Unison File Synchronizer
Version 2.52.1
Overview
Unison is a file-synchronization tool for Unix and Windows. It allows
two replicas of a collection of files and directories to be stored on
different hosts (or different disks on the same host), modified
separately, and then brought up to date by propagating the changes in
each replica to the other.
Unison shares a number of features with tools such as configuration
management packages (CVS (http://www.cyclic.com/), PRCS
(http://www.XCF.Berkeley.EDU/~jmacd/prcs.html), etc.), distributed
filesystems (Coda (http://www.coda.cs.cmu.edu/), etc.), uni-directional
mirroring utilities (rsync (http://samba.anu.edu.au/rsync/), etc.), and
other synchronizers (Intellisync (http://www.pumatech.com), Reconcile
(http://www.merl.com/reports/TR99-14/), etc). However, there are
several points where it differs:
* Unison runs on both Windows (95, 98, NT, 2k, and XP) and Unix (OSX,
Solaris, Linux, etc.) systems. Moreover, Unison works across
platforms, allowing you to synchronize a Windows laptop with a Unix
server, for example.
* Unlike a distributed filesystem, Unison is a user-level program:
there is no need to modify the kernel or to have superuser
privileges on either host.
* Unlike simple mirroring or backup utilities, Unison can deal with
updates to both replicas of a distributed directory structure.
Updates that do not conflict are propagated automatically.
Conflicting updates are detected and displayed.
* Unison works between any pair of machines connected to the
internet, communicating over either a direct socket link or
tunneling over an encrypted ssh connection. It is careful with
network bandwidth, and runs well over slow links such as PPP
connections. Transfers of small updates to large files are
optimized using a compression protocol similar to rsync.
* Unison has a clear and precise specification, described below.
* Unison is resilient to failure. It is careful to leave the replicas
and its own private structures in a sensible state at all times,
even in case of abnormal termination or communication failures.
* Unison is free; full source code is available under the GNU Public
License.
Preface
People
Benjamin Pierce (http://www.cis.upenn.edu/~bcpierce/) leads the Unison
project. The current version of Unison was designed and implemented by
Trevor Jim (http://www.research.att.com/~trevor/), Benjamin Pierce
(http://www.cis.upenn.edu/~bcpierce/), and Jérôme Vouillon
(http://www.pps.jussieu.fr/~vouillon/), with Alan Schmitt
(http://alan.petitepomme.net/), Malo Denielou, Zhe Yang
(http://www.brics.dk/~zheyang/), Sylvain Gommier, and Matthieu Goulay.
The Mac user interface was started by Trevor Jim and enormously
improved by Ben Willmore. Our implementation of the rsync
(http://samba.org/rsync/) protocol was built by Norman Ramsey
(http://www.eecs.harvard.edu/~nr/) and Sylvain Gommier. It is based on
Andrew Tridgell (http://samba.anu.edu.au/~tridge/)’s thesis work
(http://samba.anu.edu.au/~tridge/phd_thesis.pdf) and inspired by his
rsync (http://samba.org/rsync/) utility. The mirroring and merging
functionality was implemented by Sylvain Roy, improved by Malo
Denielou, and improved yet further by Stéphane Lescuyer. Jacques
Garrigue (http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/) contributed
the original Gtk version of the user interface; the Gtk2 version was
built by Stephen Tse. Sundar Balasubramaniam helped build a prototype
implementation of an earlier synchronizer in Java. Insik Shin
(http://www.cis.upenn.edu/~ishin/) and Insup Lee
(http://www.cis.upenn.edu/~lee/) contributed design ideas to this
implementation. Cedric Fournet
(http://research.microsoft.com/~fournet/) contributed to an even
earlier prototype.
Mailing Lists and Bug Reporting
Mailing Lists:
Moderated mailing lists are available for discussions among users and
discussions among developers. See
https://github.com/bcpierce00/unison/wiki/Mailing-Lists
for descriptions of what content is appropriate on which list, and
subscripion instructions.
Reporting bugs:
Reports of bugs affecting correctness or safety are of interest to many
people. If Unison is not working the way you expect, see the
instructions for debugging, reporting bugs, and asking for help at
https://github.com/bcpierce00/unison/wiki/Reporting-Bugs-and-Feature
-Requests
Feature Requests:
Requests for features likely to be of interest to others are welcome,
but will probably just be added to the ever-growing todo list. Please
see the URL in the previous section for guidance on feature requests.
Development Status
Unison is no longer under active development as a research project.
(Our research efforts are now focused on a follow-on project called
Boomerang, described at http://www.cis.upenn.edu/~bcpierce/harmony.) At
this point, there is no one whose job it is to maintain Unison, fix
bugs, or answer questions.
However, the original developers are all still using Unison daily. It
will continue to be maintained and supported for the foreseeable
future, and we will occasionally release new versions with bug fixes,
small improvements, and contributed patches.
Proposed changes to unison are welcome. They should be submitted as
pull requests. (Since safety and robustness are Unison’s most important
properties, patches will be held to high standards of clear design and
clean coding.) If you want to contribute to Unison, start by
downloading the developer tarball from the download page. For some
details on how the code is organized, etc., see the file CONTRIB.
Copying
This file is part of Unison.
Unison is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your
option) any later version.
Unison is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
The GNU General Public License can be found at
http://www.gnu.org/licenses. A copy is also included in the Unison
source distribution in the file COPYING.
Acknowledgements
Work on Unison has been supported by the National Science Foundation
under grants CCR-9701826 and ITR-0113226, Principles and Practice of
Synchronization, and by University of Pennsylvania’s Institute for
Research in Cognitive Science (IRCS).
Installation
Unison is designed to be easy to install. The following sequence of
steps should get you a fully working installation in a few minutes. If
you run into trouble, you may find the suggestions on the Frequently
Asked Questions page
(http://www.cis.upenn.edu/~bcpierce/unison/faq.html) helpful. Pre-built
binaries are available for a variety of platforms.
Unison can be used with either of two user interfaces:
1. a simple textual interface, suitable for dumb terminals (and
running from scripts), and
2. a more sophisticated graphical interface, based on Gtk2 (on
Linux/Windows) or the native UI framework (on OSX).
You will need to install a copy of Unison on every machine that you
want to synchronize. However, you only need the version with a
graphical user interface (if you want a GUI at all) on the machine
where you’re actually going to display the interface (the CLIENT
machine). Other machines that you synchronize with can get along just
fine with the textual version.
Downloading Unison
See https://github.com/bcpierce00/unison/wiki/Downloading-Unison.
If a pre-built binary of Unison is available for the client machine’s
architecture, just download it and put it somewhere in your search path
(if you’re going to invoke it from the command line) or on your desktop
(if you’ll be click-starting it).
The executable file for the graphical version (with a name including
gtkui) actually provides both interfaces: the graphical one appears by
default, while the textual interface can be selected by including -ui
text on the command line. The textui executable provides just the
textual interface.
If you don’t see a pre-built executable for your architecture, you’ll
need to build it yourself. See the section “Building Unison from
Scratch” .
Check to make sure that what you have downloaded is really executable.
Either click-start it, or type "unison -version" at the command line.
Unison can be used in three different modes: with different directories
on a single machine, with a local or a remote machine over a direct
socket connection, or with a remote machine using ssh for
authentication and secure transfer.
Running Unison
Once you’ve got Unison installed on at least one system, read the
section “Tutorial” of the user manual (or type "unison -doc tutorial")
for instructions on how to get started.
Upgrading
Upgrading to a new version of Unison is as simple as throwing away the
old binary and installing the new one.
Before upgrading, it is a good idea to run the old version one last
time, to make sure all your replicas are completely synchronized. A new
version of Unison will sometimes introduce a different format for the
archive files used to remember information about the previous state of
the replicas. In this case, the old archive will be ignored (not
deleted — if you roll back to the previous version of Unison, you will
find the old archives intact), which means that any differences between
the replicas will show up as conflicts that need to be resolved
manually.
As of version 2.52, Unison has a degree of backward and forward
compatibility. This means three things. First, it is possible for local
and remote machines to run a different version of Unison. Second, it is
possible for local and remote machines to run a version (same or
different) of Unison built with a different version of OCaml compiler
(this has been problematic historically). Lastly, it is possible to
upgrade Unison on the local machine (compiled with any OCaml version)
and keep the existing archive.
If version interoperability requirements are followed then Unison 2.52
can upgrade the archive created by earlier Unison versions. To avoid
rebuilding archive files, you must install version 2.52 built with the
same OCaml version as your previous version of Unison, and then run it
at least once on each root. Doing so will upgrade the archive file.
After upgrading the archive, you are free to swap the Unison 2.52
executable to one compiled with a different version of OCaml. The
archive file is no longer dependent on the compiler version.
Version interoperability
To ensure interoperability with different Unison versions on local and
remote machines, and to upgrade from an earlier version without
rebuilding the archive files, you have to remember these guidelines.
Upgrading from an incompatible version, while possible and normal, will
require fully scanning both roots, which can be time-consuming with big
replicas.
Unison 2.52 is compatible with:
* Unison 2.52 or newer (for as long as backwards compatibility is
maintained in the newer versions). You do not have to pay any
attention to OCaml compiler versions.
* Unison 2.51 if both versions are compiled with same OCaml compiler
version (you can see which compiler version was used by running
unison -version).
* Unison 2.48 if both versions are compiled with same OCaml compiler
version. See special notes below.
Interoperability matrix for quick reference:
Client versions Server versions
2.52 or newer 2.51 2.48
2.52 or newer full interop same OCaml version same OCaml version
2.51 same OCaml version full interop no interop
2.48 same OCaml version* no interop full interop
Special notes for Unison 2.48:
* Unison 2.48 does not show which OCaml compiler was used to compile
it. If you do not have the option of re-compiling the 2.48 version,
you have two alternatives. First (and most likely to succeed), see
what is the version of the OCaml compiler in the same package
repository where you installed Unison 2.48 from, then use Unison
2.52 compiled with that version. Second, you can just try Unison
2.52 executables compiled with different OCaml versions and see
which one works with your copy of Unison 2.48.
* When running Unison 2.48 on the client machine with Unison 2.52 or
newer on the server machine, you have to do some additional
configuration. The Unison executable name on the server must start
with unison-2.48 (just unison-2.48 is ok, as is unison-2.48.exe,
but also unison-2.48+ocaml-4.05). If using TCP socket connection to
the server then you’re all set! If using ssh then you have to add
one of the following options to your profile or as a command-line
argument on the client machine: -addversionno; see the section
“Remote Usage” , or -servercmd; see the section “Remote Shell
Method” .
Building Unison from Scratch
If a pre-built image is not available, you will need to compile it from
scratch; the sources are available from the same place as the binaries.
In principle, Unison should work on any platform to which OCaml has
been ported and on which the Unix module is fully implemented. It has
been tested on many flavors of Windows (98, NT, 2000, XP) and Unix (OS
X, Solaris, Linux, FreeBSD), and on both 32- and 64-bit architectures.
Unix
Unison can be built with or without a graphical user interface (GUI).
The build system will decide automatically depending on the libraries
installed on your system, but you can also type make UISTYLE=text to
build Unison without GUI.
You’ll need the Objective Caml compiler, available from
http://caml.inria.fr. OCaml is available from most package managers
Building and installing OCaml on Unix systems is very straightforward;
just follow the instructions in the distribution. You’ll probably want
to build the native-code compiler in addition to the bytecode compiler,
as Unison runs much faster when compiled to native code, but this is
not absolutely necessary. (Quick start: on many systems, the following
sequence of commands will get you a working and installed compiler:
first do make world opt, then su to root and do make install.)
You’ll also need the GNU make utility, which is standard on most Unix
systems. Unison’s build system is not parallelizable, so don’t use
flags that cause it to start processes in parallel (e.g. -j).
Once you’ve got OCaml installed, grab a copy of the Unison sources,
unzip and untar them, change to the new "unison" directory, and type
“make UISTYLE=text”. The result should be an executable file called
"unison". Type "./unison" to make sure the program is executable. You
should get back a usage message.
If you want to build the graphical user interface, you will need to
install some additional things:
* The Gtk2 development libraries (package libgtk2.0-dev on debian
based systems).
* OCaml bindings for Gtk2. Install them from your software
repositories (package liblablgtk2-ocaml on debian based systems).
Also available from https://github.com/garrigue/lablgtk.
* Pango, a text rendering library and a part of Gtk2. On some systems
(e.g. Ubuntu) the bindings between Pango and OCaml need to be
installed explicitly (package liblablgtk-extras-ocaml-dev on
Ubuntu).
Type make src to build Unison. If Gtk2 is available on the system,
Unison with a GUI will be built automatically.
Put the unison executable somewhere in your search path, either by
adding the Unison directory to your PATH variable or by copying the
executable to some standard directory where executables are stored. Or
just type make install to install Unison to $HOME/bin/unison.
Mac OS X
To build the text-only user interface, follow the instructions above
for building on Unix systems. You should do this first, even if you are
also planning on building the GUI, just to make sure it works.
To build the basic GUI version, you’ll first need to download and
install the XCode developer tools from Apple. Once this is done, just
type make in the src directory, and if things go well you should get an
application that you can move from uimac/build/Default/Unison.app to
wherever you want it.
