CompTIA Updated XK0-005 Exam Questions and Answers by amna

The commands that can be used together to persistently enable IPv4 forwarding in one of the Linux systems are sysctl -w net.ipv4.ip_forward=1 and sysctl –p. The first command will use sysctl to write a new value (1) to the net.ipv4.ip_forward kernel parameter, which controls whether IP forwarding is enabled or disabled for IPv4. This will enable IP forwarding immediately without rebooting. However, this change is temporary and will be lost after a reboot or a system reload. To make it permanent, we need to use the second command sysctl –p, which will load kernel parameters from /etc/sysctl.conf file. This file contains key-value pairs of kernel parameters and their values. To make sure that net.ipv4.ip_forward is set to 1 in this file, we can either edit it manually or append it using echo “net.ipv4.ip_forward=1” >> /etc/sysctl.conf.

The other options are not correct commands for persistently enabling IPv4 forwarding. The sysctl net.ipv4.ip_forward command will only display the current value of net.ipv4.ip_forward parameter, but not change it. The echo 1 > /proc/sys/net/ipv4/ip_forward command will write 1 to /proc/sys/net/ipv4/ip_forward file, which is another way to change net.ipv4.ip_forward parameter. However, this change is also temporary and will not survive a reboot or a system reload. The echo “net.ipv6.conf.all.forwarding=l” >> /etc/sysctl.conf command will append a line to /etc/sysctl.conf file that sets net.ipv6.conf.all.forwarding parameter to 1. However, this parameter controls whether IP forwarding is enabled or disabled for IPv6, not IPv4. References: sysctl(8) - Linux manual page; Configure Linux as a Router (IP Forwarding)

The issue is that the administrator did not set the default target to graphical.target. A target is a unit of systemd that groups together other units by a common purpose or state. The graphical.target is a target that starts the graphical user interface (GUI) along with other services. The administrator used the command systemct1 isolate graphical.target to switch to this target temporarily, but this does not change the default target that is activated at boot time. To make this change permanent, the administrator should have used the command systemct1 set-default graphical.target, which creates a symbolic link from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.

The other options are not correct explanations for the issue. The administrator did reboot the server properly by using systemct1 reboot, which shuts down and restarts the system cleanly. The administrator did not need to set the default target to basic.target, which is a minimal target that only starts essential services. The administrator did not shut down the server improperly, which could have caused file system corruption or data loss, but not affect the default target. References: systemct1(1) - Linux manual page; How to Change Runlevels (targets) in SystemD

The user has the wrong shell assigned to the account, which is causing the issue. The output 1 shows that the user’s shell is set to /bin/false, which is not a valid shell and will prevent the user from logging in. The output 2 shows that the user’s home directory has the correct permissions (drwxr-xr-x), and the output 3 shows that the user entered the correct password and was accepted by the SSH daemon, but the session was closed immediately due to the invalid shell. The other options are incorrect because they are not supported by the outputs. References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 13: Managing Network Services, page 413.

The command visudo -c can be used to check the validity of the sudo rules in the /etc/sudoers file. The visudo command is a tool for editing and validating the /etc/sudoers file, which defines the rules for the sudo command. The -c option checks the syntax and logic of the file and reports any errors or warnings. The command visudo -c will verify the sudo rules and help the administrator avoid any mistakes. This is the correct command to use for this task. The other options are incorrect because they either do not check the validity of the file (test, sudo, or cat) or do not exist (sudo vi check). References: CompTIA Linux+ (XK0-005) Certification Study Guide, Chapter 18: Securing Linux Systems, page 546.