What is RSync ?

Posted On 2007-05-22 by FortyPoundHead
Keywords: Command Reference
Tags: Cisco Linux
Views: 1636

Remote file copy - Synchronize file trees across local disks, directories or across a network.


# Local file to Local file
rsync [option]... Source [Source]... Dest

# Local to Remote
rsync [option]... Source [Source]... [user@]host:Dest

rsync [option]... Source [Source]... [user@]host::Dest

# Remote to Local
rsync [option]... [user@]host::Source [Dest]

rsync [option]... [user@]host:SourceDest

rsync [option]... rsync://[user@]host[:PORT]/Source [Dest]

rsync is a program that behaves in much the same way that rcp does, but has many more options and uses the rsync remote-update protocol to greatly speed up file transfers when the destination file already exists.

The rsync remote-update protocol allows rsync to transfer just the differences between two sets of files across the network link, using an efficient checksum-search algorithm described in the technical report that accompanies this package.

Some of the additional features of rsync are:

  • support for copying links, devices, owners, groups and permissions
  • exclude and exclude-from options similar to GNU tar
  • a CVS exclude mode for ignoring the same files that CVS would ignore
  • can use any transparent remote shell, including rsh or ssh
  • does not require root privileges
  • pipelining of file transfers to minimize latency costs
  • support for anonymous or authenticated rsync servers (ideal for mirroring)


There are six different ways of using rsync. They are:

  • for copying local files. This is invoked when neither source nor destination path contains a : separator
  • for copying from the local machine to a remote machine using a remote shell program as the transport (such as rsh or ssh). This is invoked when the destination path contains a single : separator.
  • for copying from a remote machine to the local machine using a remote shell program. This is invoked when the source contains a : separator.
  • for copying from a remote rsync server to the local machine. This is invoked when the source path contains a :: separator or a rsync:// URL.
  • for copying from the local machine to a remote rsync server. This is invoked when the destination path contains a :: separator.
  • for listing files on a remote machine. This is done the same way as rsync transfers except that you leave off the local destination.

Note that in all cases (other than listing) at least one of the source and destination paths must be local.


You use rsync in the same way you use rcp. You must specify a source and a destination, one of which may be remote.

Perhaps the best way to explain the syntax is some examples:

rsync *.c foo:src/

this would transfer all files matching the pattern *.c from the current directory to the directory src on the machine foo. If any of the files already exist on the remote system then the rsync remote-update protocol is used to update the file by sending only the differences. See the tech report for details.

rsync -avz foo:src/bar /data/tmp

this would recursively transfer all files from the directory src/bar on the machine foo into the /data/tmp/bar directory on the local machine. The files are transferred in "archive" mode, which ensures that symbolic links, devices, attributes, permissions, ownerships etc are preserved in the transfer. Additionally, compression will be used to reduce the size of data portions of the transfer.

rsync -avz foo:src/bar/ /data/tmp

a trailing slash on the source changes this behavior to transfer all files from the directory src/bar on the machine foo into the /data/tmp/. A trailing / on a source name means "copy the contents of this directory". Without a trailing slash it means "copy the directory". This difference becomes particularly important when using the --delete option.

You can also use rsync in local-only mode, where both the source and destination don''t have a '':'' in the name. In this case it behaves like an improved copy command.


this would list all the anonymous rsync modules available on the host (See the following section for more details.)

Connecting to an RSync Server

It is also possible to use rsync without using rsh or ssh as the transport. In this case you will connect to a remote rsync server running on TCP port 873.

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 allow proxying to port 873.

Using rsync in this way is the same as using it with rsh or ssh except that:

  • you use a double colon :: instead of a single colon to separate the hostname from the path.
  • the remote server may print a message of the day when you connect.
  • if you specify no path name on the remote server then the list of accessible paths on the server will be shown.
  • if you specify no local destination then a listing of the specified files on the remote server is provided.

Some paths on the remote server may require authentication. If so then you will receive a password prompt when you connect. You can avoid the password 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.

Running an RSync Server

An rsync server is configured using a config file which by default is called /etc/rsyncd.conf. Please see the rsyncd.conf(5) man page for more information.


To Backup the home directory using a cron job:

rsync -Cavz . fph2007:backup

Run the above over a PPP link to a duplicate directory on machine "fph2007".

To synchronize samba source trees use the following Makefile targets:


rsync -avuzb --exclude ''*~'' samba:samba/ .


rsync -Cavuzb . samba:samba/

sync: get put

this allows me to sync with a CVS directory at the other end of the link. I then do cvs operations on the remote machine, which saves a lot of time as the remote cvs protocol isn''t very efficient. I mirror a directory between my "old" and "new" ftp sites with the command

rsync -az -e ssh --delete ~ftp/pub/samba/ nimbus:"~ftp/pub/tridge/samba"

this is launched from cron every few hours.

Options Summary

Here is a short summary of the options available in rsync. Please refer to the FULL List of OPTIONS for a complete description.