Windows
Although the binary distribution should work on any version of Windows,
some people may want to build Unison from scratch on those systems too.
Bytecode version:
The simpler but slower compilation option to build a Unison executable
is to build a bytecode version. You need first install Windows version
of the OCaml compiler (version 3.07 or later, available from
http://caml.inria.fr). Then grab a copy of Unison sources and type
make NATIVE=false
to compile the bytecode. The result should be an executable file called
unison.exe.
Native version:
Building a more efficient, native version of Unison on Windows requires
a little more work. See the file INSTALL.win32 in the source code
distribution.
Installation Options
The Makefile in the distribution includes several switches that can be
used to control how Unison is built. Here are the most useful ones:
* Building with NATIVE=true uses the native-code OCaml compiler,
yielding an executable that will run quite a bit faster. We use
this for building distribution versions.
* Building with make DEBUGGING=true generates debugging symbols.
* Building with make STATIC=true generates a (mostly) statically
linked executable. We use this for building distribution versions,
for portability.
Tutorial
Preliminaries
Unison can be used with either of two user interfaces:
1. a straightforward textual interface and
2. a more sophisticated graphical interface
The textual interface is more convenient for running from scripts and
works on dumb terminals; the graphical interface is better for most
interactive use. For this tutorial, you can use either. If you are
running Unison from the command line, just typing unison will select
either the text or the graphical interface, depending on which has been
selected as default when the executable you are running was built. You
can force the text interface even if graphical is the default by adding
-ui text. The other command-line arguments to both versions are
identical.
The graphical version can also be run directly by clicking on its icon,
but this may require a little set-up (see the section “Click-starting
Unison” ). For this tutorial, we assume that you’re starting it from
the command line.
Unison can synchronize files and directories on a single machine, or
between two machines on a network. (The same program runs on both
machines; the only difference is which one is responsible for
displaying the user interface.) If you’re only interested in a
single-machine setup, then let’s call that machine the CLIENT . If
you’re synchronizing two machines, let’s call them CLIENT and SERVER .
Local Usage
Let’s get the client machine set up first and see how to synchronize
two directories on a single machine.
Follow the instructions in the section “Installation” to either
download or build an executable version of Unison, and install it
somewhere on your search path. (If you just want to use the textual
user interface, download the appropriate textui binary. If you just
want to the graphical interface—or if you will use both interfaces [the
gtkui binary actually has both compiled in]—then download the gtkui
binary.)
Create a small test directory a.tmp containing a couple of files and/or
subdirectories, e.g.,
mkdir a.tmp
touch a.tmp/a a.tmp/b
mkdir a.tmp/d
touch a.tmp/d/f
Copy this directory to b.tmp:
cp -r a.tmp b.tmp
Now try synchronizing a.tmp and b.tmp. (Since they are identical,
synchronizing them won’t propagate any changes, but Unison will
remember the current state of both directories so that it will be able
to tell next time what has changed.) Type:
unison a.tmp b.tmp
(You may need to add -ui text, depending how your unison binary was
built.)
Textual Interface:
* You should see a message notifying you that all the files are
actually equal and then get returned to the command line.
Graphical Interface:
* You should get a big empty window with a message at the bottom
notifying you that all files are identical. Choose the Exit item
from the File menu to get back to the command line.
Next, make some changes in a.tmp and/or b.tmp. For example:
rm a.tmp/a
echo "Hello" > a.tmp/b
echo "Hello" > b.tmp/b
date > b.tmp/c
echo "Hi there" > a.tmp/d/h
echo "Hello there" > b.tmp/d/h
Run Unison again:
unison a.tmp b.tmp
This time, the user interface will display only the files that have
changed. If a file has been modified in just one replica, then it will
be displayed with an arrow indicating the direction that the change
needs to be propagated. For example,
<--- new file c [f]
indicates that the file c has been modified only in the second replica,
and that the default action is therefore to propagate the new version
to the first replica. To follow Unison’s recommendation, press the “f”
at the prompt.
If both replicas are modified and their contents are different, then
the changes are in conflict: <-?-> is displayed to indicate that Unison
needs guidance on which replica should override the other.
new file <-?-> new file d/h []
By default, neither version will be propagated and both replicas will
remain as they are.
If both replicas have been modified but their new contents are the same
(as with the file b), then no propagation is necessary and nothing is
shown. Unison simply notes that the file is up to date.
These display conventions are used by both versions of the user
interface. The only difference lies in the way in which Unison’s
default actions are either accepted or overridden by the user.
Textual Interface:
* The status of each modified file is displayed, in turn. When the
copies of a file in the two replicas are not identical, the user
interface will ask for instructions as to how to propagate the
change. If some default action is indicated (by an arrow), you can
simply press Return to go on to the next changed file. If you want
to do something different with this file, press “<” or “>” to force
the change to be propagated from right to left or from left to
right, or else press “/” to skip this file and leave both replicas
alone. When it reaches the end of the list of modified files,
Unison will ask you one more time whether it should proceed with
the updates that have been selected.
When Unison stops to wait for input from the user, pressing “?”
will always give a list of possible responses and their meanings.
Graphical Interface:
* The main window shows all the files that have been modified in
either a.tmp or b.tmp. To override a default action (or to select
an action in the case when there is no default), first select the
file, either by clicking on its name or by using the up- and
down-arrow keys. Then press either the left-arrow or “<” key (to
cause the version in b.tmp to propagate to a.tmp) or the
right-arrow or “>” key (which makes the a.tmp version override
b.tmp).
Every keyboard command can also be invoked from the menus at the
top of the user interface. (Conversely, each menu item is annotated
with its keyboard equivalent, if it has one.)
When you are satisfied with the directions for the propagation of
changes as shown in the main window, click the “Go” button to set
them in motion. A check sign will be displayed next to each
filename when the file has been dealt with.
Remote Usage
Next, we’ll get Unison set up to synchronize replicas on two different
machines.
NB: Unison has not been designed to run with elevated privileges (e.g.
setuid), and it has not been audited for that environment. Therefore
Unison should be run with the userid of the owner of the files to be
synchronized, and should never be run setuid or similar. (Problems
encountered when running setuid etc. must be reproduced without setuid
before being reported as bugs.)
Follow the instructions in the Installation section to download or
build an executable version of Unison on the server machine, and
install it somewhere on your search path. (It doesn’t matter whether
you install the textual or graphical version, since the copy of Unison
on the server doesn’t need to display any user interface at all.)
It is important that the version of Unison installed on the server
machine is the same as the version of Unison on the client machine. But
some flexibility on the version of Unison at the client side can be
achieved by using the -addversionno option; see the section
“Preferences” .
Now there is a decision to be made. Unison provides two methods for
communicating between the client and the server:
* Remote shell method: To use this method, you must have some way of
invoking remote commands on the server from the client’s command
line, using a facility such as ssh. This method is more convenient
(since there is no need to manually start a “unison server” process
on the server) and also more secure, assuming you are using ssh).
* TCP socket method: This method requires only that you can get TCP
packets from the client to the server and back. It is insecure and
should not be used.
* Unix socket method: This method only works within a single machine.
It is similar to the TCP sockets method, but it is possible to
configure it securely.
Decide which of these you want to try, and continue with the section
“Remote Shell Method” or the section “Socket Method” , as appropriate.
Remote Shell Method
The standard remote shell facility on Unix systems is ssh.
Running ssh requires some coordination between the client and server
machines to establish that the client is allowed to invoke commands on
the server; please refer to the ssh documentation for information on
how to set this up.
First, test that we can invoke Unison on the server from the client.
Typing
ssh remotehostname unison -version
should print the same version information as running
unison -version
locally on the client. If remote execution fails, then either something
is wrong with your ssh setup (e.g., “permission denied”) or else the
search path that’s being used when executing commands on the server
doesn’t contain the unison executable (e.g., “command not found”).
Create a test directory a.tmp in your home directory on the client
machine.
Test that the local unison client can start and connect to the remote
server. Type
unison -testServer a.tmp ssh://remotehostname/a.tmp
Now cd to your home directory and type:
unison a.tmp ssh://remotehostname/a.tmp
The result should be that the entire directory a.tmp is propagated from
the client to your home directory on the server.
After finishing the first synchronization, change a few files and try
synchronizing again. You should see similar results as in the local
case.
If your user name on the server is not the same as on the client, you
need to specify it on the command line:
unison a.tmp ssh://username@remotehostname/a.tmp
Notes:
* If you want to put a.tmp some place other than your home directory
on the remote host, you can give an absolute path for it by adding
an extra slash between remotehostname and the beginning of the
path:
unison a.tmp ssh://remotehostname//absolute/path/to/a.tmp
* You can give an explicit path for the unison executable on the
server by using the command-line option "-servercmd
/full/path/name/of/unison" or adding
"servercmd=/full/path/name/of/unison" to your profile (see the
section “Profiles” ). Similarly, you can specify an explicit path
for the ssh program using the "-sshcmd" option. Extra arguments can
be passed to ssh by setting the -sshargs preference.
* By leveraging "-sshcmd" and "-sshargs", you can effectively use any
remote shell program, not just ssh; just remember that the roots
are still specified with ssh as the protocol, that is, they have to
start with "ssh://".
Socket Method
To run Unison over a socket connection, you must start a Unison daemon
process on the server. This process runs continuously, waiting for
connections over a given socket from client machines running Unison and
processing their requests in turn.
Since the socket method is not used by many people, its functionality
is rather limited. For example, the server can only deal with one
client at a time.
Note that the Unison daemon process is always started with a
command-line argument; not from a profile.
TCP Sockets
Warning: The TCP socket method is insecure: not only are the texts
of your changes transmitted over the network in unprotected form, it
is also possible for anyone in the world to connect to the server
process and read out the contents of your filesystem! (Of course, to
do this they must understand the protocol that Unison uses to
communicate between client and server, but all they need for this is
a copy of the Unison sources.) The socket method is provided only
for expert users with specific needs; everyone else should use the
ssh method.
To start the daemon for connections over a TCP socket, type
unison -socket NNNN
on the server machine, where NNNN is the TCP port number that the
daemon should listen on for connections from clients. (NNNN can be any
large number that is not being used by some other program; if NNNN is
already in use, Unison will exit with an error message.)
Create a test directory a.tmp in your home directory on the client
machine. Now type:
unison a.tmp socket://remotehostname:NNNN/a.tmp
Note that paths specified by the client will be interpreted relative to
the directory in which you start the server process; this behavior is
different from the ssh case, where the path is relative to your home
directory on the server. The result should be that the entire directory
a.tmp is propagated from the client to the server (a.tmp will be
created on the server in the directory that the server was started
from). After finishing the first synchronization, change a few files
and try synchronizing again. You should see similar results as in the
local case.
By default Unison will listen for incoming connections on all
interfaces. If you want to limit this to certain interfaces or
addresses then you can use the -listen command-line argument,
specifying a host name or an IP address to listen on. -listen can be
given multiple times to listen on several addresses.
Unix Domain Sockets
To start the daemon for connections over a Unix domain socket, type
unison -socket PPPP
where PPPP is the path to a Unix socket that the daemon should open for
connections from clients. (PPPP can be any absolute or relative path
the server process has access to but it must not exist yet; the socket
is created at that path when the daemon process is started.) You are
responsible for securing access to the socket path. For example, this
can be done by controlling the permissions of socket’s parent
directory, or ensuring a restrictive umask value when starting Unison.
Clients can connect to a server over a Unix domain socket by specifying
the absolute or relative path to the socket, instead of a server
address and port number:
unison a.tmp socket://{path/to/unix/socket}/a.tmp
(socket path is enclosed in curly braces).
Note that Unix domain sockets are local sockets (they exist in the
filesystem namespace). One could use Unixs socket remotely, by
forwarding access to the socket by other means, for example by using
spiped secure pipe daemon.
Using Unison for All Your Files
Once you are comfortable with the basic operation of Unison, you may
find yourself wanting to use it regularly to synchronize your commonly
used files. There are several possible ways of going about this:
1. Synchronize your whole home directory, using the Ignore facility
(see the section “Ignoring Paths” ) to avoid synchronizing
temporary files and things that only belong on one host.
2. Create a subdirectory called shared (or current, or whatever) in
your home directory on each host, and put all the files you want to
synchronize into this directory.
3. Create a subdirectory called shared (or current, or whatever) in
your home directory on each host, and put links to all the files
you want to synchronize into this directory. Use the follow
preference (see the section “Symbolic Links” ) to make Unison treat
these links as transparent.
4. Make your home directory the root of the synchronization, but tell
Unison to synchronize only some of the files and subdirectories
within it on any given run. This can be accomplished by using the
-path switch on the command line:
unison /home/username ssh://remotehost//home/username -path shared
The -path option can be used as many times as needed, to
synchronize several files or subdirectories:
unison /home/username ssh://remotehost//home/username \
-path shared \
-path pub \
-path .netscape/bookmarks.html
These -path arguments can also be put in your preference file. See
the section “Preferences” for an example.
