LFCS Practice Test 26 — 15 Questions

Question 1

To permanently disable IPv6 on a network interface, which configuration should be added to /etc/sysctl.conf?

Accepted Answer

net.ipv6.conf.all.disable_ipv6 = 1. The sysctl parameter `net.ipv6.conf.all.disable_ipv6 = 1` is the proper kernel interface to globally disable IPv6 on all network interfaces. This setting is applied via the sysctl system, which reads `/etc/sysctl.conf` at boot to configure kernel parameters. The key must use the exact `disable_ipv6` suffix (not `disable`) and the `all` scope ensures the setting applies to every interface, including future ones.

Answer

net.ipv6.conf.all.disable=1

Answer

ipv6.disable=1

Answer

net.ipv6.conf.eth0.disable_ipv6 = 1

Question 2

You are troubleshooting a Linux server that acts as a router between two networks: 10.0.1.0/24 (eth0) and 10.0.2.0/24 (eth1). IP forwarding is enabled. Hosts on 10.0.1.0/24 can ping the server's eth0 IP (10.0.1.1), but cannot ping hosts on 10.0.2.0/24 (e.g., 10.0.2.10). The server can ping both 10.0.2.10 and 10.0.1.10. The iptables FORWARD chain policy is ACCEPT. What is the most likely cause?

Accepted Answer

The hosts on 10.0.1.0/24 do not have a route to 10.0.2.0/24. The server can ping both networks, confirming IP forwarding is enabled and iptables FORWARD chain policy is ACCEPT. Hosts on 10.0.1.0/24 can ping the server's eth0 IP but not hosts on 10.0.2.0/24, which indicates the hosts lack a route to the 10.0.2.0/24 network. Without a route, packets from 10.0.1.0/24 destined for 10.0.2.0/24 are dropped at the source host because the kernel has no next-hop information for that destination.

Answer

The server cannot reach 10.0.2.10

Answer

IP forwarding is not enabled

Answer

The iptables FORWARD chain has a DROP policy

Question 3

During boot, the system drops into a shell with message 'ERROR: No suitable file system found'. Filesystem corruption is suspected. Which sequence of actions should the admin take to attempt recovery?

Accepted Answer

Determine the root device, then run 'fsck -y /dev/sda1'.. When the system drops into an emergency shell with 'ERROR: No suitable file system found', the admin must first identify the root device (e.g., using `blkid` or `lsblk`) and then run `fsck -y /dev/sda1` to attempt automatic repair of the corrupted filesystem. The `-y` flag answers 'yes' to all prompts, which is appropriate in a recovery scenario where the goal is to get the system bootable. This approach is filesystem-agnostic and works for common Linux filesystems like ext4, XFS, or btrfs, though specific tools (e.g., `xfs_repair` for XFS) may be needed if `fsck` is not suitable.

Answer

Run xfs_repair -n /dev/sda.

Answer

Run e2fsck /dev/sda1 from the emergency shell.

Answer

Mount the root filesystem manually, then run fsck.

Question 4

Which systemd unit type is used to group services and other units together for boot execution?

Accepted Answer

target. In systemd, the 'target' unit type is designed to group services, sockets, timers, and other units into a logical synchronization point for boot execution. Targets do not execute code themselves but instead define dependencies (via Wants, Requires, and After directives) that ensure all associated units are started in the correct order to reach a desired system state, such as multi-user.target or graphical.target.

Answer

socket

Answer

timer

Answer

service

Question 5

A technician configured a new network interface eth1 on a CentOS 7 server but the interface does not obtain an IPv4 address via DHCP. Which of the following is the most likely cause?

Accepted Answer

NetworkManager is not managing the interface (NM_CONTROLLED=no). When NM_CONTROLLED=no is set in the interface configuration file (/etc/sysconfig/network-scripts/ifcfg-eth1), NetworkManager will not manage that interface. Since dhclient is typically invoked by NetworkManager (or by legacy network scripts only if NM_CONTROLLED=yes), the interface will not automatically obtain an IPv4 address via DHCP. On CentOS 7, NetworkManager is the default network service, and disabling its control prevents DHCP client activation.

Answer

The interface MTU is set too high

Answer

SELinux is blocking dhclient

Answer

Firewalld is blocking DHCP ports (67/68)

Question 6

A system administrator notices that a new 500GB SSD (/dev/sdb) is not being recognized by the system after installation. The server uses UEFI and GPT partitioning. Which command should the administrator run first to verify that the disk is detected by the kernel?

Accepted Answer

lsblk. The `lsblk` command lists all block devices recognized by the kernel, including those without a filesystem or partition table. Since the disk is new and not yet partitioned, `lsblk` will show it if the kernel has detected it, making it the correct first diagnostic step.

Answer

fdisk -l /dev/sdb

Answer

cat /proc/cpuinfo

Answer

lsusb

Question 7

A service requires read-write access to a specific directory that is mounted from an NFS share. The directory is mounted via fstab with the option 'noauto'. The service starts before the mount is available. Which configuration change should be made in the service unit file to ensure the service only starts after the mount is mounted?

