XK0-006 Practice Test 29 — 15 Questions

Question 1

An administrator wants to ensure a service starts automatically at boot on a systemd-based system. Which command should be used?

Accepted Answer

systemctl enable service. On systemd-based systems, 'systemctl enable <service>' creates the necessary symlinks (typically in /etc/systemd/system/) so that the service is started automatically at boot. It does not start the service immediately; it only configures it for future boots.

Answer

systemctl start service

Answer

systemctl status service

Answer

systemctl reload service

Question 2

An administrator needs to prevent a specific user 'bob' from logging in via SSH while allowing other users. Which configuration directive should be added to /etc/ssh/sshd_config?

Accepted Answer

DenyUsers bob. The DenyUsers directive in /etc/ssh/sshd_config explicitly blocks specific usernames from logging in via SSH. By specifying 'DenyUsers bob', only user bob is denied, while all other users remain allowed. This matches the requirement to prevent bob without affecting others. AllowUsers with a whitelist would also block bob but would require listing every other user, which is impractical and not the intended solution.

Answer

AllowUsers alice charlie

Answer

PermitRootLogin no

Answer

AllowUsers bob

Question 3

A Linux administrator is troubleshooting a systemd service that fails to start. The service unit file is located at /etc/systemd/system/myservice.service. After editing the unit file, the administrator runs systemctl start myservice, but the service still uses the old configuration. Which command should be run to ensure systemd reloads the modified unit file?

Accepted Answer

systemctl daemon-reload. After modifying a systemd unit file, the systemd manager must reload its configuration to recognize the changes. The systemctl daemon-reload command performs this reload, ensuring subsequent start or restart operations use the updated unit file.

Answer

systemctl restart myservice

Answer

systemctl reenable myservice

Answer

systemctl reload myservice

Question 4

A Linux administrator is writing a systemd unit file at /etc/systemd/system/backup.service that must execute /usr/local/bin/backup.sh only after the network is fully reachable and the /mnt/archive mount is active. The unit currently has no ordering directives. Which directive should be added to the [Unit] section to satisfy this requirement?

Accepted Answer

After=network-online.target local-fs.target. Ordering in systemd is expressed with After= and Before=, which control when a unit is queued relative to others without creating a dependency. To guarantee the backup script runs only once the network is up and /mnt/archive is mounted, the [Unit] section needs After=network-online.target local-fs.target. Dependency keywords such as Requires, Wants, and BindsTo pull units in or tie lifecycles together but never enforce start ordering on their own.

Answer

Wants=network-online.target local-fs.target

Answer

Requires=network-online.target local-fs.target

Answer

BindsTo=network-online.target local-fs.target

Question 5

A Linux server hosts a web application that must be able to bind to TCP port 443. The administrator has already installed the application and configured it to listen on 443. However, when the service starts, it fails with a 'Permission denied' error. The administrator confirms that no other process is using port 443 and that the service runs as the non-root user 'webapp'. Which command should the administrator use to grant the necessary capability to the service binary without giving it full root privileges?

Accepted Answer

setcap 'cap_net_bind_service=+ep' /usr/local/bin/webapp. The service runs as a non-root user and needs to bind to a privileged port (443). Linux capabilities allow fine-grained privilege assignment. The setcap command with cap_net_bind_service grants exactly the needed capability, enabling the binary to bind to low-numbered ports without full root privileges. This follows the principle of least privilege and is the standard solution for this scenario.

Answer

chmod u+s /usr/local/bin/webapp

Answer

firewall-cmd --add-port=443/tcp --permanent

Answer

usermod -aG root webapp

Question 6

An administrator is building a container image and needs to reduce its final size while keeping the build reproducible. Which TWO practices improve image efficiency and build reliability? (Choose two.)

Accepted Answer

Combine related RUN instructions and clean package caches within the same layer.. Image efficiency hinges on layer mechanics: files removed in a later layer still occupy the earlier one, so cleanup must happen in the same RUN that created the mess. Reproducibility hinges on locked inputs, so base images and packages should be referenced by exact version or digest rather than a moving tag. Combining those two disciplines yields smaller, repeatable builds.

Answer

Add a .dockerignore file that excludes the local .git directory and build artifacts.

Answer

Use multiple FROM instructions to layer several base images into one final image.

Answer

Set the ENV HOME variable to a writable path so package managers cache downloads there.

Question 7

A Linux administrator needs a cron job that runs /usr/local/bin/collect.sh at 02:30 every Monday, Wednesday, and Friday. The job must be added for the root user without editing the global /etc/crontab file. Which command should the administrator run to open the correct crontab for editing?

Accepted Answer

crontab -u root -e. The crontab command with the -u option edits the named user's personal crontab, so crontab -u root -e reliably opens root's schedule for modification from any account with the needed privilege. The schedule line 30 2 * * 1,3,5 then executes collect.sh at 02:30 on Monday, Wednesday, and Friday, fulfilling the requirement without touching /etc/crontab.

