LFCS Practice Test 30 — 15 Questions

Question 1

A server must resolve internal hostnames using a DNS server at 10.0.0.53 before falling back to public resolvers. The administrator edits /etc/systemd/resolved.conf and sets DNS=10.0.0.53 and FallbackDNS=8.8.8.8. After restarting systemd-resolved, queries for internal names still fail. Which additional step is most likely required?

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

Accepted Answer

Ensure /etc/resolv.conf is a symlink to /run/systemd/resolve/stub-resolv.conf or /run/systemd/resolve/resolv.conf.. systemd-resolved reads DNS server settings from resolved.conf, but applications reach it through /etc/resolv.conf. If that file is not symlinked to the stub or full resolv.conf generated by systemd-resolved, the configured servers are ignored. Recreating the symlink ensures queries go through systemd-resolved and reach 10.0.0.53.

Answer

Add the search domain to /etc/hosts so internal names resolve locally.

Answer

Run resolvectl flush-caches to clear stale entries.

Answer

Set DNSSEC=no in resolved.conf because DNSSEC validation is blocking internal responses.

Question 2

An administrator needs to view the current IPv4 addresses, link state, and interface names on a Linux server without making any changes. Which command provides this information in a single invocation?

Accepted Answer

ip addr show. The ip command from iproute2 is the current standard for network configuration and inspection. ip addr show lists every interface with its operational state, MAC address, and assigned IPv4/IPv6 addresses, which is precisely the information requested. The other commands either show unrelated data or belong to deprecated tooling.

Answer

ifconfig -a

Answer

ss -tuln

Answer

ip route show

Question 3

An administrator needs to add a 2 GB swap area that persists across reboots on a server with no free partition space, using a file at /swapfile on the root filesystem. After creating the file with fallocate and running mkswap /swapfile, which additional actions are required to activate it now and at every boot?

Accepted Answer

Run swapon /swapfile and add the line '/swapfile none swap sw 0 0' to /etc/fstab.. A swap file is activated in the running system with swapon and made persistent by adding an fstab entry whose filesystem type is swap and whose dump and pass fields are both zero. Using mount instead of swapon, inventing a mkswap activation flag, or supplying a nonzero pass field all fail to produce a correctly activated and persistent swap area.

Answer

Run swapon /swapfile and add the line '/swapfile none swap defaults,nofail 0 2' to /etc/fstab.

Answer

Run mount /swapfile and add the line '/swapfile none swap sw 0 0' to /etc/fstab.

Answer

Run mkswap --activate /swapfile and add the line '/swapfile swap swap sw 0 0' to /etc/fstab.

Question 4

An administrator is preparing a new server with two unused disks, /dev/sdb and /dev/sdc, for a software RAID 1 array that will hold customer data. Which two commands are required to create the array and make it usable? (Choose two.)

Accepted Answer

mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc. Creating a usable software RAID 1 array requires two actions: mdadm --create to build the array from the member disks, and a filesystem creation command such as mkfs.ext4 on the resulting /dev/md0 device. Assembly is only for reactivating existing arrays, and pvcreate belongs to LVM. Verification with mdadm --detail is optional.

Answer

mdadm --detail /dev/md0

Answer

pvcreate /dev/sdb /dev/sdc

Answer

mdadm --assemble /dev/md0 /dev/sdb /dev/sdc

Question 5

A junior administrator needs to add a new 2 TiB disk, /dev/sdc, to a server and create a single GPT partition that spans the entire disk. The disk currently has no partition table. Which command will create the GPT partition table and the partition in one interactive session?

Accepted Answer

gdisk /dev/sdc. To create a GPT partition table and a full-disk partition on /dev/sdc, gdisk is the dedicated interactive tool. It supports GPT natively and handles large disks. fdisk may work but is traditionally MBR-oriented, mkfs.gpt is nonexistent, and the parted command shown creates an MBR label instead of GPT. gdisk is the correct choice.

Answer

fdisk /dev/sdc

Answer

mkfs.gpt /dev/sdc

Answer

parted /dev/sdc mklabel msdos

Question 6

A Linux server's root filesystem is running out of space. The administrator needs to identify which directory under /var is consuming the most disk space. Which command should the administrator use?

