010-160 Practice Questions

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’,

which points 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.

Reference:

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 chmod command is used to change the permissions of files and directories. The permissions are

represented by three sets of three characters, indicating the permissions for the owner, the group,

and the others. Each character can be either r (read), w (write), x (execute), or - (no permission). The

chmod command can use either symbolic or numeric mode to specify the permissions. In this

question, the numeric mode is used, which consists of three digits from 0 to 7. Each digit is the sum

of the permissions for each set, where r is 4, w is 2, and x is 1. For example, 7 means rwx, 6 means

rw-, and 4 means r–. Therefore, the command chmod 654 file.txt sets the permissions as follows:

The first digit 6 means rw- for the owner, which means the owner can read and write the file, but not

execute it.

The second digit 5 means r-x for the group, which means the group can read and execute the file, but

not write it.

The third digit 4 means r-- for the others, which means the others can only read the file, but not write

or execute it.

The resulting permissions are -rw-r-xr–, which is the correct answer. The other options are incorrect

because they either have the wrong permissions or the wrong file type. A regular file does not have

the d (directory) prefix, and a directory cannot have the - (no file type) prefix. Reference:

Linux Essentials Version 1.6 Objectives: 4.1. Ownership and Permissions1

Linux Essentials Version 1.6 Exam Study Resources: Linux Essentials Manual - Chapter 8. Security and

File Permissions - 8.1. Ownership and Permissions - 8.1.1. The chmod Command2

Linux Essentials Version 1.6 Exam Study Resources: Linux Essentials Manual - Appendix A. Answers to

the Exercises - Chapter 8. Security and File Permissions - 8.1. Ownership and Permissions - Exercise

8.1.12

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 first character 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. Reference:

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.

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. Reference:

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

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. Reference:

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

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. Reference: 1: Reverse DNS lookup - Wikipedia 1

The execute bit in Linux is a permission bit that allows the user to run an executable file or enter a

directory. For regular files, such as scripts or binaries, the execute bit must be set for the user to run

them. For directories, the execute bit allows the user to access the files and subdirectories inside.

Therefore, to successfully execute the script test.sh, the execute bit should be set in the file’s

permissions. This can be done by using the chmod command with the +x option, for example: chmod

+x test.sh. The other options are either irrelevant or incorrect. The file’s extension does not affect its

executability, only its association with a program. The user executing the script does not need to be

in the exec group, as long as the user has the execute permission on the file. The SetUID bit is a

special permission bit that allows the user to run the file as the file’s owner, regardless of the user’s

identity. This is not necessary for executing the script, and may pose a security risk. The #!./test.sh

syntax is invalid, as the #! is used to specify the interpreter for the script, not the script

itself. Reference:

Linux Essentials Version 1.6 Objectives1, Topic 1.4: Command Line Basics, Subtopic: Basic Shell

Commands

Linux Essentials Version 1.6 Exam Preparation Guide2, Section 1.4: Command Line Basics, Page 16

Execute vs Read bit. How do directory permissions in Linux work?3

The ls command is used to list the files and directories in a given path. By default, the ls command

displays only the file names, without any additional information. However, the ls command can also

take various options to modify its output. For example, the -l option tells ls to display the long

format, which includes the file permissions, owner, group, size, date, and name. The -h option tells ls

to display the file sizes in a human-readable format, such as KB, MB, GB, etc. The -a option tells ls to

display all files, including the hidden ones that start with a dot (.). The -n option tells ls to display the

numeric user ID and group ID instead of the user name and group name. Therefore, the only option

that does not add any additional information to the file names is the -a option. The command ls -a

will display all the file names in the current directory, including the hidden ones, but nothing

else. Reference:

Linux Essentials - Linux Professional Institute (LPI), section 2.1.1

2.1 Lesson 1 - Linux Professional Institute Certification Programs, slide 6.

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

The -R parameter of the ls command prints a recursive listing of a directory’s content, meaning that it

will list not only the files and directories in the current directory, but also the files and directories in

all the subdirectories12. For example, if you have a directory structure like this:

/home/user/ ├── dir1 │ ├── file1 │ └── file2 └── dir2 ├── file3 └── file4

You can use the command ls -R /home/user/ to list all the files and directories recursively, and the

output will look like this:

/home/user/: dir1 dir2

/home/user/dir1: file1 file2

/home/user/dir2: file3 file4

The -R parameter is also known as the --recursive option, which is the long form of the same

parameter12. You can use either -R or --recursive to achieve the same result.

Reference:

Use ls Command Recursively - Linux Handbook

How to List Files Recursively in Linux command line