Most people find that they only need to maintain a profile (or
profiles) on one of the hosts that they synchronize, since Unison is
always initiated from this host. (For example, if you’re synchronizing
a laptop with a fileserver, you’ll probably always run Unison on the
laptop.) This is a bit different from the usual situation with
asymmetric mirroring programs like rdist, where the mirroring operation
typically needs to be initiated from the machine with the most recent
changes. the section “Profiles” covers the syntax of Unison profiles,
together with some sample profiles.
Some tips on improving Unison’s performance can be found on the
Frequently Asked Questions page
(http://www.cis.upenn.edu/~bcpierce/unison/faq.html).
Using Unison to Synchronize More Than Two Machines
Unison is designed for synchronizing pairs of replicas. However, it is
possible to use it to keep larger groups of machines in sync by
performing multiple pairwise synchronizations.
If you need to do this, the most reliable way to set things up is to
organize the machines into a “star topology,” with one machine
designated as the “hub” and the rest as “spokes,” and with each spoke
machine synchronizing only with the hub. The big advantage of the star
topology is that it eliminates the possibility of confusing “spurious
conflicts” arising from the fact that a separate archive is maintained
by Unison for every pair of hosts that it synchronizes.
Going Further
On-line documentation for the various features of Unison can be
obtained either by typing
unison -doc topics
at the command line, or by selecting the Help menu in the graphical
user interface. The same information is also available in a typeset
User’s Manual (HTML or PostScript format) through
http://www.cis.upenn.edu/~bcpierce/unison.
If you use Unison regularly, you should subscribe to one of the mailing
lists, to receive announcements of new versions. See the section
“Mailing Lists and Bug Reporting” .
Basic Concepts
To understand how Unison works, it is necessary to discuss a few
straightforward concepts.
These concepts are developed more rigorously and at more length in a
number of papers, available at
http://www.cis.upenn.edu/~bcpierce/papers. But the informal
presentation here should be enough for most users.
Roots
A replica’s root tells Unison where to find a set of files to be
synchronized, either on the local machine or on a remote host. For
example,
relative/path/of/root
specifies a local root relative to the directory where Unison is
started, while
/absolute/path/of/root
specifies a root relative to the top of the local filesystem,
independent of where Unison is running. Remote roots can begin with
ssh:// to indicate that the remote server should be started with ssh:
ssh://remotehost//absolute/path/of/root
ssh://user@remotehost/relative/path/of/root
If the remote server is already running (in the socket mode), then the
syntax
socket://remotehost:portnum//absolute/path/of/root
socket://remotehost:portnum/relative/path/of/root
socket://[IPv6literal]:portnum/path
is used to specify the hostname and the port that the client Unison
should use to contact it. Syntax
socket://{path/of/socket}//absolute/path/of/root
socket://{path/of/socket}/relative/path/of/root
is used to specify the Unix domain socket the client Unison should use
to contact the server.
The syntax for roots is based on that of URIs (described in RFC 2396).
The full grammar is:
replica ::= [protocol:]//[user@][host][:port][/path]
| path
protocol ::= file
| socket
| ssh
user ::= [-_a-zA-Z0-9]+
host ::= [-_a-zA-Z0-9.]+
| \[ [a-f0-9:.]+ zone? \] IPv6 literals (no future format).
| { [^}]+ } For Unix domain sockets only.
zone ::= %[-_a-zA-Z0-9~%.]+
port ::= [0-9]+
When path is given without any protocol prefix, the protocol is assumed
to be file:. Under Windows, it is possible to synchronize with a remote
directory using the file: protocol over the Windows Network
Neighborhood. For example,
unison foo //host/drive/bar
synchronizes the local directory foo with the directory drive:\bar on
the machine host, provided that host is accessible via Network
Neighborhood. When the file: protocol is used in this way, there is no
need for a Unison server to be running on the remote host. However,
running Unison this way is only a good idea if the remote host is
reached by a very fast network connection, since the full contents of
every file in the remote replica will have to be transferred to the
local machine to detect updates.
The names of roots are canonized by Unison before it uses them to
compute the names of the corresponding archive files, so
//saul//home/bcpierce/common and //saul.cis.upenn.edu/common will be
recognized as the same replica under different names.
Paths
A path refers to a point within a set of files being synchronized; it
is specified relative to the root of the replica.
Formally, a path is just a sequence of names, separated by /. Note that
the path separator character is always a forward slash, no matter what
operating system Unison is running on. Forward slashes are converted to
backslashes as necessary when paths are converted to filenames in the
local filesystem on a particular host. (For example, suppose that we
run Unison on a Windows system, synchronizing the local root c:\pierce
with the root ssh://saul.cis.upenn.edu/home/bcpierce on a Unix server.
Then the path current/todo.txt refers to the file
c:\pierce\current\todo.txt on the client and
/home/bcpierce/current/todo.txt on the server.)
The empty path (i.e., the empty sequence of names) denotes the whole
replica. Unison displays the empty path as “[root].”
If p is a path and q is a path beginning with p, then q is said to be a
descendant of p. (Each path is also a descendant of itself.)
What is an Update?
The contents of a path p in a particular replica could be a file, a
directory, a symbolic link, or absent (if p does not refer to anything
at all in that replica). More specifically:
* If p refers to an ordinary file, then the contents of p are the
actual contents of this file (a string of bytes) plus the current
permission bits of the file.
* If p refers to a symbolic link, then the contents of p are just the
string specifying where the link points.
* If p refers to a directory, then the contents of p are just the
token “DIRECTORY” plus the current permission bits of the
directory.
* If p does not refer to anything in this replica, then the contents
of p are the token “ABSENT.”
Unison keeps a record of the contents of each path after each
successful synchronization of that path (i.e., it remembers the
contents at the last moment when they were the same in the two
replicas).
We say that a path is updated (in some replica) if its current contents
are different from its contents the last time it was successfully
synchronized. Note that whether a path is updated has nothing to do
with its last modification time—Unison considers only the contents when
determining whether an update has occurred. This means that touching a
file without changing its contents will not be recognized as an update.
A file can even be changed several times and then changed back to its
original contents; as long as Unison is only run at the end of this
process, no update will be recognized.
What Unison actually calculates is a close approximation to this
definition; see the section “Caveats and Shortcomings” .
What is a Conflict?
A path is said to be conflicting if the following conditions all hold:
1. it has been updated in one replica,
2. it or any of its descendants has been updated in the other replica,
and
3. its contents in the two replicas are not identical.
Reconciliation
Unison operates in several distinct stages:
1. On each host, it compares its archive file (which records the state
of each path in the replica when it was last synchronized) with the
current contents of the replica, to determine which paths have been
updated.
2. It checks for “false conflicts” — paths that have been updated on
both replicas, but whose current values are identical. These paths
are silently marked as synchronized in the archive files in both
replicas.
3. It displays all the updated paths to the user. For updates that do
not conflict, it suggests a default action (propagating the new
contents from the updated replica to the other). Conflicting
updates are just displayed. The user is given an opportunity to
examine the current state of affairs, change the default actions
for nonconflicting updates, and choose actions for conflicting
updates.
4. It performs the selected actions, one at a time. Each action is
performed by first transferring the new contents to a temporary
file on the receiving host, then atomically moving them into place.
5. It updates its archive files to reflect the new state of the
replicas.
Invariants
Given the importance and delicacy of the job that it performs, it is
important to understand both what a synchronizer does under normal
conditions and what can happen under unusual conditions such as system
crashes and communication failures.
Unison is careful to protect both its internal state and the state of
the replicas at every point in this process. Specifically, the
following guarantees are enforced:
* At every moment, each path in each replica has either (1) its
original contents (i.e., no change at all has been made to this
path), or (2) its correct final contents (i.e., the value that the
user expected to be propagated from the other replica).
* At every moment, the information stored on disk about Unison’s
private state can be either (1) unchanged, or (2) updated to
reflect those paths that have been successfully synchronized.
The upshot is that it is safe to interrupt Unison at any time, either
manually or accidentally. [Caveat: the above is almost true there are
occasionally brief periods where it is not (and, because of shortcoming
of the Posix filesystem API, cannot be); in particular, when it is
copying a file onto a directory or vice versa, it must first move the
original contents out of the way. If Unison gets interrupted during one
of these periods, some manual cleanup may be required. In this case, a
file called DANGER.README will be left in the .unison directory,
containing information about the operation that was interrupted. The
next time you try to run Unison, it will notice this file and warn you
about it.]
If an interruption happens while it is propagating updates, then there
may be some paths for which an update has been propagated but which
have not been marked as synchronized in Unison’s archives. This is no
problem: the next time Unison runs, it will detect changes to these
paths in both replicas, notice that the contents are now equal, and
mark the paths as successfully updated when it writes back its private
state at the end of this run.
If Unison is interrupted, it may sometimes leave temporary working
files (with suffix .tmp) in the replicas. It is safe to delete these
files. Also, if the backups flag is set, Unison will leave around old
versions of files that it overwrites, with names like
file.0.unison.bak. These can be deleted safely when they are no longer
wanted.
Unison is not bothered by clock skew between the different hosts on
which it is running. It only performs comparisons between timestamps
obtained from the same host, and the only assumption it makes about
them is that the clock on each system always runs forward.
If Unison finds that its archive files have been deleted (or that the
archive format has changed and they cannot be read, or that they don’t
exist because this is the first run of Unison on these particular
roots), it takes a conservative approach: it behaves as though the
replicas had both been completely empty at the point of the last
synchronization. The effect of this is that, on the first run, files
that exist in only one replica will be propagated to the other, while
files that exist in both replicas but are unequal will be marked as
conflicting.
Touching a file without changing its contents should never affect
whether or not Unison does an update. (When running with the fastcheck
preference set to true—the default on Unix systems—Unison uses file
modtimes for a quick first pass to tell which files have definitely not
changed; then, for each file that might have changed, it computes a
fingerprint of the file’s contents and compares it against the
last-synchronized contents. Also, the -times option allows you to
synchronize file times, but it does not cause identical files to be
changed; Unison will only modify the file times.)
It is safe to “brainwash” Unison by deleting its archive files on both
replicas. The next time it runs, it will assume that all the files it
sees in the replicas are new.
It is safe to modify files while Unison is working. If Unison discovers
that it has propagated an out-of-date change, or that the file it is
updating has changed on the target replica, it will signal a failure
for that file. Run Unison again to propagate the latest change.
Changes to the ignore patterns from the user interface (e.g., using the
‘i’ key) are immediately reflected in the current profile.
Caveats and Shortcomings
Here are some things to be careful of when using Unison.
* In the interests of speed, the update detection algorithm may
(depending on which OS architecture that you run Unison on)
actually use an approximation to the definition given in the
section “What is an Update?” .
In particular, the Unix implementation does not compare the actual
contents of files to their previous contents, but simply looks at
each file’s inode number and modtime; if neither of these have
changed, then it concludes that the file has not been changed.
Under normal circumstances, this approximation is safe, in the
sense that it may sometimes detect “false updates” but will never
miss a real one. However, it is possible to fool it, for example by
using retouch to change a file’s modtime back to a time in the
past.
* If you synchronize between a single-user filesystem and a shared
Unix server, you should pay attention to your permission bits: by
default, Unison will synchronize permissions verbatim, which may
leave group-writable files on the server that could be written over
by a lot of people.
You can control this by setting your umask on both computers to
something like 022, masking out the “world write” and “group write”
permission bits.
Unison does not synchronize the setuid and setgid bits, for
security.
* The graphical user interface is single-threaded. This means that if
Unison is performing some long-running operation, the display will
not be repainted until it finishes. We recommend not trying to do
anything with the user interface while Unison is in the middle of
detecting changes or propagating files.
* Unison does not understand hard links.
* It is important to be a little careful when renaming directories
containing ignored files.
For example, suppose Unison is synchronizing directory A between
the two machines called the “local” and the “remote” machine;
suppose directory A contains a subdirectory D; and suppose D on the
local machine contains a file or subdirectory P that matches an
ignore directive in the profile used to synchronize. Thus path
A/D/P exists on the local machine but not on the remote machine.
If D is renamed to D’ on the remote machine, and this change is
propagated to the local machine, all such files or subdirectories P
will be deleted. This is because Unison sees the rename as a delete
and a separate create: it deletes the old directory (including the
ignored files) and creates a new one (not including the ignored
files, since they are completely invisible to it).
Reference Guide
This section covers the features of Unison in detail.
Running Unison
There are several ways to start Unison.
* Typing “unison profile” on the command line. Unison will look for a
file profile.prf in the .unison directory. If this file does not
specify a pair of roots, Unison will prompt for them and add them
to the information specified by the profile.
* Typing “unison profile root1 root2” on the command line. In this
case, Unison will use profile, which should not contain any root
directives.
* Typing “unison root1 root2” on the command line. This has the same
effect as typing “unison default root1 root2.”
* Typing just “unison” (or invoking Unison by clicking on a desktop
icon). In this case, Unison will ask for the profile to use for
synchronization (or create a new one, if necessary).
The .unison Directory
Unison stores a variety of information in a private directory on each
host. If the environment variable UNISON is defined, then its value
will be used as the path/folder name for this directory. This can be
just a name, or a path.
A name on it’s own, for example UNISON=mytestname will place a folder
in the same directory that the Unison binary was run in, with that
name. Using a path like UNISON=../mytestname2 will place that folder in
the folder above where the Unison binary was run from.
