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質問 # 137
With IPv6, how many bits have been used for the interface identifier of an unicast address? (Specify the number using digits only.)
正解：
解説：
64
Explanation:
With IPv6, the interface identifier of an unicast address is typically a 64-bit value that is used to identify a host's network interface. The interface identifier can be derived from the MAC address of the network card, or it can be randomly generated or manually configured. The interface identifier is the rightmost 64 bits of the most commonly encountered address types, such as global unicast (2000::/3) and link-local (fe80::/10). The interface identifier is different from the network prefix, which is the leftmost bits of the address that indicate the network or subnet to which the host belongs. The network prefix can vary in length, depending on the address type and the subnetting scheme. The network prefix and the interface identifier are separated by a double colon (::) in the IPv6 address notation. For example, in the address
2001:db8:1234:5678:abcd:ef12:3456:7890, the network prefix is 2001:db8:1234:5678 and the interface identifier is abcd:ef12:3456:7890. References:https://study-ccna.com/ipv6-interface-identifier/
https://networklessons.com/ipv6/ipv6-eui-64-explained
質問 # 138
What information is shown by the echo $? command?
- A. The process ID of the current shell.
- B. The process ID which will be used for the next command.
- C. The exit value of the command executed immediately before echo.
- D. The exit value of the echo command.
- E. The process ID of the echo command.
正解：C
質問 # 139
What is the lowest numbered unprivileged TCP port? (Specify the number in digits only.)
正解：
解説：
1024
Explanation:
The lowest numbered unprivileged TCP port is 1024. A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535. The port numbers in the range from 0 to 1023 are the well-known ports or system ports. They are used by system processes that provide widely used types of network services. On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the well-known ports. Therefore, the lowest numbered port that can be used by a normal user without root access is 1024, which is the first unprivileged port123 Reference:
1: How to bind to port number less than 1024 with non root access?
2: lowest numbered unprivileged TCP port - Bing
3: List of TCP and UDP port numbers - Wikipedia
4: Privileged Ports - World Wide Web Consortium (W3C)
5: What is the lowest TCP port number? - TeachersCollegesj
質問 # 140
What of the following can be done by the command ifconfig? (Choose TWO correct answers.)
- A. Set a network interface active or inactive.
- B. Specify the kernel module to be used with a network interface.
- C. Allow regular users to change the network configuration of a network interface.
- D. Change the netmask used on a network interface.
- E. Specify which network services are available on a network interface.
正解：A、D
解説：
The command ifconfig can be used to set a network interface active or inactive by using the up or down options. For example, the following command will activate the eth0 interface:
sudo ifconfig eth0 up
The command ifconfig can also be used to change the netmask used on a network interface by specifying the netmask option followed by the desired netmask value. For example, the following command will change the netmask of the eth0 interface to 255.255.255.0:
sudo ifconfig eth0 netmask 255.255.255.0
The other options in the question are not possible with the ifconfig command. The command ifconfig cannot specify the kernel module to be used with a network interface. This is done by the modprobe command or the /etc/modules file. The command ifconfig cannot allow regular users to change the network configuration of a network interface. This is controlled by the sudoers file or the polkit framework. The command ifconfig cannot specify which network services are available on a network interface. This is done by the firewall rules or the /etc/services file. Reference:
[LPI Linux Administrator - Exam 102 Objectives - Topic 109: Networking Fundamentals] Linux ifconfig Command | Linuxize
15 Useful "ifconfig" Commands to Configure Network in Linux - Tecmint
ifconfig command in Linux with Examples - GeeksforGeeks
質問 # 141
Why is the correct configuration of a system's time zone important?
- A. Because NTP chooses servers nearby based on the configured time zone.
- B. Because the conversion of Unix timestamps to local time relies on the time zone configuration.
- C. Because the environment variables LANG and LC_MESSAGES are, by default, set according to the time zone.
- D. Because the time zone is saved as part of the modification times of files and cannot be changed after a file is created.
正解：B
解説：
The correct configuration of a system's time zone is important because it affects how the system displays and interprets the local time from the Unix timestamps. A Unix timestamp is a number that represents the number of seconds that have elapsed since January 1, 1970 (UTC)1. Unix timestamps are independent of time zones and are the same for all systems1. However, when a system needs to display or interpret the local time from a Unix timestamp, it needs to know the offset from UTC, which is determined by the time zone configuration23. If the time zone configuration is incorrect, the system may display or interpret the local time incorrectly, which can cause problems with scheduling tasks, logs, and other applications45.
For example, suppose a system has a Unix timestamp of 1638374400, which corresponds to December 1,
2021, 12:00:00 UTC6. If the system's time zone is configured correctly as UTC, it will display the local time as December 1, 2021, 12:00:00. However, if the system's time zone is configured incorrectly as EST (Eastern Standard Time), which is 5 hours behind UTC, it will display the local time as December 1, 2021, 07:00:00, which is 5 hours earlier than the actual local time6. This can lead to confusion and errors for the system and the user.
