Linux Network Service Troubleshooting Quiz

1. A service depends on another service (e.g., a web app depends on database). How should this be configured in systemd?

Use Requires= and After= directives in the service file

Manually start services in a shell script

Rely on alphabetical startup order

Configure it in the kernel boot parameters

2. After modifying a service configuration file, what is the correct sequence to apply changes?

Validate syntax, then systemctl daemon-reload, then systemctl restart

Reboot immediately without validation

Only restart without reloading the daemon

Modify the kernel and recompile

3. A service requires specific kernel parameters to function. Where would these be configured persistently?

/etc/sysctl.conf or /etc/sysctl.d/

/etc/rc.local

/proc/sys/net

/dev/null

4. Which environment variable is commonly used to enable debug logging in network services?

DEBUG or LOGLEVEL

PATH

HOME

SHELL

5. A service crashes immediately after starting. What is the best first diagnostic step?

Check the service logs for error messages

Immediately restart the entire server

Assume the hardware is faulty

Reinstall the entire operating system

6. When a service file contains Type=forking, what should the service do?

Exit the parent process after spawning a child

Run indefinitely in the foreground

Create multiple copies of itself

Fork only if run as root

7. A firewall rule is blocking an essential service port. Which tool can you use to check and modify firewall rules?

Firewalld (firewall-cmd) or ufw

Ifconfig

Ping

Traceroute

8. Which command shows real-time service logs and is useful for debugging a service that just failed?

Journalctl -u service_name -f

Cat /var/log/auth.log

Ls -la /var/log

Tail -n 1 /var/log/syslog

9. A service runs as root but should run as a non-root user. Where in a systemd service file is this specified?

User= and Group= directives

Environment= directive

StandardOutput= directive

Type= directive

10. Network connectivity works, but a service still cannot reach a database on another host. Which is a valid troubleshooting step?

Use telnet or nc to test connectivity to the database port

Reformat the entire disk

Change the system hostname

Disable all security updates

11. A web server fails to start after a configuration change. Which command checks if the service is running and shows its status?

Systemctl status nginx

Ps aux | grep nginx

Netstat -an | grep 80

Ifconfig eth0

12. Which tool would you use to validate the syntax of an Apache configuration file before restarting?

Apache2ctl configtest or apachectl configtest

Grep -r syntax /etc/apache2

Cat /etc/apache2/apache2.conf

Find /etc/apache2 -type f

13. A DNS service fails because the config file has a syntax error. Where would you find detailed error messages?

Journalctl -u service_name or /var/log/messages

/etc/passwd

/proc/meminfo

/sys/devices

14. You need to restart a network service without losing active connections. Which approach is best?

Use systemctl reload or reload-or-restart

Kill the process with SIGKILL

Reboot the entire system

Unplug the network cable

15. A network service logs show 'Connection refused' errors. Which of these is NOT a likely cause?

The service is not listening on the expected port

A firewall rule blocks the connection

The system has too much free disk space

The remote host is unreachable

16. Which command enables a service to start automatically at boot on a systemd system?

Systemctl enable service_name

Chkconfig service_name on

Update-rc.d service_name enable

Service service_name autostart

17. A service starts but cannot bind to its configured port. What should you check first?

Whether another process is already listening on that port

The system uptime

The BIOS settings

The user's shell environment

18. Which file typically contains DNS resolver configuration on modern Linux systems?

/etc/resolv.conf

/etc/hosts

/etc/hostname

/etc/network/interfaces

19. A systemd service fails to start with a permission denied error. What is the most likely cause?

The service file has incorrect permissions or ownership

The system clock is incorrect

Too many processes are running

The network cable is unplugged

20. You suspect port 443 is already in use. Which command displays all listening ports and their associated processes?

Ss -tulpn

Arp -a

Route -n

Ip link show

Linux Network Pro Troubleshooting a Failed Network Service Quiz