XK0-006 Practice Exam 63 — 20 Questions

Question 1

Which TWO commands are used to manage SSH key-based authentication processes? (Choose exactly two.)

Accepted Answer

ssh-keygen. The `ssh-keygen` command generates the public and private key pair used for SSH key-based authentication, while `ssh-copy-id` installs the public key on a remote server's `~/.ssh/authorized_keys` file, enabling passwordless login. Together, they form the core workflow for setting up SSH key authentication.

Answer

ssh-add

Answer

ssh-keyscan

Answer

ssh-agent

Question 2

Which command displays the amount of disk space used and available on mounted filesystems in a human-readable format (e.g., GB, MB)?

Accepted Answer

df -h. The `df -h` command displays disk space usage for all mounted filesystems, with the `-h` flag converting raw block counts into human-readable units like GB or MB. This is the standard Linux utility for reporting filesystem capacity, usage, and available space, making it the correct choice for the question.

Answer

lsblk

Answer

du -h

Answer

fdisk -l

Question 3

A Linux server that hosts a critical database application has been experiencing occasional kernel panics. The administrator wants to ensure the system automatically reboots after a panic and logs the crash dump. Which sysctl parameter should be set?

Accepted Answer

kernel.panic = 10. Setting `kernel.panic = 10` instructs the Linux kernel to wait 10 seconds after a kernel panic before automatically rebooting. This ensures the system recovers without manual intervention, and combined with a configured crash dump mechanism (e.g., kdump), the crash dump is captured before the reboot.

Answer

kernel.panic_on_warn = 10

Answer

kernel.panic_on_oops = 10

Answer

kernel.panic_print = 10

Question 4

A financial services company runs a critical trading application on a Linux server. The application logs to /var/log/trade/app.log. Recently, the application has been crashing intermittently. The administrator suspects disk space issues. Upon checking, /var/log/trade is on a separate partition with 200 GB capacity, and df -h shows only 10% used. However, the administrator notices that log rotation is not working; the log file has grown to 50 GB and is still being written to. The administrator needs to immediately free up space without stopping the application, and also ensure proper log rotation is configured. Which command sequence should the administrator use?

Accepted Answer

Run 'logrotate -f /etc/logrotate.conf' to force rotation, then verify with 'df -h'.. 'logrotate -f' forces an immediate log rotation without stopping the application, which frees disk space by compressing or removing the old log file and creating a new empty one. The administrator can then verify the freed space with 'df -h'. This approach solves both the immediate space issue and ensures proper rotation is configured for the future.

Answer

Run 'mv /var/log/trade/app.log /tmp' to move the file, then create a new empty log file, and check with 'df -h'.

Answer

Run 'systemctl stop trade && rm /var/log/trade/app.log && systemctl start trade' to stop the application, delete the log, and restart.

Answer

Run '> /var/log/trade/app.log' to truncate the log file, then check with 'df -h'.

Question 5

A user reports that their system fails to boot and displays a 'GRUB' prompt. Which command should be run first to attempt to load the operating system manually?

Accepted Answer

boot. When the system boots to a GRUB prompt, it means the bootloader has loaded but cannot find or automatically load the operating system. The `boot` command at the GRUB prompt instructs GRUB to attempt to boot the currently configured kernel and initramfs, which is the correct first step to manually load the OS.

Answer

rescue

Answer

reboot

Answer

exit

Question 6

After a system update, a custom application no longer runs due to a shared library error. The library exists on the system but is in a non-standard path. Which environment variable should be checked or set to resolve this?

Accepted Answer

LD_LIBRARY_PATH. The LD_LIBRARY_PATH environment variable tells the dynamic linker (ld.so) where to search for shared libraries before the standard system paths. When a custom application fails with a shared library error after an update, and the library exists in a non-standard path, setting LD_LIBRARY_PATH to include that path resolves the issue by allowing the linker to find the library at runtime.

Answer

LD_PRELOAD

Answer

PATH

Answer

LD_RUN_PATH

Question 7

A systems administrator creates a bash script that processes log files. The script uses a for loop to iterate over files in /var/log and runs a command on each. Which of the following would prevent the script from failing if no files match the pattern?

Accepted Answer

shopt -s nullglob. `shopt -s nullglob` causes the shell to expand a glob pattern that matches no files into an empty string rather than leaving the pattern literal. Without this setting, if no files match the pattern in `/var/log`, the for loop receives the literal pattern string (e.g., `*.log`) and attempts to process it as a filename, which would cause the command to fail or produce unexpected results. Enabling nullglob ensures the loop body simply does not execute when no matches exist, preventing script failure.

