702-100 Linux Professional Institute BSD Specialist Questions and Answers

The sysctl command is used to set and get kernel state variables, including the FreeBSD security level. The security level is a variable named kern.securelevel, which can have values from -1 to 3, with higher values indicating more restrictions. The security level can only be increased, not decreased, unless the system is rebooted or in single-user mode. The security level affects various operations, such as loading kernel modules, changing immutable flags on files, and modifying device nodes12 References: 1: https://docs.freebsd.org/en/books/handbook/security/#security-basics-securelevels  2: https://www.freebsd.org/cgi/man.cgi?query=sysctl &sektion=8

The command netcat is a versatile networking utility that can be used to read from and write to network connections using TCP or UDP protocols. It is often used for debugging and investigating the network and can be used to connect to a remote TCP service.

References:

• BSD Specialist Exam 702 Objectives - Linux Professional Institute
• FreeBSD Handbook - Networking

The /etc/printcap file on a BSD system defines the printers that are available by the Ipr printing system. The Ipr printing system is a BSD-compatible printing system that uses the lpd daemon to manage print jobs and spooling. The /etc/printcap file contains a series of entries, one for each printer, that specify the printer name, device, options, and filters. The format and syntax of the /etc/printcap file are described in the printcap(5) manual page. References:

• About Printing on FreeBSD | The FreeBSD Forums
• The BSD Printing Protocol (System Administration Guide, Volume 2) - Oracle
• Chapter 11. Printing | FreeBSD Documentation Portal

Permissions involve read, write, and execute roles that can be assigned to the owner, a group, or other users1.To use the chmod command, you must specify the permission you want to set and the file or directory you want to modify1.For example,chmod +rwx filenameto add permissions,chmod -rwx directorynameto remove permissions, orchmod +x filenameto allow executable permissions2.

There are two ways to specify the permissions with the chmod command: symbolic notation and numeric notation1.Symbolic notation uses letters and symbols to represent the user classes and the permissions1.Numeric notation uses octal numbers (0-7) to represent the permissions for each user class1.Each octal digit corresponds to a combination of read ®, write (w), and execute (x) permissions, as shown in the table below3:

Octal digit

Binary representation

Permissions

0

000

—

1

001

–x

2

010

-w-

3

011

-wx

4

100

r–

5

101

r-x

6

110

rw-

7

111

rwx

To use numeric notation, you need to provide three octal digits, one for each user class (owner, group, and others)1.For example,chmod 644 filenamemeans that the owner has read and write permissions (6), the group has read permissions (4), and others have read permissions (4)1.

In this question, the desired permission for the file text.txt is 750, which means that the owner has read, write, and execute permissions (7), the group has read and execute permissions (5), and others have no permissions (0)1. Therefore, the correct chmod command to change the permission of the file text.txt to 750 ischmod text.txt 750.

References:1: Chmod Command in Linux (File Permissions) | Linuxize2: How to change directory permissions in Linux | Pluralsight3: How to Use the chmod Command on Linux - How-To Geek

The tar command is used to create or extract compressed archive files on BSD systems. It can handle various compression formats, such as gzip, bzip2, xz, and lzma. The tar command takes different options to specify the compression type, such as -z for gzip, -j for bzip2, -J for xz, and -Z for lzma. The other options are not related to compression, but to other functions of the tar command, such as -x for extracting, -c for creating, and -v for verbose output. References:

• [tar(1) - OpenBSD manual pages]
• [FreeBSD Handbook - Chapter 3. Unix Basics]
• [FreeBSD Handbook - Chapter 18. Storage]

The adduser.conf file is used to store the default settings for the interactive adduser script on BSD systems. The adduser script is a shell script that uses the pw command to add new users to the system. It creates passwd/group entries, a home directory, copies dotfiles and sends the new user a welcome message. The adduser.conf file allows the administrator to pre-set certain configuration options, such as the default shell, home partition, login group, encryption method, etc. The other options are either invalid files or belong to other purposes. For example, login.conf is used to define login classes, pw.conf is used to configure the pw command, user.conf is used to set user-specific kernel variables, and usermgmt.conf is used to configure user management utilities. References:

