Overview
Preface
•People
•Obtaining Unison
•Community, Maintenance, and Development
•Copying
•Acknowledgements
Upgrading
•Version interoperability
Tutorial
•Preliminaries
•Local Usage
•Remote Usage
•Remote Shell Method
•Socket Method
TCP Sockets
Unix Domain Sockets
•Using Unison for All Your Files
•Using Unison to Synchronize More Than Two Machines
•Going Further
Basic Concepts
•Roots
•Paths
•What is an Update?
•What is a Conflict?
•Reconciliation
•Invariants
•Caveats and Shortcomings
Reference Guide
•Running Unison
•The .unison Directory
•Archive Files
•Preferences
•Profiles
•Sample Profiles
A Minimal Profile
A Basic Profile
A Power-User Profile
•Keeping Backups
•Merging Conflicting Versions
•The User Interface
•Interrupting a Synchronization
•Exit Code
•Path Specification
•Ignoring Paths
•Symbolic Links
•Permissions
•Access Control Lists - ACLs
•Extended Attributes - xattrs
•Cross-Platform Synchronization
•Slow Links
•Making Unison Faster on Large Files
•Fast Update Detection
•Mount Points and Removable Media
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, PRCS, etc.), distributed filesystems (Coda, etc.), uni-directional mirroring utilities (rsync, etc.), and other synchronizers (Intellisync, Reconcile, etc). However, there are several points where it differs:
Benjamin Pierce leads the Unison project. The current version of Unison was designed and implemented by Trevor Jim, Benjamin Pierce, and Jérôme Vouillon, with Alan Schmitt, Malo Denielou, Zhe Yang, 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 protocol was built by Norman Ramsey and Sylvain Gommier. It is based on Andrew Tridgell’s thesis work and inspired by his 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 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 and Insup Lee contributed design ideas to this implementation. Cedric Fournet contributed to an even earlier prototype.
Unison is primarily distributed as source code, which contains instructions in INSTALL.md:
https://github.com/bcpierce00/unison
The Unison wiki contains information about builds done as part of Continuous Integration and other sources of binaries; read the entire wiki at:
https://github.com/bcpierce00/unison/wiki
Many people use and contribute to Unison. This community has two main homes.
Most discussion is appropriate on one of the mailinglists:
https://github.com/bcpierce00/unison/wiki/Mailing-Lists
Bug reports and feature requests may be made after reading the guidelines:
https://github.com/bcpierce00/unison/wiki/Reporting-Bugs-and-Feature-Requests
Help improving Unison is welcome; see CONTRIBUTING.md in the sources.
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.
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).
(This section is perhaps misplaced, but is early because it is far better to have at least skimmed it than to not know it exists.)
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 and newer can upgrade the archive created by earlier Unison versions. To avoid rebuilding archive files when upgrading from a version older than 2.52, you must install version 2.52 or newer 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 or newer executable to one compiled with a different version of OCaml. The archive file is no longer dependent on the compiler version.
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 and newer are compatible with:
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
(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 Remote Usage section, or -servercmd
; see
the Remote Shell Method section.
Unison can be used with either of two user interfaces:
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. 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.
Let’s get the client machine set up first and see how to synchronize two directories on a single machine.
Ensure that unison is installed on your system.
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:
Graphical Interface:
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:
<
” 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:
<
” 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.
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 Preferences section.
Now there is a decision to be made. Unison provides two methods for communicating between the client and the server:
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
).Decide which of these you want to try, and continue with the Remote Shell Method section or the Socket Method section, as appropriate.
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:
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
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 Profiles section). 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.ssh
; just
remember that the roots are still specified with ssh
as the
protocol, that is, they have to start with ssh://.
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.
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.
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.
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:
unison /home/username ssh://remotehost//home/username -path sharedThe -path option can be used as many times as needed, to synchronize several files or subdirectories:
unison /home/username ssh://remotehost//home/usernameThese\
-path shared\
-path pub\
-path .netscape/bookmarks.html
-path
arguments can also be put in your preference file.
See the Preferences section 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 Profiles section
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.
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.
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 on-line information and the printed manual are essentially identical.
If you use Unison regularly, you should subscribe to one of the mailing lists, to receive announcements of new versions. See the Obtaining Unison section.
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.
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.
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.)
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:
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.
p
refers to a symbolic link, then the contents of p
are just the string specifying where the link points.
p
refers to a directory, then the
contents of p
are just the token “DIRECTORY” plus the current
permission bits of the directory.
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 Caveats and Shortcomings section.
A path is said to be conflicting if the following conditions all hold:
Unison operates in several distinct stages:
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:
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.
Here are some things to be careful of when using Unison.
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.
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.
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).
This section covers the features of Unison in detail.