Answer

set -u

Answer

set -e

Answer

shopt -s failglob

Question 8

A Linux administrator is troubleshooting a server that is running slowly. The 'sar -q' command shows a run queue length of 12 and a load average of 8.5. The CPU utilization is 90% idle. Which of the following is the most likely cause of the performance issue?

Accepted Answer

The disk I/O subsystem is a bottleneck, causing processes to wait for I/O.. The 'sar -q' output shows a high run queue length (12) and load average (8.5) despite 90% CPU idle. This indicates that processes are in an uninterruptible sleep state (D state) waiting for I/O, not contending for CPU. A disk I/O bottleneck causes processes to queue for I/O completion, inflating the load average while CPU remains idle, making D the correct answer.

Answer

The CPU is overloaded and needs to be upgraded.

Answer

The network interface is saturated.

Answer

The system is low on memory and swapping heavily.

Question 9

Match each Linux kernel parameter category to its description.

Accepted Answer

kernel: General kernel behavior and system-wide limits. Linux sysctl parameters are organized under categories such as kernel, vm, net, and fs. The kernel category handles general system limits, vm manages virtual memory, net controls networking, and fs deals with filesystem settings. Ensure each description matches its correct category.

Answer

vm: Networking parameters

Answer

kernel: Filesystem parameters

Question 10

Drag and drop the steps to add a new user to the system in the correct order.

Accepted Answer

Step 1: Create user account, Step 2: Set user password, Step 3: Configure home directory. Adding a user typically involves creating the user, setting a password, and configuring the home directory.

Answer

Step 1: Set user password, Step 2: Create user account, Step 3: Configure home directory

Answer

Step 1: Configure home directory, Step 2: Create user account, Step 3: Set user password

Answer

Step 1: Create user account, Step 2: Configure home directory, Step 3: Set user password

Question 11

Which command will run a container in detached mode with the name 'web' and map host port 8080 to container port 80, using the nginx image?

Accepted Answer

docker run -d --name web -p 8080:80 nginx. `docker run` creates and starts a new container. The `-d` flag runs it in detached mode (background), `--name web` assigns the name 'web', `-p 8080:80` maps host port 8080 to container port 80, and `nginx` specifies the image to use. This is the standard syntax for deploying a container with port mapping and a custom name.

Answer

docker exec -d --name web -p 8080:80 nginx

Answer

docker start -d --name web -p 8080:80 nginx

Answer

docker run -it --name web -p 8080:80 nginx

Question 12

Drag and drop the steps to mount a new filesystem in the correct order.

Accepted Answer

Create mount point directory, then mount device, then update /etc/fstab, then verify mount. Mounting a filesystem requires creating a mount point and using the mount command with the device and mount point.

Answer

Mount device, then create mount point, then update /etc/fstab, then verify mount

Answer

Update /etc/fstab, then create mount point, then mount device, then verify mount

Answer

Verify mount, then create mount point, then mount device, then update /etc/fstab

Question 13

A technician needs to replace the string 'old_config' with 'new_config' in the file /etc/app.conf and save the changes in place. Which sed command accomplishes this?

Accepted Answer

sed -i 's/old_config/new_config/g' /etc/app.conf. The -i flag edits the file in place, and the s///g substitution replaces all occurrences.

Answer

sed 's/old_config/new_config/' /etc/app.conf

Answer

sed -n 's/old_config/new_config/p' /etc/app.conf

Answer

sed -i 's/old_config/new_config/' /etc/app.conf

Question 14

Drag and drop the steps to recover a forgotten root password in single-user mode in the correct order.

Accepted Answer

Reboot and edit GRUB to append 'init=/bin/bash' to the kernel line, then boot to a shell, then remount root as read-write, then change root password and reboot.. Root password recovery involves booting into single-user mode and remounting root as rw.

Answer

Change root password, then remount root as read-write, then reboot and edit GRUB, then boot to a shell.

Answer

Reboot and edit GRUB to append 'init=/bin/bash', then remount root as read-write, then boot to a shell, then change root password and reboot.

Answer

Boot to a shell, then reboot and edit GRUB, then remount root as read-write, then change root password.

Question 15

An administrator wants to change the default systemd target to multi-user.target so the system boots to a text console. Which command should be used?

Accepted Answer

systemctl set-default multi-user.target. systemctl set-default multi-user.target sets the default target. systemctl isolate changes the current target but not the default. enable and mask are for services, not targets.

