From "man rsync":
CONNECTING TO AN RSYNC DAEMON
It is also possible to use rsync without a remote shell as the transport. In this case you will directly connect to a remote rsync daemon, typi‐
cally using TCP port 873. (This obviously requires the daemon to be running on the remote system, so refer to the STARTING AN RSYNC DAEMON TO
ACCEPT CONNECTIONS section below for information on that.)
Using rsync in this way is the same as using it with a remote shell except that:
o you either use a double colon :: instead of a single colon to separate the hostname from the path, or you use an rsync:// URL.
o the first word of the “path” is actually a module name.
o the remote daemon may print a message of the day when you connect.
o if you specify no path name on the remote daemon then the list of accessible paths on the daemon will be shown.
o if you specify no local destination then a listing of the specified files on the remote daemon is provided.
o you must not specify the --rsh (-e) option.
An example that copies all the files in a remote module named “src”:
rsync -av host::src /dest
Some modules on the remote daemon may require authentication. If so, you will receive a password prompt when you connect. You can avoid the pass‐
word prompt by setting the environment variable RSYNC_PASSWORD to the password you want to use or using the --password-file option. This may be
useful when scripting rsync.
WARNING: On some systems environment variables are visible to all users. On those systems using --password-file is recommended.
You may establish the connection via a web proxy by setting the environment variable RSYNC_PROXY to a hostname:port pair pointing to your web
proxy. Note that your web proxy’s configuration must support proxy connections to port 873.