LPI 010-160 - Linux Essentials Certificate Exam - version 1.6

The last command in Linux is used to display the list of all the users logged in and out since the file /var/log/wtmp was created1. The output of the last command shows the username, the terminal, the IP address, the login time and date, and the duration of the session for each record2. The option E is the only one that matches this format. Theother options are not related to the last command. Option A shows a list of commands executed by a user. Option B shows the password change information for a user. Option C shows the last login information for a user. Option D shows the mount information for a filesystem. References:

Linux Essentials Version 1.6 Objectives3, Topic 1.4: Command Line Basics, Subtopic: Basic Shell Commands

Linux last Command Tutorial for Beginners (8 Examples)4

Linux Essentials Version 1.6 Exam Preparation Guide, Section 1.4: Command Line Basics, Page 16

The correct statement about Free Software is that it may be modified by anyone using it. This is one of the four essential freedoms of Free Software, which are: the freedom to run the program as you wish, for any purpose; the freedom to study how the program works, and change it so it does your computing as you wish; the freedom to redistribute copies so you can help your neighbor; and the freedom to distribute copies of your modified versions to others1. Access to the source code is a precondition for these freedoms1.

The other statements are false for the following reasons:

Free Software is not developed by volunteers only. It can be developed by anyone, including individuals, companies, organizations, or communities. Some Free Software developers are paid for their work, while others do it as a hobby or for social benefit1.

Free Software does not have to be available free of charge. It can be sold or given away for any price. The term “free” refers to the users’ freedom, not the price of the software1. However, Free Software users have the freedom to redistribute copies, so they can obtain the software at no charge from someone who has a copy1.

Free Software does not only run on Linux. It can run on any operating system that supports it, such as Windows, MacOS, BSD, or Android. Linux is an example of a Free Software operating system, but not the only one1.

Free Software is not only distributed as a compiled binary. It can also be distributed as source code, or both. In fact, Free Software must provide access to the source code, otherwise the users cannot study or modify the software1.

References:

What is Free Software? - GNU Project - Free Software Foundation

 The top command is a Linux command that shows the running processes on the system. It provides a dynamic real-time view of the system performance and resource usage. The top command can display various information about the processes, such as their process ID, user, priority, state, CPU and memory usage, command name, and more. The top command can also sort the processes by different criteria, such as CPU or RAM consumption, by using the interactive commands. The top command is useful for monitoring the system load and identifying the processes that are consuming the most resources. References:

Linux Essentials Topic 104: The Linux Operating System, section 104.3: Basic features and commands of the Linux standard shells.

Linux Essentials Topic 106: Security and File Permissions, section 106.4: Monitor and manage Linux processes.

The return value of a shell script after successful execution is 0. This is a convention followed by most UNIX and Linux commands, programs, and utilities. A return value of 0 indicates that the command or script completed successfully, without any errors. A return value of non-zero (1-255) indicates that the command or script failed, and the value can be interpreted as an error code. The return value of a command or script is stored in the special variable $? and can be used to test the outcome of a command or script123. For example, the following script will print a message based on the return value of the ls command:

#!/bin/bash ls if [ $? -eq 0 ]; then echo “ls command executed successfully” else echo “ls command failed” fi

References: 1: Exit and Exit Status - Linux Documentation Project 2: Linux Passwd Command Help and Examples 3: bash - Which is the best way to check return result? - Unix & Linux Stack Exchange

The /proc/ directory is a virtual file system that contains information about the system and the processes running on it. It is not a conventional file system that stores files on a disk, but rather a dynamic view of the kernel’s data structures. One of the features of the /proc/ directory is that it contains one subdirectory for each process running on the system, which is named after the process ID (PID). For example, the subdirectory /proc/1/ contains information about the process with PID 1, which is usually the init process. The process subdirectories contain various files that provide information about the process, such as its status, memory usage, open files, environment variables, command line arguments, and more. The /proc/ directory also contains a symbolic link called ‘self’, whichpoints to the process that is accessing the /proc/ file system. Therefore, the correct answer is D. One directory per running process.

The other options are incorrect because:

A. One directory per installed program. This is not true, as the /proc/ directory does not contain information about installed programs, but only about running processes. Installed programs are usually stored in other directories, such as /bin/, /usr/bin/, /opt/, etc.

B. One device file per hardware device. This is not true, as the /proc/ directory does not contain device files, but only virtual files that represent kernel data. Device files are usually stored in the /dev/ directory, which is another special file system that provides access to hardware devices.

C. One file per existing user account. This is not true, as the /proc/ directory does not contain information about user accounts, but only about processes. User accounts are usually stored in the /etc/ directory, which contains configuration files, such as /etc/passwd/ and /etc/shadow/, that define the users and their passwords.

E. One log file per running service. This is not true, as the /proc/ directory does not contain log files, but only information files. Log files are usually stored in the /var/log/ directory, which contains various files that record the activities of the system and the services.