Therefore, the correct answer is A. Because the conversion of Unix timestamps to local time relies on the time zone configuration.
References: 1: Unix time - Wikipedia 2: How to Set or Change the Time Zone in Linux - TecAdmin 3: Set the date, time, and timezone on a Linux server 4: Configure the time zone (TZ) on Linux systems - Linux Audit 5: Setting the timezone under Linux - Learn Linux Configuration 6: Epoch Converter - Unix Timestamp Converter
質問 # 142
The X11 configuration file xorg.conf is grouped into sections. How is the content of the section SectionName associated with that section?
- A. It is placed between the tags <Section name="SectionName"> and </Section>
- B. It is placed in curly brackets as in Section SectionName { ... }.
- C. It is placed after an initial unindented Section "SectionName" and must be indented by exactly one tab character.
- D. It is placed after the row [SectionName].
- E. It is placed between a line containing Section "SectionName" and a line containing EndSection.
正解：E
質問 # 143
Of the ways listed, which is the best way to temporarily suspend a single user's ability to interactively login?
- A. Change the user name in /etc/passwd.
- B. Use change to expire the user account.
- C. Place the command logout in the user's profile.
- D. Add the user name to /etc/nologin.
- E. Change the user's password.
正解：B
解説：
The best way to temporarily suspend a single user's ability to interactively login is to use the chage command to expire the user account. The chage command can modify the expiration date of a user account, which is stored in the /etc/shadow file. By setting the expiration date to a past date, the user account will be locked and the user will not be able to login. This method is temporary because the expiration date can be changed again to a future date or removed to unlock the user account. For example, to expire the user account linuxconfig, we can use the following command:
# chage -E 0 linuxconfig
This will set the expiration date to January 1, 1970, which is the epoch date. To check the expiration date of a user account, we can use the -l option:
# chage -l linuxconfig
Last password change : Aug 24, 2021
Password expires : never
Password inactive : never
Account expires : Jan 01, 1970
Minimum number of days between password change : 0
Maximum number of days between password change : 99999
Number of days of warning before password expires : 7
To remove the expiration date of a user account, we can use the -E option with an empty argument:
# chage -E "" linuxconfig
The other options are either invalid or not recommended. Adding the user name to /etc/nologin will not work, because /etc/nologin is a file that contains a message to be displayed to users who try to login when the system is down for maintenance. Changing the user's password is not a good idea, because it will affect the user's authentication and may cause security issues. Changing the user name in /etc/passwd will also affect the user's authentication and may cause inconsistencies with other files and services. Placing the command logout in the user's profile will not prevent the user from logging in, but only log them out immediately after login, which is not very elegant or secure. Reference: 1: How to disable user login with Linux nologin - LinuxConfig.org 2: Disable a user's login without disabling the account - Unix & Linux Stack Exchange 3: How to Block or Disable Normal User Logins in Linux? - GeeksforGeeks 4: How to Disable User Logins on Linux | Baeldung on Linux 5: How to Disable a User in Linux - Linux Nightly 6: How to deactivate or disable a user account in Ubuntu 20.04 LTS - Vitux 7: chage(1) - Linux manual page
質問 # 144
What is true regarding a default route?
- A. When a default route is set, all other routes are disabled until the default route is deleted.
- B. The default route is only used if there is not a more specific route to a destination host or network.
- C. The default route is always used first. When the default route is not available more specific routes are tried.
- D. Without a default route, no network communication even in directly attached networks is possible.
正解：B
解説：
A default route is a special type of route that specifies where to send packets when there is no explicit route for the destination in the routing table. A default route is usually configured on a router or a gateway that connects to another network, such as the internet. A default route is often represented by the destination 0.0.0.0/0, which means any IP address.
A default route is not always used first. It is only used as a last resort, when there is no more specific route for the destination. For example, if a host wants to send a packet to 192.168.1.10, and the routing table contains the following entries:
Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0 The host will use the first entry, which is more specific, and send the packet directly to 192.168.1.10 via eth0 interface. The second entry, which is the default route, will not be used in this case. However, if the host wants to send a packet to 8.8.8.8, which is not in the same network, the host will use the default route and send the packet to 192.168.1.1, which is the gateway to the internet.
Setting a default route does not disable other routes. It only adds an entry to the routing table that can be used when no other route matches the destination. Other routes are still valid and can be used if they are more specific.
Without a default route, network communication in directly attached networks is still possible, as long as there are routes for those networks in the routing table. However, network communication to other networks that are not directly connected will not be possible, unless there are specific routes for those networks in the routing table.
