010-160 Sample Questions Answers

The passwd command in Linux is used to change the password of a user account. A normal user can run passwd to change their own password, and a system administrator (the superuser) can use passwd to change another user’s password, or define how that account’s password can beused or changed1. The passwd command can also be used to lock or unlock a user account. Locking a user account means disabling the user’s ability to log in to the system, while unlocking a user account means restoring the user’s ability to log in. To lock a user account, the passwd command can be used with the -l option, followed by the username. To unlock a user account, the passwd command can be used with the -u option, followed by the username12. The passwd command cannot be used to change a user’s username, create a new user account, or create a new user group. These tasks require different commands, such as usermod, useradd, orgroupadd345. References: 1: Linux Passwd Command Help and Examples 2: Passwd command in Linux: 8 Practical Examples 3: usermod(8) - Linux man page 4: useradd(8) - Linux man page 5: groupadd(8) - Linux man page

The command ls …/Documents/ lists the contents of the directory /home/user/Documents/. The reason is that the argument …/Documents/ is a relative path that refers to the parent directory of the current directory, which is /home/user/, followed by the subdirectory Documents/. The ls command displays the files and directories in the specified path, or the current directory if no path is given. The command does not change the current directory, so the user remains in /home/user/Downloads/. References:

• Linux Essentials Exam Objectives, Version 1.6, Topic 103.1, Weight 2
• Linux Essentials Certification Guide, Chapter 3, Page 49-50
• Ls Command in Linux (List Files and Directories) | Linuxize

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

 A shell script is a file that contains a series of commands that can be executed by a shell interpreter. To execute a shell script, there are two main methods:

• Method 1: Specify the path to the script file. This method requires that the script file has the execute permission, which can be granted by using the chmod command. The script file also needs to have a shebang line at the beginning, which indicates which interpreter to use for the script. For example, #!/bin/bash means to use the bash interpreter. To execute the script using this method, you can type the absolute path or the relative path to the script file. If you are in the same directory as the script file, you can use the ./ prefix to indicate the current directory. For example, ./test.sh will execute the test.sh script in the current directory.
• Method 2: Pass the script file as an argument to the interpreter. This method does not require the execute permission or the shebang line for the script file. You can simply use the name of the interpreter followed by the script file name as an argument. For example, bash test.sh will execute the test.sh script using the bash interpreter.

Therefore, the correct answers are D and E. A. run test.sh is incorrect because run is not a valid command in Linux. B. ${test.sh} is incorrect because this syntax is used for variable expansion, not for executing a script. C. cmd ./test.sh is incorrect because cmd is not a valid command in Linux. References:

• Linux Essentials Topic 105: The Power of the Command Line, section 105.3: Basic shell scripting.
• How to Run a Shell Script in Linux [Essentials Explained] - It’s FOSS
• How To Execute a Command with a Shell Script in Linux | DigitalOcean
• How To Run the .sh File Shell Script In Linux / UNIX

Most commands on Linux can display information on their usage by running the command with the option -h or --help. This option shows a brief summary of the command syntax, options, arguments, and examples. For example, running ls -h or ls --help will display the usage information for the ls command, which lists files and directories. The -h or --help option is a standard convention for most Linux commands, and it is useful for learning how to use a command or checking its available options. However, some commands may not support this option, or may use a different option to display usage information. In that case, you can use the man command to access the manual page for the command, which provides more detailed information on the command usage, description, options, arguments, examples, and references. For example, running man ls will display the manual page for the ls command. The man command is one of the applications covered in the Linux Essentials certification program from the Linux Professional Institute (LPI). References:

• Linux Essentials - Linux Professional Institute (LPI)
• Linux Commands Cheat Sheet: Beginner to Advanced - GeeksforGeeks

 Web browser cookies are small pieces of data that are stored by a website on a user’s browser. They are used to remember information about the user, such as preferences, login details, shopping cart items, etc. Cookies can also be used to identify and track users across different websites, which can have implications for privacy and security. For example, cookies can be used to show targeted ads based on the user’s browsing history, or to collect personal information without the user’s consent. Cookies are not inherently dangerous, but they can pose some risks if they are misused or compromised by malicious actors. References:

• Linux Essentials - Linux Professional Institute (LPI), section 1.4.2
• 1.4 Lesson 1 - Linux Professional Institute Certification Programs, slide 18

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

 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 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

A web server is a program that listens for requests from web browsers and serves web pages, images, or other resources. Apache HTTPD and NGINX are two popular web servers that can run on Linux systems. They can handle multiple protocols, such as HTTP, HTTPS, FTP, and SMTP. Postfix, Curl, and Dovecot are not web servers, but they are related to web or network services. Postfix is a mail transfer agent (MTA) that can send and receive emails. Curl is a command-line tool that can transfer data from or to a web server. Dovecot is a mail delivery agent (MDA) that can store and retrieve emails from a local mailbox. References:

• Linux Essentials - Linux Professional Institute (LPI), section 1.2 Major Open Source Applications
• LPI Linux Essentials 010-160 - Testprep Training Tutorials, section 4.4 Your Computer on the Network

A symbolic link, also known as a symlink or soft link, is a special type of file that points to another file or directory by its name. A symbolic link can point to a file or directory on the same or different file system, as long as the target is accessible. For example, you can create a symbolic link to a file on a USB drive or a network share, as long as the device is mounted or the connection is established. However, if the target of the symbolic link is moved, renamed, or deleted, the link becomes broken and does not work. To create a symbolic link, you can use the ln command with the -s or --symbolic option, followed by the target name and the link name. For example, ln -s /mnt/usb/file.txt link.txt creates a symbolic link named link.txt that points to the file.txt on the USB drive mounted at /mnt/usb.