Answer

systemctl isolate multi-user.target

Answer

systemctl enable multi-user.target

Answer

systemctl mask multi-user.target

Question 16

A system administrator is using Ansible to deploy a web application across multiple servers. The playbook uses a variable `app_version` defined in a group_vars file for the `webservers` group. The playbook fails with the error: 'ERROR! 'app_version' is undefined'. The administrator confirms that the variable is correctly spelled and defined in `/etc/ansible/group_vars/webservers`. The playbook runs successfully on the Ansible control node but fails on all managed nodes. What is the most likely cause of this error?

Accepted Answer

The group_vars file is not being loaded because the inventory path is not correctly specified.. The error 'app_version' is undefined despite the variable being correctly defined in `/etc/ansible/group_vars/webservers` indicates that Ansible is not loading that group_vars file. This typically happens when the inventory path specified in the ansible.cfg or command line does not point to the directory containing the group_vars folder. Ansible automatically loads group_vars only from the directory where the inventory file resides, not from a hardcoded path like `/etc/ansible/group_vars/` unless the inventory is also located there.

Answer

The variable `app_version` is misspelled in the task.

Answer

The playbook uses `loop` keyword incorrectly.

Answer

The playbook is missing a `vars_files` directive to include the variable file.

Question 17

Which directory in the Filesystem Hierarchy Standard (FHS) contains essential user commands available to all users, such as 'ls' and 'cp'?

Accepted Answer

/bin. /bin contains essential user binaries. /sbin is for system binaries (usually root). /usr/bin contains non-essential user binaries. /opt is for optional software.

Answer

/sbin

Answer

/opt

Answer

/usr/bin

Question 18

Scenario: A financial services company runs a critical application on a Linux server that stores sensitive customer data. The server is configured with a firewall (iptables) that only allows SSH (port 22) and HTTPS (port 443) from the internal network (10.0.0.0/8). Recently, the security team detected unauthorized access attempts from an external IP address (203.0.113.5) targeting port 22. The administrator needs to block this specific IP while maintaining current access rules. The existing iptables rules are: 
- INPUT chain policy ACCEPT 
- Rule 1: -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT 
- Rule 2: -A INPUT -p tcp --dport 22 -s 10.0.0.0/8 -j ACCEPT 
- Rule 3: -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT 
- Rule 4: -A INPUT -j DROP 
The administrator wants to block 203.0.113.5 from any access. Which command should be added?

Accepted Answer

iptables -I INPUT 1 -s 203.0.113.5 -j DROP. Inserting the DROP rule at position 1 with `-I INPUT 1` ensures it is evaluated before the existing ESTABLISHED,RELATED rule (Rule 1). Since iptables processes rules sequentially, placing the block early prevents the malicious IP from being matched by the ESTABLISHED,RELATED rule, which would otherwise accept its packets if a related connection existed. This maintains the existing SSH and HTTPS access rules for the internal network while explicitly dropping all traffic from 203.0.113.5.

Answer

iptables -I INPUT 5 -s 203.0.113.5 -j DROP

Answer

iptables -A INPUT -s 203.0.113.5 -j DROP

Answer

iptables -I INPUT 1 -s 203.0.113.5 -j ACCEPT

Question 19

Refer to the exhibit. The administrator receives an email that a cron job failed. What is the most likely cause?

Accepted Answer

The script has an unmatched if statement.. The cron job failed because the script contains an unmatched if statement, which causes a syntax error when the shell interprets the script. Cron jobs execute scripts in a non-interactive shell, and any syntax error will cause the script to exit with a non-zero status, triggering the failure email. The unmatched if statement prevents the script from completing execution, leading to the reported failure.

Answer

The script is not executable.

Answer

The script is missing a shebang line.

Answer

The cron daemon is not running.

Question 20

Refer to the exhibit. A system administrator notices that the cleanup script runs at 2:00 AM every day but sometimes does not execute. The log shows no output from the script. Which step should be taken to investigate?

Accepted Answer

Change the script to log output to a file.. The script runs but produces no log output, indicating it may be failing silently. Redirecting the script's stdout and stderr to a file (e.g., `>> /var/log/cleanup.log 2>&1`) captures error messages and output, allowing the administrator to see why the script sometimes does not execute or fails. This is the most direct way to diagnose a cron job that runs but yields no visible results.

Answer

Verify that the script is executable by the root user.

Answer

Check the syslog for cron execution messages.

Answer

Add a MAILTO directive to the crontab.