LFCS Service Configuration Practice Test 3 — 15 Questions

Question 1

A system administrator wants to configure a custom service to start automatically at boot. Which command accomplishes this?

Accepted Answer

systemctl enable custom.service. The `systemctl enable custom.service` command creates the necessary symlinks in the systemd unit file directories (e.g., `/etc/systemd/system/multi-user.target.wants/`) so that the service is automatically started at boot. This is the correct method to configure a custom service for automatic startup in a systemd-based Linux distribution.

Answer

systemctl daemon-reload custom.service

Answer

systemctl reenable custom.service

Answer

systemctl start custom.service

Question 2

After editing a service unit file, which command must be run for changes to take effect?

Accepted Answer

systemctl daemon-reload. When a service unit file is edited, systemd must be notified to reload its configuration from disk. The `systemctl daemon-reload` command instructs systemd to re-read all unit files, applying any changes to the unit definitions without requiring a full system reboot. This is necessary because systemd caches unit file contents in memory, and only a daemon-reload will update that cache.

Answer

systemctl restart <service>

Answer

systemctl reenable <service>

Answer

systemctl reload <service>

Question 3

Which command displays the current status of all active services?

Accepted Answer

systemctl list-units --type=service --state=active. `systemctl list-units --type=service --state=active` filters systemd units to show only those of type 'service' that are currently in the 'active' state (i.e., running or exited but still considered active). This is the precise command to list all active services without showing inactive or failed units.

Answer

systemctl status --all

Answer

systemctl show --type=service

Answer

systemctl list-unit-files --type=service

Question 4

A service requires read-write access to a specific directory that is mounted from an NFS share. The directory is mounted via fstab with the option 'noauto'. The service starts before the mount is available. Which configuration change should be made in the service unit file to ensure the service only starts after the mount is mounted?

Accepted Answer

Add After=mnt-nfs.mount and Requires=mnt-nfs.mount. The service requires the NFS mount to be available before it starts. The `After=mnt-nfs.mount` directive ensures the service unit is ordered after the mount unit, and `Requires=mnt-nfs.mount` makes the mount a hard dependency: if the mount fails or is not active, the service will not start. This combination is necessary because the mount is defined with `noauto` in fstab, meaning it is not automatically mounted at boot; the mount unit must be explicitly started (e.g., by a dependency or another unit) before the service.

Answer

Add Before=mnt-nfs.mount and Requires=mnt-nfs.mount

Answer

Add Wants=mnt-nfs.mount and After=mnt-nfs.mount

Answer

Add After=mnt-nfs.mount and BindsTo=mnt-nfs.mount

Question 5

A system administrator is debugging why a service named 'myapp.service' fails to start. He runs 'systemctl status myapp.service' and sees the status 'failed' with details 'Exit code: 1' and 'Failed with result exit-code'. Which command should be used next to view the full log of the service?

Accepted Answer

journalctl -u myapp.service. The correct command is `journalctl -u myapp.service` because it retrieves the full systemd journal logs for the specified unit, showing detailed error messages, stdout/stderr output, and timestamps that explain why the service exited with code 1. The `-u` flag filters the journal to entries related to that specific service unit, which is essential for debugging exit-code failures.

Answer

systemctl show myapp.service

Answer

journalctl -x -u myapp.service

Answer

systemctl list-dependencies myapp.service

Question 6

A service unit file includes the following: [Install] WantedBy=multi-user.target. What does this directive accomplish?

Accepted Answer

The service is enabled by symlinking in multi-user.target.wants.. The `WantedBy=multi-user.target` directive in the `[Install]` section of a systemd service unit file does not directly start the service when the target is entered. Instead, when the service is enabled (via `systemctl enable`), systemd creates a symbolic link from the service unit file into the `multi-user.target.wants/` directory. This symlink causes systemd to automatically start the service as a dependency when `multi-user.target` is activated, effectively enabling the service for that target.

Answer

The service is stopped when multi-user.target is stopped.

Answer

The service conflicts with multi-user.target.

Answer

The service is automatically started when the system enters multi-user.target.

Question 7

A system administrator cannot restart a service because another unit 'stop' the request. The status message says 'Unit test.service is not running, but has pending stop job'. What is the most likely cause?