If UNISON is not defined, then the directory depends on which operating
system you are using. In Unix, the default is to use $HOME/.unison. In
Windows, if the environment variable USERPROFILE is defined, then the
directory will be $USERPROFILE\.unison; otherwise if HOME is defined,
it will be $HOME\.unison; otherwise, it will be c:\.unison. On OS X,
$HOME/.unison will be used if it is present, but
$HOME/Library/Application Support/Unison will be created and used by
default.
The archive file for each replica is found in the .unison directory on
that replica’s host. Profiles (described below) are always taken from
the .unison directory on the client host.
Note that Unison maintains a completely different set of archive files
for each pair of roots.
We do not recommend synchronizing the whole .unison directory, as this
will involve frequent propagation of large archive files. It should be
safe to do it, though, if you really want to. Synchronizing just the
profile files in the .unison directory is definitely OK.
Archive Files
The name of the archive file on each replica is calculated from
* the canonical names of all the hosts (short names like saul are
converted into full addresses like saul.cis.upenn.edu),
* the paths to the replicas on all the hosts (again, relative
pathnames, symbolic links, etc. are converted into full, absolute
paths), and
* an internal version number that is changed whenever a new Unison
release changes the format of the information stored in the
archive.
This method should work well for most users. However, it is
occasionally useful to change the way archive names are generated.
Unison provides two ways of doing this.
The function that finds the canonical hostname of the local host (which
is used, for example, in calculating the name of the archive file used
to remember which files have been synchronized) normally uses the
gethostname operating system call. However, if the environment variable
UNISONLOCALHOSTNAME is set, its value will be used instead. This makes
it easier to use Unison in situations where a machine’s name changes
frequently (e.g., because it is a laptop and gets moved around a lot).
A more powerful way of changing archive names is provided by the
rootalias preference. The preference file may contain any number of
lines of the form:
rootalias = //hostnameA//path-to-replicaA -> //hostnameB/path-to-replicaB
When calculating the name of the archive files for a given pair of
roots, Unison replaces any root that matches the left-hand side of any
rootalias rule by the corresponding right-hand side.
So, if you need to relocate a root on one of the hosts, you can add a
rule of the form:
rootalias = //new-hostname//new-path -> //old-hostname/old-path
Note that root aliases are case-sensitive, even on case-insensitive
file systems.
Warning: The rootalias option is dangerous and should only be used if
you are sure you know what you’re doing. In particular, it should only
be used if you are positive that either (1) both the original root and
the new alias refer to the same set of files, or (2) the files have
been relocated so that the original name is now invalid and will never
be used again. (If the original root and the alias refer to different
sets of files, Unison’s update detector could get confused.) After
introducing a new rootalias, it is a good idea to run Unison a few
times interactively (with the batch flag off, etc.) and carefully check
that things look reasonable—in particular, that update detection is
working as expected.
Preferences
Many details of Unison’s behavior are configurable by user-settable
“preferences.”
Some preferences are boolean-valued; these are often called flags.
Others take numeric or string arguments, indicated in the preferences
list by n or xxx. Some string arguments take the backslash as an escape
to include the next character literally; this is mostly useful to
escape a space or the backslash; a trailing backslash is ignored and is
useful to protect a trailing whitespace in the string that would
otherwise be trimmed. Most of the string preferences can be given
several times; the arguments are accumulated into a list internally.
There are two ways to set the values of preferences: temporarily, by
providing command-line arguments to a particular run of Unison, or
permanently, by adding commands to a profile in the .unison directory
on the client host. The order of preferences (either on the command
line or in preference files) is not significant. On the command line,
preferences and other arguments (the profile name and roots) can be
intermixed in any order.
To set the value of a preference p from the command line, add an
argument -p (for a boolean flag) or -p n or -p xxx (for a numeric or
string preference) anywhere on the command line. To set a boolean flag
to false on the command line, use -p=false.
Here are all the preferences supported by Unison. This list can be
obtained by typing unison -help.
Usage: unison [options]
or unison root1 root2 [options]
or unison profilename [options]
Basic options:
General:
-doc xxx show documentation ('-doc topics' lists topics)
-version print version and exit
What to sync:
-group synchronize group attributes
-ignore xxx add a pattern to the ignore list
-ignorenot xxx add a pattern to the ignorenot list
-nocreation xxx prevent file creations on one replica
-nodeletion xxx prevent file deletions on one replica
-noupdate xxx prevent file updates and deletions on one replica
-owner synchronize owner
-path xxx path to synchronize
-perms n part of the permissions which is synchronized
-root xxx root of a replica (should be used exactly twice)
-times synchronize modification times
How to sync:
-batch batch mode: ask no questions at all
How to sync (text interface (CLI) only):
-auto automatically accept default (nonconflicting) actions
-silent print nothing except error messages
-terse suppress status messages
Text interface (CLI):
-i interactive profile mode (text UI); command-line only
Advanced options:
Fine-tune sync:
-atomic xxx add a pattern to the atomic list
-follow xxx add a pattern to the follow list
-force xxx force changes from this replica to the other
-forcepartial xxx add a pattern to the forcepartial list
-ignorecase xxx identify upper/lowercase filenames (true/false/default)
-immutable xxx add a pattern to the immutable list
-immutablenot xxx add a pattern to the immutablenot list
-links xxx allow the synchronization of symbolic links
(true/false/default)
-merge xxx add a pattern to the merge list
-nocreationpartial xxx add a pattern to the nocreationpartial list
-nodeletionpartial xxx add a pattern to the nodeletionpartial list
-noupdatepartial xxx add a pattern to the noupdatepartial list
-prefer xxx choose this replica's version for conflicting changes
-preferpartial xxx add a pattern to the preferpartial list
-rsrc xxx synchronize resource forks (true/false/default)
How to sync:
-backup xxx add a pattern to the backup list
-backupcurr xxx add a pattern to the backupcurr list
-backupcurrnot xxx add a pattern to the backupcurrnot list
-backupdir xxx directory for storing centralized backups
-backuploc xxx where backups are stored ('local' or 'central')
-backupnot xxx add a pattern to the backupnot list
-backupprefix xxx prefix for the names of backup files
-backups (deprecated) keep backup copies of all files (see also
'backup')
-backupsuffix xxx a suffix to be added to names of backup files
-confirmbigdel ask about whole-replica (or path) deletes (default true)
-confirmmerge ask for confirmation before committing results of a merge
-copyonconflict keep copies of conflicting files
-dontchmod when set, never use the chmod system call
-fastcheck xxx do fast update detection (true/false/default)
-fat use appropriate options for FAT filesystems
-ignoreinodenumbers ignore inode number changes when detecting updates
-maxbackups n number of backed up versions of a file
-numericids don't map uid/gid values by user/group names
-sortbysize list changed files by size, not name
-sortfirst xxx add a pattern to the sortfirst list
-sortlast xxx add a pattern to the sortlast list
-sortnewfirst list new before changed files
How to sync (text interface (CLI) only):
-repeat xxx synchronize repeatedly (text interface only)
-retry n re-try failed synchronizations N times (text ui only)
Text interface (CLI):
-color xxx use color output for text UI (true/false/default)
-dumbtty do not change terminal settings in text UI
Graphical interface (GUI):
-height n height (in lines) of main window in graphical interface
Remote connections:
-addversionno add version number to name of unison on server
-clientHostName xxx set host name of client
-halfduplex (deprecated) force half-duplex communication with the
server
-killserver kill server when done (even when using sockets)
-listen xxx listen on this name or addr in server socket mode (can
repeat)
-rsync activate the rsync transfer mode (default true)
-servercmd xxx name of unison executable on remote server
-socket xxx act as a server on a socket
-sshargs xxx other arguments (if any) for remote shell command
-sshcmd xxx path to the ssh executable
-stream (deprecated) use a streaming protocol for transferring
file contents (default true)
-testserver exit immediately after the connection to the server
-xferbycopying optimize transfers using local copies (default true)
Archive management:
-ignorearchives ignore existing archive files
Other:
-addprefsto xxx file to add new prefs to
-contactquietly suppress the 'contacting server' message during startup
-copymax n maximum number of simultaneous copyprog transfers
-copyprog xxx external program for copying large files
-copyprogrest xxx variant of copyprog for resuming partial transfers
-copyquoterem xxx add quotes to remote file name for copyprog
(true/false/default)
-copythreshold n use copyprog on files bigger than this (if >=0, in Kb)
-diff xxx set command for showing differences between files
-ignorelocks ignore locks left over from previous run (dangerous!)
-include xxx include a profile's preferences
-key xxx define a keyboard shortcut for this profile (in some UIs)
-label xxx provide a descriptive string label for this profile
-log record actions in logfile (default true)
-logfile xxx logfile name
-maxerrors n maximum number of errors before a directory transfer is
aborted
-maxsizethreshold n prevent transfer of files bigger than this (if >=0, in
Kb)
-maxthreads n maximum number of simultaneous file transfers
-mountpoint xxx abort if this path does not exist
-rootalias xxx register alias for canonical root names
-showarchive show 'true names' (for rootalias) of roots and archive
-source xxx include a file's preferences
-ui xxx select UI ('text' or 'graphic'); command-line only
-unicode xxx assume Unicode encoding in case insensitive mode
-watch when set, use a file watcher process to detect changes
Expert options:
-debug xxx debug module xxx ('all' -> everything, 'verbose' -> more)
-dumparchives dump contents of archives just after loading
-fastercheckUNSAFE skip computing fingerprints for new files (experts only!)
-selftest run internal tests and exit
Here, in more detail, is what they do. Many are discussed in greater
detail in other sections of the manual.
It should be noted that some command-line arguments are handled
specially during startup, including -doc, -help, -version, -socket, and
-ui. They are expected to appear on the command-line only, not in a
profile. In particular, -version and -doc will print to the standard
output, so they only make sense if invoked from the command-line (and
not a click-launched gui that has no standard output). Furthermore, the
actions associated with these command-line arguments are executed
without loading a profile or doing the usual command-line parsing.
addprefsto xxx
By default, new preferences added by Unison (e.g., new ignore
clauses) will be appended to whatever preference file Unison was
told to load at the beginning of the run. Setting the preference
addprefsto filename makes Unison add new preferences to the file
named filename instead.
addversionno
When this flag is set to true, Unison will use
unison-currentmajorversionnumber instead of just unison as the
remote server command (note that the minor version number is
dropped – e.g., unison-2.51). This allows multiple binaries for
different versions of unison to coexist conveniently on the same
server: whichever version is run on the client, the same version
will be selected on the server.
atomic xxx
This preference specifies paths for directories whose contents
will be considered as a group rather than individually when they
are both modified. The backups are also made atomically in this
case. The option backupcurr however has no effect on atomic
directories.
auto
When set to true, this flag causes the user interface to skip
asking for confirmations on non-conflicting changes. (More
precisely, when the user interface is done setting the
propagation direction for one entry and is about to move to the
next, it will skip over all non-conflicting entries and go
directly to the next conflict.)
backup xxx
Including the preference -backup pathspec causes Unison to keep
backup files for each path that matches pathspec; directories
(nor their permissions or any other metadata) are not backed up.
These backup files are kept in the directory specified by the
backuplocation preference. The backups are named according to
the backupprefix and backupsuffix preferences. The number of
versions that are kept is determined by the maxbackups
preference.
The syntax of pathspec is described in the section “Path
Specification” .
backupcurr xxx
Including the preference -backupcurr pathspec causes Unison to
keep a backup of the current version of every file matching
pathspec. This file will be saved as a backup with version
number 000. Such backups can be used as inputs to external
merging programs, for instance. See the documentatation for the
merge preference. For more details, see the section “Merging
Conflicting Versions” .
The syntax of pathspec is described in the section “Path
Specification” .
backupcurrnot xxx
Exceptions to backupcurr, like the ignorenot preference.
backupdir xxx
If this preference is set, Unison will use it as the name of the
directory used to store backup files specified by the backup
preference, when backuplocation is set to central. It is checked
after the UNISONBACKUPDIR environment variable.
backuploc xxx
This preference determines whether backups should be kept
locally, near the original files, or in a central directory
specified by the backupdir preference. If set to local, backups
will be kept in the same directory as the original files, and if
set to central, backupdir will be used instead.
backupnot xxx
The values of this preference specify paths or individual files
or regular expressions that should not be backed up, even if the
backup preference selects them—i.e., it selectively overrides
backup.
backupprefix xxx
When a backup for a file NAME is created, it is stored in a
directory specified by backuplocation, in a file called
backupprefixNAMEbackupsuffix. backupprefix can include a
directory name (causing Unison to keep all backup files for a
given directory in a subdirectory with this name), and both
backupprefix and backupsuffix can contain the string $VERSION,
which will be replaced by the age of the backup (1 for the most
recent, 2 for the second most recent, and so on...). This
keyword is ignored if it appears in a directory name in the
prefix; if it does not appear anywhere in the prefix or the
suffix, it will be automatically placed at the beginning of the
suffix.