References:

The /proc Filesystem — The Linux Kernel documentation

A Beginner’s Guide to the /proc File System in Linux - Tecmint

Appendix E. The proc File System Red Hat Enterprise Linux 6 | Red Hat …

Chapter 5. The proc File System Red Hat Enterprise Linux 4 | Red Hat …

proc file system in Linux - GeeksforGeeks

The backslash character () is used to escape the meaning of the next character in a command line. This means that the next character is treated as a literal character, not as a special character. For example, if you want to use a space in a file name, you can use a backslash before the space to prevent the shell from interpreting it as a separator. Similarly, if you want to split a long command line across multiple lines, you can use a backslash at the end of each line to tell the shell that the command is not finished yet. The shell will ignore the newline character and continue reading the next line as part of the same command. For example, you can write:

ls -l/home/user/Documents

instead of:

ls -l /home/user/Documents

Both commands will produce the same output, but the first one is easier to read and type. References:

Linux Essentials - Linux Professional Institute (LPI), section 2.1.2

2.1 Command Line Basics - Linux Professional Institute Certification Programs, slide 7.

Linux passwords are not stored in plain text, but in a scrambled or encrypted form known as a hash. A hash is a one-way function that transforms a string of characters into a fixed-length value. The same input always produces the same hash, but it is impossible to reverse the process and recover the original input from the hash. This way, the system can verify the user’s password without exposing it to anyone who can read the file where the hashes are stored. The file that contains the password hashes is /etc/shadow, which is only readable by the root user or members of the shadow group. The passwd utility is used to change the user’s password, which updates the hash in the /etc/shadow file. References: Linux Essentials 1.6 Topic 105: Security and File Permissions, How to Change Account Passwords on Linux, Where is my password stored on Linux?

 Reverse DNS lookups query DNS servers for a PTR (pointer) record; if the server does not have a PTR record, it cannot resolve a reverse lookup. PTR records store IP addresses with their segments reversed, and they append “.in-addr.arpa” to that. For example, if a domain has an IP address of 192.0.2.1, the PTR record will store the domain’s information under 1.2.0.192.in-addr.arpa. In IPv6, the latest version of the Internet Protocol, PTR records are stored within the “.ip6.arpa” domain instead of ".in-addr.arpa."1 Therefore, the name of the IP address 198.51.100.165 is stored in the PTR record for 165.100.51.198.in-addr.arpa. References: 1: Reverse DNS lookup - Wikipedia 1

The sort command is used to sort the lines of a file or a stream of input according to a specified criterion, such as alphabetical order, numerical order, reverse order, etc. By default, the sort command sorts the lines in ascending alphabetical order, using the firstcharacter of each line as the key. For example, the command sort data.csv will sort the lines of the file data.csv in alphabetical order and display the output on the screen. If you want to save the sorted output to a new file, you can use the redirection operator (>) to specify the output file name. For example, the command sort data.csv > sorted_data.csv will sort the lines of the file data.csv in alphabetical order and save the output to a new file named sorted_data.csv. The other commands are either invalid or do not perform the sorting operation. The a…z command does not exist, the abc command is a text editor, the wc command counts the number of words, lines, and bytes in a file, and the grep command searches for a pattern in a file or a stream of input. Therefore, the correct answer is B. References:

Linux Essentials - Linux Professional Institute (LPI), section 2.3.2

LPI Linux Essentials Study Guide: Exam 010 v1.6, 3rd Edition, chapter 4, page 95.

 The reason why the script.sh does not display the content of the variable MYVAR is that the variable is not exported to the environment of the script. When a script is executed, it runs in a separate process that inherits the environment variables from the parent process, but not the shell variables. A shell variable is a variable that is defined and visible only in the current shell session, while an environment variable is a variable that is exported to the environment and visible to all processes that run in that environment1.

To make a shell variable an environment variable, we need to use the export command. The export command takes a shell variable name and adds it to the environment of the current shell and any subshells or processes that are created from it2. For example, to export the variable MYVAR with the value value, we can use:

export MYVAR=value

This will make the variable MYVAR available to the script.sh when it is executed, and the script will print the value of MYVAR as expected. Alternatively, we can also use the export command with the -n option to remove a variable from the environment, or with the -p option to list all the environment variables2.

The other options are not valid ways to set MYVAR as an environment variable. The !MYVAR=value option is not a valid syntax for setting a variable in bash. The env MYVAR=value option will run the env command with the MYVAR=value argument, which will print the environment variables with the addition of MYVAR=value, but it will not affect the current shell or the script.sh3. The MYVAR=value option will set MYVAR as a shell variable, but not as an environment variable, so it will not be visible to the script.sh1. The $MYVAR=value option will try to set the variable whose name is the value of MYVAR to the value value, which is not what we want4. References:

Linux Essentials Exam Objectives, Version 1.6, Topic 103.1, Weight 2

Linux Essentials Certification Guide, Chapter 3, Page 51-52

env(1) - Linux manual page

Bash Variables - LinuxConfig.org