LFCS Practice Test 29 — 15 Questions

Question 1

A system administrator wants to change the default runlevel (target) of a Linux system from graphical.target to multi-user.target. Which command should they use?

Accepted Answer

systemctl set-default multi-user.target. The default target is set by the /etc/systemd/system/default.target symlink. The systemctl set-default command manages this symlink, pointing it to the desired target. isolate switches the current runtime state but does not persist. enable is for enabling units to start automatically, not for setting the boot target. Therefore, set-default is the correct command.

Answer

systemctl default multi-user.target

Answer

systemctl isolate multi-user.target

Answer

systemctl enable multi-user.target

Question 2

A Linux server needs to resolve the hostname db.internal.example.com to an IP address. The administrator wants to query the DNS server directly without relying on the local resolver cache. Which command should be used?

Accepted Answer

dig db.internal.example.com. The dig command is the standard tool for querying DNS servers directly. It sends a DNS query and displays the response, bypassing local caching mechanisms like nscd or systemd-resolved. Other commands either rely on the system resolver, display local host information, or show configuration files without performing a lookup.

Answer

hostname -f

Answer

ping db.internal.example.com

Answer

cat /etc/resolv.conf

Question 3

A Linux administrator is creating a custom systemd timer unit named backup.timer to schedule a daily backup script. The administrator wants the timer to trigger the backup service exactly at 2:00 AM every day, regardless of when the system was last booted. Which timer directive should be used in the [Timer] section of backup.timer?

Accepted Answer

OnCalendar=*-*-* 02:00:00. To schedule a task at a specific time of day, such as 2:00 AM daily, the OnCalendar directive is used with a calendar expression. The expression *-*-* 02:00:00 matches every day at 2:00 AM. Other timer directives like OnBootSec, OnStartupSec, and OnUnitActiveSec are monotonic and relative to events like boot or last activation, so they cannot guarantee a fixed wall-clock time. Therefore, OnCalendar is the correct choice for this scenario.

Answer

OnStartupSec=2h

Answer

OnUnitActiveSec=24h

Answer

OnBootSec=2h

Question 4

A system administrator is creating a systemd service unit for a custom application. The application requires that a specific environment variable, APP_ENV=production, be set before the service starts. The administrator wants this variable to be available only to this service, not system-wide. Which directive should be used in the service unit file?

Accepted Answer

Environment=APP_ENV=production. The Environment= directive in a systemd service unit sets environment variables specifically for that service. It does not affect the system-wide environment. EnvironmentFile= requires an external file, SetEnvironment= is not a valid directive, and PassEnvironment= only forwards existing variables from the manager. Therefore, Environment= is the correct choice.

Answer

PassEnvironment=APP_ENV

Answer

EnvironmentFile=/etc/sysconfig/myapp

Answer

SetEnvironment=APP_ENV=production

Question 5

A junior administrator has installed a new 4 TB SATA disk as /dev/sdb on a RHEL 9 server and wants to use it as a single XFS filesystem mounted at /data. The disk currently has no partition table. Which command should be run first to create an XFS filesystem directly on the whole device?

Accepted Answer

mkfs.xfs /dev/sdb. Creating an XFS filesystem on a raw block device is done with mkfs.xfs followed by the device path. Because the new 4 TB disk has no partition table and the requirement is a single filesystem spanning the entire device, targeting /dev/sdb directly is correct. Partitioning is optional when the whole disk is dedicated to one filesystem.

Answer

mkfs -t xfs /dev/sdb1

Answer

xfs_growfs /dev/sdb

Answer

fdisk /dev/sdb && mkfs.xfs /dev/sdb

Question 6

A Linux server's root filesystem is filling up quickly. You suspect that a user's process is writing a large log file and that the file has been deleted, but the space is still held. Which command will show the deleted file and the process holding it open?

Accepted Answer

lsof +L1. The correct tool is lsof +L1, which specifically finds open files with a link count of zero, meaning they have been deleted but are still held open by a process. This is the standard method to identify the culprit consuming disk space invisibly to df and du.

