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Port 37 (time)

IANA assigns port 37 to time: Time.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
time TCP Time Jon Postel -
time UDP Time Jon Postel -

Check what is listening on port 37

Linux: is anything listening on TCP 37?
sudo ss -tlnp 'sport = :37'
Linux: UDP 37
sudo ss -ulnp 'sport = :37'
Linux / macOS: which process owns the port
sudo lsof -nP -i :37
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':37 '
Windows (Command Prompt)
netstat -ano | findstr :37
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 37 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 37
From Windows
Test-NetConnection HOST -Port 37
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 37

Block port 37 in the firewall

ufw
sudo ufw deny 37/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 37 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 37 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 37' -Direction Inbound -Protocol TCP -LocalPort 37 -Action Block
ufw
sudo ufw deny 37/udp
iptables
sudo iptables -A INPUT -p udp --dport 37 -j DROP
nftables
sudo nft add rule inet filter input udp dport 37 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 37' -Direction Inbound -Protocol UDP -LocalPort 37 -Action Block

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