What to copy:

-r, --recursive recurse into directories
-R, --relative use relative path names
--exclude=PATTERN exclude files matching PATTERN
--exclude-from=FILE exclude patterns listed in FILE
-I, --ignore-times don''t exclude files that match length and time
--size-only only use file size when determining if a file should be transferred
--modify-window=NUM Timestamp window (seconds) for file match (default=0)
--include=PATTERN don''t exclude files matching PATTERN
--include-from=FILE don''t exclude patterns listed in FILE

How to copy it:

-n, --dry-run show what would have been transferred
-l, --links copy symlinks as symlinks
-L, --copy-links copy the referent of symlinks
--copy-unsafe-links copy links outside the source tree
--safe-links ignore links outside the destination tree
-H, --hard-links preserve hard links
-D, --devices preserve devices (root only)
-g, --group preserve group
-o, --owner preserve owner (root only)
-p, --perms preserve permissions
-t, --times preserve times
-S, --sparse handle sparse files efficiently
-x, --one-file-system don''t cross filesystem boundaries
-B, --block-size=SIZE checksum blocking size (default 700)
-e, --rsh=COMMAND specify rsh replacement
--rsync-path=PATH specify path to rsync on the remote machine
--numeric-ids don''t map uid/gid values by user/group name
--timeout=TIME set IO timeout in seconds
-W, --whole-file copy whole files, no incremental checks

Destination options:

-a, --archive archive mode
-b, --backup make backups (default ~ suffix)
--backup-dir make backups into this directory
--suffix=SUFFIX override backup suffix
-z, --compress compress file data
-c, --checksum always checksum
-C, --cvs-exclude auto ignore files in the same way CVS does
--existing only update files that already exist
--delete delete files that don''t exist on the sending side
--delete-excluded also delete excluded files on the receiving side
--delete-after delete after transferring, not before
--force force deletion of directories even if not empty
--ignore-errors delete even if there are IO errors
--max-delete=NUM don''t delete more than NUM files
--log-format=FORMAT log file transfers using specified format
--partial keep partially transferred files
--progress show progress during transfer
-P equivalent to --partial --progress
--stats give some file transfer stats
-T --temp-dir=DIR create temporary files in directory DIR
--compare-dest=DIR also compare destination files relative to DIR
-u, --update update only (don''t overwrite newer files)

Misc Others:

--address=ADDRESS bind to the specified address
--blocking-io use blocking IO for the remote shell
--bwlimit=KBPS limit I/O bandwidth, KBytes per second
--config=FILE specify alternate rsyncd.conf file
--daemon run as a rsync daemon
--no-detach do not detach from the parent
--password-file=FILE get password from FILE
--port=PORT specify alternate rsyncd port number
-f, --read-batch=FILE read batch file
-F, --write-batch write batch file
--version print version number
-v, --verbose increase verbosity
-q, --quiet decrease verbosity
-h, --help show this help screen

Tips on how to use each of the options above can be found in the FULL List of OPTIONS and Exit Values

Exclude Patterns

The exclude and include patterns specified to rsync allow for flexible selection of which files to transfer and which files to skip.

rsync builds an ordered list of include/exclude options as specified on the command line. When a filename is encountered, rsync checks the name against each exclude/include pattern in turn. The first matching pattern is acted on.

  • If it is an exclude pattern, then that file is skipped.
  • If it is an include pattern then that filename is not skipped.
  • If no matching include/exclude pattern is found then the filename is not skipped.

Note that when used with -r (which is implied by -a), every subcomponent of every path is visited from top down, so include/exclude patterns get applied recursively to each subcomponent.

Note also that the --include and --exclude options take one pattern each. To add multiple patterns use the --include-from and --exclude-from options or multiple --include and --exclude options.

The patterns can take several forms. The rules are:

  • if the pattern starts with a / then it is matched against the start of the filename, otherwise it is matched against the end of the filename. Thus "/foo" would match a file called "foo" at the base of the tree. On the other hand, "foo" would match any file called "foo" anywhere in the tree because the algorithm is applied recursively from top down; it behaves as if each path component gets a turn at being the end of the file name.
  • if the pattern ends with a / then it will only match a directory, not a file, link or device.
  • if the pattern contains a wildcard character from the set *?[ then expression matching is applied using the shell filename matching rules. Otherwise a simple string match is used.
  • if the pattern includes a double asterisk "**" then all wildcards in the pattern will match slashes, otherwise they will stop at slashes.
  • if the pattern contains a / (not counting a trailing /) then it is matched against the full filename, including any leading directory. If the pattern doesn''t contain a / then it is matched only against the final component of the filename. Again, remember that the algorithm is applied recursively so "full filename" can actually be any portion of a path.
  • if the pattern starts with "+ " (a plus followed by a space) then it is always considered an include pattern, even if specified as part of an exclude option. The "+ " part is discarded before matching.
  • if the pattern starts with "- " (a minus followed by a space) then it is always considered an exclude pattern, even if specified as part of an include option. The "- " part is discarded before matching.
  • if the pattern is a single exclamation mark ! then the current include/exclude list is reset, removing all previously defined patterns.

