LFCS Service Configuration Practice Test 2 — 15 Questions

Question 1

Which two commands produce output that includes the current runlevel or target? (Choose two.)

Accepted Answer

runlevel. Option C (runlevel) is correct because it prints the previous and current runlevel (e.g., 'N 5' or '5 3'), directly reporting the current runlevel. Option D (who -r) is correct because it displays the current runlevel along with the time of last runlevel change, e.g., 'run-level 5  2024-01-01 10:00'. Option A (systemctl list-units --type=target) lists loaded target units but does not indicate which one is currently active as the runlevel/target. Option B (systemctl show-environment) prints environment variables for the systemd manager, not the runlevel or target. Option E (systemctl get-default) shows the default target configured to boot into, not the current runlevel or active target.

Answer

systemctl list-units --type=target

Answer

systemctl show-environment

Answer

systemctl get-default

Question 2

Which two statements are true about systemd socket activation? (Choose two.)

Accepted Answer

The service unit must include 'Sockets=<socket unit>' to bind the service to the socket.. Option C is correct because a service unit that is triggered by a socket unit must reference that socket via the Sockets= directive in its [Unit] section (e.g., Sockets=sshd.socket), which binds the service to the socket and establishes the dependency. Option D is correct because the core purpose of systemd socket activation is on-demand startup: systemd listens on the socket and starts the associated service only when a connection or datagram arrives, then passes the listening file descriptor to the service. Option A is not required, since the [Install] section only controls enablement (e.g., WantedBy=) and is not mandatory for socket activation to function. Option B is incorrect because the service unit uses Type=simple, forking, or notify as appropriate; 'socket' is a unit type for the .socket file, not a valid service Type. Option E is incorrect because socket activation works with AF_UNIX, AF_INET, and AF_INET6 sockets, including both TCP and UDP, not only TCP.

Answer

The socket unit file must have an [Install] section.

Answer

Socket activation requires the service to be of type 'socket'.

Answer

Socket activation only works with TCP sockets.

Question 3

Which three of the following are valid reasons to use 'systemctl mask' instead of 'systemctl disable'? (Choose three.)

Accepted Answer

To ensure that even 'systemctl start' fails.. Option C is correct because masking a unit links it to /dev/null, so any attempt to start it—including an explicit 'systemctl start'—fails with an error rather than launching the service. Option D is correct because a masked unit cannot be pulled in as a dependency by another unit, so it cannot be enabled or started indirectly through Requires/Wants relationships. Option E is correct because masking blocks manual activation as well, not just boot-time activation, which is the key difference from 'disable'. Options A and B are not correct: masking does not hide a unit from status commands (it still appears, typically shown as masked), and it does not make the service 'completely unavailable' in the sense of removing it—the unit file still exists and can be unmasked, so the blanket wording is inaccurate.

Answer

To hide the service from status commands.

Answer

To make the service completely unavailable to the system.

Question 4

Refer to the exhibit. What is the most likely cause of the sshd service failure?

Accepted Answer

The sshd_config file is misconfigured.. The exhibit shows that the sshd service fails to start, and the most likely cause is a misconfiguration in the sshd_config file. When sshd is started via systemd, a syntax error or invalid directive in /etc/ssh/sshd_config will cause the daemon to exit immediately, resulting in a failed status. This is a common issue because sshd validates its configuration file at startup and will refuse to run if it finds an error.

Answer

The OPTIONS environment variable is not set.

Answer

The service is not enabled to start at boot.

Answer

There is a syntax error in the unit file.

Question 5

A company runs a monitoring agent service (monitor.service) that must start after the network is fully up and the DNS resolver is ready. The service currently has the following dependencies in its unit file:

[Unit]
Description=Monitoring Agent
After=network.target
Wants=network.target

[Service]
ExecStart=/usr/bin/monitor

The service starts, but often fails to resolve hostnames because DNS is not yet available. Which change should be made to the unit file to ensure the service only starts after DNS is ready?

Accepted Answer

Add a dependency: After=nss-lookup.target. `nss-lookup.target` is a synchronization point that indicates the hostname resolution subsystem (including DNS) is fully operational. By adding `After=nss-lookup.target`, the monitor service will not start until DNS resolution is available, solving the hostname resolution failures. The existing `Wants=network.target` is insufficient because `network.target` only signals that basic network interfaces are configured, not that DNS services are ready.