One thing to be careful of: If the backuploc preference is set
to local, Unison will automatically ignore all files whose
prefix and suffix match backupprefix and backupsuffix. So be
careful to choose values for these preferences that are
sufficiently different from the names of your real files.
backups
(Deprecated) Setting this flag to true is equivalent to setting
backuplocation to local and backup to Name *.
backupsuffix xxx
See backupprefix for full documentation.
batch
When this is set to true, the user interface will ask no
questions at all. Non-conflicting changes will be propagated;
conflicts will be skipped.
clientHostName xxx
When specified, the host name of the client will not be guessed
and the provided host name will be used to find the archive.
color xxx
When set to true, this flag enables color output in text mode
user interface. When set to false, all color output is disabled.
Default is to enable color if the NO_COLOR environment variable
is not set.
confirmbigdel
When this is set to true, Unison will request an extra
confirmation if it appears that the entire replica has been
deleted, before propagating the change. If the batch flag is
also set, synchronization will be aborted. When the path
preference is used, the same confirmation will be requested for
top-level paths. (At the moment, this flag only affects the text
user interface.) See also the mountpoint preference.
confirmmerge
Setting this preference causes both the text and graphical
interfaces to ask the user if the results of a merge command may
be committed to the replica or not. Since the merge command
works on temporary files, the user can then cancel all the
effects of applying the merge if it turns out that the result is
not satisfactory. In batch-mode, this preference has no effect.
Default is false.
contactquietly
If this flag is set, Unison will skip displaying the ‘Contacting
server’ message (which some users find annoying) during startup.
copymax n
A number indicating how many instances of the external copying
utility Unison is allowed to run simultaneously (default to 1).
copyonconflict
When this flag is set, Unison will make a copy of files that
would otherwise be overwritten or deleted in case of conflicting
changes, and more generally whenever the default behavior is
overridden. This makes it possible to automatically resolve
conflicts in a fairly safe way when synchronizing continuously,
in combination with the -repeat watch and -prefer newer
preferences.
copyprog xxx
A string giving the name of an external program that can be used
to copy large files efficiently (plus command-line switches
telling it to copy files in-place). The default setting invokes
rsync with appropriate options—most users should not need to
change it.
copyprogrest xxx
A variant of copyprog that names an external program that should
be used to continue the transfer of a large file that has
already been partially transferred. Typically, copyprogrest will
just be copyprog with one extra option (e.g., --partial, for
rsync). The default setting invokes rsync with appropriate
options—most users should not need to change it.
copyquoterem xxx
When set to true, this flag causes Unison to add an extra layer
of quotes to the remote path passed to the external copy
program. This is needed by rsync, for example, which internally
uses an ssh connection requiring an extra level of quoting for
paths containing spaces. When this flag is set to default, extra
quotes are added if the value of copyprog contains the string
rsync.
copythreshold n
A number indicating above what filesize (in kilobytes) Unison
should use the external copying utility specified by copyprog.
Specifying 0 will cause all copies to use the external program;
a negative number will prevent any files from using it. The
default is -1. See the section “Making Unison Faster on Large
Files” for more information.
debug xxx
This preference is used to make Unison print various sorts of
information about what it is doing internally on the standard
error stream. It can be used many times, each time with the name
of a module for which debugging information should be printed.
Possible arguments for debug can be found by looking for calls
to Util.debug in the sources (using, e.g., grep). Setting -debug
all causes information from all modules to be printed (this mode
of usage is the first one to try, if you are trying to
understand something that Unison seems to be doing wrong);
-debug verbose turns on some additional debugging output from
some modules (e.g., it will show exactly what bytes are being
sent across the network).
diff xxx
This preference can be used to control the name and command-line
arguments of the system utility used to generate displays of
file differences. The default is ‘diff -u OLDER NEWER’. If the
value of this preference contains the substrings CURRENT1 and
CURRENT2, these will be replaced by the names of the files to be
diffed. If the value of this preference contains the substrings
NEWER and OLDER, these will be replaced by the names of files to
be diffed, NEWER being the most recently modified file of the
two. Without any of these substrings, the two filenames will be
appended to the command. In all cases, the filenames are
suitably quoted.
doc xxx
The command-line argument -doc secname causes unison to display
section secname of the manual on the standard output and then
exit. Use -doc all to display the whole manual, which includes
exactly the same information as the printed and HTML manuals,
modulo formatting. Use -doc topics to obtain a list of the names
of the various sections that can be printed.
dontchmod
By default, Unison uses the ’chmod’ system call to set the
permission bits of files after it has copied them. But in some
circumstances (and under some operating systems), the chmod call
always fails. Setting this preference completely prevents Unison
from ever calling chmod.
dumbtty
When set to true, this flag makes the text mode user interface
avoid trying to change any of the terminal settings. (Normally,
Unison puts the terminal in ‘raw mode’, so that it can do things
like overwriting the current line.) This is useful, for example,
when Unison runs in a shell inside of Emacs.
When dumbtty is set, commands to the user interface need to be
followed by a carriage return before Unison will execute them.
(When it is off, Unison recognizes keystrokes as soon as they
are typed.)
This preference has no effect on the graphical user interface.
dumparchives
When this preference is set, Unison will create a file
unison.dump on each host, containing a text summary of the
archive, immediately after loading it.
fastcheck xxx
When this preference is set to true, Unison will use the
modification time and length of a file as a ‘pseudo inode
number’ when scanning replicas for updates, instead of reading
the full contents of every file. (This does not apply to the
very first run, when Unison will always scan all files
regardless of this switch). Under Windows, this may cause Unison
to miss propagating an update if the modification time and
length of the file are both unchanged by the update. However,
Unison will never overwrite such an update with a change from
the other replica, since it always does a safe check for updates
just before propagating a change. Thus, it is reasonable to use
this switch under Windows most of the time and occasionally run
Unison once with fastcheck set to false, if you are worried that
Unison may have overlooked an update. For backward
compatibility, yes, no, and default can be used in place of
true, false, and auto. See the section “Fast Update Detection”
for more information.
fastercheckUNSAFE
THIS FEATURE IS STILL EXPERIMENTAL AND SHOULD BE USED WITH
EXTREME CAUTION.
When this flag is set to true, Unison will compute a
’pseudo-fingerprint’ the first time it sees a file (either
because the file is new or because Unison is running for the
first time). This enormously speeds update detection, but it
must be used with care, as it can cause Unison to miss
conflicts: If a given path in the filesystem contains files on
both sides that Unison has not yet seen, and if those files have
the same length but different contents, then Unison will not
notice the presence of a conflict. If, later, one of the files
is changed, the changed file will be propagated, overwriting the
other.
Moreover, even when the files are initially identical, setting
this flag can lead to potentially confusing behavior: if a newly
created file is later touched without being modified, Unison
will treat this conservatively as a potential change (since it
has no record of the earlier contents) and show it as needing to
be propagated to the other replica.
Most users should leave this flag off – the small time savings
of not fingerprinting new files is not worth the cost in terms
of safety. However, it can be very useful for power users with
huge replicas that are known to be already synchronized (e.g.,
because one replica is a newly created duplicate of the other,
or because they have previously been synchronized with Unison
but Unison’s archives need to be rebuilt). In such situations,
it is recommended that this flag be set only for the initial run
of Unison, so that new archives can be created quickly, and then
turned off for normal use.
fat
When this is set to true, Unison will use appropriate options to
synchronize efficiently and without error a replica located on a
FAT filesystem on a non-Windows machine: do not synchronize
permissions (perms = 0); never use chmod (dontchmod = true);
treat filenames as case insensitive (ignorecase = true); do not
attempt to synchronize symbolic links (links = false); ignore
inode number changes when detecting updates (ignoreinodenumbers
= true). Any of these change can be overridden by explicitly
setting the corresponding preference in the profile.
follow xxx
Including the preference -follow pathspec causes Unison to treat
symbolic links matching pathspec as ‘invisible’ and behave as if
the object pointed to by the link had appeared literally at this
position in the replica. See the section “Symbolic Links” for
more details. The syntax of pathspec is described in the section
“Path Specification” .
force xxx
Including the preference -force root causes Unison to resolve
all differences (even non-conflicting changes) in favor of root.
This effectively changes Unison from a synchronizer into a
mirroring utility.
You can also specify -force newer (or -force older) to force
Unison to choose the file with the later (earlier) modtime. In
this case, the -times preference must also be enabled.
This preference is overridden by the forcepartial preference.
This preference should be used only if you are sure you know
what you are doing!
forcepartial xxx
Including the preference forcepartial = PATHSPEC -> root causes
Unison to resolve all differences (even non-conflicting changes)
in favor of root for the files in PATHSPEC (see the section
“Path Specification” for more information). This effectively
changes Unison from a synchronizer into a mirroring utility.
You can also specify forcepartial PATHSPEC -> newer (or
forcepartial PATHSPEC older) to force Unison to choose the file
with the later (earlier) modtime. In this case, the -times
preference must also be enabled.
This preference should be used only if you are sure you know
what you are doing!
group
When this flag is set to true, the group attributes of the files
are synchronized. Whether the group names or the group
identifiers are synchronized depends on the preference numerids.
halfduplex
(Deprecated) When this flag is set to true, Unison network
communication is forced to be half duplex (the client and the
server never simultaneously emit data). If you experience
unstabilities with your network link, this may help.
height n
Used to set the height (in lines) of the main window in the
graphical user interface.
i
Provide this preference in the command line arguments to enable
interactive profile manager in the text user interface.
Currently only profile listing and interactive selection are
available. Preferences like batch and silent remain applicable
to synchronization functionality.
ignore xxx
Including the preference -ignore pathspec causes Unison to
completely ignore paths that match pathspec (as well as their
children). This is useful for avoiding synchronizing temporary
files, object files, etc. The syntax of pathspec is described in
the section “Path Specification” , and further details on
ignoring paths is found in the section “Ignoring Paths” .
ignorearchives
When this preference is set, Unison will ignore any existing
archive files and behave as though it were being run for the
first time on these replicas. It is not a good idea to set this
option in a profile: it is intended for command-line use.
ignorecase xxx
When set to true, this flag causes Unison to treat filenames as
case insensitive—i.e., files in the two replicas whose names
differ in (upper- and lower-case) ‘spelling’ are treated as the
same file. When the flag is set to false, Unison will treat all
filenames as case sensitive. Ordinarily, when the flag is set to
default, filenames are automatically taken to be
case-insensitive if either host is running Windows or OSX. In
rare circumstances it may be useful to set the flag manually.
ignoreinodenumbers
When set to true, this preference makes Unison not take
advantage of inode numbers during fast update detection. This
switch should be used with care, as it is less safe than the
standard update detection method, but it can be useful with
filesystems which do not support inode numbers.
ignorelocks
When this preference is set, Unison will ignore any lock files
that may have been left over from a previous run of Unison that
was interrupted while reading or writing archive files; by
default, when Unison sees these lock files it will stop and
request manual intervention. This option should be set only if
you are positive that no other instance of Unison might be
concurrently accessing the same archive files (e.g., because
there was only one instance of unison running and it has just
crashed or you have just killed it). It is probably not a good
idea to set this option in a profile: it is intended for
command-line use.
ignorenot xxx
This preference overrides the preference ignore. It gives a list
of patterns (in the same format as ignore) for paths that should
definitely not be ignored, whether or not they happen to match
one of the ignore patterns.
Note that the semantics of ignore and ignorenot is a little
counter-intuitive. When detecting updates, Unison examines paths
in depth-first order, starting from the roots of the replicas
and working downwards. Before examining each path, it checks
whether it matches ignore and does not match ignorenot; in this
case it skips this path and all its descendants. This means
that, if some parent of a given path matches an ignore pattern,
then it will be skipped even if the path itself matches an
ignorenot pattern. In particular, putting ignore = Path * in
your profile and then using ignorenot to select particular paths
to be synchronized will not work. Instead, you should use the
path preference to choose particular paths to synchronize.
immutable xxx
This preference specifies paths for directories whose immediate
children are all immutable files — i.e., once a file has been
created, its contents never changes. When scanning for updates,
Unison does not check whether these files have been modified;
this can speed update detection significantly (in particular,
for mail directories).
immutablenot xxx
This preference overrides immutable.
include xxx
Include preferences from a profile. include name reads the
profile "name" (or file "name" in the .unison directory if
profile "name" does not exist) and includes its contents as if
it was part of a profile or given directly on command line.
key xxx
Used in a profile to define a numeric key (0-9) that can be used
in the user interface to switch immediately to this profile.
killserver
When set to true, this flag causes Unison to kill the remote
server process when the synchronization is finished. This
behavior is the default for ssh connections, so this preference
is not normally needed when running over ssh; it is provided so
that socket-mode servers can be killed off after a single run of
Unison, rather than waiting to accept future connections. (Some
users prefer to start a remote socket server for each run of
Unison, rather than leaving one running all the time.)
label xxx
Used in a profile to provide a descriptive string documenting
its settings. (This is useful for users that switch between
several profiles, especially using the ‘fast switch’ feature of
the graphical user interface.)
links xxx
When set to true, this flag causes Unison to synchronize
symbolic links. When the flag is set to false, symbolic links
will result in an error during update detection. Ordinarily,
when the flag is set to default, symbolic links are synchronized
except when one of the hosts is running Windows. On a Windows
client, Unison makes an attempt to detect if symbolic links are
supported and allowed by user privileges. You may have to get
elevated privileges to create symbolic links.