Accepted Answer

A previous stop command is still being processed. The message 'Unit test.service is not running, but has pending stop job' indicates that systemd has queued a stop operation for the service, but the stop job has not yet completed. This typically happens when a previous 'systemctl stop' command was issued but the service's stop process (e.g., ExecStop script) is still running or hanging. Until that job finishes, any attempt to restart the service will be blocked because systemd serializes jobs for the same unit.

Answer

The service unit file has RefuseManualStop=yes

Answer

The service has a dependency that is stopping

Answer

The service is masked

Question 8

An administrator wants to run a script daily at 2 AM. They create a timer unit and a service unit. The service unit uses Type=oneshot. Which of the following timer configurations is correct?

Accepted Answer

OnCalendar=*-*-* 02:00:00. `OnCalendar=*-*-* 02:00:00` specifies an absolute calendar event that triggers the timer at 2:00 AM every day, regardless of when the system booted or when the service last ran. This matches the requirement to run a script daily at a fixed time, and it works correctly with a `Type=oneshot` service unit.

Answer

OnUnitActiveSec=24h

Answer

OnBootSec=1d

Answer

OnActiveSec=24h

Question 9

A service unit has the directive 'ExecStartPre=/bin/true' and 'ExecStart=/usr/bin/myapp'. What is the effect of ExecStartPre?

Accepted Answer

It runs a pre-start script; if it fails, the service is not started.. ExecStartPre is a systemd directive that specifies a command to run before the main ExecStart command. If the ExecStartPre command fails (returns a non-zero exit code), systemd will not proceed to start the service, unless the '-' prefix is used to ignore failure. Here, /bin/true always succeeds (exit code 0), so it does not block the service, but the directive itself is designed to enforce a pre-start check.

Answer

It sets an environment variable.

Answer

It runs a post-start script.

Answer

It runs a pre-start script; if it fails, the service still starts.

Question 10

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

Accepted Answer

runlevel. The `runlevel` command displays the previous and current runlevel from the `/var/run/utmp` file, making it a direct way to see the current runlevel. The `who -r` command reads the same utmp file and prints the current runlevel along with the time of the last runlevel change, so both commands produce output that includes the current runlevel or target.

Answer

systemctl list-units --type=target

Answer

systemctl show-environment

Answer

systemctl get-default

Question 11

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.. The service unit must include a 'Sockets=' directive (e.g., 'Sockets=myapp.socket') to explicitly bind the service to the corresponding socket unit. This tells systemd which socket(s) the service should accept connections from when activated. Without this directive, the service will not receive the file descriptors for the socket, and activation will fail.

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 12

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.. 'systemctl mask' creates a symlink from the unit file to /dev/null, which causes all attempts to start the service (including 'systemctl start') to fail silently. This is a stronger action than 'systemctl disable', which only removes the symlinks that enable automatic startup but still allows manual starting via 'systemctl start'.

Answer

To hide the service from status commands.

Answer

To make the service completely unavailable to the system.

Question 13

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 14

Refer to the exhibit. An administrator tries to start myapp.service with 'systemctl start myapp.service' but receives 'Failed to start myapp.service: Unit myapp.service is not loaded properly: Invalid argument'. What is the most likely issue?

Accepted Answer

The unit file has a syntax error.. The error 'Unit myapp.service is not loaded properly: Invalid argument' indicates that systemd attempted to parse the unit file but encountered a syntax error or an invalid directive. This typically happens when a key-value pair in the unit file is malformed, such as a missing equals sign, an unsupported option, or a value that does not conform to systemd's expected format. Unlike a runtime failure (e.g., a missing ExecStart binary), this error occurs during the loading phase, before any execution attempt.

Answer

The service name is misspelled.

Answer

The ExecStart path is invalid.

Answer

The service is masked.

Question 15

Refer to the exhibit. The service unit file has Restart=on-failure, but systemctl show displays Restart=no. What is the most likely reason?

Accepted Answer

The unit file was edited but systemctl daemon-reload was not run.. The most likely reason is that the unit file was edited but `systemctl daemon-reload` was not executed. When a service unit file is modified, systemd does not automatically reload the configuration; it continues to use the cached version until `systemctl daemon-reload` is run. This explains why `systemctl show` displays `Restart=no` despite the file containing `Restart=on-failure`.

Answer

The User=backup directive overrides Restart.

Answer

The unit is not enabled.

Answer

The Restart directive is only valid for Type=simple.