LFCS Practice Test 4 — 10 Questions

Question 1

Order the steps to create a systemd service unit that runs a script at boot.

Accepted Answer

Create the unit file, then enable the service for boot, then start the service, then check the status.. Creating the unit file, enabling for boot, starting, and checking status are standard steps.

Answer

Start the service, then create the unit file, then enable for boot, then check status.

Answer

Enable the service for boot, then create the unit file, then start, then check status.

Answer

Create the unit file, then start the service, then enable for boot, then check status.

Question 2

Match each Linux permission type to its symbolic representation.

Accepted Answer

Read: r. In Linux, standard file permissions are represented by symbols: read (r), write (w), and execute (x). Each permission type maps to a unique symbol. Confusion often arises from swapping these symbols.

Answer

Read: w

Answer

Write: x

Answer

Execute: r

Question 3

A custom systemd service unit file has been created but the service fails to start with 'Exec format error'. What is the most likely cause?

Accepted Answer

The ExecStart command path is incorrect or missing shebang. The 'Exec format error' in systemd indicates that the binary or script specified in the ExecStart directive cannot be executed, typically because the path is incorrect, the file is not executable, or (most commonly) the script lacks a valid shebang line (e.g., #!/bin/bash). Without a shebang, the kernel does not know which interpreter to use, causing an execve() failure.

Answer

The unit file has incorrect permissions

Answer

The user does not have permission to start the service

Answer

The service is disabled

Question 4

A junior administrator issued the command 'usermod -L alice' to lock the account of user alice. However, alice is still able to log in via SSH using a public key. What is the most likely reason?

Accepted Answer

The usermod -L command only locks the password but does not prevent SSH key-based authentication.. The `usermod -L` command locks the user's password by placing an exclamation mark (!) in the second field of the /etc/shadow file, which prevents password-based authentication. However, SSH public key authentication does not rely on the password field; it uses the authorized_keys file and the SSH daemon's public key challenge-response mechanism. Therefore, even with a locked password, the user can still log in via SSH if their public key is present in ~/.ssh/authorized_keys.

Answer

The usermod -L command only changes the user's shell to /sbin/nologin.

Answer

The usermod -L command requires a restart of the SSH service to take effect.

Answer

The usermod -L command is not effective on accounts with a UID less than 1000.

Question 5

Which THREE commands can be used to list all users currently logged into the system?

Accepted Answer

w. The w command (A) is correct because it reads /var/run/utmp and displays every user currently logged in along with their terminal, source host, login time, idle time, and current process. The users command (C) is correct because it prints a space-separated list of the login names of all users currently logged into the system, derived from utmp. The who command (E) is correct because it also reads utmp and lists currently logged-in users with their terminal, login time, and remote host. The last command (B) is not correct here because it reads /var/log/wtmp and shows historical login/logout records, including past sessions, not only users currently logged in. The id command (D) is not correct because it displays the UID, GID, and group memberships of a single specified or current user rather than listing all logged-in users.

Answer

last

Answer

id

Question 6

After creating an XFS filesystem on /dev/sdb1, an admin mounts it and writes data. Later, they run 'xfs_info /mnt/data' and see the filesystem was created with default settings. What is the default inode size for XFS on a typical Linux system?

Accepted Answer

256 bytes. The default inode size for XFS on a typical Linux system is 256 bytes. This is set at filesystem creation time and provides a balance between supporting extended attributes (like ACLs and SELinux contexts) and minimizing metadata overhead. The `xfs_info` command confirms the default settings, which include this 256-byte inode size.

Answer

512 bytes

Answer

128 bytes

Answer

4096 bytes

Question 7

Based on the journalctl output, what is the most likely cause of the service failure?

Accepted Answer

Another process is already using port 8080.. The journalctl output shows a bind error on port 8080 with 'Address already in use'. This indicates that another process is already listening on that port, preventing the service from starting. In systemd, such a failure is logged with the specific errno EADDRINUSE, which directly points to a port conflict.

Answer

The service configuration file has a syntax error.

Answer

The system is out of memory.

Answer

The service is trying to write to a read-only filesystem.

Question 8

A service named webserver.service is failing to start. The administrator wants to see the most recent error messages related to this service. Which command provides this information?

Accepted Answer

journalctl -u webserver.service. The `journalctl -u webserver.service` command queries the systemd journal for all log entries associated with the specified unit, showing the most recent error messages in reverse chronological order. This is the standard way to view detailed, time-stamped error logs for a failing service, as `journalctl` provides access to the binary journal that captures stdout, stderr, and syslog messages from the service.

Answer

systemctl status webserver.service --full

Answer

systemctl list-units --type=service | grep webserver

Answer

systemctl is-active webserver.service

Question 9

An e-commerce company runs a critical application on a Linux server that occasionally becomes unresponsive. The server has 64GB RAM and runs a Java application. The operations team notices that during peak hours, the system becomes very slow and eventually the application crashes with 'OutOfMemoryError'. After restart, it works fine for a while. They suspect a memory leak but also want to ensure the system does not go down during peak hours. The system uses systemd to manage the Java service. The administrator needs to implement a solution that: (1) automatically restarts the service if it becomes unresponsive, (2) limits the memory usage of the service to prevent OOM kills on the system, and (3) provides early warning of high memory usage. Which of the following approaches best meets these requirements?

Accepted Answer

Configure systemd service with WatchdogSec=30, Restart=on-failure, MemoryMax=32G. Also set up a log watcher that alerts when memory usage exceeds 28G via journalctl and a custom script.. It uses systemd's WatchdogSec to detect unresponsiveness and Restart=on-failure to automatically restart the service, while MemoryMax=32G enforces a hard memory limit via cgroups to prevent OOM kills. The custom log watcher provides early warning by alerting when memory usage exceeds 28G, satisfying all three requirements.

Answer

Set up a cron job to run every minute that checks memory usage with free and if > 90%, restart the service with systemctl restart. Also configure MemoryMax=32G in the systemd unit.

Answer

Configure sysctl vm.overcommit_memory=2 to prevent overcommit, and allocate huge pages for Java. Also set Restart=always in the systemd unit.

Answer

Use ulimit -v 33554432 in the service script to limit virtual memory, and set Restart=always. Also configure a cron job to send alerts when dmesg shows OOM.

Question 10

A system administrator is setting up a high-availability cluster using shared storage. Which filesystem is best suited for this environment where multiple nodes need simultaneous read-write access to the same filesystem?

Accepted Answer

GFS2. GFS2 (Global File System 2) is a shared-disk cluster filesystem designed for high-availability environments where multiple nodes require simultaneous read-write access to the same filesystem. It uses a distributed lock manager (DLM) to coordinate access across nodes, ensuring data consistency without requiring a single metadata server. This makes it ideal for active-active cluster configurations with shared block storage.

Answer

Btrfs

Answer

XFS

Answer

ext4