702-100 Sample Questions Answers

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

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 groups command is used to show the current user’s group memberships on BSD systems. The command prints the names of the primary and secondary groups that the user belongs to, separated by spaces. The primary group is the one that is assigned to new files and directories created by the user. The secondary groups are the ones that grant additional permissions or access to the user. For example, the output of groups for a user named alice might look like this:

alice wheel staff

This means that alice’s primary group is alice, and her secondary groups are wheel and staff. The wheel group is typically used for granting administrative privileges, such as using the su or sudo commands. The staff group might be used for granting access to certain resources or directories that are shared by a group of users.

The other options are either invalid commands or do not show the user’s group memberships. For example, group is not a valid command, ident is used to query an ident protocol server, showuser is not a valid command, and who is used to show who is logged on the system.

References:

• groups - FreeBSD groups(1) Manual Page1
• Group Management - FreeBSD Handbook2

 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

The zfs snapshot command creates a snapshot of a ZFS dataset, which is a point-in-time copy of the data. The snapshot name is specified as follows: filesystem@snapname or volume@snapname. The snapshot name must satisfy the naming requirements in ZFS Component Naming Requirements1. In this case, the command zfs snapshot space/data@snap1 creates a snapshot of the dataset space/data named snap1. The other options are either invalid or do not create a snapshot. References: 1:https://docs.oracle.com/cd/E19253-01/819-5461/gbcya/index.html

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

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 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

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 pw utility is a command-line utility for the FreeBSD system user and group files, allowing the superuser an easy way of adding, modifying and removing users and groups. To lock a user account on a FreeBSD system, the pw lock command can be used with the username as an argument. This will prevent the user from logging in orchanging their password. To unlock a user account, the pw unlock command can be used with the username as an argument. This will restore the user’s access to the system. References:

• FreeBSD locking an account - nixCraft
• FreeBSD: How To Add, Delete Or Modify Users
• How to: FreeBSD User Administration - Atlantic.Net

The file /etc/rc.conf contains values for Management Information Bases (MIBs) which are set during system startup. This file is used to configure system-wide settings, including the enabling and disabling of services, network settings, and other startup configurations2.

References:

• FreeBSD Handbook - The FreeBSD Booting Process

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 setenv command is used to set an environment variable in the csh or tcsh shell. The syntax is setenv VAR VALUE, where VAR is the name of the variable and VALUE is the value to assign to it. The TZ variable is used to specify the timezone for the shell and its subprocesses. To set the timezone to GMT (Greenwich Mean Time), the command is setenv TZ GMT. This will affect the output of commands like date and ls that display time information. The other options are either invalid syntax or belong to other shells, such as bash or sh. References:

• setenv - Linux setenv command help and examples1
• TZ - FreeBSD Environment Variables2

The wq! command is used to save a file and quit the vi editor, even if the file is read-only. The w command means write, the q command means quit, and the ! command means force. By combining these commands, the vi editor will override the file permissions and save the changes to the file, then exit the editor. The other options are either invalid syntax or do not force the write operation. For example, wq will save and quit only if the file is writable, ql will quit without saving, and fw! will force write but not quit. References:

• [vi] - FreeBSD vi(1) Manual Page
• [wq!] - How to save a file in vi / vim editor in Linux / Unix

The command pkg upgrade is used to update FreeBSD packages to newer versions. It compares the versions of installed packages with those in the repositories and performs upgrades as necessary. The pkg update command is used to update the repository catalog, but it does not perform the actual package upgrades1.

References:

• FreeBSD Handbook - Packages and Ports