Answer

Replace After=network.target with After=network-online.target and add Requires=network-online.target

Answer

Add Before=network.target to delay the start

Answer

Set Type=idle in the [Service] section

Question 6

A company runs a web application stack consisting of a frontend web server (web.service) and a backend application server (app.service). The app.service uses Restart=on-failure to automatically restart if it crashes. The administrator wants the web.service to automatically restart whenever app.service restarts, so that the frontend remains in sync with the backend. Which directive should be added to the web.service unit file's [Unit] section to achieve this?

Accepted Answer

PartOf=app.service. (PartOf=app.service) is correct because when app.service stops or restarts, PartOf causes systemd to stop or restart web.service as well, keeping the frontend in sync with the backend. Unlike BindsTo, PartOf does not create a strict dependency that would prevent app.service from starting independently, and it ensures the frontend follows the backend's state changes without requiring the backend to be fully operational for the frontend to start.

Answer

BindsTo=app.service

Answer

Requires=app.service

Answer

Wants=app.service

Question 7

A company runs an Apache HTTP server hosting multiple virtual hosts on a single server. The server is managed by systemd. After editing the configuration file for one of the virtual hosts, the administrator notices that the entire Apache service fails to start with a syntax error. Other virtual hosts are currently down because the service failed. The administrator must resolve the issue with minimal downtime and without affecting the configuration of the working virtual hosts. Which course of action is most appropriate?

Accepted Answer

Run 'apachectl configtest' to validate all configurations, fix any reported errors, then run 'systemctl reload httpd'.. The correct approach is to validate the configuration with 'apachectl configtest' (or 'httpd -t') to identify the syntax error, fix it, and then use 'systemctl reload httpd' to apply the change without dropping existing connections. Reload sends SIGHUP to Apache, which re-reads configuration and gracefully restarts workers, minimizing downtime for other virtual hosts.

Answer

Check the Apache error log to identify the syntax error, fix the configuration, and run 'systemctl restart httpd'.

Answer

Run 'systemctl restart httpd' immediately to apply the change; the error will be logged.

Answer

Disable the problematic virtual host file by renaming it, then restart Apache to bring up the other sites.

Question 8

A Linux administrator is configuring a systemd service unit file for a web application. The service must be started only after the network is online and the database service (db.service) is running. The administrator wants to ensure that if db.service fails, the web application service is also stopped. Which TWO directives should be added to the [Unit] section of the web application's unit file to achieve these requirements? (Choose two.)

Accepted Answer

After=network-online.target db.service. The web service must start after the network and database, and must stop if the database fails. After=network-online.target db.service ensures ordering. Requires=db.service creates a hard dependency so that if db.service fails, the web service is stopped. Together, they meet the requirements. Wants= is too weak, BindsTo= is stronger but not necessary here, and PartOf= does not provide ordering.

Answer

BindsTo=db.service

Answer

Wants=network-online.target

Answer

PartOf=db.service

Question 9

A system administrator is troubleshooting a custom systemd service that fails to start. The service unit file includes the following directives: Type=simple, ExecStart=/usr/local/bin/myapp, User=myapp, and Group=myapp. The service fails with a permission denied error when accessing /var/log/myapp.log. The file is owned by root:root with mode 0644. Which two actions will resolve the permission issue? (Choose two.)

Accepted Answer

Use the LogsDirectory=myapp directive in the service unit to create a writable log directory.. The service runs as user myapp and needs to write to /var/log/myapp.log, but the file is owned by root with mode 0644, denying write access. Changing ownership to myapp:myapp grants the necessary write permission. Alternatively, using LogsDirectory=myapp creates a dedicated log directory owned by the service user, which is a clean systemd solution.

Answer

Change the file permissions of /var/log/myapp.log to 0666.

Answer

Modify the service unit to set User=root.

Answer

Add the myapp user to the root group.

Question 10

A custom systemd service unit needs to be configured so that it automatically restarts if it exits with a non-zero exit code, but does not restart if it is stopped cleanly by an administrator. Which two directives should be used? (Choose two.)

