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Port 4026 (as-debug)

IANA assigns port 4026 to as-debug: Graphical Debug Server.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
as-debug TCP Graphical Debug Server Steve Halverson -
as-debug UDP Graphical Debug Server Steve Halverson -

Check what is listening on port 4026

Linux: is anything listening on TCP 4026?
sudo ss -tlnp 'sport = :4026'
Linux: UDP 4026
sudo ss -ulnp 'sport = :4026'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4026
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4026 '
Windows (Command Prompt)
netstat -ano | findstr :4026
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4026 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4026
From Windows
Test-NetConnection HOST -Port 4026
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4026

Block port 4026 in the firewall

ufw
sudo ufw deny 4026/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4026 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4026 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4026' -Direction Inbound -Protocol TCP -LocalPort 4026 -Action Block
ufw
sudo ufw deny 4026/udp
iptables
sudo iptables -A INPUT -p udp --dport 4026 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4026 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4026' -Direction Inbound -Protocol UDP -LocalPort 4026 -Action Block

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