rsync
What is Port 873?
Port 873 is the default port for the rsync daemon, a fast and versatile file synchronization and transfer tool widely used on Unix/Linux systems. Rsync uses a delta-transfer algorithm that only sends the differences between source and destination files, making it extremely efficient for incremental backups and mirroring. When running in daemon mode, rsync listens on port 873 and serves defined modules (shared directories) to authorized clients. Rsync can also run over SSH (port 22) without using the daemon, which is the more common and secure approach. The rsync protocol supports compression, partial transfers, and can handle millions of files efficiently. It is the backbone of many backup solutions, mirror systems, and deployment pipelines.
Common Uses
- Server backup and incremental file synchronization
- Mirror site maintenance for software repositories
- Website deployment and content distribution
- Data replication between servers
Technical Details
Copy-paste commands to check port 873 (rsync) from your terminal
Test connectivity
nc -zv example.com 873
curl -v --max-time 5 http://example.com:873/
telnet example.com 873
nmap -p 873 -sV example.com
(echo > /dev/tcp/example.com/873) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 873/tcp
sudo iptables -A INPUT -p tcp --dport 873 -j ACCEPT
sudo firewall-cmd --permanent --add-port=873/tcp && sudo firewall-cmd --reload
Security Considerations
Rsync daemon mode on port 873 has limited security — it supports basic password authentication but no encryption. Prefer running rsync over SSH for encrypted transfers. If the daemon must be used, restrict access via IP whitelisting in rsyncd.conf, use strong passwords, and set modules to read-only where possible. Never expose rsync daemon to the internet without restrictions.
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