LFCS Practice Test 2 — 30 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

Question 11

A financial firm requires all internal SSH connections to be encrypted with at least 256-bit ciphers. An administrator is configuring the SSH server. Which configuration line should be added to /etc/ssh/sshd_config?

Accepted Answer

Ciphers aes256-ctr. The Ciphers directive in sshd_config explicitly controls the symmetric encryption algorithms used to encrypt SSH session data. The cipher aes256-ctr provides 256-bit encryption, meeting the firm's requirement for at least 256-bit ciphers. Other directives like MACs, KexAlgorithms, or HostKeyAlgorithms do not directly set the encryption cipher strength.

Answer

MACs hmac-sha2-256

Answer

KexAlgorithms diffie-hellman-group-exchange-sha256

Answer

HostKeyAlgorithms ssh-rsa

Question 12

Which TWO of the following are valid ways to mount a filesystem with the 'noexec' option to prevent execution of binaries?

Accepted Answer

mount -o noexec /dev/sdb1 /mnt/data. Option A is correct because the mount command's -o flag accepts the noexec mount option directly, so 'mount -o noexec /dev/sdb1 /mnt/data' mounts the device /dev/sdb1 at /mnt/data with binary execution disabled. Option E is correct because the fourth field of an /etc/fstab entry holds the mount options, so adding 'noexec' there (e.g., 'defaults,noexec') makes the filesystem mount with noexec persistently at boot or on 'mount -a'. Option B is wrong because 'exec' is the opposite of noexec and explicitly permits execution. Option C is wrong because 'defaults' expands to rw,suid,dev,exec,auto,nouser,async, which includes exec and thus allows binaries to run. Option D is wrong because 'mount --bind' merely mirrors one directory tree onto another and does not itself set the noexec option.

Answer

Add 'exec' to the fourth field of /etc/fstab for the entry.

Answer

Add 'defaults' to the fourth field of /etc/fstab for the entry.

Answer

mount --bind /mnt/data1 /mnt/data2

Question 13

An administrator is troubleshooting a server that runs a critical application. The server has 16 GB of RAM and 8 CPU cores. The administrator notices that the server becomes very slow during peak hours. Analysis of 'iostat -x 1' shows that the average wait time (await) for the main disk (sda) is consistently above 1000 ms, while the average service time (svctm) is around 5 ms. What is the most likely cause?

Accepted Answer

There is a large queue of I/O requests waiting to be serviced.. The 'await' value in iostat represents the average time (in milliseconds) for I/O requests to be serviced, including time spent waiting in the queue. With 'await' at 1000+ ms and 'svctm' at only 5 ms, the vast majority of the time is spent waiting, not being serviced. This indicates a large queue of pending I/O requests, which is the direct cause of the slowdown.

Answer

The CPU is overloaded, causing processes to wait for CPU time.

Answer

The system is using swap space heavily, causing disk I/O.

Answer

The disk is experiencing hardware errors.

Question 14

A system administrator needs to ensure the Apache httpd service starts automatically on system boot. Which command should they use?

Accepted Answer

systemctl enable httpd. The `systemctl enable httpd` command creates the necessary symlinks in the systemd unit configuration directories (typically `/etc/systemd/system/multi-user.target.wants/`) to ensure the Apache httpd service starts automatically at boot time. This is the correct approach because `enable` configures the service to be started on system startup, whereas `start` only runs it immediately without affecting boot behavior.

Answer

systemctl start httpd

Answer

systemctl disable httpd

Answer

systemctl reload httpd

Question 15

Refer to the exhibit. The output of 'ps aux' shows a process named 'process_hog' with PID 1234 consuming 99.5% CPU. The process is stuck in an infinite loop and does not respond to SIGTERM. Which signal should be used to forcefully terminate it?

Accepted Answer

kill -9 1234. SIGKILL (signal 9) cannot be caught, blocked, or ignored by a process, making it the only reliable way to terminate a process that is stuck in an infinite loop and unresponsive to SIGTERM. Since the process does not respond to SIGTERM (signal 15), a forceful kill with kill -9 is necessary.