Reference:
How to Set the Default Gateway in Linux - How-To Geek
Linux setup default gateway with route command - nixCraft
How to set a default route permanently in Linux - Xmodulo
質問 # 145
Where is the system journal stored?
- A. /proc/log and /proc/klog
- B. /var/ jlog/ and /var/jlogd/
- C. /var/log/syslog.bin or /var/log/syslog-jrn
- D. /etc/system/journal / or /usr/1ib/sysLend/journal/
- E. /run/Iog/journal/or/var/log/journal/
正解：E
質問 # 146
Which of the following files is not read directly by a Bash login shell?
- A. -/.bash_profile
- B. -/.bash_login
- C. -/.bashrc
- D. /etc/profile
- E. -/.profile
正解：C
質問 # 147
Which mechanism does ssh use to interact with the SSH agent?
- A. Using the fixed socket .ssh-agent/ipc.
- B. Creating an alias replacing ssh with calls to ssh-agent.
- C. Starting ssh-agent as a child process for each ssh invocation.
- D. Connecting to port 2222 which is used by the system-wide SSH agent.
- E. Evaluating environment variables such as SSH_AUTH_SOCK.
正解：E
質問 # 148
Which of the following are requirements in order to run a shell script like a regular command from anywhere in the filesystem? (Choose THREE correct answers.)
- A. The script file must be found in the $PATH.
- B. The script must begin with a shebang-line (#!) that points to the correct interpreter.
- C. The user issuing the command must be in the group script.
- D. The file system on which the script resides must be mounted with the option scripts.
- E. The script file must have the executable permission bit set.
正解：A、B、E
解説：
In order to run a shell script like a regular command from anywhere in the filesystem, the following requirements must be met:
The script file must be found in the $PATH. The $PATH is a variable that contains a list of directories where the shell looks for executable files when a command is issued. If the script file is not in one of these directories, the shell will not be able to find it unless the full path is specified.
The script file must have the executable permission bit set. This is a file attribute that determines whether the file can be executed by the user, the group, or others. The executable permission bit can be set using the chmod command, for example: chmod +x script.sh.
The script must begin with a shebang-line (#!) that points to the correct interpreter. This is a special line at the beginning of the script that tells the shell which program to use to run the script, such as #!/bin/bash for bash scripts, or #!/usr/bin/perl for perl scripts. The shebang-line must match the exact path of the interpreter, otherwise the script will not run.
The other options are not requirements for running a shell script like a regular command. There is no such group as script, and the file system mount option scripts does not exist. Reference:
[LPI Linux Essentials - Topic 105: Shells, Scripting and Data Management]
[LPI Linux Professional - Exam 102 Objectives - Topic 105: Shells and Shell Scripting]
質問 # 149
Which of the following commands shows the current color depth of the X Server?
- A. xcolordepth
- B. cat /etc/X11
- C. xcdepth
- D. xwininfo
- E. xcd
正解：D
解説：
The command that can be used to show the current color depth of the X Server is xwininfo. xwininfo is a command-line tool that provides information about X windows. When executed, it opens a small window and waits for the user to select a window by clicking on it. Then, it displays various characteristics about the window in question, such as its geometry, position, size, depth, class, name, id, and more. The depth value indicates the number of bits per pixel used to represent the colors of the window. xwininfo is part of the X Window System, which is a graphical user interface system for Unix-like operating systems. xwininfo can be useful for debugging, testing, or scripting purposes.
The other options are incorrect because they are either invalid commands or do not show the color depth of the X Server:
* xcd is not a valid command in Linux. It may be confused with cd, which is used to change the current working directory.
* xcdepth is not a valid command in Linux. It may be confused with xrandr, which is used to change the screen resolution and orientation.
* xcolordepth is not a valid command in Linux. It may be confused with xcalib, which is used to load, alter, and query the color profile of the X display.
* cat /etc/X11 is not a command, but a directory. cat is used to concatenate files and print them to the standard output. /etc/X11 is a directory that contains configuration files for the X Window System.
However, these files do not necessarily show the current color depth of the X Server, as it may be overridden by other settings or options. References:
https://bing.com/search?q=command+to+show+color+depth+of+X+Server
https://x.org/releases/X11R7.5/doc/man/man5/xorg.conf.5.html
質問 # 150
Which of the following features are provided by SPICE? (Choose two.)
- A. Replacing Xorg as local X11 server.
- B. Accessing graphical applications on a remote host.
- C. Connecting local USB devices to remote applications.
- D. Downloading and locally installing applications from a remote machine.
- E. Uploading and running a binary program on a remote machine.