Accepted Answer

Restart=on-failure. The goal is to restart only on failure, not on clean exit. Restart=on-failure already restarts only on non-zero exit or signal. However, an administrator stop may result in a clean exit (status 0), so Restart=on-failure alone would not restart on clean exit anyway. But RestartPreventExitStatus=0 explicitly prevents restart on exit status 0, providing an extra safeguard. Using both ensures that even if the service is configured with a broader Restart policy, a clean exit will not trigger a restart. The combination of Restart=on-failure and RestartPreventExitStatus=0 is correct.

Answer

Restart=always

Answer

RestartSec=5

Answer

SuccessExitStatus=0

Question 11

A system administrator is creating a systemd service unit for a custom application that must run after the database service (db.service) is started and must stop before the database service stops. The administrator wants to ensure proper ordering and dependency. Which TWO directives should be used in the custom service unit file? (Choose two.)

Accepted Answer

Requires=db.service. After=db.service ensures the custom service starts after the database, and systemd reverses this ordering for shutdown, so it stops before the database. Requires=db.service establishes a hard dependency: if the database fails, the custom service will not start, and if the database is stopped, the custom service is stopped too. Together they provide both ordering and dependency, meeting the requirement.

Answer

Before=db.service

Answer

Wants=db.service

Answer

Conflicts=db.service

Question 12

A system administrator is configuring a service that should be restarted automatically if it exits with a non-zero exit code, but not if it is stopped cleanly. The service unit currently has Restart=on-failure. However, the administrator notices that the service sometimes restarts even after a clean exit. Which additional directive should be added to prevent restarts on clean exits?

Accepted Answer

RestartPreventExitStatus=0. To prevent a service from restarting after a clean exit while still restarting on failure, the RestartPreventExitStatus= directive should be used with exit code 0. This explicitly tells systemd not to restart when the service exits with status 0, overriding the Restart=on-failure behavior for that specific code.

Answer

SuccessExitStatus=0

Answer

RestartForceExitStatus=0

Answer

RestartSec=0

Question 13

A system administrator configures a web server using systemd. After creating a custom service unit file, the administrator runs `systemctl daemon-reload` but the service still fails to start with a 'Unit not found' error. What is the most likely cause?

Accepted Answer

The service name was misspelled in the `systemctl start` command.. The 'Unit not found' error after `systemctl daemon-reload` typically indicates that systemd cannot locate a unit with the specified name. While correct placement of unit files is important, systemd scans both /etc/systemd/system/ and /usr/lib/systemd/system/ after a daemon-reload. Therefore, placing a custom unit in /usr/lib/systemd/system/ would not cause this error. The most likely cause is that the service name was misspelled in the `systemctl start` command. A simple typo would lead to a 'Unit not found' message because systemd looks for an exact match. Other options like forgetting `systemctl enable` or group membership do not affect unit discovery at start time.

Answer

The administrator forgot to run `systemctl enable` before starting the service.

Answer

The unit file is placed in /usr/lib/systemd/system/ instead of /etc/systemd/system/.

Answer

The administrator is not in the 'systemd' group.

Question 14

A server runs a custom application that listens on TCP port 8080. The administrator wants to ensure the application starts automatically on boot and restarts if it crashes. Which systemd unit file directive should be used to achieve the restart behavior?

Accepted Answer

Restart=on-failure. The `Restart=on-failure` directive in a systemd unit file instructs systemd to automatically restart the service unit when it exits with a non-zero exit code, is terminated by a signal (including SIGKILL), or times out. This directly satisfies the requirement for the application to restart if it crashes, as a crash typically results in an unclean exit that triggers the restart condition.

Answer

RestartSec=5

Answer

Type=notify

Answer

RemainAfterExit=yes

Question 15

An administrator needs to configure a service to run as a non-root user for security reasons. Which systemd unit file directive accomplishes this?

Accepted Answer

User=myuser. The `User=` directive in a systemd unit file specifies the user (by name or UID) under which the service process runs. By setting `User=myuser`, the service executes with the privileges of that non-root user, reducing the attack surface and adhering to the principle of least privilege. This is the standard systemd mechanism for dropping root privileges for a service.

Answer

AmbientCapabilities=CAP_NET_BIND_SERVICE

Answer

DynamicUser=yes

Answer

Group=myuser