# WHATPORT(873)

## NAME

port 873 — rsync daemon — rsync in daemon mode — public mirrors run it on purpose, and so do accidentally exposed backups.

Protocol: TCP

## DESCRIPTION

Running `rsync --daemon` opens TCP 873 and serves named modules defined in rsyncd.conf, each mapping to a directory tree with its own read-only, auth-users and hosts-allow settings. This is the native rsync protocol, not rsync-over-SSH, and modules configured without auth-users are readable by anyone who connects — which is exactly how Linux distribution and CPAN mirrors are meant to work. It is also the classic accidental data leak: a backup module left world-readable, or worse, writable. Listing modules requires no credentials, so a connect immediately tells you what is on offer.

## EXPOSURE

**Expose with care.** Fine for a deliberate public mirror with read-only modules; anything else needs auth-users, hosts-allow, and a check that no module exports a filesystem root.

## CHECK

```sh
rsync rsync://rsync.samba.org/
```

## SEE ALSO

- docs — [rsync project home](https://rsync.samba.org/) (rsync.samba.org)
- docs — [rsyncd.conf(5) manual page](https://download.samba.org/pub/rsync/rsyncd.conf.5) (download.samba.org)
- source — [rsync source repository](https://github.com/RsyncProject/rsync) (github.com)

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