netstat and ss (connection listing) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this ss command?

You run the command ss -tuln on a Linux system. What does this command show?

Linux CLI

ss -tuln

A Lists all TCP and UDP sockets that are listening, showing numeric addresses and ports.

B Lists all established TCP connections only, resolving hostnames.

C Shows all UDP sockets including those in TIME_WAIT state.

D Displays all network interfaces and their IP addresses.

💡 Hint

Look at the flags: -t (TCP), -u (UDP), -l (listening), -n (numeric).

The ss -tuln command lists all listening TCP and UDP sockets with numeric addresses and ports. It does not show established connections or resolve hostnames.

💻 Command Output

intermediate

What is the output of this netstat command?

You run netstat -an | grep ESTABLISHED. What does this command output?

Linux CLI

netstat -an | grep ESTABLISHED

A Lists all active TCP connections that are currently established, showing numeric addresses.

B Lists all UDP sockets that are listening.

C Shows routing table entries with established routes.

D Displays all network interfaces and their MAC addresses.

💡 Hint

The -a flag shows all sockets, -n numeric addresses, and grep ESTABLISHED filters connections in established state.

The command lists all TCP connections that are currently established, showing numeric IP addresses and ports.

📝 Syntax

advanced

Which ss command syntax correctly shows all UDP sockets including listening and non-listening?

Choose the correct ss command to list all UDP sockets, both listening and non-listening.

A ss -t -a

B ss -l -u

C ss -u -a

D ss -a -t

💡 Hint

The -u flag is for UDP, -a shows all sockets.

ss -u -a lists all UDP sockets including listening and non-listening. Other options either show TCP sockets or only listening sockets.

🔧 Debug

advanced

Why does this netstat command fail with an error?

You run netstat -ltupn and get an error: "netstat: option requires an argument -- 'p'". What is wrong?

Linux CLI

netstat -ltupn

A The <code>-p</code> option is deprecated and not supported in this netstat version.

B The <code>-p</code> option is missing a value; it requires a protocol name after it.

C The options are in wrong order; <code>-p</code> must come before <code>-n</code>.

D The <code>-p</code> option requires root privileges to show process info; running as normal user causes error.

💡 Hint

Check if you have permission to use -p option.

The -p option shows process info but requires root privileges. Running as a normal user causes this error.

🚀 Application

expert

How many TCP connections are in the LISTEN state after running this command?

You run ss -tn state LISTEN on a server. The output shows these lines:

LISTEN 0      128          0.0.0.0:22        0.0.0.0:*
LISTEN 0      100          [::]:80           [::]:*

How many TCP connections are in the LISTEN state?

Linux CLI

ss -tn state LISTEN

A 0

B 2

C 1

D 128

💡 Hint

Count the number of LISTEN lines in the output.

There are two lines showing TCP sockets in LISTEN state, so the count is 2.