Port 512 (exec, biff)

IANA assigns port 512 to exec, biff: remote process execution; authentication performed using passwords and UNIX login names.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference

exec TCP remote process execution; authentication performed using passwords and UNIX login names - -

biff UDP used by mail system to notify users of new mail received; currently receives messages only from processes on the same machine - -

Linux: is anything listening on TCP 512?

sudo ss -tlnp 'sport = :512'

Linux: UDP 512

sudo ss -ulnp 'sport = :512'

Linux / macOS: which process owns the port

sudo lsof -nP -i :512

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':512 '

Windows (Command Prompt)

netstat -ano | findstr :512

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 512 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 512

From Windows

Test-NetConnection HOST -Port 512

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 512

ufw

sudo ufw deny 512/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 512 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 512 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 512' -Direction Inbound -Protocol TCP -LocalPort 512 -Action Block

ufw

sudo ufw deny 512/udp

iptables

sudo iptables -A INPUT -p udp --dport 512 -j DROP

nftables

sudo nft add rule inet filter input udp dport 512 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 512' -Direction Inbound -Protocol UDP -LocalPort 512 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.