The +/- rules are most useful in exclude lists, allowing you to have a single exclude list that contains both include and exclude options.

If you end an exclude list with --exclude ''*'', note that since the algorithm is applied recursively that unless you explicitly include parent directories of files you want to include then the algorithm will stop at the parent directories and never see the files below them. To include all directories, use --include ''*/'' before the --exclude ''*''.

Here are some exclude/include examples:

  • --exclude "*.o" would exclude all filenames matching *.o
  • --exclude "/foo" would exclude a file in the base directory called foo
  • --exclude "foo/" would exclude any directory called foo.
  • --exclude "/foo/*/bar" would exclude any file called bar two levels below a base directory called foo.
  • --exclude "/foo/**/bar" would exclude any file called bar two or more levels below a base directory called foo.
  • --include "*/" --include "*.c" --exclude "*" would include all directories and C source files
  • --include "foo/" --include "foo/bar.c" --exclude "*" would include only foo/bar.c (the foo/ directory must be explicitly included or it would be excluded by the "*")

Batch Mode

The following call generates 4 files that encapsulate the information for synchronizing the contents of target_dir with the updates found in src_dir

$ rsync -F [other rsync options here] \
/somewhere/src_dir /somewhere/target_dir

The generated files are labeled with a common timestamp:

  • rsync_argvs. command-line arguments
  • rsync_flist. rsync internal file metadata
  • rsync_csums. rsync checksums
  • rsync_delta. data blocks for file update & change

Symbolic Links

Three basic behaviours are possible when rsync encounters a symbolic link in the source directory.

By default, symbolic links are not transferred at all. A message "skipping non-regular" file is emitted for any symlinks that exist.

If --links is specified, then symlinks are recreated with the same target on the destination. Note that --archive implies --links.

If --copy-links is specified, then symlinks are "collapsed" by copying their referent, rather than the symlink.

rsync also distinguishes "safe" and "unsafe" symbolic links. An example where this might be used is a web site mirror that wishes ensure the rsync module they copy does not include symbolic links to /etc/passwd in the public section of the site. Using --copy-unsafe-links will cause any links to be copied as the file they point to on the destination. Using --safe-links will cause unsafe links to be ommitted altogether.


rsync occasionally produces error messages that may seem a little cryptic. The one that seems to cause the most confusion is "protocol version mismatch - is your shell clean?".

This message is usually caused by your startup scripts or remote shell facility producing unwanted garbage on the stream that rsync is using for its transport. The way to diagnose this problem is to run your remote shell like this:

rsh remotehost /bin/true > out.dat

then look at out.dat. If everything is working correctly then out.dat should be a zero length file. If you are getting the above error from rsync then you will probably find that out.dat contains some text or data. Look at the contents and try to work out what is producing it. The most common cause is incorrectly configured shell startup scripts (such as .cshrc or .profile) that contain output statements for non-interactive logins.

If you are having trouble debugging include and exclude patterns, then try specifying the -vv option. At this level of verbosity rsync will show why each individual file is included or excluded.


Once installed you can use rsync to any machine that you can use rsh to. rsync uses rsh for its communications, unless both the source and destination are local.

You can also specify an alternative to rsh, either by using the -e command line option, or by setting the RSYNC_RSH environment variable.

One common substitute is to use ssh, which offers a high degree of security.

Note that rsync must be installed on both the source and destination machines.

Environment Variables

The CVSIGNORE environment variable supplements any ignore patterns in .cvsignore files. See the --cvs-exclude option for more details.

The RSYNC_RSH environment variable allows you to override the default shell used as the transport for rsync. This can be used instead of the -e option.

The RSYNC_PROXY environment variable allows you to redirect your rsync client to use a web proxy when connecting to a rsync daemon. You should set RSYNC_PROXY to a hostname:port pair.

Setting RSYNC_PASSWORD to the required password allows you to run authenticated rsync connections to a rsync daemon without user intervention. Note that this does not supply a password to a shell transport such as ssh.

The USER or LOGNAME environment variables are used to determine the default username sent to a rsync server.

The HOME environment variable is used to find the user''s default .cvsignore file.


About the Author

FortyPoundHead has posted a total of 1974 articles.


Comments On This Post

No comments on this post yet!

Do you have a thought relating to this post? You can post your comment here. If you have an unrelated question, you can use the Q&A section to ask it.

Or you can drop a note to the administrators if you're not sure where you should post.

Your IP address is:

Before you can post, you need to prove you are human. If you log in, this test goes away.

Recent Forum Posts

SSL Now Active
dwirch posted on June 16, 2017 at about 8:40 in Site News

SSL Now Active
dwirch posted on June 13, 2017 at about 7:59 in Site News

Coding Archive?
dwirch posted on June 3, 2017 at about 12:54 in Site News

Job Spammer: Bharti Jigyasi
dwirch posted on June 2, 2017 at about 16:57 in Spammers

Coding Archive?
dwirch posted on May 25, 2017 at about 12:38 in Site News

BWASL returns
dwirch posted on May 13, 2017 at about 15:24 in Site News