A UDT wrapper for rsync that improves throughput of large data transfers over long distances.
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UDR is a wrapper around rsync that enables rsync to use UDT.


./src: UDR source code ./udt: UDT source code, documentation and license


make -e os=XXX arch=YYY 

XXX: [LINUX(default), BSD, OSX]
YYY: [IA32(default), POWERPC, IA64, AMD64]


OpenSSL (libssl and libcrypto)
Currently, UDR has mainly been tested on Linux so your mileage may vary on another OS. UDT has been well tested on all of the provided options.


UDR must be on the client and server machines that data will be transferred between. UDR uses ssh to do authentication and automatically start the server-side UDR process. At least one UDP port needs to be open between the machines, by default UDR starts with port 9000 and looks for an open port up to 9100, changing this is an option. Encryption is off by default. When turned on encryption uses OpenSSL with aes-128 by default.

Basic usage:

udr [udr options] rsync [rsync options] src dest

UDR options:

[-a starting port number] default is 9000
[-b ending port number] default is 9100
[-n aes-128 | aes-192 | aes-256 | bf | des-ede3] turns on encryption, if crypto is not specified aes-128 is the default
[-p path] local path for the .udr_key file used for encryption, default is the current directory
[-c remote udr location] by default udr assumes that udr is in your path on the remote system, here you can specify the location explicitly
[-o server port] port to access a UDR server, default is 9000 [-v] verbose mode, typically for debugging purposes
[--version] print out the version
[-d timeout] specify duration in seconds in which to kill remaining threads if no data is transfered after connected, default is 15s [-i ip] specify the interface by ip that the remote process will bind to

The rsync [rsync options] should take any of the standard rsync options, except the -e/--rsh flag which how UDR interfaces with rsync.

A basic example command:

udr rsync -av --stats --progress /home/user/tmp/ hostname.com:/home/user/tmp

A command with udr options:

udr -c /home/user/udr/src/udr -a 8000 -b 8010 rsync -av --stats --progress /home/user/tmp/ hostname.com:/home/user/tmp


After the rsync data transfer is complete, the local udr thread is shutdown by a signal. Rsync thinks this is abnormal and prints out the error "rsync error: sibling process terminated abnormally", which can be ignored. However, the transfer should be complete, if other rsync errors appear these are true errors.


The UDR server allows UDR transfers for users without accounts, similar to rsync server functionality. The UDR server is written in python, listens on a TCP port and mainly manages launching rsync processes with the "using rsync-daemon features via a remote-shell connection" ability of rsync (see rsync man page for details). The UDR server requies UDR version 0.9.2 or above.

Basic server usage:

python udrserver.py [-v] [-s] [-c configfile] start|stop|restart|foreground

UDR server options:

[-c config file] specify the location of the config file, default is /etc/udrd.conf
[-s] silent mode, don't print message on start|stop|restart
[-v] verbose mode, mainly for debugging purposes

UDR server configuration:

The UDR server requires a configuration file, by default it looks for /etc/udrd.conf. The format of the file is a list of parameter of the format 'name = value'. An example config file is provided, the available parameters are:

  • address: IP address to bind to, default is
  • server port: TCP port for the server to listen on, default is 9000
  • start port: first UDP port to begin UDR connections on, default is 9000
  • end port: last UDP port to begin UDR connections on, default is 9100
  • log file: log file for UDR, default is /udr.log
  • log level: level of logging used, based on the python logging module, default is INFO
  • pid file: pid file used for daemon, default is /var/run/udrd.pid
  • udr: path to udr command, default is udr
  • rsyncd conf: rsyncd.conf file to use for the rsync part of the configuration
  • uid: user name or uid that the server should run as when started as root, default is nobody when run as root
  • gid: group name or gid that the server should run as when started as root, default is nogroup when run as root
  • specify ip: IP address for udr receiver to bind to, default is any connected interface

Most standard rsyncd.conf options should work like normal. Known exceptions are:

Max Connections

The max connections option does not work, but the number of connections can be limited by the range of start and end port in the udrd.conf file because one connection requires one port. For example, if you only want 50 connections, set the start port to 9000 and the end port to 9050. If the max connections option is set, the rsync processes will try to write to the lock file, which they often do not have permission to and will return the error "@ERROR: failed to open lock file". You can set the lock file location in rsyncd.conf or remove the max connections option.

UID/GID and chroot

It is not recommended to run UDR server as root. However, then the rsync use chroot option will not be available. If chroot is desired, the uid/gid options in udrd.conf must be explicitly set to root. UDR will then parse and use the global uid/gid settings in rsyncd.conf for spawned subprocesses. However, it does not currently support different uid/gid for each module.

WARNING: UDR server has only be tested in read only mode, it is not recommended to enable write access.

Connecting to the UDR server

To connect to the UDR server, use double colons instead of the single colon, similar to connecting to a rsync daemon. Listing files is also the same as with rsync.

Basic example command for downloading from a UDR server:

udr rsync -av --stats --progress hostname.com::module/path/to/file /home/user/target

List modules available:

udr rsync hostname.com::

List files on server:

udr rsync hostname.com::module/path/to/file