LFCS Practice Test 26 — 15 Questions

Question 1

A Linux server uses a software RAID1 array /dev/md0 assembled from /dev/sdb1 and /dev/sdc1. The administrator wants to replace the failing disk /dev/sdc with a new disk /dev/sdd without losing data or interrupting service. Which two steps are required to correctly replace the disk in the array? (Choose two.)

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Mark /dev/sdc1 as failed with mdadm /dev/md0 --fail /dev/sdc1, then remove it with mdadm /dev/md0 --remove /dev/sdc1.. To replace a disk in a RAID1 array, the failed disk must first be marked failed and removed from the array. Then the new disk, partitioned identically, is added with mdadm --add, which triggers a rebuild. These two steps maintain data integrity and restore redundancy without recreating or resizing the array.

Answer

Recreate the array with mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdd1.

Answer

Run mdadm --grow /dev/md0 --raid-devices=2 to resize the array after adding the new disk.

Answer

Use dmsetup remove /dev/md0 to detach the array, then re-add the new disk.

Question 2

An administrator is configuring a new server with two 1 TiB NVMe disks, /dev/nvme0n1 and /dev/nvme1n1, and wants to use LVM to create a single logical volume that spans both disks for a database. The volume group will be named vg_db and the logical volume lv_db. Which two commands are required to initialize the disks for LVM and create the volume group? (Choose two.)

Accepted Answer

pvcreate /dev/nvme0n1 /dev/nvme1n1. To prepare the disks and create the volume group, the administrator must first initialize the disks as physical volumes with pvcreate, then create the volume group with vgcreate, adding both physical volumes. lvcreate is a later step for creating the logical volume, mkfs.ext4 would destroy LVM metadata, and vgextend applies only to existing volume groups. The two required commands are pvcreate and vgcreate.

Answer

lvcreate -L 2T -n lv_db vg_db

Answer

mkfs.ext4 /dev/nvme0n1 /dev/nvme1n1

Answer

vgextend vg_db /dev/nvme1n1

Question 3

A storage administrator must add a persistent secondary IPv4 address 192.0.2.50/24 to interface eth1 on a RHEL 9 server using NetworkManager. The primary address is already configured. Which command adds the address so that it survives a reboot?

Accepted Answer

nmcli con mod eth1 +ipv4.addresses 192.0.2.50/24 && nmcli con up eth1. On RHEL 9, NetworkManager stores connection profiles, and nmcli con mod edits them persistently. Using the + prefix before ipv4.addresses appends the new address to the existing list, preserving the primary address. Reactivating the connection with nmcli con up applies the change immediately, and the profile ensures the secondary address returns after a reboot.

Answer

ip addr add 192.0.2.50/24 dev eth1

Answer

echo 'IPADDR1=192.0.2.50' >> /etc/sysconfig/network-scripts/ifcfg-eth1 && systemctl restart network

Answer

nmcli con mod eth1 ipv4.addresses 192.0.2.50/24 && nmcli con up eth1

Question 4

A Linux server has two interfaces, ens5 (203.0.113.10/24) and ens6 (10.20.0.0/24 gateway for internal clients). Internal clients must reach the internet through ens5. The administrator has enabled net.ipv4.ip_forward=1 and configured NAT on ens5, but clients still cannot reach external hosts. Which two additional checks are most likely to resolve the problem? (Choose two.)

Accepted Answer

Confirm that the MASQUERADE or SNAT rule matches the outbound interface and source subnet correctly.. When IP forwarding and NAT appear configured but clients still fail, the two most common culprits are a restrictive FORWARD chain that drops inter-interface traffic and a NAT rule whose interface or source match is wrong. Both must be verified because either alone prevents end-to-end connectivity for the internal subnet.

Answer

Disable the reverse path filter by setting net.ipv4.conf.all.rp_filter to 2.

Answer

Add a static route on the internal clients pointing to the public internet address 203.0.113.10 as the next hop.

Answer

Ensure that the server's default route points to the upstream router on the ens5 network.