listen xxx
When acting as a server on a TCP socket, Unison will by default
listen on "any" address (0.0.0.0 and [::]). This command-line
argument allows to specify a different listening address and can
be repeated to listen on multiple addresses. Listening address
can be specified as a host name or an IP address.
log
When this flag is set, Unison will log all changes to the
filesystems on a file.
logfile xxx
By default, logging messages will be appended to the file
unison.log in your .unison directory. Set this preference if you
prefer another file. It can be a path relative to your .unison
directory. Sending SIGUSR1 will close the logfile; the logfile
will be re-opened (and created, if needed) automatically, to
allow for log rotation.
maxbackups n
This preference specifies the number of backup versions that
will be kept by unison, for each path that matches the predicate
backup. The default is 2.
maxerrors n
This preference controls after how many errors Unison aborts a
directory transfer. Setting it to a large number allows Unison
to transfer most of a directory even when some files fail to be
copied. The default is 1. If the preference is set too high,
Unison may take a long time to abort in case of repeated
failures (for instance, when the disk is full).
maxsizethreshold n
A number indicating above what filesize (in kilobytes) Unison
should flag a conflict instead of transferring the file. This
conflict remains even in the presence of force or prefer
options. A negative number will allow every transfer
independently of the size. The default is -1.
maxthreads n
This preference controls how much concurrency is allowed during
the transport phase. Normally, it should be set reasonably high
to maximize performance, but when Unison is used over a
low-bandwidth link it may be helpful to set it lower (e.g. to 1)
so that Unison doesn’t soak up all the available bandwidth. The
default is the special value 0, which mean 20 threads when file
content streaming is desactivated and 1000 threads when it is
activated.
merge xxx
This preference can be used to run a merge program which will
create a new version for each of the files and the backup, with
the last backup and both replicas. The syntax of pathspec -> cmd
is described in the section “Path Specification” , and further
details on Merging functions are present in the section “Merging
Conflicting Versions” .
mountpoint xxx
Including the preference -mountpoint PATH causes Unison to
double-check, at the end of update detection, that PATH exists
and abort if it does not. This is useful when Unison is used to
synchronize removable media. This preference can be given more
than once. See the section “Mount Points and Removable Media” .
nocreation xxx
Including the preference -nocreation root prevents Unison from
performing any file creation on root root.
This preference can be included twice, once for each root, if
you want to prevent any creation.
nocreationpartial xxx
Including the preference nocreationpartial = PATHSPEC -> root
prevents Unison from performing any file creation in PATHSPEC on
root root (see the section “Path Specification” for more
information). It is recommended to use BelowPath patterns when
selecting a directory and all its contents.
nodeletion xxx
Including the preference -nodeletion root prevents Unison from
performing any file deletion on root root.
This preference can be included twice, once for each root, if
you want to prevent any deletion.
nodeletionpartial xxx
Including the preference nodeletionpartial = PATHSPEC -> root
prevents Unison from performing any file deletion in PATHSPEC on
root root (see the section “Path Specification” for more
information). It is recommended to use BelowPath patterns when
selecting a directory and all its contents.
noupdate xxx
Including the preference -noupdate root prevents Unison from
performing any file update or deletion on root root.
This preference can be included twice, once for each root, if
you want to prevent any update.
noupdatepartial xxx
Including the preference noupdatepartial = PATHSPEC -> root
prevents Unison from performing any file update or deletion in
PATHSPEC on root root (see the section “Path Specification” for
more information). It is recommended to use BelowPath patterns
when selecting a directory and all its contents.
numericids
When this flag is set to true, groups and users are synchronized
numerically, rather than by name.
The special uid 0 and the special group 0 are never mapped via
user/group names even if this preference is not set.
owner
When this flag is set to true, the owner attributes of the files
are synchronized. Whether the owner names or the owner
identifiers are synchronizeddepends on the preference numerids.
path xxx
When no path preference is given, Unison will simply synchronize
the two entire replicas, beginning from the given pair of roots.
If one or more path preferences are given, then Unison will
synchronize only these paths and their children. (This is useful
for doing a fast sync of just one directory, for example.) Note
that path preferences are interpreted literally—they are not
regular expressions.
perms n
The integer value of this preference is a mask indicating which
permission bits should be synchronized. It is set by default to
0o1777: all bits but the set-uid and set-gid bits are
synchronised (synchronizing theses latter bits can be a security
hazard). If you want to synchronize all bits, you can set the
value of this preference to −1. If one of the replica is on a
FAT [Windows] filesystem, you should consider using the fat
preference instead of this preference. If you need Unison not to
set permissions at all, set the value of this preference to 0
and set the preference dontchmod to true.
prefer xxx
Including the preference -prefer root causes Unison always to
resolve conflicts in favor of root, rather than asking for
guidance from the user, except for paths marked by the
preference merge. (The syntax of root is the same as for the
root preference, plus the special values newer and older.)
This preference is overridden by the preferpartial preference.
This preference should be used only if you are sure you know
what you are doing!
preferpartial xxx
Including the preference preferpartial = PATHSPEC -> root causes
Unison always to resolve conflicts in favor of root, rather than
asking for guidance from the user, for the files in PATHSPEC
(see the section “Path Specification” for more information).
(The syntax of root is the same as for the root preference, plus
the special values newer and older.)
This preference should be used only if you are sure you know
what you are doing!
repeat xxx
Setting this preference causes the text-mode interface to
synchronize repeatedly, rather than doing it just once and
stopping. If the argument is a number, Unison will pause for
that many seconds before beginning again. When the argument is
watch, Unison relies on an external file monitoring process to
synchronize whenever a change happens.
retry n
Setting this preference causes the text-mode interface to try
again to synchronize updated paths where synchronization fails.
Each such path will be tried N times.
root xxx
Each use of this preference names the root of one of the
replicas for Unison to synchronize. Exactly two roots are
needed, so normal modes of usage are either to give two values
for root in the profile, or to give no values in the profile and
provide two on the command line. Details of the syntax of roots
can be found in the section “Roots” .
The two roots can be given in either order; Unison will sort
them into a canonical order before doing anything else. It also
tries to ‘canonize’ the machine names and paths that appear in
the roots, so that, if Unison is invoked later with a slightly
different name for the same root, it will be able to locate the
correct archives.
rootalias xxx
When calculating the name of the archive files for a given pair
of roots, Unison replaces any roots matching the left-hand side
of any rootalias rule by the corresponding right-hand side.
rsrc xxx
When set to true, this flag causes Unison to synchronize
resource forks and HFS meta-data. On filesystems that do not
natively support resource forks, this data is stored in
Carbon-compatible ._ AppleDouble files. When the flag is set to
false, Unison will not synchronize these data. Ordinarily, the
flag is set to default, and these data are automatically
synchronized if either host is running OSX. In rare
circumstances it is useful to set the flag manually.
rsync
Unison uses the ’rsync algorithm’ for ’diffs-only’ transfer of
updates to large files. Setting this flag to false makes Unison
use whole-file transfers instead. Under normal circumstances,
there is no reason to do this, but if you are having trouble
with repeated ’rsync failure’ errors, setting it to false should
permit you to synchronize the offending files.
selftest
Run internal tests and exit. This option is mostly for
developers and must be used carefully: in particular, it will
delete the contents of both roots, so that it can install its
own files for testing. This flag only makes sense on the command
line. When it is provided, no preference file is read: all
preferences must be specified on thecommand line. Also, since
the self-test procedure involves overwriting the roots and
backup directory, the names of the roots and of the backupdir
preference must include the string "test" or else the tests will
be aborted. (If these are not given on the command line, dummy
subdirectories in the current directory will be created
automatically.)
servercmd xxx
This preference can be used to explicitly set the name of the
Unison executable on the remote server (e.g., giving a full path
name), if necessary.
showarchive
When this preference is set, Unison will print out the ’true
names’of the roots, in the same form as is expected by the
rootalias preference.
silent
When this preference is set to true, the textual user interface
will print nothing at all, except in the case of errors. Setting
silent to true automatically sets the batch preference to true.
socket xxx
Start unison as a server listening on a TCP socket (with TCP
port number as argument) or a local socket (aka Unix domain
socket) (with socket path as argument).
sortbysize
When this flag is set, the user interface will list changed
files by size (smallest first) rather than by name. This is
useful, for example, for synchronizing over slow links, since it
puts very large files at the end of the list where they will not
prevent smaller files from being transferred quickly.
This preference (as well as the other sorting flags, but not the
sorting preferences that require patterns as arguments) can be
set interactively and temporarily using the ’Sort’ menu in the
graphical and text user interfaces.
sortfirst xxx
Each argument to sortfirst is a pattern pathspec, which
describes a set of paths. Files matching any of these patterns
will be listed first in the user interface. The syntax of
pathspec is described in the section “Path Specification” .
sortlast xxx
Similar to sortfirst, except that files matching one of these
patterns will be listed at the very end.
sortnewfirst
When this flag is set, the user interface will list newly
created files before all others. This is useful, for example,
for checking that newly created files are not ‘junk’, i.e., ones
that should be ignored or deleted rather than synchronized.
source xxx
Include preferences from a file. source name reads the file
"name" in the .unison directory and includes its contents as if
it was part of a profile or given directly on command line.
sshargs xxx
The string value of this preference will be passed as additional
arguments (besides the host name and the name of the Unison
executable on the remote system) to the ssh command used to
invoke the remote server. The backslash is an escape character.
sshcmd xxx
This preference can be used to explicitly set the name of the
ssh executable (e.g., giving a full path name), if necessary.
stream
(Deprecated) When this preference is set, Unison will use an
experimental streaming protocol for transferring file contents
more efficiently. The default value is true.
terse
When this preference is set to true, the user interface will not
print status messages.
testserver
Setting this flag on the command line causes Unison to attempt
to connect to the remote server and, if successful, print a
message and immediately exit. Useful for debugging installation
problems. Should not be set in preference files.
times
When this flag is set to true, file modification times (but not
directory modtimes) are propagated.
ui xxx
This preference selects either the graphical or the textual user
interface. Legal values are graphic or text.
Because this option is processed specially during Unison’s
start-up sequence, it can only be used on the command line. In
preference files it has no effect.
If the Unison executable was compiled with only a textual
interface, this option has no effect. (The pre-compiled binaries
are all compiled with both interfaces available.)
unicode xxx
When set to true, this flag causes Unison to perform case
insensitive file comparisons assuming Unicode encoding. This is
the default. When the flag is set to false, a Latin 1 encoding
is assumed. When Unison runs in case sensitive mode, this flag
only makes a difference if one host is running Windows or Mac OS
X. Under Windows, the flag selects between using the Unicode or
8bit Windows API for accessing the filesystem. Under Mac OS X,
it selects whether comparing the filenames up to decomposition,
or byte-for-byte.
version
Print the current version number and exit. (This option only
makes sense on the command line.)
watch
Unison uses a file watcher process, when available, to detect
filesystem changes; this is used to speed up update detection.
Setting this flag to false disables the use of this process.
xferbycopying
When this preference is set, Unison will try to avoid
transferring file contents across the network by recognizing
when a file with the required contents already exists in the
target replica. This usually allows file moves to be propagated
very quickly. The default value is true.
Profiles
A profile is a text file that specifies permanent settings for roots,
paths, ignore patterns, and other preferences, so that they do not need
to be typed at the command line every time Unison is run. Profiles
should reside in the .unison directory on the client machine. If Unison
is started with just one argument name on the command line, it looks
for a profile called name.prf in the .unison directory. If it is
started with no arguments, it scans the .unison directory for files
whose names end in .prf and offers a menu (provided that the Unison
executable is compiled with the graphical user interface). If a file
named default.prf is found, its settings will be offered as the default
choices.
To set the value of a preference p permanently, add to the appropriate
profile a line of the form
p = true
for a boolean flag or
p = <value>
for a preference of any other type.
Whitespaces around p and xxx are ignored. A profile may also include
blank lines and lines beginning with #; both are ignored.
When Unison starts, it first reads the profile and then the command
line, so command-line options will override settings from the profile.
Profiles may also include lines of the form include name, which will
cause the file name (or name.prf, if name does not exist in the .unison
directory) to be read at the point, and included as if its contents,
instead of the include line, was part of the profile. Include lines
allows settings common to several profiles to be stored in one place. A
similar line of the form source name does the same except that it does
not attempt to add a suffix to name. Similar lines of the form include?
name or source? name do the same as their respective lines without the
question mark except that it does not constitue an error to specify a
non-existing file name. In name the backslash is an escape character.
A profile may include a preference ‘label = desc’ to provide a
description of the options selected in this profile. The string desc is
listed along with the profile name in the profile selection dialog, and
displayed in the top-right corner of the main Unison window in the
graphical user interface.
The graphical user-interface also supports one-key shortcuts for
commonly used profiles. If a profile contains a preference of the form
‘key = n’, where n is a single digit, then pressing this digit key will
cause Unison to immediately switch to this profile and begin
synchronization again from scratch. In this case, all actions that have
been selected for a set of changes currently being displayed will be
discarded.