Accepted Answer

Add After=mnt-nfs.mount and Requires=mnt-nfs.mount. The service requires the NFS mount to be available before it starts. The `After=mnt-nfs.mount` directive ensures the service unit is ordered after the mount unit, and `Requires=mnt-nfs.mount` makes the mount a hard dependency: if the mount fails or is not active, the service will not start. This combination is necessary because the mount is defined with `noauto` in fstab, meaning it is not automatically mounted at boot; the mount unit must be explicitly started (e.g., by a dependency or another unit) before the service.

Answer

Add Before=mnt-nfs.mount and Requires=mnt-nfs.mount

Answer

Add Wants=mnt-nfs.mount and After=mnt-nfs.mount

Answer

Add After=mnt-nfs.mount and BindsTo=mnt-nfs.mount

Question 8

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

Accepted Answer

gpasswd -a. The `gpasswd -a` command adds a user to a specified group, and `usermod -aG` appends a user to a supplementary group without removing them from other groups. Both commands modify the `/etc/group` file to include the user in the group's member list, making them correct for adding an existing user to a supplementary group.

Answer

useradd -G

Answer

addgroup

Answer

groupmod

Question 9

A user wants to view the contents of a compressed file file.txt.gz without decompressing it permanently. Which two commands can be used? (Choose two.)

Accepted Answer

gunzip -c file.txt.gz. `gunzip -c` decompresses the file to standard output, allowing the user to view the contents without modifying the original compressed file. Option B is correct because `zcat` is equivalent to `gunzip -c` and reads the compressed file directly, outputting the decompressed data to the terminal without permanent decompression.

Answer

gzip -l file.txt.gz

Answer

gzip -d file.txt.gz

Answer

gzip -k file.txt.gz

Question 10

Which TWO directives are typically used in a systemd service unit file to configure dependencies?

Accepted Answer

Wants. B is correct because the `Wants` directive in a systemd service unit file specifies a weaker dependency: the listed units are started if possible, but the current unit will still activate even if they fail. E is correct because the `Requires` directive creates a stronger dependency: the listed units must be successfully started for the current unit to start; if they fail, the current unit is deactivated. Both are fundamental for defining service dependencies in systemd.

Answer

After

Answer

Before

Answer

Alias

Question 11

Which TWO commands can display a list of active TCP connections listening on the system? (Choose two.)

Accepted Answer

ss -tuln. `ss -tuln` displays TCP (`-t`) and UDP (`-u`) sockets in a listening (`-l`) state with numeric (`-n`) addresses and ports, directly showing active TCP listening connections. Option D is correct because `netstat -tuln` performs the same function, listing TCP and UDP listening sockets with numeric output, and is the traditional tool for this purpose.

Answer

nmcli connection show

Answer

ifconfig

Answer

ip route show

Question 12

A user needs to view the contents of a compressed log file /var/log/syslog.gz without first decompressing it. Which command should they use?

Accepted Answer

zcat /var/log/syslog.gz. `zcat` is specifically designed to read the contents of gzip-compressed files without permanently decompressing them. It decompresses the data on the fly and sends the output to stdout, allowing the user to view the log file's contents directly from the terminal.

Answer

gzip -d /var/log/syslog.gz

Answer

gunzip /var/log/syslog.gz

Answer

cat /var/log/syslog.gz

Question 13

A Linux administrator is troubleshooting a service that is running as the 'nobody' user but keeps failing because it cannot write to its log file. The log file is located at /var/log/app.log. Which TWO of the following methods will allow the service to write to the log file while maintaining security best practices?

Accepted Answer

Add an ACL entry for user nobody with write permission using setfacl.. Using setfacl to add an ACL entry for the 'nobody' user grants write permission without altering the file's ownership or group, preserving the principle of least privilege. ACLs provide fine-grained access control beyond traditional Unix permissions, allowing the service to write while other users and processes retain their existing access restrictions.

Answer

Delete /var/log/app.log and restart the service.

Answer

Change the group of /var/log/app.log to nogroup and set group write permission.

Answer

Change the permissions of /var/log/app.log to 777.

Question 14

To display the first 10 lines of a file named 'log.txt', which command is correct?

Accepted Answer

head log.txt. The `head` command is designed to display the first 10 lines of a file by default. Running `head log.txt` outputs the first 10 lines of the file without any additional options, making it the correct choice for this task.

Answer

less log.txt

Answer

tail log.txt

Answer

cat log.txt

Question 15

A production web server is experiencing intermittent high load. The administrator suspects that a specific Apache module is causing memory leaks. Which approach is most effective for isolating the issue without restarting the server?

Accepted Answer

Use strace -p <PID> on the Apache process and analyze system calls for memory allocation patterns.. D is correct because strace attaches to a running Apache process and traces its system calls, including memory-related calls like mmap, brk, and malloc. By analyzing these calls over time, the administrator can identify abnormal memory allocation patterns indicative of a leak in a specific module, all without restarting the server.

Answer

Check the Apache error log for memory-related errors.

Answer

Disable all modules in httpd.conf and reload the configuration.

Answer

Use top to monitor the memory usage of httpd processes over time.