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Port 431 (utmpcd)

IANA assigns port 431 to utmpcd: UTMPCD.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
utmpcd TCP UTMPCD - -
utmpcd UDP UTMPCD - -

Check what is listening on port 431

Linux: is anything listening on TCP 431?
sudo ss -tlnp 'sport = :431'
Linux: UDP 431
sudo ss -ulnp 'sport = :431'
Linux / macOS: which process owns the port
sudo lsof -nP -i :431
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':431 '
Windows (Command Prompt)
netstat -ano | findstr :431
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 431 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 431
From Windows
Test-NetConnection HOST -Port 431
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 431

Block port 431 in the firewall

ufw
sudo ufw deny 431/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 431 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 431 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 431' -Direction Inbound -Protocol TCP -LocalPort 431 -Action Block
ufw
sudo ufw deny 431/udp
iptables
sudo iptables -A INPUT -p udp --dport 431 -j DROP
nftables
sudo nft add rule inet filter input udp dport 431 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 431' -Direction Inbound -Protocol UDP -LocalPort 431 -Action Block

Related ports

429ocs-amu, ocs_amu430utmpsd432iasd433nnsp

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