Day 5 - Network and Service Lab Mock Exam + Wrong-Answer Notes

📌 Key Takeaways

• This week's axis is network and service lab tasks: address configuration (Day 1), service config directives (Day 2), shell scripts (Day 3), and security (Day 4).
• Today we compress the week into a 12-question mock exam for review. The explanations are wrong-answer notes that also point out why the other choices are traps.
• In lab tasks, a single character (option, directive, direction) decides pass or fail. Partial credit is stingy here.
• Three of the four choices are traps with one wrong direction, option, or spelling, so the elimination method of finding the error and crossing it out is fast.
• When you read a question, recall in order: ① which area is it, ② temporary or persistent, ③ which file or command.

Quick Review of This Week's Essentials

• Network configuration : Separate temporary (ip addr add/ip route add) from persistent (BOOTPROTO/ONBOOT=yes/IPADDR in ifcfg-*, nmcli con).
• With nmcli, you must reactivate with con up after modifying for it to take effect.
• The diagnostic ladder is ip a → ping gw → ping 8.8.8.8 → dig. For port checks, use ss -tuln.
• Service config files : httpd DocumentRoot/Listen, named type master + SOA Serial + records (A/MX/CNAME/PTR).
• dhcpd range/fixed-address, vsftpd anonymous_enable/chroot_local_user, smb.conf path/writable.
• exports: no space before the parenthesis and root_squash; sshd: PermitRootLogin no.
• Shell scripts : no spaces around the assignment =, spaces inside the brackets of if [ -gt/-eq/-f/-d ], for/while/case (done/done/esac).
• Call functions without parentheses, and memorize $(...), $?, while read ... done < file, and sort|uniq -c|sort -rn as patterns.
• Security : iptables direction (INPUT/OUTPUT/FORWARD), -A/-I/-P/-j, ACCEPT/DROP/REJECT, service iptables save.
• firewalld: --permanent then --reload; SELinux: modes and chcon/restorecon.
• rsyslog: facility.priority (.none/.=); logrotate: rotate N/compress.

💡 Pass signal: Lab tasks ask for "the exact command/directive that does this." If the direction, options, and spelling are exact, you are right; if even one is wrong, it is zero points.

🔍 Solving strategy: When you read a question, recall in order ① which area (network/service/script/security), ② temporary or persistent, ③ which file or command. Since three of the four choices are traps with one wrong direction, option, or spelling, the elimination method of finding the error and crossing it out is faster than picking the answer.

📖 Glossary

• Temporary / persistent configuration : Configuration that disappears at reboot (ip) / configuration that remains in a file and persists (ifcfg-*, nmcli con).
• ONBOOT : The directive in ifcfg-* that decides whether the interface is brought up automatically at boot. If it is not yes, it does not come up.
• Diagnostic ladder : A method of breaking things down in the order IP → gateway → external IP → domain to narrow down where it is blocked.
• SOA Serial : The version number of the zone data. It must be raised so the secondary (slave) server picks up the change.
• exports whitespace trap : An NFS syntax trap where a space between the client and the parenthesis opens the options to all hosts.
• PermitRootLogin : The directive that decides whether root may log in directly over SSH. Blocking is no.
• done < file : The redirection that attaches input so while read reads the file line by line. It goes after done.
• --permanent + --reload : The two steps in firewalld of saving permanently and then applying to the current session. Doing only one is half the job.
• SELinux context : The label attached to files and processes. If permissions are right but access is blocked, suspect this.
• facility.priority : The "source.severity" pair rsyslog uses to split logs. .none excludes, .= means only that level, and the default is that level and above.

📝 Practice Questions

Click a choice to reveal the answer and explanation.

Question 1

Which command combination temporarily assigns the address 192.168.0.50/24 to eth0 and sets the default gateway to 192.168.0.1?

• Aip addr add 192.168.0.50/24 dev eth0; ip route add default via 192.168.0.1
• Bip addr set 192.168.0.50 eth0; route default 192.168.0.1
• Cip link add 192.168.0.50/24 eth0; ip route default 192.168.0.1
• Difconfig eth0 192.168.0.50; ip route add 192.168.0.1 default

Question 2

In the ifcfg-eth0 file, which combination of directives uses a static IP and makes the interface activate automatically even after a reboot?