There are several ways to start Unison.
.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.
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.
The name of the archive file on each replica is calculated from
saul
are converted into full addresses like saul.cis.upenn.edu
),
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.
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: -acl synchronize ACLs -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) -xattrignore xxx add a pattern to the xattrignore list -xattrignorenot xxx add a pattern to the xattrignorenot list -xattrs synchronize extended attributes (xattrs) 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 -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.
true
, the ACLs of files and directories are synchronized. The type of ACLs depends on the platform and filesystem support. On Unix-like platforms it can be NFSv4 ACLs, for example.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.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.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 Path Specification section.
merge
preference. For more details, see the Merging Conflicting Versions section.The syntax of pathspec is described in the Path Specification section.
backupcurr
, like the ignorenot
preference.central
. It is checked after the UNISONBACKUPDIR environment variable.local
, backups will be kept in the same directory as the original files, and if set to central
, backupdir will be used instead.NAME
is created, it is stored in a directory specified by backuplocation, in a file called backupprefixNAME
backupsuffix. 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.
Name *
.-repeat watch
and -prefer newer
preferences.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 -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 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.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.
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 Fast Update Detection section for more information.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.
You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
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!
You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
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!
true
, the group attributes of the files are synchronized. Whether the group names or the group identifiers are synchronized depends on the preference numerids.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.
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.)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.backup
. The default is 2.You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
This preference can be included twice, once for each root, if you want to prevent any creation.
You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
This preference can be included twice, once for each root, if you want to prevent any deletion.
You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
This preference can be included twice, once for each root, if you want to prevent any update.
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.
true
, the owner attributes of the files are synchronized. Whether the owner names or the owner identifiers are synchronizeddepends on the preference numerids.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.root
preference, plus the special values newer
and older
.) You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
This preference is overridden by the preferpartial
preference.
This preference should be used only if you are sure you know what you are doing!
root
preference, plus the special values newer
and older
.) You can also specify a unique prefix or suffix of the path of one of the roots or a unique prefix of the hostname of a remote root.
This preference should be used only if you are sure you know what you are doing!
watch
, Unison relies on an external file monitoring process to synchronize whenever a change happens. You can combine the two with a +
character to use file monitoring and also do a full scan every specificed number of seconds. For example, watch+3600
will react to changes immediately and additionally do a full scan every hour.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 Roots section.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.
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
, except that files matching one of these patterns will be listed at the very end.ssh
command used to invoke the remote server. The backslash is an escape character.true
, file modification times (but not directory modtimes) are propagated.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.)
Path
and Regex
forms over the Name
form. The pattern is applied to the name of extended attribute, not to path. On Linux, attributes in the security and trusted namespaces are ignored by default (this is achieved by pattern Regex !(security|trusted)[.].*); also attributes used to store POSIX ACL are ignored by default (this is achieved by pattern Path !system.posix_acl_*). To sync attributes in one or both of these namespaces, see the xattrignorenot
preference. Note that the namespace name must be prefixed with a "!" (applies on Linux only). All names not prefixed with a "!" are taken as strictly belonging to the user namespace and therefore the "!user." prefix is never used.xattrignore
) for extended attributes that should not be ignored, whether or not they happen to match one of the xattrignore
patterns. It is possible to synchronize only desired attributes by ignoring all attributes (for example, by setting xattrignore
to Path * and then adding xattrignorenot
for extended attributes that should be synchronized. On Linux, attributes in the security and trusted namespaces are ignored by default. To sync attributes in one or both of these namespaces, you may add an xattrignorenot
pattern like Path !security.* to sync all attributes in the security namespace, or Path !security.selinux to sync a specific attribute in an otherwise ignored namespace. A pattern like Path !system.posix_acl_* can be used to sync POSIX ACLs on Linux. Note that the namespace name must be prefixed with a "!" (applies on Linux only). All names not prefixed with a "!" are taken as strictly belonging to the user namespace and therefore the "!user." prefix is never used.true
, the extended attributes of files and directories are synchronized. System extended attributes are not synchronized.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.
A profile may include blank lines and lines beginning with #; both are ignored.
Spaces and tabs before and after p and xxx are ignored.
Spaces, tabs, and non-printable characters within values are not
treated specially, so that e.g. root = /foo bar
refers to a
directory containing a space.
(On systems using newline for line ending, carriage returns are
currently ignored, but this is not part of the specification.)
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 constitute 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.
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
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
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.
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 create 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
.) Note that central storage of backups can lead to
backup files being stored in a different filesystem than the original
files, which could have different security properties and different
amounts of available storage.
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
(default 2) controls how many
previous versions of each file are kept (including the current
version), following the usual plan of deleting the oldest when
creating a new one.
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.