Question 5

A system administrator needs to configure a new systemd service unit file for a custom application. The service should start after the network is fully online and requires the /opt/data directory to be mounted. Which section of the unit file should contain the After= and Requires= directives to define these dependencies?

Accepted Answer

[Unit]. Dependency and ordering directives such as After= and Requires= are placed in the [Unit] section because they describe the unit's relationships with other units and targets. The [Service] section is for execution parameters, [Install] for enabling, and [Path] for path units. Thus, [Unit] is correct.

Answer

[Path]

Answer

[Install]

Answer

[Service]

Question 6

An administrator needs to temporarily assign the IPv4 address 172.16.5.20/24 to interface ens3, which is currently up but unconfigured. The change should not persist across reboots. Which command accomplishes this?

Accepted Answer

ip addr add 172.16.5.20/24 dev ens3. Runtime address assignment on Linux is performed with the iproute2 ip addr add command, which targets a named interface and does not alter persistent configuration. NetworkManager's nmcli modifies stored profiles and persists changes, while ifconfig is legacy. The ip command is the current, supported tool for non-persistent interface changes.

Answer

nmcli con mod ens3 ipv4.addresses 172.16.5.20/24

Answer

ip link set ens3 address 172.16.5.20/24

Answer

ifconfig ens3 172.16.5.20 netmask 255.255.255.0 up

Question 7

An administrator is troubleshooting name resolution on a server. Queries for internal names succeed, but every query for external names fails with 'connection timed out; no servers could be reached'. The file /etc/resolv.conf contains 'nameserver 10.20.30.40' and 'nameserver 10.20.30.41'. The internal DNS servers are reachable, and the administrator wants to test which external name servers actually respond. Which command best performs this test?

Accepted Answer

dig @8.8.8.8 example.com. To determine whether an external resolver responds, the query must be sent directly to that resolver rather than to the servers in resolv.conf. The dig command's @server syntax does exactly this, bypassing local configuration. If a direct query to a public resolver succeeds, the problem is with the internal servers' forwarding or recursion; if it fails, outbound DNS traffic is likely blocked.

Answer

getent hosts example.com

Answer

nslookup 8.8.8.8 example.com

Answer

dig example.com

Question 8

A Linux administrator is managing a systemd service called app.service that runs a Java application. The service is configured with Restart=on-failure and RestartSec=5. After a recent update, the application crashes immediately upon start with exit code 1. The administrator notices that systemd keeps restarting the service every 5 seconds indefinitely. Which command should the administrator use to view the number of times the service has been restarted and the current restart limit status?

Accepted Answer

systemctl show app.service -p NRestarts -p StartLimitBurst -p StartLimitIntervalSec. To see the number of restarts and the restart limit configuration, systemctl show with specific properties is the correct tool. NRestarts gives the count, while StartLimitBurst and StartLimitIntervalSec define the rate limiting. Other commands provide logs or status but not these internal counters.

Answer

journalctl -u app.service -n 50

Answer

systemctl status app.service

Answer

systemctl list-units --state=failed

Question 9

A file server has an XFS filesystem on /dev/vg_data/lv_share that is nearly full. The volume group has 50 GB of free space. The administrator runs lvextend -L +20G /dev/vg_data/lv_share, which succeeds. However, df -h still reports the original size. What should the administrator do next to make the additional space usable?

Accepted Answer

Run xfs_growfs /mountpoint, where /mountpoint is the current mount point of the filesystem.. After extending an LV that hosts an XFS filesystem, the filesystem itself must be grown separately. The XFS-specific tool is xfs_growfs, which is invoked with the mount point and can be run while the filesystem is mounted. This expands the filesystem to use the additional space, after which df will show the new size.

Answer

Run partprobe /dev/vg_data/lv_share to make the kernel reread the partition table.

Answer

Run resize2fs /dev/vg_data/lv_share to expand the filesystem to the new size.

Answer

Unmount the filesystem, run lvresize --resizefs /dev/vg_data/lv_share, then remount it.

