LFCS Practice Test 8 — 10 Questions

Question 1

A server is running out of disk space. Which command will show the disk usage of the root filesystem in a human-readable format?

Accepted Answer

df -h /. The `df -h /` command displays disk usage for the root filesystem (`/`) in a human-readable format (e.g., GB, MB) by using the `-h` flag. This is the standard tool for checking filesystem-level disk space, not directory-level usage.

Answer

ls -lh /

Answer

fdisk -l /

Answer

du -sh /

Question 2

Refer to the exhibit. The administrator receives alerts that the root filesystem is almost full. Which command could free up space by removing old log files?

Accepted Answer

find /var/log -name '*.log' -mtime +30 -delete. The `find` command with `-name '*.log'` targets log files, `-mtime +30` selects files modified more than 30 days ago, and `-delete` removes them. This safely frees space by purging only old logs, preserving recent logs needed for troubleshooting.

Answer

truncate -s 0 /var/log/syslog

Answer

rm -rf /var/log/*

Answer

du -sh /var/log

Question 3

An administrator needs to encrypt a block device (/dev/sdc) using LUKS. Which command creates an encrypted LUKS container on the device?

Accepted Answer

cryptsetup luksFormat /dev/sdc. `cryptsetup luksFormat /dev/sdc` initializes the block device with a LUKS header, setting up an encrypted container that can later be opened with a passphrase or key file. This is the standard command for creating a new LUKS partition, as it writes the LUKS metadata and prepares the device for encryption.

Answer

cryptsetup luksOpen /dev/sdc encrypted_device

Answer

openssl enc -aes-256-cbc -in /dev/sdc -out /dev/sdc.enc

Answer

dm-crypt create encrypted /dev/sdc

Question 4

Refer to the exhibit. The administrator attempted to create a user 'newuser' but received an error. Which command should be used to check if the user already exists?

Accepted Answer

cat /etc/passwd | grep newuser. The /etc/passwd file stores all user account information, and using cat to pipe its contents through grep allows the administrator to search for the specific username 'newuser'. If the user exists, grep will output the matching line; if not, no output is returned. This is a standard, quick method to verify user existence without modifying system state.

Answer

passwd -S newuser

Answer

usermod -c newuser

Answer

userdel -v newuser

Question 5

An administrator is investigating why the 'tomcat' service fails to start on a RHEL 8 server. The output of 'systemctl status tomcat' shows: 'Loaded: loaded (/etc/systemd/system/tomcat.service; enabled; vendor preset: disabled) Active: failed (Result: exit-code) since ... Process: 4567 ExecStart=/opt/tomcat/bin/startup.sh (code=exited, status=1/FAILURE)'. The 'journalctl -u tomcat' shows: 'Error: JAVA_HOME is not defined correctly, cannot execute /usr/lib/jvm/java-11-openjdk/bin/java'. The admin checks /opt/tomcat/bin/startup.sh and sees it references JAVA_HOME. The admin verifies that Java 11 is installed at /usr/lib/jvm/java-11-openjdk. Which action should the admin take to fix the service?

Accepted Answer

Add 'Environment=JAVA_HOME=/usr/lib/jvm/java-11-openjdk' to the [Service] section of /etc/systemd/system/tomcat.service and run 'systemctl daemon-reload && systemctl restart tomcat'.. Systemd services can have environment variables set via the `Environment=` directive in the unit file. Adding `JAVA_HOME=/usr/lib/jvm/java-11-openjdk` to the `[Service]` section ensures the variable is available to the `ExecStart` process. Running `systemctl daemon-reload` reloads the unit definition, and `systemctl restart tomcat` applies the change. This is the proper method for configuring environment variables for systemd-managed services on RHEL 8.

Answer

Edit /opt/tomcat/bin/startup.sh and hardcode JAVA_HOME.

Answer

Run the startup script manually with 'bash /opt/tomcat/bin/startup.sh'.

Answer

Set JAVA_HOME globally using 'export JAVA_HOME=/usr/lib/jvm/java-11-openjdk' in /etc/profile.

