CyberHunter
Local dataset, no network
// Other services

Port 540: uucpd

Port 540 is assigned by IANA to uucp (uucpd).

540

How uucp works

Other services
client:540uucpresponse client:540uucpresponse

The client sends a request to port 540 and the uucp service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Well-known (0-1023)
Category
Other services
01 Security

Is port 540 dangerous?

We have no specific security note for port 540. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 540

ServicePortTransportDescriptionReferenceUpdated
uucp 540 TCP, UDP uucpd - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 540, and is it reachable?

Linux

sudo ss -ltnup 'sport = :540'      # process listening on 540
sudo lsof -nP -i :540

macOS

sudo lsof -nP -i :540

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 540 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 540
netstat -ano | findstr :540

From another machine

nmap -p 540 -sV <host>
sudo nmap -sU -p 540 <host>
nc -zv <host> 540

Block it in the firewall

sudo ufw deny 540/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 540" -Direction Inbound -LocalPort 540 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 540 used for?

Port 540 is assigned by IANA to uucp (uucpd).

Is port 540 TCP or UDP?

Port 540 is registered for TCP and UDP.

Is it safe to open port 540?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Close the port if nothing on the host needs it.

How do I check if port 540 is open?

On Linux run "ss -ltnup 'sport = :540'", on macOS "lsof -nP -i :540", and on Windows "netstat -ano | findstr :540" to see the local process. From another machine, "nmap -p 540 <host>" shows whether it is reachable.

05 Related
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