Question 10

A junior administrator is troubleshooting a server and needs to inspect the manual page for the 'ip' command, but the system is a minimal install where the man pages for that package were not installed. The administrator still wants the short one-line usage summary for 'ip' printed directly to the terminal. Which command should they run?

Accepted Answer

ip --help. The utility's own --help option is parsed by the binary itself, so it produces usage information regardless of whether any documentation packages exist on the machine. Because the scenario explicitly describes a minimal install with no man pages, the only reliable way to obtain the short usage summary is to invoke the command with its built-in help flag.

Answer

info ip

Answer

whatis ip

Answer

man ip

Question 11

A Linux administrator is troubleshooting a custom systemd service named data-sync.service that repeatedly fails with the error 'start request repeated too quickly'. The unit file has Restart=always and RestartSec=5. Which command should the administrator use to reset the failed state and clear the restart counter so the service can be started again?

Accepted Answer

systemctl reset-failed data-sync.service. When a systemd service is configured with Restart=always and crashes repeatedly, systemd enforces a start limit (default 5 starts in 10 seconds) and then refuses further starts with the error 'start request repeated too quickly'. To recover, the administrator must clear the failed state and restart counter using systemctl reset-failed, after which the service can be started normally. This command is specifically designed for this purpose and is the correct tool for the scenario.

Answer

systemctl daemon-reload

Answer

systemctl restart data-sync.service

Answer

systemctl kill data-sync.service

Question 12

An administrator needs to change the ownership of the directory /srv/www to user webadmin and group webteam, including all existing files and subdirectories. Which command accomplishes this?

Accepted Answer

chown -R webadmin:webteam /srv/www. The chown command changes file ownership, and the -R flag applies the change recursively. Specifying both user and group as webadmin:webteam in one invocation sets the owner and group for the directory and everything beneath it. This is the standard, efficient way to recursively reassign ownership for a web directory.

Answer

chmod -R webadmin:webteam /srv/www

Answer

usermod -R webadmin:webteam /srv/www

Answer

chown webadmin:webteam /srv/www

Question 13

A Linux server is configured with a custom systemd service unit for a backup script. After editing /etc/systemd/system/backup.service to add an EnvironmentFile directive, the administrator runs 'systemctl start backup' but systemctl status shows the unit still using the old environment. Which command should the administrator run to apply the unit file changes?

Accepted Answer

systemctl daemon-reload. After editing a systemd unit file, systemd continues using the previously loaded definition until it is told to reload. The daemon-reload subcommand makes systemd re-parse all unit files, applying changes such as new EnvironmentFile directives. Only then will a subsequent start or restart use the updated environment. The other subcommands act on the running service or enablement state without refreshing the unit definition.

Answer

systemctl reenable backup

Answer

systemctl restart backup

Answer

systemctl reload backup

Question 14

A Linux server has a filesystem mounted at /data that is running out of space. The administrator needs to identify which directories under /data are consuming the most disk space and then safely remove old log files. Which two commands should the administrator use? (Choose two.)

Accepted Answer

du -sh /data/*. To find which directories are using the most space, du -sh /data/* provides a per-directory summary. After identifying the culprit, find can precisely locate and delete old log files based on age, avoiding accidental removal of recent data. df only shows filesystem totals, ls -lR is too verbose, and rm -rf is destructive and indiscriminate.

Answer

df -h /data

Answer

ls -lR /data | less

Answer

rm -rf /data/*

Question 15

A junior administrator needs to mount an ISO image located at /opt/images/install.iso to the directory /mnt/iso without burning it to a physical disc. Which command should be used?

Accepted Answer

mount -o loop /opt/images/install.iso /mnt/iso. Mounting an ISO file requires the loop option so the kernel can treat the file as a block device and read its ISO9660 filesystem. The mount -o loop command is the simplest and most common way to achieve this. Alternatives like specifying only the filesystem type or using a bind mount do not correctly expose the ISO's contents.

Answer

losetup /dev/loop0 /opt/images/install.iso && mount /dev/loop0 /mnt/iso

Answer

mount --bind /opt/images/install.iso /mnt/iso

Answer

mount -t iso9660 /opt/images/install.iso /mnt/iso