Sample Profiles
A Minimal Profile
Here is a very minimal profile file, such as might be found in
.unison/default.prf:
# Roots of the synchronization
root = /home/bcpierce
root = ssh://saul//home/bcpierce
# Paths to synchronize
path = current
path = common
path = .netscape/bookmarks.html
A Basic Profile
Here is a more sophisticated profile, illustrating some other useful
features.
# Roots of the synchronization
root = /home/bcpierce
root = ssh://saul//home/bcpierce
# Paths to synchronize
path = current
path = common
path = .netscape/bookmarks.html
# Some regexps specifying names and paths to ignore
ignore = Name temp.*
ignore = Name *~
ignore = Name .*~
ignore = Path */pilot/backup/Archive_*
ignore = Name *.o
ignore = Name *.tmp
# Window height
height = 37
# Keep a backup copy of every file in a central location
backuplocation = central
backupdir = /home/bcpierce/backups
backup = Name *
backupprefix = $VERSION.
backupsuffix =
# Use this command for displaying diffs
diff = diff -y -W 79 --suppress-common-lines
# Log actions to the terminal
log = true
A Power-User Profile
When Unison is used with large replicas, it is often convenient to be
able to synchronize just a part of the replicas on a given run (this
saves the time of detecting updates in the other parts). This can be
accomplished by splitting up the profile into several parts — a common
part containing most of the preference settings, plus one “top-level”
file for each set of paths that need to be synchronized. (The include
mechanism can also be used to allow the same set of preference settings
to be used with different roots.)
The collection of profiles implementing this scheme might look as
follows. The file default.prf is empty except for an include directive:
# Include the contents of the file common
include common
Note that the name of the common file is common, not common.prf; this
prevents Unison from offering common as one of the list of profiles in
the opening dialog (in the graphical UI).
The file common contains the real preferences:
# Roots of the synchronization
root = /home/bcpierce
root = ssh://saul//home/bcpierce
# (... other preferences ...)
# If any new preferences are added by Unison (e.g. 'ignore'
# preferences added via the graphical UI), then store them in the
# file 'common' rather than in the top-level preference file
addprefsto = common
# Names and paths to ignore:
ignore = Name temp.*
ignore = Name *~
ignore = Name .*~
ignore = Path */pilot/backup/Archive_*
ignore = Name *.o
ignore = Name *.tmp
Note that there are no path preferences in common. This means that,
when we invoke Unison with the default profile (e.g., by typing ’unison
default’ or just ’unison’ on the command line), the whole replicas will
be synchronized. (If we never want to synchronize the whole replicas,
then default.prf would instead include settings for all the paths that
are usually synchronized.)
To synchronize just part of the replicas, Unison is invoked with an
alternate preference file—e.g., doing ’unison workingset’, where the
preference file workingset.prf contains
path = current/papers
path = Mail/inbox
path = Mail/drafts
include common
causes Unison to synchronize just the listed subdirectories.
The key preference can be used in combination with the graphical UI to
quickly switch between different sets of paths. For example, if the
file mail.prf contains
path = Mail
batch = true
key = 2
include common
then pressing 2 will cause Unison to look for updates in the Mail
subdirectory and (because the batch flag is set) immediately propagate
any that it finds.
Keeping Backups
When Unison overwrites (or deletes) a file or directory while
propagating changes from the other replica, it can keep the old version
around as a backup. There are several preferences that control
precisely where these backups are stored and how they are named.
To enable backups, you must give one or more backup preferences. Each
of these has the form
backup = <pathspec>
where <pathspec> has the same form as for the ignore preference. For
example,
backup = Name *
causes Unison to keep backups of all files and directories. The
backupnot preference can be used to give a few exceptions: it specifies
which files and directories should not be backed up, even if they match
the backup pathspec.
It is important to note that the pathspec is matched against the path
that is being updated by Unison, not its descendants. For example, if
you set backup = Name *.txt and then delete a whole directory named foo
containing some text files, these files will not be backed up because
Unison will just check that foo does not match *.txt. Similarly, if the
directory itself happened to be called foo.txt, then the whole
directory and all the files in it will be backed up, regardless of
their names.
Backup files can be stored either centrally or locally. This behavior
is controlled by the preference backuplocation, whose value must be
either central or local. (The default is central.)
When backups are stored locally, they are kept in the same directory as
the original.
When backups are stored centrally, the directory used to hold them is
controlled by the preference backupdir and the environment variable
UNISONBACKUPDIR. (The environment variable is checked first.) If
neither of these are set, then the directory .unison/backup in the
user’s home directory is used.
The preference maxbackups controls how many previous versions of each
file are kept (including the current version).
By default, backup files are named .bak.VERSION.FILENAME, where
FILENAME is the original filename and VERSION is the backup number (1
for the most recent, 2 for the next most recent, etc.). This can be
changed by setting the preferences backupprefix and/or backupsuffix. If
desired, backupprefix may include a directory prefix; this can be used
with backuplocation = local to put all backup files for each directory
into a single subdirectory. For example, setting
backuplocation = local
backupprefix = .unison/$VERSION.
backupsuffix =
will put all backups in a local subdirectory named .unison. Also, note
that the string $VERSION in either backupprefix or backupsuffix (it
must appear in one or the other) is replaced by the version number.
This can be used, for example, to ensure that backup files retain the
same extension as the originals.
For backward compatibility, the backups preference is also supported.
It simply means backup = Name * and backuplocation = local.
Merging Conflicting Versions
Unison can invoke external programs to merge conflicting versions of a
file. The preference merge controls this process.
The merge preference may be given once or several times in a preference
file (it can also be given on the command line, of course, but this
tends to be awkward because of the spaces and special characters
involved). Each instance of the preference looks like this:
merge = <PATHSPEC> -> <MERGECMD>
The <PATHSPEC> here has exactly the same format as for the ignore
preference (see the section “Path Specification” ). For example, using
“Name *.txt” as the <PATHSPEC> tells Unison that this command should be
used whenever a file with extension .txt needs to be merged.
Many external merging programs require as inputs not just the two files
that need to be merged, but also a file containing the last
synchronized version. You can ask Unison to keep a copy of the last
synchronized version for some files using the backupcurrent preference.
This preference is used in exactly the same way as backup and its
meaning is similar, except that it causes backups to be kept of the
current contents of each file after it has been synchronized by Unison,
rather than the previous contents that Unison overwrote. These backups
are kept on both replicas in the same place as ordinary backup
files—i.e. according to the backuplocation and backupdir preferences.
They are named like the original files if backupslocation is set to
’central’ and otherwise, Unison uses the backupprefix and backupsuffix
preferences and assumes a version number 000 for these backups.
The <MERGECMD> part of the preference specifies what external command
should be invoked to merge files at paths matching the <PATHSPEC>.
Within this string, several special substrings are recognized; these
will be substituted with appropriate values before invoking a sub-shell
to execute the command.
* CURRENT1 is replaced by the name of (a temporary copy of) the local
variant of the file.
* CURRENT2 is replaced by the name of a temporary file, into which
the contents of the remote variant of the file have been
transferred by Unison prior to performing the merge.
* CURRENTARCH is replaced by the name of the backed up copy of the
original version of the file (i.e., the file saved by Unison if the
current filename matches the path specifications for the
backupcurrent preference, as explained above), if one exists. If no
archive exists and CURRENTARCH appears in the merge command, then
an error is signalled.
* CURRENTARCHOPT is replaced by the name of the backed up copy of the
original version of the file (i.e., its state at the end of the
last successful run of Unison), if one exists, or the empty string
if no archive exists.
* NEW is replaced by the name of a temporary file that Unison expects
to be written by the merge program when it finishes, giving the
desired new contents of the file.
* PATH is replaced by the path (relative to the roots of the
replicas) of the file being merged.
* NEW1 and NEW2 are replaced by the names of temporary files that
Unison expects to be written by the merge program when it is only
able to partially merge the originals; in this case, NEW1 will be
written back to the local replica and NEW2 to the remote replica;
NEWARCH, if present, will be used as the “last common state” of the
replicas. (These three options are provided for later compatibility
with the Harmony data synchronizer.)
* BATCHMODE is replaced according to the batch mode of Unison; if it
is in batch mode, then a non empty string (“batch”) is substituted,
otherwise the empty string is substituted.
To accommodate the wide variety of programs that users might want to
use for merging, Unison checks for several possible situations when the
merge program exits:
* If the merge program exits with a non-zero status, then merge is
considered to have failed and the replicas are not changed.
* If the file NEW has been created, it is written back to both
replicas (and stored in the backup directory). Similarly, if just
the file NEW1 has been created, it is written back to both
replicas.
* If neither NEW nor NEW1 have been created, then Unison examines the
temporary files CURRENT1 and CURRENT2 that were given as inputs to
the merge program. If either has been changed (or both have been
changed in identical ways), then its new contents are written back
to both replicas. If either CURRENT1 or CURRENT2 has been deleted,
then the contents of the other are written back to both replicas.
* If the files NEW1, NEW2, and NEWARCH have all been created, they
are written back to the local replica, remote replica, and backup
directory, respectively. If the files NEW1, NEW2 have been created,
but NEWARCH has not, then these files are written back to the local
replica and remote replica, respectively. Also, if NEW1 and NEW2
have identical contents, then the same contents are stored as a
backup (if the backupcurrent preference is set for this path) to
reflect the fact that the path is currently in sync.
* If NEW1 and NEW2 (resp. CURRENT1 and CURRENT2) are created (resp.
overwritten) with different contents but the merge command did not
fail (i.e., it exited with status code 0), then we copy NEW1 (resp.
CURRENT1) to the other replica and to the archive.
This behavior is a design choice made to handle the case where a
merge command only synchronizes some specific contents between two
files, skipping some irrelevant information (order between entries,
for instance). We assume that, if the merge command exits normally,
then the two resulting files are “as good as equal.” (The reason we
copy one on top of the other is to avoid Unison detecting that the
files are unequal the next time it is run and trying again to merge
them when, in fact, the merge program has already made them as
similar as it is able to.)
You can disable a merge by setting a <MERGECMD> that does nothing. For
example you can override the merging of text files specified in a
profile by typing on the command line:
unison profile -merge 'Name *.txt -> echo SKIP'
If the confirmmerge preference is set and Unison is not run in batch
mode, then Unison will always ask for confirmation before actually
committing the results of the merge to the replicas.
You can detect batch mode by testing BATCHMODE; for example to avoid a
merge completely do nothing:
merge = Name *.txt -> [ -z "BATCHMODE" ] && mergecmd CURRENT1 CURRENT2
A large number of external merging programs are available. For example,
on Unix systems setting the merge preference to
merge = Name *.txt -> diff3 -m CURRENT1 CURRENTARCH CURRENT2
> NEW || echo "differences detected"
will tell Unison to use the external diff3 program for merging.
Alternatively, users of emacs may find the following settings
convenient:
merge = Name *.txt -> emacs -q --eval '(ediff-merge-files-with-ancestor
"CURRENT1" "CURRENT2" "CURRENTARCH" nil "NEW")'
(These commands are displayed here on two lines to avoid running off
the edge of the page. In your preference file, each command should be
written on a single line.)
Users running emacs under windows may find something like this useful:
merge = Name * -> C:\Progra~1\Emacs\emacs\bin\emacs.exe -q --eval
"(ediff-files """CURRENT1""" """CURRENT2""")"
Users running Mac OS X (you may need the Developer Tools installed to
get the opendiff utility) may prefer
merge = Name *.txt -> opendiff CURRENT1 CURRENT2 -ancestor CURRENTARCH -merg
e NEW
Here is a slightly more involved hack. The opendiff program can operate
either with or without an archive file. A merge command of this form
merge = Name *.txt ->
if [ CURRENTARCHOPTx = x ];
then opendiff CURRENT1 CURRENT2 -merge NEW;
else opendiff CURRENT1 CURRENT2 -ancestor CURRENTARCHOPT -merge NE
W;
fi
(still all on one line in the preference file!) will test whether an
archive file exists and use the appropriate variant of the arguments to
opendiff.
Linux users may enjoy this variant:
merge = Name * -> kdiff3 -o NEW CURRENTARCHOPT CURRENT1 CURRENT2
Ordinarily, external merge programs are only invoked when Unison is not
running in batch mode. To specify an external merge program that should
be used no matter the setting of the batch flag, use the mergebatch
preference instead of merge.
Please post suggestions for other useful values of the merge
preference to the unison-users mailing list—we’d like to give
several examples here.
The User Interface
Both the textual and the graphical user interfaces are intended to be
mostly self-explanatory. Here are just a few tricks:
* By default, when running on Unix the textual user interface will
try to put the terminal into the “raw mode” so that it reads the
input a character at a time rather than a line at a time. (This
means you can type just the single keystroke “>” to tell Unison to
propagate a file from left to right, rather than “> Enter.”)
There are some situations, though, where this will not work — for
example, when Unison is running in a shell window inside Emacs.
Setting the dumbtty preference will force Unison to leave the
terminal alone and process input a line at a time.
Exit Code
When running in the textual mode, Unison returns an exit status, which
describes whether, and at which level, the synchronization was
successful. The exit status could be useful when Unison is invoked from
a script. Currently, there are four possible values for the exit
status:
* 0: successful synchronization; everything is up-to-date now.
* 1: some files were skipped, but all file transfers were successful.