Question 6

You are a senior Linux administrator for a large data center. A junior admin reports that a newly deployed application server (192.168.100.50/24, default gateway 192.168.100.1) cannot communicate with a legacy server (192.168.200.50/24, default gateway 192.168.200.1). The two subnets are connected via a router (192.168.100.1 and 192.168.200.1). From the app server, you can ping the legacy server's IP successfully. However, when you try to establish an SSH session from the app server to the legacy server, it times out. You check the legacy server's firewall (ufw) and find that it allows SSH (port 22) from the entire 192.168.0.0/16 range. You also confirm that the SSH daemon is running and listening on 0.0.0.0:22. What is the most likely cause?

Accepted Answer

The app server's firewall (ufw) is blocking incoming SSH responses.. The app server can ping the legacy server successfully, which confirms that ICMP traffic (Layer 3) passes through the router and that the legacy server's firewall allows ICMP. However, SSH (TCP port 22) fails because the app server's own firewall (ufw) is blocking the incoming SSH response packets (SYN-ACK) from the legacy server. Since the SSH client initiates the connection from the app server, the response packets must be allowed by the app server's firewall; if ufw on the app server blocks established or related incoming traffic, the TCP handshake cannot complete, resulting in a timeout.

Answer

The router is dropping TCP packets due to ACLs.

Answer

The legacy server's firewall is not allowing SSH; the rule might be misconfigured.

Answer

The legacy server's SSH service is not listening on the correct interface.

Question 7

A developer needs to temporarily allow incoming TCP connections on port 8080 for testing. Which iptables command adds a rule to the INPUT chain to accept this traffic?

Accepted Answer

iptables -A INPUT -p tcp --dport 8080 -j ACCEPT. The INPUT chain processes traffic destined for the local system, and the `--dport 8080` flag matches incoming TCP packets with destination port 8080. The `-j ACCEPT` target allows these packets through, which is exactly what is needed to temporarily permit incoming TCP connections on port 8080 for testing.

Answer

iptables -A OUTPUT -p tcp --sport 8080 -j ACCEPT

Answer

iptables -A FORWARD -p tcp --dport 8080 -j ACCEPT

Answer

iptables -I INPUT 1 -p tcp --dport 8080 -j DROP

Question 8

Which two commands can add an existing user to a supplementary group?

Accepted Answer

gpasswd -a. Option B, gpasswd -a, is correct because gpasswd with the -a (add) flag adds an existing user to a named supplementary group, e.g. `gpasswd -a alice developers`, modifying /etc/group without altering the user's primary group. Option E, usermod -aG, is correct because usermod with -G specifies supplementary groups and the -a (append) flag ensures the listed group is added to the user's existing supplementary group set rather than replacing it, e.g. `usermod -aG developers alice`. Option A, useradd -G, is wrong here because useradd creates new accounts and its -G flag sets supplementary groups only at account-creation time, so it cannot add an already-existing user. Option C, addgroup, is wrong because it is a Debian/Ubuntu convenience script for creating a new group (and optionally adding a user at creation), not the standard command for adding an existing user to an existing supplementary group. Option D, groupmod, is wrong because it modifies a group's attributes such as its name (-n) or GID (-g), and does not manage user membership.

Answer

useradd -G

Answer

addgroup

Answer

groupmod

Question 9

Which THREE commands can be used to view the contents of a file?

Accepted Answer

cat. The `cat` command (option C) is a standard Unix utility that reads files sequentially and outputs their contents to the standard output. It is one of the most basic and direct ways to view the entire content of a file in the terminal.

Answer

grep

Answer

find

Question 10

A system administrator needs to create a new ext4 filesystem on /dev/sdb1 with a reserved block percentage of 2% instead of the default 5%. Which command should be used?

Accepted Answer

mkfs.ext4 -m 2 /dev/sdb1. The `-m` flag in `mkfs.ext4` sets the reserved block percentage for the superuser, and specifying `-m 2` overrides the default of 5% to reserve only 2% of the blocks on the new ext4 filesystem on /dev/sdb1.

Answer

mkfs.ext4 -R 2 /dev/sdb1

Answer

mkfs.ext4 -r 2 /dev/sdb1

Answer

tune2fs -m 2 /dev/sdb1