HTTPfy

Port 4040 (yo-main)

IANA assigns port 4040 to yo-main: Yo.net main service.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
yo-main TCP Yo.net main service John Tintor -
yo-main UDP Yo.net main service John Tintor -

Check what is listening on port 4040

Linux: is anything listening on TCP 4040?
sudo ss -tlnp 'sport = :4040'
Linux: UDP 4040
sudo ss -ulnp 'sport = :4040'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4040
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4040 '
Windows (Command Prompt)
netstat -ano | findstr :4040
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4040 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4040
From Windows
Test-NetConnection HOST -Port 4040
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4040

Block port 4040 in the firewall

ufw
sudo ufw deny 4040/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4040 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4040 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4040' -Direction Inbound -Protocol TCP -LocalPort 4040 -Action Block
ufw
sudo ufw deny 4040/udp
iptables
sudo iptables -A INPUT -p udp --dport 4040 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4040 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4040' -Direction Inbound -Protocol UDP -LocalPort 4040 -Action Block

Related ports

4038fazzt-ptp4039fazzt-admin4041houston4042ldxp

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