正解：B、C
解説：
SPICE is a protocol that allows users to access graphical applications on a remote host, such as a virtual machine or a server, using a client program. SPICE also supports connecting local USB devices to remote applications, such as printers, scanners, or flash drives, using a feature called USB redirection. SPICE does not replace Xorg as the local X11 server, nor does it allow downloading and locally installing applications or uploading and running binary programs from a remote machine. These are features that are provided by other tools, such as SSH, SCP, or RDP. References:
* Features - spice-space.org
* SPICE - Wikipedia
* SPICE ModelWhat is SPICE?| Electronics Basics | ROHM
質問 # 151
Which command makes the shell variable named VARIABLE visible to subshells?
- A. env VARIABLE
- B. export $VARIABLE
- C. export VARIABLE
- D. set $VARIABLE
- E. set VARIABLE
正解：C
解説：
The export command makes the shell variable named VARIABLE visible to subshells. This means that any child process that is spawned from the current shell will inherit the value of VARIABLE. The export command does not need a dollar sign ($) 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. Reference:
[LPI Linux Essentials - Topic 105: Shells, Scripting and Data Management]
[LPI Linux Administrator - Exam 102 Objectives - Topic 105: Shells and Shell Scripting]
質問 # 152
Which of the following lines are valid in the file /etc/hosts? (Choose TWO correct answers.)
- A. www.example.com www 203.0.13.15
- B. www.example.com,www 203.0.13.15,2001:db8::15
- C. 2003.0.113.15,2001:db8::15 www.example.com www
- D. 203.0.113.15 www.example.com www
- E. 2001:db8::15 www.example.com www
正解：D、E
質問 # 153
Which of the following keywords can be used in the file /etc/resolv.conf? (Choose TWO correct answers.)
- A. search
- B. nameserver
- C. lookup
- D. substitute
- E. method
正解：A、B
解説：
The file /etc/resolv.conf is the configuration file for the DNS resolver, which translates domain names to IP addresses by querying the DNS servers. The file supports several keywords that provide various types of resolver information. Two of the keywords that can be used in /etc/resolv.conf are:
* nameserver: This keyword specifies the IP address of the DNS server that the resolver can query against.
Up to three nameservers can be configured, and the resolver will try them in order until one responds or all fail.
* search: This keyword specifies a list of search domains that the resolver will append to the domain name when performing a query. For example, if the search list is example.com example.net, and the resolver queries for host, it will try host.example.com and host.example.net in order. The search list can have up to six domains, with a maximum of 256 characters in total.
The other keywords in the question are not valid for /etc/resolv.conf. The file does not support any keywords for substitution, lookup, or method. However, there are other keywords that can be used, such as:
* domain: This keyword specifies the local domain name of the system. It is mutually exclusive with the search keyword, and only one instance of either can be used.
* options: This keyword specifies various options that modify the behavior of the resolver. For example, the option rotate can be used to rotate the nameservers in a round-robin fashion, instead of trying them in order. Multiple options can be specified, separated by spaces.
References:
* 3: The /etc/resolv.conf File | Baeldung on Linux
* 1: /etc/resolv.conf - QNX
* 4: Chapter 33. Manually configuring the /etc/resolv.conf file
質問 # 154
What is true about the Hop Limit field in the IPv6 header?
- A. For multicast packages, the field's value is always 1.
- B. The field is not changed during the transport of a package.
- C. Each router forwarding the packet decreases the field's value.
- D. The field is transmitted within a hop-by-hop extension header.
- E. Each router forwarding the packet increases the field's value.
正解：C
解説：
The Hop Limit field in the IPv6 header is similar to the Time to Live (TTL) field in the IPv4 header. It specifies the maximum number of hops (routers) that a packet can traverse before reaching its destination.
Each router that receives the packet decrements the Hop Limit field by one and forwards the packet. If the Hop Limit field reaches zero, the packet is discarded and an ICMPv6 error message is sent back to the source. This mechanism prevents packets from loopingindefinitely in the network12 References: 1: IPv6 packet - Wikipedia 2: IP Time to Live (TTL) and Hop Limit Basics - Packet Pushers
質問 # 155
Which of the following commands puts the output of the command date into the shell variable mydate?
- A. mydate="$((date))"
- B. mydate="exec date"
- C. mydate="date"
- D. mydate="${date}"
- E. mydate="$(date)"
正解：E
解説：
(date)"∗∗Comprehensive∗∗Thecorrectwaytoputtheoutputofthecommanddateintotheshellvariablemydateistousecommandsubstitutionwiththesyntax(command). This will execute the command in a subshell and replace the expression with its standard output. The double quotes around the expression will prevent word splitting and globbing of the output. The other options are incorrect because they will either assign a literal string to the variable, use an invalid syntax, or try to execute the command as an arithmetic expression. Reference:
[LPI Linux Essentials - Topic 105: Shells, Scripting and Data Management]
[LPI Linux Administrator - Exam 102 Objectives - Topic 105: Shells and Shell Scripting]
質問 # 156
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