• adduser - FreeBSD adduser(8) Manual Page1
• adduser.conf - FreeBSD adduser.conf(5) Manual Page2
• [pw] - FreeBSD pw(8) Manual Page

According to the BSD disklabel documentation1, the device name for a BSD disk slice consists of three parts: the disk name, the partition letter, and the slice number. The disk name is determined by the driver and the order of detection, and it usually follows the pattern of sdX, where X is a letter from a to z. The partition letter is a lowercase letter from a to p, excluding c, which is reserved for the whole disk. The slice number is a decimal number from 0 to 15, indicating the MBR partition that contains the BSD disklabel. Therefore, the device name for the first BSD disk slice in the disk label on the first partition on the second SATA disk on OpenBSD is /dev/sdlp2d, where sdl is the disk name, p is the partition letter, and 2 is the slice number.

References1: BSD disklabel - Wikipedia

Nmap is a program that can be used to enumerate all responsive hosts on a subnet. Nmap stands for Network Mapper, and it is a tool that can perform network discovery, port scanning, service detection, vulnerability assessment, and more. Nmap can send different types of packets to probe the hosts on a subnet and determine which ones are alive and what services they are running. Nmap can also perform OS fingerprinting, which can identify the operating system of the target hosts. Nmap has many options and features that can customize the scan according to the user’s needs and preferences. The other programs are not suitable for enumerating all responsive hosts on a subnet, because:

• A. traceroute: This program is used to trace the route of packets from the source host to the destination host. It can show the intermediate hops and the latency of each hop. However, it cannot show all the hosts on a subnet, only the ones that are on the path to the destination.
• B. netstat: This program is used to display the status of network connections, routing tables, interface statistics, and more. It can show the local and remote addresses and ports of the active connections, but it cannot show all the hosts on a subnet, only the ones that are connected to the local host.
• D. rtso1: This is not a valid program name, but it may be a typo for rtso, which is a program that can perform TCP SYN scanning. However, this program is not as versatile and powerful as nmap, and it can only scan TCP ports, not UDP or other protocols.
• E. route: This program is used to manipulate the routing table, which is used to determine the next hop for a packet based on its destination address. It can show the destination, gateway, interface, and flags of each route, but it cannot show all the hosts on a subnet, only the ones that are reachable via a specific gateway. References: 6: https://nmap.org/book/man.html 7: https://www.freebsd.org/cgi/man.cgi?query=traceroute&sektion=8 : https://www.freebsd.org/cgi/man.cgi?query=netstat&sektion=1 : https://www.freebsd.org/cgi/man.cgi?query=rtso&sektion=1 : https://www.freebsd.org/cgi/man.cgi?query=route&sektion=8

The last command displays a list of the last logged in users on a BSD system. The output consists of several columns that show the user name, the terminal name, the login date and time, and the logout date and time or the current status. The option C is the only line that matches the format of the last command output. It shows that the user root logged in on the terminal ttyv0 on Saturday, May 18, 2023 at 13:35 and is still logged in. The other options are either invalid lines or belong to othercommands or sources. For example, option A is the output of the uptime command, option B is a line from the /var/log/auth.log file, option D is a line from the ps command, and option E is the output of the uname -a command. References:

• [last] - FreeBSD last(1) Manual Page
• [How to use the last command in Linux] - Linuxize

To update FreeBSD, the freebsd-update fetch command is used to download available binary updates, and the freebsd-update install command is used to apply the downloaded updates to the system. These commands are part of the freebsd-update utility, which supports binary security and errata updates to the FreeBSD base system without the need for manual compilation and installation2.

