run any command as any user without a password.

Explanation
The message in /var/log/messages indicates that the server is running out of file descriptors. A file descriptor is a non-negative integer identifier for an open file in Linux. Each process has a table of open file descriptors where a new entry is appended upon opening a new file. There is a limit on how many file descriptors a process can open at a time, which depends on the system configuration and the user privileges. If a process tries to open more files than the limit, it will fail with an error message like "Too many open files". This could cause connections to be closed unexpectedly or other problems with the application.
The other options are not correct causes for the connection issue. The process mysqld is not using too many semaphores, which are synchronization mechanisms for processes that share resources. Semaphores are not related to file descriptors or open files. Something is not starving the server resources, which could mean high CPU usage, memory pressure, disk I/O, network congestion, or other factors that affect performance. These could cause slowdowns or timeouts, but not file descriptor exhaustion. The amount of RAM allocated to the server is not too high, which could cause swapping or paging if it exceeds the physical memory available. This could also affect performance, but not file descriptor availability. References: File Descriptor Requirements (Linux Systems); Limits on the Number of Linux File Descriptors

Explanation
The administrator should use the command kill -TERM to forcibly stop the process. The kill command is a tool for sending signals to processes on Linux systems. Signals are messages that inform the processes about certain events and actions. The processes can react to the signals by performing predefined or user-defined actions, such as terminating, suspending, resuming, or ignoring. The -TERM option specifies the signal name or number that the kill command should send. The TERM signal, which stands for terminate, is the default signal that the kill command sends if no option is specified. The TERM signal requests the process to terminate gracefully, by closing any open files, releasing any resources, and performing any cleanup tasks.
However, if the process does not respond to the TERM signal, the kill command can send a stronger signal, such as the KILL signal, which forces the process to terminate immediately, without any cleanup. The administrator should use the command kill -TERM to forcibly stop the process. This is the correct answer to the question. The other options are incorrect because they either do not terminate the process (kill -1 or kill -3) or do not terminate the process forcibly (kill -15 or kill -HUP). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 14: Managing Processes, page 431.

Explanation
To give the support group access to modify the config file while preserving the current ownership, the administrator can execute the command chmod 664 config . This will change the permissions of the config file to read and write for the owner and group, and read only for others. The owner and group of the file will remain as root and app respectively. The other commands will not achieve this task, but either change the group ownership, set an access control list, or set a setgid bit. References:
[CompTIA Linux+ Study Guide], Chapter 3: Working with Files, Section: Changing File Permissions
[How to Use chmod Command in Linux]