Port 873: rsync
Port 873 is rsync, used by the rsync daemon to synchronize files and directories efficiently by transferring only the parts of a file that changed. Most rsync usage today tunnels over SSH on port 22 instead, but the standalone daemon still listens here.
| Port number | 873 |
|---|---|
| Service | rsync file synchronization |
| Protocol | TCP |
| Category | File transfer |
| Default encryption | No |
How do I check whether port 873 is open?
Port 873 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 873 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 873 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':873 ' | Lists the process bound to port 873 on Linux. On macOS use lsof -nP -iTCP:873 -sTCP:LISTEN, on Windows netstat -ano | findstr :873 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 873 used for?
Port 873 is rsync, used by the rsync daemon to synchronize files and directories efficiently by transferring only the parts of a file that changed. Most rsync usage today tunnels over SSH on port 22 instead, but the standalone daemon still listens here.
Is port 873 TCP or UDP?
Port 873 (rsync) uses TCP.
Is port 873 secure?
Port 873 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 873 on my firewall?
Only if you specifically need rsync. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.