XK0-006 Practice Test 14 — 15 Questions

Question 1

Which directory in the FHS contains essential user command binaries that are needed in single-user mode?

Accepted Answer

/bin. The /bin directory, as defined by the Filesystem Hierarchy Standard (FHS), contains essential user command binaries (e.g., ls, cp, mv) that are required for booting, repairing, and operating the system in single-user mode. Single-user mode mounts only the root filesystem, so /bin must be on the root partition to provide these critical utilities without relying on other filesystems like /usr.

Answer

/usr/bin

Answer

/sbin

Answer

/opt/bin

Question 2

A CentOS 7 web server experienced an abrupt power loss. Upon reboot, the httpd service fails to start. The administrator runs `systemctl status httpd` and sees 'Active: failed (Result: exit-code)'. The journal displays 'Permission denied: "/var/www/html/index.html"'. The file `/var/www/html/index.html` has permissions `-rw-r--r--` and is owned by `apache:apache`. SELinux is in enforcing mode. Which action should the administrator take to resolve the issue?

Accepted Answer

Execute restorecon -R /var/www/html to restore SELinux contexts.. The httpd service fails because SELinux is in enforcing mode and the file /var/www/html/index.html has an incorrect SELinux context, likely httpd_sys_content_t. The restorecon -R /var/www/html command restores the default SELinux security contexts for the directory and its contents, allowing Apache to read the file. This is the standard fix when SELinux contexts are lost or corrupted, such as after a power loss or file restoration.

Answer

Disable SELinux temporarily with setenforce 0.

Answer

Change the file ownership to root:root using chown.

Answer

Set the SELinux boolean httpd_can_network_connect to on.

Question 3

A DevOps engineer is building a Docker image for a web application. They want to ensure the image is as small as possible and that sensitive data is not left in layers. Which two practices help achieve these goals? (Choose TWO.)

Accepted Answer

Using multi-stage builds to separate build and runtime environments.. Combining RUN commands reduces layers, and using multi-stage builds avoids including build tools in the final image.

Answer

Using the ADD instruction instead of COPY.

Answer

Using the latest tag for base images.

Answer

Installing all packages in a single layer.

Question 4

Which TWO commands effectively disable a systemd service to prevent it from starting, either automatically or manually? (Select 2.)

Accepted Answer

systemctl disable. `systemctl disable` removes the symlinks that cause the service to start automatically at boot, preventing automatic starts. `systemctl mask` creates a strong symlink to `/dev/null`, which makes the service impossible to start either automatically or manually, as any attempt to start it is silently redirected to nothing.

Answer

systemctl stop

Answer

systemctl reset-failed

Answer

systemctl kill

Question 5

A system administrator needs to identify which processes are consuming the most memory on a Linux server. Which two commands can be used? (Select TWO).

Accepted Answer

ps -aux. The `ps -aux` command displays all running processes with detailed information, including memory usage (%MEM and RSS). The `top` command provides a real-time, interactive view of processes sorted by memory consumption by default. Both commands directly show per-process memory usage, making them suitable for identifying the most memory-intensive processes.

Answer

vmstat

Answer

free -m

Answer

df -h

Question 6

A Linux administrator needs to add a new user named 'jdoe' with a home directory and a bash shell. Which command accomplishes this?

Accepted Answer

useradd -m -s /bin/bash jdoe. The useradd command with -m creates the home directory and -s sets the shell. useradd -m -s /bin/bash jdoe is correct.

Answer

usermod -m -s /bin/bash jdoe

Answer

adduser jdoe --home /home/jdoe --shell /bin/bash

Answer

passwd -m jdoe

Question 7

A security audit reveals that users can change their password without meeting complexity requirements. Which PAM module should be configured to enforce password complexity?

Accepted Answer

pam_pwquality. pam_pwquality is the module that enforces password quality rules like length, character classes, etc.

