LPIC-1 Essential System Services and Networking — Timed 10 Questions

Question 1

A system administrator notices that the NTP service on a Linux server is not synchronizing time with external NTP servers. The administrator runs 'ntpq -p' and sees that all servers listed have a 'reach' value of 0. Which of the following is the most likely cause?

Accepted Answer

A firewall is blocking UDP port 123.. The `reach` value of 0 in `ntpq -p` output indicates that the NTP client has received no responses from any of the configured servers. Since NTP uses UDP port 123 for communication, a firewall blocking this port would prevent the client from sending or receiving NTP packets, resulting in zero reachability. This is the most common cause when all servers show a reach of 0.

Answer

The system timezone is incorrectly set.

Answer

The NTP service is configured to use the local clock.

Answer

The NTP server is using a different NTP version.

Question 2

A web server running Apache on Linux is experiencing slow response times. The administrator runs 'netstat -tuln' and sees many connections in TIME_WAIT state. Which of the following is the best course of action to improve performance?

Accepted Answer

Enable TCP keepalive and adjust kernel parameters for faster reuse.. Option C is correct because TIME_WAIT connections indicate that the server is waiting for lingering packets before fully closing TCP sockets. Enabling TCP keepalive and adjusting kernel parameters like net.ipv4.tcp_tw_reuse (or net.ipv4.tcp_tw_recycle in older kernels) allows the kernel to reuse sockets in TIME_WAIT state for new connections, reducing resource exhaustion and improving performance under high connection rates.

Answer

Increase the KeepAliveTimeout directive.

Answer

Disable the KeepAlive directive.

Answer

Increase the MaxKeepAliveRequests directive.

Question 3

Which of the following commands will display the default gateway of a Linux system?

Accepted Answer

ip route show. The `ip route show` command displays the kernel routing table, which includes the default gateway as a default route (typically `default via <gateway-IP>`). This is the standard modern tool for viewing routing information on Linux systems.

Answer

arp -a

Answer

netstat -i

Answer

ifconfig

Question 4

A database server on a Linux system is configured to listen on TCP port 3306. The administrator wants to restrict access to the database server to only the local network (192.168.1.0/24) using iptables. Which of the following iptables rules achieves this?

Accepted Answer

iptables -A INPUT -p tcp --dport 3306 -s 192.168.1.0/24 -j ACCEPT. Option C is correct because it adds an INPUT chain rule that accepts TCP traffic destined for port 3306 only when the source address is within the 192.168.1.0/24 subnet. This effectively restricts incoming database connections to the local network, while all other sources are implicitly dropped by the default INPUT policy or subsequent rules.

Answer

iptables -A INPUT -p tcp --dport 3306 -d 192.168.1.0/24 -j DROP

Answer

iptables -A OUTPUT -p tcp --dport 3306 -d 192.168.1.0/24 -j ACCEPT

Answer

iptables -A OUTPUT -p tcp --sport 3306 -s 192.168.1.0/24 -j ACCEPT

Question 5

A user reports that they cannot connect to a remote server using SSH. The administrator checks the SSH server status and it is running. Which of the following is the most likely cause?

Accepted Answer

A firewall is blocking port 22.. SSH operates over TCP port 22 by default. If the SSH server is running but the client cannot connect, a firewall blocking port 22 is the most likely cause because it would prevent the TCP handshake from completing, even though the SSH daemon (sshd) is active and listening.

Answer

The client's subnet mask is incorrect.

Answer

The client cannot resolve the server's hostname.

Answer

The SSH server is using UDP instead of TCP.

Question 6

A system administrator is configuring a Linux server to act as a router. The server has two network interfaces: eth0 (192.168.1.1/24) and eth1 (10.0.0.1/24). Which of the following commands enables IP forwarding on this server?

Accepted Answer

sysctl -w net.ipv4.ip_forward=1. Option D is correct because the `sysctl -w net.ipv4.ip_forward=1` command immediately enables IP forwarding at runtime by writing the value 1 to the kernel parameter `net.ipv4.ip_forward`. This is the standard and recommended method for enabling packet forwarding between interfaces on a Linux router, allowing traffic to be routed between the 192.168.1.0/24 and 10.0.0.0/24 networks.

Answer

route add default gw 10.0.0.1

Answer

sysctl -w net.ipv4.ip_forward=1

Answer

echo 1 > /proc/sys/net/ipv4/ip_forward

Question 7

An administrator is troubleshooting a DNS issue. The command 'dig @8.8.8.8 example.com' returns a response, but 'host example.com' returns 'Host not found'. Which of the following is the most likely cause?

Accepted Answer

The /etc/resolv.conf file is misconfigured.. The command 'dig @8.8.8.8 example.com' succeeds, proving that the DNS server at 8.8.8.8 is reachable and functional, and that network connectivity is fine. However, 'host example.com' fails because it uses the system's default resolver, which reads /etc/resolv.conf to determine which DNS server to query. If /etc/resolv.conf is misconfigured (e.g., missing or incorrect nameserver entries), the resolver cannot reach a valid DNS server, resulting in 'Host not found'.

Answer

The network interface is down.

Answer

The /etc/hosts file is corrupt.

Answer

The DNS server at 8.8.8.8 is not responding.

Question 8

Which TWO of the following are valid methods to configure network interfaces on a Linux system? (Choose two.)

Accepted Answer

Editing /etc/network/interfaces file.. Option A is correct because the `/etc/network/interfaces` file is the primary configuration file for network interfaces on Debian-based Linux distributions (e.g., Ubuntu). It allows static or dynamic (DHCP) configuration of interfaces using directives like `iface`, `address`, and `netmask`, and is read by the `ifup` and `ifdown` commands at boot or on demand.

Answer

Using the 'ifconfig' command.

Answer

Using the 'route' command.

Answer

Editing /etc/sysconfig/network-scripts/ network configuration files.

Question 9

Which THREE of the following are true regarding the use of systemd-networkd for network configuration? (Choose three.)

Accepted Answer

It can assign static IP addresses using .network files.. Option A is correct because systemd-networkd uses .network files (e.g., /etc/systemd/network/10-static.network) to assign static IP addresses via the [Address] section. This allows precise control over IPv4/IPv6 addresses, subnet masks, and gateways without relying on DHCP.

Answer

Configuration files are stored in /etc/network/.

Answer

It supports bonding of multiple interfaces.

Question 10

Refer to the exhibit. The administrator wants to ensure that SSH service starts automatically after a system reboot. Based on the output, what is the current status of this setting?

Accepted Answer

The service is enabled and will start at boot.. The `systemctl is-enabled sshd` command returns 'enabled', which means the SSH service is configured to start automatically at boot. This is confirmed by the output in the exhibit, showing that the service is enabled and will start during system initialization.

Answer

The service is disabled and will not start at boot.

Answer

The service is static and cannot be enabled.

Answer

The service is not running.