Accepted Answer

du -sh /var/*. The command 'du -sh /var/*' provides a concise summary of disk usage for each top-level item in /var, making it easy to spot the largest directory. It uses the -s option to summarize and -h for human-readable output. Other commands either show filesystem-level usage, list individual files, or produce excessive output, none of which efficiently identify the largest directory under /var.

Answer

ls -lR /var | sort -k5 -n

Answer

df -h /var

Answer

find /var -type d -exec du -sh {} \;

Question 7

A junior administrator needs to mount the XFS filesystem on /dev/sdb1 at /srv/files for the current session only, without creating a persistent entry. Which command accomplishes this?

Accepted Answer

mount -t xfs /dev/sdb1 /srv/files. A one-off mount for the current session is performed with the mount command, specifying the device, the existing mount point, and optionally the filesystem type via -t. No fstab entry is created, so the mount does not survive a reboot. Formatting tools, shell redirection into fstab, and starting nonexistent systemd units do not mount a filesystem for the current session.

Answer

systemctl start srv-files.mount

Answer

mount /dev/sdb1 /srv/files >> /etc/fstab

Answer

mkfs.xfs /dev/sdb1 /srv/files

Question 8

A server's root filesystem is filling up. An administrator needs to find the largest regular files under /var, sorted from largest to smallest, while avoiding errors from unreadable directories that are not owned by the administrator. Which command is most appropriate?

Accepted Answer

find /var -type f -printf '%s %p
' 2>/dev/null | sort -rn | head -n 20. The precise approach is to use find restricted to regular files, print size and path, discard error output, then sort numerically in reverse and take the top entries. This avoids directory totals and unreadable-path noise. Recursive ls parsing is unreliable, du shows directory aggregates, and searching only directories answers a different question.

Answer

find /var -type d -exec du -sh {} + | sort -rh

Answer

du -ah /var | sort -rh | head -n 20

Answer

ls -lR /var | sort -k5 -n | tail -n 20

Question 9

A system administrator needs to ensure that the /dev/sdb1 filesystem is automatically mounted at /data with the noatime option at boot. The filesystem's UUID is known. Which entry in /etc/fstab is correct?

Accepted Answer

UUID=1234-5678 /data ext4 defaults,noatime 0 2. The correct /etc/fstab entry must use the UUID for stable identification, specify the mount point, filesystem type, include defaults and noatime in the options, and set the dump and pass fields appropriately (0 and 2 for a non-root filesystem). The entry with UUID, defaults,noatime, 0, and 2 meets all these criteria.

Answer

UUID=1234-5678 /data ext4 noatime 0 2

Answer

/dev/sdb1 /data ext4 defaults,noatime 0 1

Answer

UUID=1234-5678 /data ext4 defaults,noatime 1 2

Question 10

A junior administrator has a USB flash drive at /dev/sdb that will be used exclusively as a data disk on a Linux server. They need to create an XFS filesystem on the whole device (no partitions). Which command accomplishes this?

Accepted Answer

mkfs.xfs /dev/sdb. Creating an XFS filesystem on a whole block device is done with the mkfs.xfs command followed by the device path. XFS is commonly used for data volumes and supports being placed directly on an unpartitioned disk. The other commands either grow or repair an existing XFS filesystem and cannot initialize a new one.

Answer

xfs_growfs /dev/sdb

Answer

mkfs -t xfs -c /dev/sdb

Answer

xfs_repair /dev/sdb

Question 11

A Linux server has a single network interface ens3. You need to assign the static address 10.10.10.5/24 with gateway 10.10.10.1 using NetworkManager. The connection profile is named 'static-ens3'. Which command correctly applies the IPv4 address, disables DHCP, and sets the gateway, all in one step?

Accepted Answer

nmcli con mod static-ens3 ipv4.addresses 10.10.10.5/24 ipv4.gateway 10.10.10.1 ipv4.method manual. The correct command uses 'nmcli con mod' to modify the existing connection profile named static-ens3. It sets the IPv4 address, gateway, and changes the method to manual, which disables DHCP. This is the standard way to apply a static configuration with NetworkManager. After modification, the connection must be reactivated for the changes to take effect.