* 2: non-fatal failures occurred during file transfer.
* 3: a fatal error occurred, or the execution was interrupted.
The graphical interface does not return any useful information through
the exit status.
Path Specification
Several Unison preferences (e.g., ignore/ignorenot, follow,
sortfirst/sortlast, backup, merge, etc.) specify individual paths or
sets of paths. These preferences share a common syntax based on
regular-expressions. Each preference is associated with a list of path
patterns; the paths specified are those that match any one of the path
pattern.
* Pattern preferences can be given on the command line, or, more
often, stored in profiles, using the same syntax as other
preferences. For example, a profile line of the form
ignore = pattern
adds pattern to the list of patterns to be ignored.
* Each pattern can have one of three forms. The most general form is
a Posix extended regular expression introduced by the keyword
Regex. (The collating sequences and character classes of full Posix
regexps are not currently supported).
Regex regexp
For convenience, three other styles of pattern are also recognized:
Name name
matches any path in which the last component matches name,
Path path
matches exactly the path path, and
BelowPath path
matches the path path and any path below. The name and path
arguments of the latter forms of patterns are not regular
expressions. Instead, standard “globbing” conventions can be used
in name and path:
+ a * matches any sequence of characters not including / (and
not beginning with ., when used at the beginning of a name)
+ a ? matches any single character except / (and leading .)
+ [xyz] matches any character from the set {x, y, z }
+ {a,bb,ccc} matches any one of a, bb, or ccc. (Be careful not
to put extra spaces after the commas: these will be
interpreted literally as part of the strings to be matched!)
* The path separator in path patterns is always the forward-slash
character “/” — even when the client or server is running under
Windows, where the normal separator character is a backslash. This
makes it possible to use the same set of path patterns for both
Unix and Windows file systems.
* A path specification may be followed by the separator “ -> ” itself
followed by a string which will be associated to the matching
paths:
Path path -> associated string
Not all pathspec preferences use these associated strings but all
pathspec preferences are parsed identically and the strings may be
ignored. Only the last match of the separator string on the line is
used as a delimiter. Thus to allow a path specification to contain
the separator string, append an associated string to it, even if it
is not used. The associated string cannot contain the separator
string.
Some examples of path patterns appear in the section “Ignoring Paths” .
Associated strings are used by the preference merge.
Ignoring Paths
Most users of Unison will find that their replicas contain lots of
files that they don’t ever want to synchronize — temporary files, very
large files, old stuff, architecture-specific binaries, etc. They can
instruct Unison to ignore these paths using patterns introduced in the
section “Path Specification” .
For example, the following pattern will make Unison ignore any path
containing the name CVS or a name ending in .cmo:
ignore = Name {CVS,*.cmo}
The next pattern makes Unison ignore the path a/b:
ignore = Path a/b
Path patterns do not skip filenames beginning with . (as Name patterns
do). For example,
ignore = Path */tmp
will include .foo/tmp in the set of ignore directories, as it is a
path, not a name, that is ignored.
The following pattern makes Unison ignore any path beginning with a/b
and ending with a name ending by .ml.
ignore = Regex a/b/.*\.ml
Note that regular expression patterns are “anchored”: they must match
the whole path, not just a substring of the path.
Here are a few extra points regarding the ignore preference.
* If a directory is ignored, all its descendants will be too.
* The user interface provides some convenient commands for adding new
patterns to be ignored. To ignore a particular file, select it and
press “i”. To ignore all files with the same extension, select it
and press “E” (with the shift key). To ignore all files with the
same name, no matter what directory they appear in, select it and
press “N”. These new patterns become permanent: they are
immediately added to the current profile on disk.
* If you use the include directive to include a common collection of
preferences in several top-level preference files, you will
probably also want to set the addprefsto preference to the name of
this file. This will cause any new ignore patterns that you add
from inside Unison to be appended to this file, instead of
whichever top-level preference file you started Unison with.
* Ignore patterns can also be specified on the command line, if you
like (this is probably not very useful), using an option like
-ignore 'Name temp.txt'.
* Be careful about renaming directories containing ignored files.
Because Unison understands the rename as a delete plus a create,
any ignored files in the directory will be lost (since they are
invisible to Unison and therefore they do not get recreated in the
new version of the directory).
* There is also an ignorenot preference, which specifies a set of
patterns for paths that should not be ignored, even if they match
an ignore pattern. However, the interaction of these two sets of
patterns can be a little tricky. Here is exactly how it works:
+ Unison starts detecting updates from the root of the
replicas—i.e., from the empty path. If the empty path matches
an ignore pattern and does not match an ignorenot pattern,
then the whole replica will be ignored. (For this reason, it
is not a good idea to include Name * as an ignore pattern. If
you want to ignore everything except a certain set of files,
use Name ?*.)
+ If the root is a directory, Unison continues looking for
updates in all the immediate children of the root. Again, if
the name of some child matches an ignore pattern and does not
match an ignorenot pattern, then this whole path including
everything below it will be ignored.
+ If any of the non-ignored children are directories, then the
process continues recursively.
Symbolic Links
Ordinarily, Unison treats symbolic links in Unix replicas as “opaque”:
it considers the contents of the link to be just the string specifying
where the link points, and it will propagate changes in this string to
the other replica.
It is sometimes useful to treat a symbolic link “transparently,” acting
as though whatever it points to were physically in the replica at the
point where the symbolic link appears. To tell Unison to treat a link
in this manner, add a line of the form
follow = pathspec
to the profile, where pathspec is a path pattern as described in the
section “Path Specification” .
Not all Windows versions and file systems support symbolic links;
Unison will refuse to propagate an opaque symbolic link from Unix to
Windows and flag the path as erroneous if the support or privileges are
lacking on the Windows side. When a Unix replica is to be synchronized
with such Windows system, all symbolic links should match either an
ignore pattern or a follow pattern.
You may need to acquire extra privileges to create symbolic links under
Windows. By default, this is only allowed for administrators. Unison
may not be able to automatically detect support for symbolic links
under Windows. In that case, set the preference links to true
explicitly.
Permissions
Synchronizing the permission bits of files is slightly tricky when two
different filesystems are involved (e.g., when synchronizing a Windows
client and a Unix server). In detail, here’s how it works:
* When the permission bits of an existing file or directory are
changed, the values of those bits that make sense on both operating
systems will be propagated to the other replica. The other bits
will not be changed.
* When a newly created file is propagated to a remote replica, the
permission bits that make sense in both operating systems are also
propagated. The values of the other bits are set to default values
(they are taken from the current umask, if the receiving host is a
Unix system).
* For security reasons, the Unix setuid and setgid bits are not
propagated.
* The Unix owner and group ids are not propagated. (What would this
mean, in general?) All files are created with the owner and group
of the server process.
Cross-Platform Synchronization
If you use Unison to synchronize files between Windows and Unix
systems, there are a few special issues to be aware of.
Case conflicts. In Unix, filenames are case sensitive: foo and FOO can
refer to different files. In Windows, on the other hand, filenames are
not case sensitive: foo and FOO can only refer to the same file. This
means that a Unix foo and FOO cannot be synchronized onto a Windows
system — Windows won’t allow two different files to have the “same”
name. Unison detects this situation for you, and reports that it cannot
synchronize the files.
You can deal with a case conflict in a couple of ways. If you need to
have both files on the Windows system, your only choice is to rename
one of the Unix files to avoid the case conflict, and re-synchronize.
If you don’t need the files on the Windows system, you can simply
disregard Unison’s warning message, and go ahead with the
synchronization; Unison won’t touch those files. If you don’t want to
see the warning on each synchronization, you can tell Unison to ignore
the files (see the section “Ignoring Paths” ).
Illegal filenames. Unix allows some filenames that are illegal in
Windows. For example, colons (‘:’) are not allowed in Windows
filenames, but they are legal in Unix filenames. This means that a Unix
file foo:bar can’t be synchronized to a Windows system. As with case
conflicts, Unison detects this situation for you, and you have the same
options: you can either rename the Unix file and re-synchronize, or you
can ignore it.
Slow Links
Unison is built to run well even over relatively slow links such as
modems and DSL connections.
Unison uses the “rsync protocol” designed by Andrew Tridgell and Paul
Mackerras to greatly speed up transfers of large files in which only
small changes have been made. More information about the rsync protocol
can be found at the rsync web site (http://samba.anu.edu.au/rsync/).
If you are using Unison with ssh, you may get some speed improvement by
enabling ssh’s compression feature. Do this by adding the option
“-sshargs -C” to the command line or “sshargs = -C” to your profile.
Making Unison Faster on Large Files
Unison’s built-in implementation of the rsync algorithm makes
transferring updates to existing files pretty fast. However, for
whole-file copies of newly created files, the built-in transfer method
is not highly optimized. Also, if Unison is interrupted in the middle
of transferring a large file, it will attempt to retransfer the whole
thing on the next run.
These shortcomings can be addressed with a little extra work by telling
Unison to use an external file copying utility for whole-file
transfers. The recommended one is the standalone rsync tool, which is
available by default on most Unix systems and can easily be installed
on Windows systems using Cygwin.
If you have rsync installed on both hosts, you can make Unison use it
simply by setting the copythreshold flag to something non-negative. If
you set it to 0, Unison will use the external copy utility for all
whole-file transfers. (This is probably slower than letting Unison copy
small files by itself, but can be useful for testing.) If you set it to
a larger value, Unison will use the external utility for all files
larger than this size (which is given in kilobytes, so setting it to
1000 will cause the external tool to be used for all transfers larger
than a megabyte).
If you want to use a different external copy utility, set both the
copyprog and copyprogrest preferences—the former is used for the first
transfer of a file, while the latter is used when Unison sees a
partially transferred temp file on the receiving host. Be careful here:
Your external tool needs to be instructed to copy files in place
(otherwise if the transfer is interrupted Unison will not notice that
some of the data has already been transferred, the next time it tries).
The default values are:
copyprog = rsync --inplace --compress
copyprogrest = rsync --partial --inplace --compress
You may also need to set the copyquoterem preference. When it is set to
true, this causes Unison to add an extra layer of quotes to the remote
path passed to the external copy program. This is is needed by rsync,
for example, which internally uses an ssh connection, requiring an
extra level of quoting for paths containing spaces. When this flag is
set to default, extra quotes are added if the value of copyprog
contains the string rsync. The default value is default, naturally.
If a directory transfer is interrupted, the next run of Unison will
automatically skip any files that were completely transferred before
the interruption. (This behavior is always on: it does not depend on
the setting of the copythreshold preference.) Note, though, that the
new directory will not appear in the destination filesystem until
everything has been transferred—partially transferred directories are
kept in a temporary location (with names like .unison.DIRNAME....)
until the transfer is complete.
Fast Update Detection
If your replicas are large and at least one of them is on a Windows
system, you may find that Unison’s default method for detecting changes
(which involves scanning the full contents of every file on every
sync—the only completely safe way to do it under Windows) is too slow.
Unison provides a preference fastcheck that, when set to true, causes
it to use file creation times as ’pseudo inode numbers’ when scanning
replicas for updates, instead of reading the full contents of every
file.
When fastcheck is set to no, Unison will perform slow
checking—re-scanning the contents of each file on each
synchronization—on all replicas. When fastcheck is set to default
(which, naturally, is the default), Unison will use fast checks on Unix
replicas and slow checks on Windows replicas.
This strategy may cause Unison to miss propagating an update if the
modification time and length of the file are both unchanged by the
update. However, Unison will never overwrite such an update with a
change from the other replica, since it always does a safe check for
updates just before propagating a change. Thus, it is reasonable to use
this switch most of the time and occasionally run Unison once with
fastcheck set to no, if you are worried that Unison may have overlooked
an update.
Fastcheck is (always) automatically disabled for files with extension
.xls or .mpp, to prevent Unison from being confused by the habits of
certain programs (Excel, in particular) of updating files without
changing their modification times.
Mount Points and Removable Media
Using Unison removable media such as USB drives can be dangerous unless
you are careful. If you synchronize a directory that is stored on
removable media when the media is not present, it will look to Unison
as though the whole directory has been deleted, and it will proceed to
delete the directory from the other replica—probably not what you want!
To prevent accidents, Unison provides a preference called mountpoint.
Including a line like
mountpoint = foo
in your preference file will cause Unison to check, after it finishes
detecting updates, that something actually exists at the path foo on
both replicas; if it does not, the Unison run will abort.
Click-starting Unison
On Windows NT/2k/XP systems, the graphical version of Unison can be
invoked directly by clicking on its icon. On Windows 95/98 systems,
click-starting also works, as long as you are not using ssh. Due to an
incompatibility with OCaml and Windows 95/98 that is not under our
control, you must start Unison from a DOS window in Windows 95/98 if
you want to use ssh.
When you click on the Unison icon, two windows will be created:
Unison’s regular window, plus a console window, which is used only for
giving your password to ssh (if you do not use ssh to connect, you can
ignore this window). When your password is requested, you’ll need to
activate the console window (e.g., by clicking in it) before typing. If
you start Unison from a DOS window, Unison’s regular window will appear
and you will type your password in the DOS window you were using.
To use Unison in this mode, you must first create a profile (see the
section “Profiles” ). Use your favorite editor for this.
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