Answer

kill -2 1234

Answer

kill -15 1234

Answer

kill -19 1234

Question 16

You are managing a Linux server that hosts a critical web application. The server is running low on disk space in the root filesystem, and you need to free up space urgently. You run 'df -h' and see that /dev/sda1 is mounted on / and is 95% full. You also notice that /var/log/messages is over 2 GB in size. The application writes logs to /var/log/app.log, which is also large. The server has a separate /var partition that has plenty of free space. The application must continue running with minimal downtime. You need to compress and rotate logs without losing any data, and ensure that the root filesystem has at least 10% free space. Which of the following actions should you take first to achieve this goal?

Accepted Answer

Use logrotate with the 'copytruncate' option to rotate /var/log/app.log and move the rotated file to /var/old_logs/.. Logrotate with the 'copytruncate' option allows the application to continue writing to the same file descriptor while the current log is copied and then truncated to zero length. This avoids any application downtime and the rotated log can be moved to the separate /var partition (which has free space) for compression or archiving, freeing space on the root filesystem without data loss.

Answer

Delete /var/log/app.log and /var/log/messages to free space quickly.

Answer

Stop the application, truncate /var/log/app.log, then restart the application.

Answer

Compress /var/log/app.log using gzip and keep it in place.

Question 17

A system administrator needs to create a shared group 'projectx' and add existing users 'bob' and 'carol' to it. The users need to collaborate on files in a directory /projectx. What is the correct sequence of commands to set up the group and ensure new files created in /projectx are automatically owned by the group 'projectx'?

Accepted Answer

groupadd projectx; usermod -aG projectx bob; usermod -aG projectx carol; chmod g+s /projectx. It uses `groupadd` to create the group, `usermod -aG` to append users to the group without removing them from other groups, and `chmod g+s` to set the setgid bit on the directory. The setgid bit ensures that new files created in /projectx inherit the group ownership of the directory (projectx), enabling collaboration.

Answer

groupadd projectx; usermod -G projectx bob carol; chmod 2770 /projectx

Answer

addgroup projectx; adduser bob projectx; adduser carol projectx; chmod u+s /projectx

Answer

groupadd projectx; usermod -G projectx bob; usermod -G projectx carol; chmod g+s /projectx

Question 18

A systemd-networkd managed interface enp1s0 needs to be configured with a static IP address 192.168.1.100/24 and a default gateway via 192.168.1.1. Which .network file configuration is correct?

Accepted Answer

[Match]
Name=enp1s0
[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1. Systemd-networkd uses the `[Match]` section with `Name=` to match the interface, and the `[Network]` section with `Address=` to assign a static IP address and `Gateway=` to set the default gateway. The syntax `Address=192.168.1.100/24` is the proper directive for defining a static IP address in a .network file, and `Gateway=192.168.1.1` correctly specifies the default gateway.

Answer

[Match]
Interface=enp1s0
[Network]
StaticIP=192.168.1.100/24
Gateway=192.168.1.1

Answer

[Link]
Name=enp1s0
[Network]
IPAddress=192.168.1.100/24
Gateway=192.168.1.1

Answer

[Match]
Name=enp1s0
[Network]
Address=192.168.1.100/24
DefaultGateway=192.168.1.1

Question 19

Which file stores the encrypted password (or password hash) for user accounts?

Accepted Answer

/etc/shadow. /etc/shadow is correct because it stores encrypted password hashes for user accounts, along with password aging information. It is readable only by root to prevent unauthorized access to password hashes. The /etc/passwd file historically stored passwords but now only contains user account information, with the password field replaced by an 'x' indicating the hash is in /etc/shadow.

Answer

/etc/group

Answer

/etc/passwd

Answer

/etc/gshadow

Question 20

A user wants to find all files in /var/log that have been modified within the last 2 days. Which command should they use?

Accepted Answer

find /var/log -mtime -2. The `find` command with `-mtime -2` searches for files whose content was last modified less than 2 days ago (i.e., within the last 48 hours). The minus sign before the number indicates 'less than' or 'within the last N days', which matches the user's requirement to find files modified within the last 2 days.

Answer

find /var/log -mmin -2880

Answer

find /var/log -mtime +2

Answer

find /var/log -mtime 2