Answer

crontab -l -u root

Answer

systemctl edit cron

Answer

crontab -e

Question 8

A Linux administrator is preparing a new server that uses systemd-boot as the boot loader. The administrator wants to verify the current boot loader entries and their order. Which command should the administrator run?

Accepted Answer

bootctl list. The bootctl list command displays all systemd-boot entries and their sequence, which is exactly what the administrator needs to verify the boot loader configuration on a system using systemd-boot. The other tools either manage different boot loaders (GRUB), interact with UEFI firmware (efibootmgr), or assume systemd-boot is a service (systemctl), so they do not provide the required information.

Answer

efibootmgr -v

Answer

grub-mkconfig -o /boot/grub/grub.cfg

Answer

systemctl status systemd-boot

Question 9

A Linux administrator is troubleshooting a server that fails to mount a filesystem listed in /etc/fstab during boot, causing the system to drop into emergency mode. The administrator wants to prevent the system from entering emergency mode if this particular mount fails, while still attempting to mount it. Which fstab option should be added to the mount entry?

Accepted Answer

nofail. The nofail option in /etc/fstab instructs systemd to ignore mount failures for that entry, allowing the boot to proceed even if the device is unavailable. This prevents the system from dropping into emergency mode. The other options either do not affect error handling or are already implied by defaults, so they do not provide the needed resilience.

Answer

nouser

Answer

auto

Answer

defaults

Question 10

A Linux administrator needs to change the runlevel of a systemd-based system to a state where only a single user can log in for maintenance, without starting network services. Which systemd target should the administrator use?

Accepted Answer

rescue.target. The rescue.target is the systemd equivalent of single-user mode, providing a minimal environment with only essential services and no networking. It allows the administrator to log in as root for maintenance tasks. The emergency.target is more restrictive and mounts the root filesystem read-only, while multi-user and graphical targets start networking and multiple users. Therefore, rescue.target is the correct choice.

Answer

emergency.target

Answer

multi-user.target

Answer

graphical.target

Question 11

An administrator wants to restrict SSH access to only users in the 'sshusers' group. Which configuration directive should be added to /etc/ssh/sshd_config?

Accepted Answer

AllowGroups sshusers. The AllowGroups directive in /etc/ssh/sshd_config explicitly permits SSH login only for users who are members of the specified group(s). When AllowGroups sshusers is set, any user not in the 'sshusers' group is denied access, regardless of other settings. This is the correct and direct way to restrict SSH access to a specific group.

Answer

AllowUsers sshusers

Answer

Match Group sshusers

Answer

DenyGroups all

Question 12

A system administrator wants to view the last 10 lines of a log file and also save those lines to another file for analysis. Which command should the administrator use?

Accepted Answer

tail -n 10 file | tee output.txt. The command 'tail -n 10 file | tee output.txt' displays the last 10 lines of the file and simultaneously writes those lines to output.txt. The tail command extracts the last 10 lines, and tee duplicates the output to both the terminal and the specified file.

Answer

head -n 10 file | tee output.txt

Answer

cat file | tee output.txt

Answer

tee output.txt < tail -n 10 file

Question 13

A Linux administrator is writing a script that must wait for a background process to finish before continuing. The process ID is stored in a variable. Which command should be used to wait for this process?

Accepted Answer

wait $PID. The `wait` command in Bash, when given a specific process ID (PID), suspends execution of the calling shell script until that background process terminates. This directly fulfills the requirement to wait for a specific background process whose PID is stored in a variable.

Answer

sleep 10

Answer

wait

Answer

kill -0 $PID

Question 14

An administrator is managing a server using systemd and needs to control services and units. Which THREE of the following are valid systemd commands for service management? (Choose three.)

Accepted Answer

systemctl mask. B is correct because 'systemctl mask' creates a symlink to /dev/null, making a unit completely unavailable and preventing it from being started manually or by dependencies. This is a valid systemd command for service management.

Answer

service start

Answer

chkconfig on

Question 15

A Linux administrator is configuring a persistent mount for a new 2TB XFS filesystem on /dev/sdb1 so it mounts automatically at /data with quota accounting enabled. The administrator edits /etc/fstab and adds the entry, then runs mount -a to validate it. Which fstab field combination correctly applies user and group quota accounting on this XFS mount?

Accepted Answer

/dev/sdb1  /data  xfs  defaults,uquota,gquota  0 0. XFS uses its own quota mount keywords rather than the legacy ext-family usrquota/grpquota options. Specifying uquota and gquota in the fourth fstab field enables both user and group quota accounting each time the filesystem mounts, which satisfies the requirement for automatic quota enforcement at boot. The remaining options either use unsupported keywords or disable quotas entirely.

Answer

/dev/sdb1  /data  xfs  defaults,quota  0 0

Answer

/dev/sdb1  /data  xfs  defaults,noquota  0 0

Answer

/dev/sdb1  /data  xfs  defaults,usrquota,grpquota  0 0