When attempting to listen for UDP traffic on port 2115 using netcat -ul -p2115, you'll encounter a usage statement because the traditional BSD version of netcat doesn't support the -p flag for specifying ports in UDP listen mode.

Here's the proper way to listen for UDP packets on a specific port:


nc -ul 2115


Or alternatively:

nc -u -l 2115


The behavior varies between netcat implementations:

• BSD netcat (original): Doesn't use -p for listening ports
• GNU netcat (ncat): Supports -p flag consistently
• OpenBSD netcat: Follows original BSD syntax

To test your UDP listener, open another terminal and send test data:

echo "test" | nc -u localhost 2115


If you need more advanced UDP monitoring:

# Using socat
socat UDP-RECV:2115 -

# Using tcpdump
tcpdump -i lo udp port 2115 -vv -X


For continuous monitoring with verbose output:

nc -ulvk 2115

The -v flag provides verbose output and -k keeps the connection open for multiple packets.

When attempting to listen on UDP port 2115 using the command:

netcat -ul -p2115

Many Linux users encounter the frustrating "usage statement" error. The issue stems from differences between netcat implementations across Unix-like systems.

The original netcat syntax has evolved differently in various implementations:

# Traditional BSD version (fails with -p for UDP)
netcat -ul -p2115

# GNU netcat (ncat) alternative
ncat -ulp 2115

# BusyBox version (common in embedded systems)
nc -ul -p 2115

For most modern netcat implementations (like the GNU version), the correct command structure is:

netcat -u -l 2115

Or alternatively:

nc -ul 2115

To confirm your UDP listener is working properly:

# In one terminal:
nc -ul 2115

# In another terminal:
echo "test" | nc -u localhost 2115

You should see "test" appear in the first terminal window.

For maximum compatibility across different netcat versions:

# Option 1: Explicit port without -p flag
nc -ul 2115

# Option 2: Using socat (more reliable alternative)
socat UDP-RECV:2115 -

If you're still having issues:

• Check if netcat is actually installed (which nc or which netcat)
• Verify port availability (sudo netstat -tulnp | grep 2115)
• Test with firewall disabled temporarily
• Try running as root in case of port restrictions

For production systems, consider more robust tools:

# Using socat for persistent listening
socat UDP-LISTEN:2115,fork -

# Using Python for custom UDP handling
import socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(('0.0.0.0', 2115))
while True:
    data, addr = sock.recvfrom(1024)
    print(f"Received: {data.decode()} from {addr}")