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Port 540 (uucp)

IANA assigns port 540 to uucp: uucpd.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
uucp TCP uucpd - -
uucp UDP uucpd - -

Check what is listening on port 540

Linux: is anything listening on TCP 540?
sudo ss -tlnp 'sport = :540'
Linux: UDP 540
sudo ss -ulnp 'sport = :540'
Linux / macOS: which process owns the port
sudo lsof -nP -i :540
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':540 '
Windows (Command Prompt)
netstat -ano | findstr :540
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 540 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 540
From Windows
Test-NetConnection HOST -Port 540
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 540

Block port 540 in the firewall

ufw
sudo ufw deny 540/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 540 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 540 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 540' -Direction Inbound -Protocol TCP -LocalPort 540 -Action Block
ufw
sudo ufw deny 540/udp
iptables
sudo iptables -A INPUT -p udp --dport 540 -j DROP
nftables
sudo nft add rule inet filter input udp dport 540 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 540' -Direction Inbound -Protocol UDP -LocalPort 540 -Action Block

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All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.