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Port 5023 (htuilsrv)

IANA assigns port 5023 to htuilsrv: Htuil Server for PLD2.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
htuilsrv TCP Htuil Server for PLD2 Dennis Reinhardt -
htuilsrv UDP Htuil Server for PLD2 Dennis Reinhardt -

Check what is listening on port 5023

Linux: is anything listening on TCP 5023?
sudo ss -tlnp 'sport = :5023'
Linux: UDP 5023
sudo ss -ulnp 'sport = :5023'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5023
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5023 '
Windows (Command Prompt)
netstat -ano | findstr :5023
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5023 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5023
From Windows
Test-NetConnection HOST -Port 5023
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5023

Block port 5023 in the firewall

ufw
sudo ufw deny 5023/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5023 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5023 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5023' -Direction Inbound -Protocol TCP -LocalPort 5023 -Action Block
ufw
sudo ufw deny 5023/udp
iptables
sudo iptables -A INPUT -p udp --dport 5023 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5023 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5023' -Direction Inbound -Protocol UDP -LocalPort 5023 -Action Block

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