Answer

df -h

Answer

du -sh /var/log

Answer

fuser -m /

Question 7

A Linux administrator is configuring a custom systemd service called backup.service. The service should run a backup script only when the server is connected to AC power and not running on battery. Which condition directive should be added to the [Unit] section of backup.service?

Accepted Answer

ConditionACPower=true. ConditionACPower=true is the correct directive because it directly checks whether the system is running on AC power. When the system is on battery, the condition fails, and systemd skips the unit. This prevents the backup from running and draining battery. Other conditions check file existence, kernel command line, or capabilities, none of which reliably indicate AC power status.

Answer

ConditionKernelCommandLine=ac

Answer

ConditionCapability=CAP_SYS_ADMIN

Answer

ConditionPathExists=/sys/class/power_supply/AC/online

Question 8

A Linux server has its time zone set to UTC, but the administrator wants the system clock to be synchronized by an internal NTP server at 10.0.0.10. The system uses systemd and chrony is already installed. Which command should the administrator run to configure the NTP server and make it persistent?

Accepted Answer

Edit /etc/chrony.conf to include 'server 10.0.0.10 iburst' and restart chronyd. Configuring chrony requires editing its configuration file, usually /etc/chrony.conf, to specify the NTP server, and then restarting the chronyd service to apply the changes. This makes the configuration persistent. The other options either change the time zone, use an incorrect chronyc subcommand, or attempt to use the wrong service, none of which set the NTP server as needed.

Answer

timedatectl set-timezone America/New_York

Answer

chronyc sources add 10.0.0.10

Answer

systemctl enable --now ntp.service

Question 9

A security analyst needs to search for the literal string 'error: failed to connect' in all .log files under /var/log, including subdirectories. The search should be case-insensitive and display line numbers. Which command should they use?

Accepted Answer

grep -rin "error: failed to connect" /var/log --include='*.log'. To recursively search only .log files with case-insensitivity and line numbers, use grep with -r, -i, -n, and --include. The --include='*.log' ensures only files with that extension are processed, while -r traverses subdirectories. This combination meets all stated requirements.

Answer

grep -rin "error: failed to connect" /var/log/*.log

Answer

grep -rin "error: failed to connect" /var/log --exclude='*.log'

Answer

grep -rl "error: failed to connect" /var/log

Question 10

An administrator needs to allow incoming SSH connections on port 22 from the 192.168.50.0/24 subnet while blocking all other incoming SSH traffic, without disrupting existing established connections. Which command sequence using nftables accomplishes this?

Accepted Answer

nft add rule inet filter input tcp dport 22 ip saddr 192.168.50.0/24 accept; nft add rule inet filter input tcp dport 22 drop. nftables evaluates rules in the order they appear within a chain. To allow a specific source and block the rest, the accept rule for that source must precede the drop rule for the port. Reversing the order or inverting the match conditions produces the opposite of the desired policy.

Answer

nft add rule inet filter input tcp dport 22 drop; nft add rule inet filter input tcp dport 22 ip saddr 192.168.50.0/24 accept

Answer

nft add rule inet filter input tcp dport 22 ip saddr 192.168.50.0/24 drop; nft add rule inet filter input tcp dport 22 accept

Answer

nft add rule inet filter input ip saddr 192.168.50.0/24 tcp dport 22 accept; nft add rule inet filter input tcp dport 22 reject

Question 11

An administrator is auditing a server and needs to list only the users whose primary group is 'developers'. The system has many users, and the administrator wants a precise, scriptable one-liner that parses /etc/passwd. Which command accomplishes this?

Accepted Answer

getent passwd | awk -F: '$4=="'"$(getent group developers | cut -d: -f3)"'" {print $1}'. The passwd database stores the primary group as a numeric GID in the fourth field, so the reliable approach is to resolve the group name to its GID and compare numerically. Using getent keeps the query consistent with NSS sources such as LDAP or SSSD, which plain file greps would miss.

