702-100 Practice Exam Questions with Answers Linux Professional Institute BSD Specialist Certification

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 find command is used to search for files and directories that match certain criteria. The - -type option specifies the type of file to look for, and the d argument means directories. The . argument means the current directory. Therefore, the command find - -type d searches for all directories within the current directory. The other options are either invalid or do not match the question. References: 1: https://www.comptia.org/training/books/a-core-1-220-1101-study-guide, page 301  2: https://www.howtogeek.com/771399/how-to-use-the-find-command-in-linux/, section “The Linux find Command”

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 -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 umask command in BSD is used to set default permissions for files or directories the user creates1. The umask value is permissions to deny, taken off whatever permissions would be given by default2. The default permission values for files are 666 (rw-rw-rw-), meaning read and write for user, group, and others3. The umask value of 022 means that the permissions to deny are 022 (—w–w-), meaning write for group and others. To calculate the default permissions for newly created files, we need to subtractthe umask value from the default permission value, using bitwise AND operation4. For example:

666 - 022 = 644 rw-rw-rw- - —w–w- = rw-r–r–

Therefore, the default permissions for newly created files with a umask of 022 are 644 (rw-r–r–), meaning read and write for user, and read for group and others.

References: 1: Umask command in Linux with examples - GeeksforGeeks 2: Different permission between directory and file with ‘umask’ - Unix & Linux Stack Exchange 3: Default File Permissions (umask) - docs.oracle.com 4: What is Umask and How to Use It {Update Default Linux File Permissions} - phoenixNAP KB

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 mailer.conf file is used to configure the mailer programs on a BSD system. It allows the system administrator to replace the default mailer programs, such as sendmail, with alternative ones, such as postfix or exim. The mailer.conf file contains a series of entries, each consisting of a label, an equal sign, and a command. The label is the name of the default mailer program, and the command is the path to the alternative mailer program that will be executed instead. For example, to replace sendmail with postfix, the mailer.conf file should contain the following entries:

sendmail /usr/local/sbin/sendmail send-mail /usr/local/sbin/sendmail mailq /usr/local/sbin/sendmail newaliases /usr/local/sbin/sendmail hoststat /usr/local/sbin/sendmail purgestat /usr/local/sbin/sendmail

The mailer.conf file is read by the mailwrapper program, which is a binary that acts as a wrapper for the mailer programs. The mailwrapper program is installed as /usr/sbin/sendmail and /usr/libexec/sendmail/sendmail, and it invokes the appropriate mailer program based on the mailer.conf file. Therefore, to replace the system MTA with another mail server program, the mailer.conf file needs to be updated with the path to the new MTA. References:

• Chapter 31. Electronic Mail | FreeBSD Documentation Portal
• DragonFlyBSD: mta

The swapctl command is used to list, add, or delete swap devices on BSD systems. It can also display the total amount of swap space available and used. The swapctl command takes various options to perform different actions, such as -l to list the swap devices, -a to add a swap device, -d to delete a swap device, and -s to show the swapsummary. The other options are not valid BSD commands for managing swap devices. References:

• swapctl(8) - OpenBSD manual pages
• FreeBSD Handbook - Chapter 19. The FreeBSD Booting Process
• FreeBSD Handbook - Chapter 9. Configuring the FreeBSD Kernel

The zpool create command is used to initialize ZFS on one or more block devices and create a storage pool. A storage pool is a collection of devices that provide physical storage and data replication for ZFS datasets. The zpool create command takes the name of the pool and the devices to be added as arguments. For example, zpool create mypool c0t0d0 c0t1d0 c0t2d0 would create a pool named mypool with three devices. The other options are either invalid or do not initialize ZFS. References: 1: https://www.comptia.org/training/books/a-core-1-220-1101-study-guide, page 302  2: https://docs.oracle.com/cd/E19253-01/819-5461/gbchx/index.html, section “Creating a ZFS Storage Pool”

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

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

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

This line stems from an ARP table because it shows the association between an IP address (192.168.122.1) and a MAC address (52:54:00: a3:4e: 0e) on a network interface (em0). ARP stands for Address Resolution Protocol, which is used to map IP addresses to MAC addresses on a local network. An ARP table is a list of these mappings that is maintained by each host on the network. The other lines are not from an ARP table, but from different sources, such as:

• B. inet 192.168.122.11 netmask 0xffffff00 broadcast 192.168.122.255: This line is from the output of the ifconfig command, which displays the configuration of network interfaces. It shows the IP address, netmask, and broadcast address of the interface.
• C. 127.0.0.1 localhost localhost.my.domain: This line is from the /etc/hosts file, which is used to map hostnames to IP addresses. It shows that the loopback address (127.0.0.1) is associated with the hostname localhost and the fully qualified domain name localhost.my.domain.
• D. tcp4 0 0 192.168.122.11.22 192.168.122.1.38058 ESTABLISHED: This line is from the output of the netstat command, which displays the status of network connections. It shows that there is an established TCP connection between the local host (192.168.122.11) on port 22 and the remote host (192.168.122.1) on port 38058.
• E. localhost link#2 UH lo0: This line is from the output of the route command, which displays the routing table. It shows that the destination localhost is reachable via the link layer interface lo0, which is the loopback interface. The UH flags indicate that the route is up and uses a host-specific gateway. References: 1: https://docs.freebsd.org/en/books/handbook/network-arp/ 2: https://www.freebsd.org/cgi/man.cgi?query=ifconfig&sektion=8 3: https://www.freebsd.org/cgi/man.cgi?query=hosts&sektion=5 4: https://www.freebsd.org/cgi/man.cgi?query=netstat&sektion=1 5: https://www.freebsd.org/cgi/man.cgi?query=route&sektion=8