Answer

pam_faillock

Answer

pam_unix

Answer

pam_tally2

Question 8

A Linux administrator needs to check the listening TCP ports on a server. Which command should be used to view only listening TCP ports and the associated processes?

Accepted Answer

ss -tlnp. The `ss -tlnp` command displays only TCP sockets (`-t`), listening sockets (`-l`), numeric addresses/ports (`-n`), and the associated process information (`-p`). This is the modern replacement for `netstat` and is the most direct way to view listening TCP ports and their processes on a Linux system.

Answer

lsof -iTCP -sTCP:LISTEN

Answer

nmap -sT localhost

Answer

netstat -tlnp

Question 9

Which command displays the amount of free and used disk space on all mounted file systems in a human-readable format?

Accepted Answer

df -h. df -h shows disk space in human-readable units. du shows disk usage per directory; lsblk lists block devices; mount shows mounted filesystems but not space usage.

Answer

du -h /

Answer

lsblk -h

Answer

mount -h

Question 10

A system administrator is investigating a performance issue and wants to view kernel-related messages. Which three commands can be used to access kernel ring buffer messages? (Choose three.)

Accepted Answer

dmesg. dmesg displays kernel ring buffer. journalctl -k shows kernel messages from systemd journal. cat /var/log/kern.log if available, but /var/log/messages often contains kernel messages; however, the question expects common commands.

Answer

tail -f /var/log/syslog

Answer

systemctl status

Question 11

An administrator is configuring iptables on a server. The requirements are: allow incoming SSH (port 22) from the 192.168.1.0/24 network, drop all other incoming traffic, and allow all outgoing traffic. Which three iptables rules achieve this? (Choose THREE.)

Accepted Answer

iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT. Default policies: INPUT DROP, OUTPUT ACCEPT. Then allow SSH from subnet.

Answer

iptables -P FORWARD ACCEPT

Answer

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

Question 12

An administrator wants to allow the user 'ops' to run only the command '/usr/bin/systemctl restart httpd' via sudo on a specific host 'webserver'. Which /etc/sudoers entry is correct?

Accepted Answer

ops webserver=(root) /usr/bin/systemctl restart httpd. The format is: username hostname=(runas) command. For host-specific, use the hostname. The correct entry is 'ops webserver=(root) /usr/bin/systemctl restart httpd'.

Answer

ops ALL=(root) /usr/bin/systemctl restart httpd

Answer

ops webserver=(ALL) /usr/bin/systemctl restart httpd

Answer

ops webserver=(root) ALL

Question 13

An administrator wants to ensure that a web service starts after the database service has fully initialized. Which TWO methods can be used to achieve this ordering dependency in systemd?

Accepted Answer

Add Requires=db.service in the [Unit] section. `Requires=db.service` in the `[Unit]` section declares a strong dependency: if `db.service` fails to start, `web.service` will not be started. Option B is correct because `After=db.service` in the `[Unit]` section of `web.service` ensures that `web.service` starts only after `db.service` has reached the 'active' state, enforcing the required ordering. Together, these two directives guarantee both dependency and sequencing.

Answer

Add BindsTo=db.service in the [Unit] section

Answer

Add Wants=db.service in the [Unit] section

Answer

Add PartOf=db.service in the [Unit] section

Question 14

A security administrator is reviewing SSH configuration. Which TWO settings enhance security by limiting authentication attempts and preventing password-based logins? (Choose two.)

Accepted Answer

MaxAuthTries 3. MaxAuthTries sets maximum authentication attempts. PasswordAuthentication no disables password auth, forcing key-based.

Answer

Protocol 2

Answer

PermitRootLogin no

Answer

Port 2222

Question 15

To limit the number of processes a user can create, which file should be configured?

Accepted Answer

/etc/security/limits.conf. /etc/security/limits.conf sets resource limits per user/group, including nproc (number of processes).

Answer

/etc/pam.d/login

Answer

/etc/ulimit.conf

Answer

/etc/systemd/system.conf