Answer

grep developers /etc/passwd

Answer

getent passwd | awk -F: '$4=="developers" {print $1}'

Answer

getent group developers

Question 12

A Linux server running NetworkManager has a Wi-Fi interface wlp3s0 that must connect to the corporate WPA2-Enterprise network 'CorpNet' with 802.1X PEAP authentication, using identity 'jdoe' and password 'S3cr3t!'. The administrator wants to create and activate this connection entirely from the command line without editing configuration files manually. Which sequence of commands will accomplish this?

Accepted Answer

nmcli con add type wifi ifname wlp3s0 con-name CorpNet ssid CorpNet, then nmcli con modify CorpNet wifi-sec.key-mgmt wpa-eap 802-1x.eap peap 802-1x.identity jdoe 802-1x.password 'S3cr3t!', then nmcli con up CorpNet. The correct approach uses 'nmcli con add type wifi' to create a profile, then 'nmcli con modify' to set 'wifi-sec.key-mgmt wpa-eap' and the 802.1X parameters (EAP method, identity, password), and finally 'nmcli con up' to activate it. WPA2-Enterprise requires 802.1X/EAP configuration, not a pre-shared key, and the connection type must match the wireless interface for NetworkManager to manage it properly.

Answer

nmcli con add type ethernet ifname wlp3s0 con-name CorpNet, then nmcli con up CorpNet

Answer

nmcli con add type wifi ifname wlp3s0 con-name CorpNet ssid CorpNet wifi-sec.key-mgmt wpa-psk wifi-sec.psk 'S3cr3t!'

Answer

nmcli dev wifi connect CorpNet password 'S3cr3t!'

Question 13

A technician must locate every regular file beneath /var that is larger than 100 MB and was modified more than 30 days ago, then list them. Which TWO find expressions achieve this? (Choose two.)

Accepted Answer

find /var -type f -size +100M -mtime +30 -print. Two variants are correct because find's implicit print makes -print optional, and both retain the -type f, -size +100M, and -mtime +30 tests. Substituting atime measures access rather than modification, dropping the type test admits non-regular entries, and using double-dash predicates is a syntax error that prevents execution.

Answer

find /var -type f -size +100M -atime +30 -print

Answer

find /var -size +100M -mtime +30 -exec ls -l {} \;

Answer

find /var --type f --size +100M --mtime +30 -print

Question 14

A Linux server has a single network interface enp3s0 that must obtain its IPv4 address automatically from a DHCP server on the local subnet. The administrator prefers to manage this connection with NetworkManager and wants the setting to persist across reboots. Which command will configure the connection profile named 'Wired connection 1' to use DHCP?

Accepted Answer

nmcli con mod 'Wired connection 1' ipv4.method auto. NetworkManager stores connection settings in profiles, and the ipv4.method property controls how IPv4 addressing is obtained. Setting it to auto enables DHCP for that profile. Modifying the profile with nmcli con mod makes the change persistent, unlike temporary ip commands. The other options either configure static addressing, use an invalid command syntax, or only activate an existing profile without changing its addressing method.

Answer

nmcli dev connect enp3s0

Answer

ip addr add dev enp3s0 dhcp

Answer

nmcli con mod 'Wired connection 1' ipv4.method manual

Question 15

A Linux server is experiencing performance degradation. The administrator suspects that a process is consuming excessive CPU. Which two commands can be used to identify the top CPU-consuming processes in real-time? (Choose two.)

Accepted Answer

top. To identify top CPU-consuming processes, tools that show per-process CPU usage are needed. top provides a real-time, interactive view, while ps aux --sort=-%cpu gives a sorted snapshot. Both allow the administrator to see which processes are using the most CPU. vmstat and iostat show system-wide CPU statistics but not per-process details, and free is for memory. Therefore, top and ps with sorting are the correct choices.

Answer

vmstat 1

Answer

free -m

Answer

iostat -c