Port 873 (rsync daemon)

rsync in daemon mode (rsync://), used by Linux mirrors and backup systems. rsync over SSH uses port 22 instead.

Well-known (system) port, 0-1023 TCP File transfer and storage Do not expose to the internet

What port 873 is used for

rsync in daemon mode (rsync://), used by Linux mirrors and backup systems. rsync over SSH uses port 22 instead.

Security: should port 873 be open?

Do not expose to the internet. Misconfigured rsync modules without 'auth users' expose whole file systems and backups. Use rsync over SSH unless you run a public mirror.

IANA assignment

Service nameProtoDescriptionAssigneeReference

rsync TCP rsync Andrew Tridgell -

rsync UDP rsync Andrew Tridgell -

Check what is listening on port 873

Linux: is anything listening on TCP 873?

sudo ss -tlnp 'sport = :873'

Linux / macOS: which process owns the port

sudo lsof -nP -i :873

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':873 '

Windows (Command Prompt)

netstat -ano | findstr :873

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 873 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 873

From Windows

Test-NetConnection HOST -Port 873

Block port 873 in the firewall

ufw

sudo ufw deny 873/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 873 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 873 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 873' -Direction Inbound -Protocol TCP -LocalPort 873 -Action Block

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