Free Practice Questions for LPI 102-500 Exam

 The export command makes the shell variable named VARIABLE visible to subshells. This means that any child process that is spawned from the current shell will inherit the value of VARIABLE. The export command does not need a dollar sign ($) before the variable name, as that would expand the variable to its value. The set command only affects the current shell and does not export the variable to subshells. The env command can be used to run a command in a modified environment, but it does not export the variable to subshells either. References:

[LPI Linux Essentials - Topic 105: Shells, Scripting and Data Management]

[LPI Linux Administrator - Exam 102 Objectives - Topic 105: Shells and Shell Scripting]

The set command is used to display or modify the shell variables and functions in the current shell. When used without any arguments, it prints the names and values of all shell variables, including environment variables and user-defined variables, in alphabetical order. The output also includes the shell options and the positional parameters. The set command can be used in any POSIX-compliant shell, such as bash, zsh, ksh, etc123.

The other options are not correct because:

env is used to print or modify the environment variables, not the shell variables. It does not show the user-defined variables or the shell options. It can also be used to run a command in a modified environment45.

env -a is an invalid option for the env command. The -a option is not supported by the env command in any standard or common implementation45.

echo $ENV is used to print the value of the environment variable ENV, not the list of all shell variables. The ENV variable is usually set to the name of a file that contains commands or aliases to be executed by the shell. It is mainly used by the ksh and some versions of bash .

References: 1: How can I list all shell variables? - Unix & Linux Stack Exchange 2: 2.1 Command Line Basics - Linux Professional Institute Certification … 3: set - The Open Group Base Specifications Issue 7, 2018 edition 4: How to set and list environment variables on Linux 5: env - The Open Group Base Specifications Issue 7, 2018 edition : What is the difference between .bash_profile and .bashrc? - Unix & Linux Stack Exchange : ENV - The Open Group Base Specifications Issue 7, 2018 edition

 The /etc/xinetd.d/ directory holds the files that configure the xinetd service when using several configuration files instead of an integrated configuration file. Each file in this directory corresponds to a specific service that is managed by xinetd, such as telnet, ftp, ssh, etc. The name of the file matches the name of the service. The files in this directory contain service-specific options that override or supplement the global options defined in the /etc/xinetd.conf file. The files are read only when the xinetd service is started, so any changes require a restart of the service. The /etc/xinetd.d/ directory allows for a modular and flexible configuration of the xinetd service, as well as easier management and maintenance of the individual service files. References:

How to configure xinetd ? - Red Hat Customer Portal

Understanding /etc/xinetd.d directory under Linux

xinetd - Wikipedia

The tcpd program is a wrapper for network services that use the TCP protocol. It intercepts incoming connection requests and checks them against the rules specified in the /etc/hosts.allow and /etc/hosts.deny files. If the connection is allowed, tcpd executes the actual service program and passes the connection to it. If the connection is denied, tcpd logs the attempt and sends an error message to the client. The tcpd program can be used to enhance the security and control of network access to various services, such as SSH, FTP, Telnet, etc.

The other programs listed are not directly related to the hosts.allow file, although they may be affected by it if they are wrapped by tcpd. The inetd and xinetd programs are super-servers that listen for incoming connections and launch the appropriate service program. The fingerd program is a service that provides information about users on a remote system. The mountd program is a service that handles NFS mount requests from clients. References:

tcpd(8) - Linux man page

Control server access using hosts.allow and hosts.deny files

hosts.allow format and example on Linux

The option in the chrony configuration file that changes the initial interval of polls to a NTP server in order to speed up the initial synchronization is iburst. The iburst option allows chronyd to send four requests to the server at intervals of 2 seconds or less, instead of the interval specified by the minpoll option, which is usually 64 seconds. This way, chronyd can make the first update of the clock shortly after start1. The iburst option is recommended for all servers, especially if the network connectivity is not reliable1.

The other options are not valid or do not have the same effect as iburst. The quickstart option does not exist in the chrony configuration file. The fast option is used to specify a fast initial correction of the system clock, but it does not change the polling interval1. The fsync option is used to enable or disable synchronization of the system clock to the real-time clock (RTC) every 11 minutes1. The flood option is used to enable a mode of operation where chronyd sends a burst of requests to the server at a high rate, which can be useful for testing or initial synchronization of a very inaccurate clock1.

References:

LPI Linux Essentials: 1.4. Using sudo

LPI Linux Administrator: 102.5. Use Debian package management

LPI Linux Engineer: 201.1. Measure and Troubleshoot Resource Usage

LPI Linux Professional Certification Program

1

SMTP stands for Simple Mail Transfer Protocol, which is a standard for sending and receiving email messages over the Internet. An open relay is a SMTP server that is configured to allow anyone on the Internet to send email through it, without verifying the identity or the origin of the sender. This can be exploited by spammers and hackers to send large volumes of unwanted or malicious email, while hiding their true identity and location. Open relays are considered a security risk and a source of spam, and are often blocked or blacklisted by other email servers. To prevent open relays, SMTP servers should be configured to only accept email from authorized users or domains, and to reject or filter email from unknown or suspicious sources. References:

Open mail relay - Wikipedia

What is Open Relay? - Definition from Techopedia

What is an open relay and how do I close one? - Validity Help Center

LPI Linux Essentials: 1.5 Security and File Permissions: 1.5.3 Network Security

LPIC-1: System Administrator: 102.5 Implement basic network security: 102.5.1 TCP Wrappers

This command will find all the files in the /usr directory that have the user ID (UID) of 0, which is the root user, and have the permission of 4000, which is the SUID bit. The SUID bit allows the file to be executed with the privileges of the file owner, regardless of who runs it. The -uid option tests for a specific UID, and the -perm option tests for a specific permission. The + sign before the permission means that at least those bits are set; the - sign means that exactly those bits are set. The other options are either invalid or do not match the criteria. References:

LPIC-1 Exam 102 Objectives, Topic 104: Devices, Linux Filesystems, Filesystem Hierarchy Standard, 104.4 Find system files and place files in the correct location, Key Knowledge Areas: Search for files by type, size, or time

find manual page, -uid and -perm options description

Find Command in Linux with Practical Examples, Example 8: Find Files with SUID and SGID Permissions

 The command nmtui is a curses application that provides easy access to the NetworkManager on the command line. It is included in the networkmanager package, along with nmcli, which is another command line interface for NetworkManager. nmtui allows the user to view, edit, activate and deactivate network connections, as well as set the system hostname. It has a simple and user-friendly interface that can be navigated with the keyboard or mouse12. References: 1: Wireless Network Manager command line ncurses GUI. 2: NetworkManager - ArchWiki.