702-100 Questions and Answers

The command pkg_add is used to install binary packages on OpenBSD systems. It is a utility for installing and upgrading software packages from binary files. When using pkg_add, the system will fetch and install the specified package, along with any dependencies it may have123.

References:

• OpenBSD manual pages - packages(7)
• nixCraft - OpenBSD install or add binary software package using pkg_add

A symbolic link, or symlink, is a special type of file that points to another file or directory on the file system1. When creating a symbolic link with the ln command, the syntax is as follows:

ln -s target link

where target is the file or directory to link to, and link is the name of the symbolic link2. If the link name already exists, the ln command will fail and display an error message indicating that the target already exists3. This is because the ln command does not overwrite existing files or directories by default4. Therefore, the only way to create a symbolic link with the same name as an existing file or directory is to manually remove the existing target first, and then run the ln command again. Alternatively, the ln command can be used with the -f (force) option, which will remove the existing target and create the symbolic link in one step4. However, this option is not mentioned in the question, so the correct answer is A.

References: 1: How to Create Symbolic Links in Linux [Complete Guide] - Linux Handbook 2: Ln Command in Linux (Create Symbolic Links) | Linuxize 3: How to Create and Use Symbolic Links (aka Symlinks) on Linux - How-To Geek 4: Symbolic Links in Unix/Linux - Stack Abuse

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 /etc/nsswitch.conf file defines the order of the name resolution methods used on a NetBSD system. It specifies the sources and their priority for various databases, such as hosts, services, protocols, etc. The sources can be files, DNS, NIS, or other services. For example, the following line in /etc/nsswitch.conf indicates that the hosts database should be looked up first in the /etc/hosts file, then in the DNS server, and finally in the NIS server:

hosts: files dns nis

References:

• nsswitch.conf(5) - NetBSD Manual Pages
• Chapter 23. The NetBSD Network Configuration Files

The cat command is used to concatenate and display files. The mail command is used to send and receive mail messages. The pipe symbol (I) is used to redirect the output of one command to the input of another command. Therefore, the command cat myconfigfile I mail me@mycompany.com sends the contents of the file myconfigfile by email to me@mycompany.com. The cat command reads the file and displays its contents to the standard output, which is then piped to the mail command, which reads the standard input and sends it as a mail message to the specified address. The mail command also prompts the user to enter a subject line and optionally some additional headers for the message. Alternatively, the subject line can be specified by the -s option of the mail command. For example, the command cat myconfigfile I mail -s "My config file" me@mycompany.com sends the same message with the subject “My config file”. References:

• [cat - FreeBSD], the manual page for the cat command on FreeBSD.
• [mail - FreeBSD], the manual page for the mail command on FreeBSD.
• [How to send email from the Linux command line - LinuxConfig.org], a tutorial on how to use the mail command and other email clients on Linux.

The command df -h displays the disk space usage of all mounted filesystems in a human-readable format. It shows the size, used, available, and percentage of each filesystem, as well as the mount point. This command can be used to check the local filesystems that are currently mounted.

https://unix.stackexchange.com/questions/24182/how-to-get-the-complete-and-exact-list-of-mounted-filesystems-in-linux

https://www.tecmint.com/find-mounted-file-systems-in-linux/

https://itslinuxfoss.com/check-filesystem-mounted-linux/

The file /boot/loader.conf on OpenBSD is used to specify the kernel image that the bootloader should load. This file contains various settings that can be used to control the boot process, including kernel parameters and device driver options.

References:

• boot(8) - OpenBSD manual pages

The nice command is used to run a command with a modified scheduling priority, which affects how much CPU time the command receives. The priority can be specified by the -n option, which takes an integer value between -20 and 19, where lower values indicate higher priority. By default, the nice value is incremented by 10, which means the command runs with lower priority than normal. Only the superuser can specify a negative increment, which means the command runs with higher priority than normal. For example, the command nice -n 5 date runs the date command with a priority of 5, while the command nice -n -10 ls runs the ls command with a priority of -10, but only if the user is the superuser. The nice command is useful for running CPU-intensive commands that do not need to finish quickly, or for running commands that need more CPU time than normal. References:

• nice - FreeBSD, the manual page for the nice command on FreeBSD.
• HowTo: Use ps, kill, nice, and killall To Manage processes in FreeBSD and OS X Unix Operating System - nixCraft, a tutorial on how to use the nice command and other process management commands on FreeBSD and OS X.

The command locate.updatedb updates the database used by locate to find files. The locate command searches for files by name in a pre-built database of files and directories. The database is usually updated periodically by a cron job, but the locate.updatedb command can be used to manually update it. The command may require root privileges to run, depending on the system configuration. References:

• BSD Specialist Exam 702 Objectives, Topic 715: Basic Unix Skills, 715.4 Searching and Extracting Data from Files
• FreeBSD Handbook, Chapter 7: Finding and Installing Software, 7.2.3 Using locate(1) to Find Files Quickly

The -e option of the crontab command opens the current user’s crontab in an editor. The editor used is determined by the environment variables VISUAL or EDITOR. If neither of these variables is set, the default editor is vi. The user can edit the crontab file to add, modify, or delete cron jobs, which are scheduled commands or scripts that run at a specified time or interval. The crontab file has the following format:

minute hour day-of-month month day-of-week command

Each field can be a number, a range, a list, or an asterisk (*), which means all possible values. The command can be any valid shell command or script. For example, the following crontab entry runs the backup.sh script every day at 2:30 AM:

30 2 * * * /home/user/backup.sh

To save and install the crontab file, the user needs to exit the editor. The crontab command will check the syntax of the file and report any errors. If the file is valid, it will be installed and the cron daemon will execute the cron jobs according to the schedule. References:

• crontab(1) - Linux manual page
• FreeBSD Handbook: 11.6. Scheduling Tasks

 The sysrc command is used in FreeBSD and NetBSD to manage system-wide daemon and service settings, including those that are started at boot time. It allows administrators to safely edit system rc files, such as /etc/rc.conf, where services to be started at boot time are specified1.

References:

• FreeBSD Handbook - rc.conf
• FreeBSD Man Pages - sysrc

In FreeBSD, theunamecommand is used to display system information. The option-vspecifically displays the version of the running operating system. This information is critical for system administrators and users who need to know the exact version of the OS they are working with, particularly when troubleshooting, updating, or configuring the system for specific software requirements.

https://man.freebsd.org/cgi/man.cgi?query=uname &sektion=1&format=html

The -v or --version option of the uname command displays the version level of the operating system. This is a string that identifies the release date and patch level of the system. For example, on FreeBSD, the output would be something like:

FreeBSD 13.0-RELEASE-p4 #0: Tue Aug 24 07:12:34 UTC 2021

This indicates that the system is running FreeBSD 13.0, with the fourth patch applied, and that the kernel was built on August 24, 2021. The version level can be useful to determine the compatibility and security of the system, as well as to report bugs or issues.

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