References:

• FreeBSD Handbook - freebsd-update

The cron job syntax consists of five fields that specify the time and date of execution, followed by the command or script to run. The fields are: minute, hour, day of month, month, and day of week. Each field can have a specific value, a range, a list, a wildcard (), or a step value. The wildcard () means any possible value for that field. The option B sets the minute field to 0 and the hour field to *, which means the script will run at the 0th minute of every hour, regardless of the day, month, or weekday. This is equivalent to once per hour. The other options are either invalid syntax or do not match the desired frequency. For example, option A sets all fields to *, which means the script will run every minute of every hour of every day, month, and weekday. Option C sets the minute field to * and the hour field to 0, which means the script will run every minute of the 0th hour, or once per day at midnight. Option D has a typo (o instead of *) and option E sets the day of month field to o, which is not a valid value. References:

• crontab - FreeBSD crontab(5) Manual Page1
• Crontab Explained in Linux [With Examples] - Linux Handbook2

This command and option can be used to perform a reverse DNS lookup, which is the process of finding the domain name or hostname associated with an IP address. The dig command is a tool that can query DNS servers for various types of records, such as A, MX, NS, PTR, etc. The -x option tells dig to perform a reverse DNS lookup by sending a PTR query to the DNS server. For example, to perform a reverse DNS lookup for the IP address 8.8.8.8, the following command can be used:

dig -x 8.8.8.8

The output of this command will show the PTR record for 8.8.8.8, which is dns.google. This means that the hostname for 8.8.8.8 is dns.google. Reverse DNS lookups are useful for verifying the identity of a host, checking for mail server configuration, or troubleshooting network problems

The subnet mask 255.255.224.0 corresponds to the hexadecimal netmask 0xffffe000 shown in the output. This subnet mask indicates a subnet with 19 bits for the network portion and 13 bits for the host portion, allowing for a large number of hosts within the subnet.

References:

• BSD Specialist Exam 702 Objectives - Linux Professional Institute
• FreeBSD Handbook - Networking

The excerpt C is a valid if condition in the Bourne shell because it uses the correct syntax and operators for the test command. The syntax of the if statement in the Bourne shell is:

if test-commands; then consequent-commands; [elif more-test-commands; then more-consequents;] [else alternate-consequents;] fi

The test-commands are any commands that return a status of 0 (true) or non-zero (false). The test command is a common way to perform various tests on files, strings, and numbers. The test command has the following format:

test expression

The expression consists of one or more primaries, which are unary or binary operators that evaluate to true or false. The primaries can be combined with the following operators:

! expression: Logical NOT expression -a expression: Logical AND expression -o expression: Logical OR ( expression ): Parentheses for grouping

The excerpt C uses the test command with the following expression:

“$var” = “test”

This expression tests if the value of the variable $var is equal to the string “test”. The = operator is a string comparison operator that returns true if the strings are equal. The double quotes around the variable and the string are used to prevent word splitting and globbing by the shell. The spaces around the operator are also required by the test command.

The excerpt C also uses the correct syntax for the then and fi keywords, which mark the beginning and the end of the if statement. The then keyword must be on the same line as the test command, or on a new line after a semicolon. The fi keyword must be on a new line.

The other excerpts are invalid for various reasons:

• The excerpt A uses the && operator instead of the -a operator for logical AND. The && operator is a shell operator that executes the second command only if the first command succeeds. The test command does not recognize the && operator as a valid argument. The excerpt A also uses the != operator instead of the -ne operator for numeric comparison. The != operator is a string comparison operator that returns true if the strings are not equal. The -ne operator is a numeric comparison operator that returns true if the numbers are not equal.
• The excerpt B uses the [ [ construct instead of the test command. The [ [ construct is a shell keyword that performs conditional expressions similar to the test command, but with some extensions and differences. The [ [ construct is not part of the POSIX standard and is not supported by all shells. The Bourne shell does not support the [ [ construct, and will treat it as a command name. The excerpt B also uses the wrong syntax for the then keyword, which must be on a new line or after a semicolon.
• The excerpt D uses the wrong syntax for the test command, which requires a space after the opening bracket and before the closing bracket. The excerpt D also uses the wrong syntax for the fi keyword, which must be on a new line.

The file /etc/hostname.em0 contains the configuration for the network interface em0 on an OpenBSD system. This file specifies the IP address, netmask, gateway, and other options for the interface. The file is read by the netstart script during boot or when the interface is restarted. The file name is derived from the interface name, which is usually based on the driver name and the device number. For example, em0 is the first interface using the em driver, which supports Intel PRO/1000 network adapters.

References:

• Networking | OpenBSD Handbook
• [hostname.if(5) - OpenBSD manual pages]