The command that displays manual pages for Linux commands is the man command. The man command is used to display the manual pages for a given command or topic. For example, to view the manual page for the ls command, you can type:

man ls

This will open the manual page for the ls command in a pager, which allows you to scroll and search through the text. You can also specify the section number of the manual page if there are multiple pages with the same name. For example, to view the manual page for the passwd command in section 1, you can type:

man 1 passwd

The man command is one of the most useful and important commands for learning and using Linux. It provides detailed information about the syntax, options, arguments, examples, and other aspects of a command or topic. You can also use the --help option to get a brief summary of the usage and options of a command. For example, to get a quick help for the man command, you can type:

man --help

To learn more about the man command and how to use it effectively, you can refer to the following resources:

• Linux Essentials Exam Objectives, Version 1.6, Topic 103.1, Weight 2
• Linux Essentials Certification Guide, Chapter 3, Page 51-52
• How to Access Manual Pages for Linux Commands - Linux Tutorials - Learn Linux Configuration
• How to Easily Read a Linux Man Page - Make Tech Easier

To remove a directory, you need to use a command that can delete directories, not just files. The rm command can only remove files by default, unless you use the -r option, which stands for recursive. This option tells rm to delete the directory and all of its contents, including subdirectories and files. The rmdir command can also remove directories, but only if they are empty. If the directory contains any files or subdirectories, rmdir will fail and display an error message. Therefore, the correct commands to remove Downloads, assuming it is empty, are rmdir Downloads and rm -r Downloads. The other commands are either invalid or do not work on directories. References:

• Linux Essentials - Linux Professional Institute (LPI), section 2.3.1
• LPI Linux Essentials Study Guide: Exam 010 v1.6, 3rd Edition, chapter 4, page 93.

The files /etc/passwd and /etc/group are the source of the information in the following output:

uid=1000 (bob) gid=1000 (bob) groups=1000 (bob), 10 (wheel), 150 (docker), 1001 (libvirt) (wireshark), 989

The /etc/passwd file contains information about user accounts, such as the username, password, user ID (UID), group ID (GID), full name, home directory, and login shell1. The /etc/group file contains information about groups, such as the group name, password, group ID (GID), and members2.

The output shows the UID, GID, and group membership of the user bob. The UID and GID of bob are 1000, which can be found in the /etc/passwd file. The groups that bob belongs to are bob, wheel, docker, libvirt, wireshark, and 989, which can be found in the /etc/group file. The group names are shown in parentheses after the GID, except for the last group, which has no name.

The other options are not files that store user and group information in Linux. The /etc/id file does not exist by default. The /home/index file is not a standard file and has no relation to user and group information. The /var/db/users file is not a standard file and has no relation to user and group information. References:

• Linux Essentials Exam Objectives, Version 1.6, Topic 103.1, Weight 2
• Linux Essentials Certification Guide, Chapter 3, Page 51-52
• Linux Filesystem Hierarchy, Chapter 3, Page 17-18
• Linux Users and Groups, Chapter 2, Page 9-10

The keyword for is used in a shell script to begin a loop that iterates over a list of items or a range of numbers. The syntax of the for loop is as follows:

for in do done

The variable is assigned to each element of the in turn, and the are executed for each iteration. The can be a sequence of words, numbers, filenames, or other values. If the is omitted, the for loop will iterate over the positional parameters ($1, $2, …). The do and done keywords mark the beginning and the end of the loop body, respectively. The for loop is one of the three types of loops in shell scripting, along with the while and until loops. References: 1: Looping Statements |Shell Script - GeeksforGeeks 1 2: unix - Shell script "for" loop syntax - Stack Overflow 2 3: For Loop Shell Scripting - javatpoint 3

When a user account is deleted, the files owned by that user are not automatically deleted from the file system, unless they are in the user’s home directory. The files residing outside the home directory will remain unchanged, but they will have an invalid owner. The owner of a file is identified by a numeric user ID (UID), which is mapped to a user name by the /etc/passwd file. When a user is deleted, the corresponding entry in the /etc/passwd file is removed, but the UID of the file is not changed. Therefore, when listing the file’s details, the UID of the former owner is shown instead of the user name. For example, if the user alice with UID 1001 is deleted, and she owns a file named report.txt in the /tmp directory, the output of ls -l /tmp/report.txt will look something like this:

-rw-r–r-- 1 1001 users 1024 Nov 20 14:11 /tmp/report.txt

The user root is not set as the new owner of the file, nor is the file moved to /lost+found or removed from the file system. The /lost+found directory is used to store files that are recovered from a corrupted file system after running the fsck command, not from deleted user accounts. The file system check does not affect the ownership or permissions of the files, unless there is a serious inconsistency that needs to be fixed. References:

• Linux Essentials - Linux Professional Institute (LPI), section 5.2.1
• 5.2 Lesson 1 - Linux Professional Institute Certification Programs, slide 6.

 Ubuntu Linux LTS and Red Hat Enterprise Linux are two Linux distributions that meet the requirements of hosting services for a period of several years and receiving important security updates from their Linux distribution. LTS stands for Long Term Support, which means that these versions of Ubuntu Linux are supported by Canonical, the company behind Ubuntu, for five years with security patches, bug fixes, and software updates1. Red Hat Enterprise Linux is a commercial Linux distribution that offers a stable and secure platform for enterprise applications, with a 10-year life cycle and regular security updates from Red Hat, the company behind RHEL2. Fedora Linux, Debian GNU/Linux Unstable, and Ubuntu Linux non-LTS are not suitable for the requirements, because they have shorter support cycles and are more focused on providing the latest features and software versions, rather than stability and security. Fedora Linux releases a new version every six months and each version is supported for 13 months3. Debian GNU/Linux Unstable is the development branch of Debian, which is constantly updated with new packages and changes, but is not intended for production use4. Ubuntu Linux non-LTS releases a new version every six months and each version is supported for nine months1. References:

• Ubuntu release cycle | Ubuntu
• Red Hat Enterprise Linux Life Cycle - Red Hat Customer Portal
• Fedora Release Life Cycle - Fedora Project Wiki
• Debian Unstable - Debian Wiki

The commands man ls and info ls are used to get information on the proper use of ls. The man command displays the manual page for a given command, which contains a description, synopsis, options, examples, and other details. The info command displays the info page for a given command, which is similar to the manual page but may have more information and hyperlinks. The option ls, usage ls, and manual ls commands are not valid commands in Linux and will result in an error message. References:

• Linux Essentials Exam Objectives, Version 1.6, Topic 103.1, Weight 2
• Linux Essentials Certification Guide, Chapter 3, Page 51-52
• Ls Command in Linux (List Files and Directories) | Linuxize