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Port 501 (stmf)

IANA assigns port 501 to stmf: STMF.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
stmf TCP STMF Alan Ungar -
stmf UDP STMF Alan Ungar -

Check what is listening on port 501

Linux: is anything listening on TCP 501?
sudo ss -tlnp 'sport = :501'
Linux: UDP 501
sudo ss -ulnp 'sport = :501'
Linux / macOS: which process owns the port
sudo lsof -nP -i :501
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':501 '
Windows (Command Prompt)
netstat -ano | findstr :501
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 501 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 501
From Windows
Test-NetConnection HOST -Port 501
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 501

Block port 501 in the firewall

ufw
sudo ufw deny 501/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 501 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 501 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 501' -Direction Inbound -Protocol TCP -LocalPort 501 -Action Block
ufw
sudo ufw deny 501/udp
iptables
sudo iptables -A INPUT -p udp --dport 501 -j DROP
nftables
sudo nft add rule inet filter input udp dport 501 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 501' -Direction Inbound -Protocol UDP -LocalPort 501 -Action Block

Related ports

499iso-ill500IKE (IPsec)502Modbus/TCP503intrinsa

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