Answer

nmcli con mod static-ens3 ipv4.addresses 10.10.10.5/24 ipv4.gateway 10.10.10.1 ipv4.method auto

Answer

nmcli con up static-ens3 ipv4.addresses 10.10.10.5/24 ipv4.gateway 10.10.10.1 ipv4.method manual

Answer

nmcli con add type ethernet ifname ens3 ipv4.addresses 10.10.10.5/24 ipv4.gateway 10.10.10.1 ipv4.method manual

Question 12

A junior administrator must temporarily assign the address 172.16.5.20/24 to interface eth1 on a running server so that a migration can be tested, and the change must not survive a reboot. Which command accomplishes this?

Accepted Answer

ip addr add 172.16.5.20/24 dev eth1. Temporary address changes are made directly in the kernel with the iproute2 ip addr add command. This affects the running system only and is lost on reboot, which is exactly what the migration test requires. Persistent configuration tools such as NetworkManager profiles or network configuration files would write the change to disk and reapply it at boot.

Answer

ip link set eth1 up && ip route add 172.16.5.20/24 dev eth1

Answer

ifconfig eth1 172.16.5.20 netmask 255.255.255.0

Answer

nmcli con mod eth1 ipv4.addresses 172.16.5.20/24 && nmcli con up eth1

Question 13

A Linux server is configured as a router with IP forwarding enabled. It has two interfaces: eth0 (203.0.113.5/24) and eth1 (192.168.1.1/24). Clients on 192.168.1.0/24 need to reach the internet via eth0. The administrator has set up NAT using iptables with the rule: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE. However, clients cannot access external websites. Which two actions should the administrator take to resolve the issue? (Choose two.)

Accepted Answer

Verify that IP forwarding is enabled by checking the value of net.ipv4.ip_forward.. For a Linux router to forward traffic between interfaces, IP forwarding must be enabled, and the FORWARD chain must permit the traffic. Even with MASQUERADE configured, if either condition is not met, packets will be dropped. The administrator should verify net.ipv4.ip_forward and ensure FORWARD rules allow traffic from the internal to external interface.

Answer

Add a SNAT rule instead of MASQUERADE for better performance.

Answer

Disable the firewall on the clients to allow outbound connections.

Answer

Configure a default route on the router pointing to the ISP gateway.

Question 14

An administrator is troubleshooting a server with a software RAID 1 array on /dev/md0. One disk, /dev/sdc, has failed and been replaced. The administrator runs `mdadm /dev/md0 --add /dev/sdc1` and sees the array rebuilding, but after a reboot the new disk is no longer part of the array. Which action should the administrator take to ensure the replacement disk is automatically reassembled into the array at boot?

Accepted Answer

Run `mdadm --detail --scan >> /etc/mdadm.conf` and update the initramfs.. Software RAID arrays are reassembled at boot from configuration stored in /etc/mdadm.conf and embedded in the initramfs. After adding a replacement disk, the administrator must regenerate that configuration and rebuild the initramfs so the new member is recognized. Growing the array, adding the component to fstab, or relying on a manual assemble command does not provide persistent boot-time assembly.

Answer

Add an entry for /dev/sdc1 to /etc/fstab with the `nofail` option.

Answer

Run `mdadm --grow /dev/md0 --raid-devices=2` to force the array to accept the new disk.

Answer

Run `mdadm --assemble --scan` and rely on the kernel to remember the array across reboots.

Question 15

An administrator is troubleshooting a server where the root filesystem is on an LVM logical volume. The system fails to boot and drops to an initramfs prompt with the error 'Volume group "vg_root" not found'. The administrator verifies that the physical volumes are present and the volume group exists when booting from a rescue disk. Which action is most likely to resolve the boot issue?

Accepted Answer

Recreate the initramfs with the appropriate LVM configuration and modules included.. The error indicates that the initramfs is not activating the volume group during early boot. This usually happens when the initramfs was built without the necessary LVM modules or configuration, or after a kernel update that did not include LVM support. Rebuilding the initramfs with the correct LVM configuration ensures the volume group is found and activated, allowing the system to boot.

Answer

Edit /etc/lvm/lvm.conf to set the 'locking_type' to 0 and rebuild the initramfs.

Answer

Run vgchange -ay vg_root from the initramfs prompt and then continue booting.

Answer

Add the volume group to /etc/fstab with the 'noauto' option to prevent automatic activation.