• ABOOTPROTO=dhcp, ONBOOT=no
• BBOOTPROTO=static, ONBOOT=yes
• CBOOTPROTO=auto, ONBOOT=yes
• DBOOTPROTO=static, ONBOOT=no

Question 3

ping 8.8.8.8 succeeds but ping www.example.com fails. Which file should you check?

• A/etc/hosts.allow
• B/etc/resolv.conf
• C/etc/sysconfig/iptables
• D/etc/exports

Question 4

After editing a BIND zone file, what must you do to propagate the change to the secondary (slave) server?

• ALower the Refresh value to 0
• BIncrease the SOA Serial value
• CIncrease the Expire value
• DSet the TTL to 0

Question 5

Among the following /etc/exports entries, which is the faulty setting that unintentionally opens rw to all hosts?

• A/data 192.168.1.0/24(rw,sync)
• B/data 192.168.1.0/24 (rw,sync)
• C/data 192.168.1.10(ro)
• D/data *(ro)

Question 6

Which sshd_config setting blocks direct remote login by root on an SSH server?

• APermitRootLogin yes
• BPermitRootLogin no
• CPasswordAuthentication no
• DPermitEmptyPasswords no

Question 7

In the following shell script fragments, which line has a syntax error?

• Aname="linux"
• Bif [ "$count" -gt 5 ]; then
• Cfor i in 1 2 3; do
• Dtotal = $((a + b))

Question 8

Which is the correct blank for a script that reads the file users.txt line by line to create user accounts? while read u; do useradd "$u"; done ____ users.txt

• A> users.txt
• B< users.txt
• C| users.txt
• D>> users.txt

Question 9

Which iptables command allows only incoming TCP connections to port 443 (HTTPS) from outside?

• Aiptables -A OUTPUT -p tcp --sport 443 -j ACCEPT
• Biptables -A INPUT -p tcp --dport 443 -j ACCEPT
• Ciptables -A FORWARD -p udp --dport 443 -j DROP
• Diptables -P INPUT -p tcp --dport 443 -j ACCEPT

Question 10

How do you allow port 8080/tcp in firewalld so that it persists after reboot and takes effect immediately?

• ARun only firewall-cmd --add-port=8080/tcp
• Bfirewall-cmd --permanent --add-port=8080/tcp, then firewall-cmd --reload
• CRun only firewall-cmd --permanent --add-port=8080/tcp
• Dfirewall-cmd --add-service=8080 --reload

Question 11

"File permissions (rwx) are correct, but the web server cannot access a certain directory. After setenforce 0, access works." What is the most appropriate permanent fix?

• APermanently disable SELinux by setting it to Disabled
• BApply the correct context with restorecon or semanage fcontext
• COpen all permissions with chmod 777
• DBlock port 80 in the firewall

Question 12

Which is the correct description of the logrotate settings daily, rotate 7, compress?

• ARotates weekly and keeps 7
• BRotates daily, keeps the latest 7 (about one week) compressed, and deletes the excess
• CRotates when the log exceeds 7MB
• DRotates once every 7 days without compression

Summary of Easy-to-Miss Traps

I gathered the traps that mock exams catch most often into one table. Reviewing just this table right before the exam is also fine.

⚠️ Exam-room mindset: Partial credit in lab tasks is stingy. One direction (INPUT/OUTPUT), one space, or one missing --reload makes the whole answer wrong. After writing a command, run it once in your head and double-check "what exactly happens if I execute this?"

Wrap-Up

We compressed the week into 12 questions. The core of network lab tasks is telling temporary from persistent (ip is volatile, ifcfg ONBOOT=yes/nmcli con is persistent) and layer-by-layer diagnosis (IP works but the domain fails = DNS). Service configuration is a battle of memorizing 1:1 directive mappings (DocumentRoot, SOA Serial, range, PermitRootLogin no, the exports whitespace trap) with exact spelling. For scripts, syntactic rigor (no spaces around =, spaces inside brackets, done < file) is vital, and in security, direction, options, --reload, and context decide pass or fail. Revisit the questions you missed until you can explain in words "what is wrong and why" for each choice. A lab exam is a test of writing exactly what you know.