The other options are not true about links in a Linux file system. A symbolic link can point to a directory as well as a file. A hard link, which is a direct reference to the same data as another file, can only point to a file and not a directory. A hard link cannot span across different file systems, because it depends on the inode number, which is unique within a file system. When the target of the symbolic link is moved, the link is not automatically updated, but becomes broken. Any user can create hard links, as long as they have the permission to read and write the target file and the link directory.

References:

• Linux Essentials - Linux Professional Institute (LPI)
• Ln Command in Linux (Create Symbolic Links) | Linuxize

The useradd command in Linux is used to create new user accounts on the system1. The -m option tells the command to create the user’s home directory as /home/username and copy the files from /etc/skel directory to the user’s home directory2. The /etc/skel directory contains the default configuration files for new users3. Therefore, the command useradd -m tux will add the new user tux and create the user’s home directory with default configuration files. The other options are either invalid or do not create the user’s home directory. References:

• Linux Essentials Version 1.6 Objectives, Topic 1.4: Command Line Basics, Subtopic: Basic Shell Commands
• Linux Essentials Version 1.6 Exam Preparation Guide, Section 1.4: Command Line Basics, Page 16
• Linux useradd Command Tutorial for Beginners (15 Examples)

CentOS is a Linux distribution that is based on the source code of Red Hat Enterprise Linux (RHEL). It is a free and open-source community-supported OS that provides an enterprise-level computing platform. CentOS is fully compatible with RHEL and can run the same applications and packages. Therefore, CentOS allows the team members to apply as much of their Red Hat Enterprise Linux knowledge as possible for their hobby project. References:

• Linux Essentials Version 1.6 Objectives1, Topic 1.1: Linux Evolution and Popular Operating Systems, Subtopic: Linux Distributions
• Linux Essentials Version 1.6 Exam Preparation Guide2, Section 1.1: Linux Evolution and Popular Operating Systems, Page 7
• CentOS Website3, About CentOS Linux
• Red Hat Enterprise Linux derivatives - Wikipedia4

 The correct command to set the variable USERNAME to the value bob is USERNAME=bob. This command assigns the string bob to the variable name USERNAME, using the equal sign (=) as the assignment operator. There is no space around the equal sign, and the variable name and value are case-sensitive. This command sets a shell variable, which is only valid in the current shell session. To make the variable an environment variable, which can be inherited by child processes and subshells, you need to use the export command, such as export USERNAME=bob. The other commands are not valid for setting variables in Linux. The set command is used to set orunset shell options and positional parameters, not variables. The $ sign is used to reference the value of a variable, not to assign it. The == sign is used for comparison, not assignment. The var keyword is not used in Linux, but in some other programming languages. The <= sign is used for redirection, not assignment. References:

• Linux Essentials - Linux Professional Institute (LPI)
• How to Set and List Environment Variables in Linux | Linuxize

 Linux hardware drivers are software components that enable the Linux kernel to communicate with various devices, such as keyboards, mice, printers, scanners, network cards, etc. Drivers are either compiled into the Linux kernel or are loaded as kernel modules. Kernel modules are pieces of code that can be loaded and unloaded into the kernelon demand. They extend the functionality of the kernel without requiring to rebuild or reboot the system. Drivers that are compiled into the kernel are always available, but they increase the size and complexity of the kernel. Drivers that are loaded as kernel modules are only available when needed, but they require a matching version of the kernel and the module. Linux supports a large number of hardware devices, thanks to the efforts of the open source community and some vendors who provide drivers for their products. However, some devices may not have a driver available for Linux, or may require a proprietary driver that is not included in the Linux distribution. In such cases, the user may need to install the driver manually from the vendor’s website or from a third-party repository. References:

• Linux Essentials - Linux Professional Institute (LPI), section 2.2.1
• LPI Linux Essentials Study Guide: Exam 010 v1.6, 3rd Edition, chapter 3, page 67.

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 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.

The correct permissions for the /tmp directory are rwxrwxrwt, which means that the owner, group, and others have read, write, and execute permissions, and that the sticky bit is set. The sticky bit is a special permission that prevents users from deleting or renaming files that they do not own in a shared directory. The /tmp directory is used for storing temporary files that may be created by different users and processes, so it needs to be accessible and writable by all, but also protected from unauthorized deletion or modification of files. The rwxrwxrwt permissions can be set by using the chmod command with either the octal mode 1777 or the symbolic mode a+trwx. References: : [File system permissions] : [Sticky bit] : [chmod]