Other than maxbackups
(which will never delete the last
backup), there are no other mechanisms for deleting backups.
For backward compatibility, the backups
preference is also supported.
It simply means backup = Name *
and backuplocation = local
.
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 Path Specification section). 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 created 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 stored
in 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. Note that there are no mechanisms (beyond the limit on the number of
backups for each file) to remove backup files.
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:
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.
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.
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.
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 -merge 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 NEW; 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.
Both the textual and the graphical user interfaces are intended to be mostly self-explanatory. Here are just a few tricks:
>
” 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.
It is possible to interrupt an ongoing synchronization process before it completes. Different user interfaces offer different ways of doing it.
Graphical Interface:
Textual Interface:
In the text interface, to interrupt synchronization before it is finished,
press “Ctrl-C” (or send signal SIGINT
or SIGTERM
). This will
interrupt update propagation as quickly as possible but still complete proper
cleanup. If the process does not stop even after pressing “Ctrl-C” then keep
doing it repeatedly. This will bypass cleanup procedures and terminates the
process forcibly (similar to SIGKILL
). Doing so may leave the archives
or replicas in an inconsistent state or locked.
When synchronizing continuously (time interval repeat or with filesystem
monitoring), interrupting with “Ctrl-C” or with signal SIGINT
or
SIGTERM
works the same way as described above and will additionally stop
the continuous process. To stop only the continuous process and let the last
synchronization complete normally, send signal SIGUSR2
instead.
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:
The graphical interface does not return any useful information through the exit status.
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.
ignore = pattern
adds pattern to the list of patterns to be ignored.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:
*
matches any sequence of characters not including /
(and not beginning with .
, when used at the beginning of a
name)
?
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!)
->
” itself
followed by a string which will be associated to the matching paths:
Path path -> associated stringNot 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 Ignoring Paths section. Associated strings are used by the preference merge.
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 Path Specification section.
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.
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 'Name temp.txt'
.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:
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 ?*
.)
ignore
pattern and does not match an ignorenot
pattern, then
this whole path including everything below it will be ignored.
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 Path Specification section.
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.
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:
setuid
and setgid
bits are not propagated.
owner
and group
preferences) by mapping names or by numeric ids (see
numericids
preference).
Unison allows synchronizing access control lists (ACLs) on platforms and filesystems that support them. In general, synchronization makes sense only in case both replicas support the same type of ACLs and recognize same users and groups. In some cases you may be able to go beyond that and synchronize ACLs to a replica that couldn’t fully use them—this may be be useful for the purpose of preserving ACLs.
If one of the replicas does not support any type of ACLs then Unison will not attempt ACL synchronization. If the other replica does support ACLs then those will remain intact.
If both replicas support ACLs of any supported type then you can
request Unison to try ACL synchronization (acl
preference).
Success of synchronization depends on permissions of the owner and
group of Unison process (Unison must have permissions to set ACL)
and the compatibility of ACL types on both replicas.
An ACL is propagated as a single unit, with all ACEs. There is no merging of ACEs from the replicas.
Caveat: ACE inheritance may in certain scenarios cause synchronization inconsistencies. In Windows, only explicit ACEs are synchronized; inherited ACEs are not actively synchronized, but Windows will propagate ACEs from parent directories (unless inheritance is explicitly prevented on a file or a directory—this prevention is also synchronized). Due to inheritance, the ultimately effective ACL may be different, or provide different access, even after synchronization.
Unison currently supports the following platforms and ACL types:
Not all filesystems on the listed platforms support all ACL types (or any ACLs at all).
Synchronizing POSIX ACLs on Linux is not supported directly. However, it is
possible to synchronize these ACLs with another Linux system by synchronizing
extended attributes (xattrs) instead, because POSIX ACLs are stored as xattrs
by Linux. This is disabled by default (see the Extended
Attributes - xattrs section). A simple way to enable syncing POSIX ACLs on Linux is
to enable the preference xattrs
and add a preference
xattrignorenot
with a value Path !system.posix_acl_*. The
*
will be expanded to include both posix_acl_access
and
posix_acl_default
attributes – if you only want to sync either one,
just remove the *
and type out the attribute name in full. If you want
to prevent other xattrs from being synced then add an xattrignore
with a
value Path * (value Regex .* will also work).
Unison allows synchronizing extended attributes on platforms and filesystems that support them. System attributes are not synchronized. What exactly is considered a system attribute is platform-dependent. Synchronization is possible cross-platform, but see caveats below.
If one of the replicas does not support extended attributes then Unison will not attempt attribute synchronization. If the other replica does support extended attributes then those will remain intact.
If both replicas support extended attributes then you can request
Unison to try attribute synchronization (xattrs
preference).
Extended attributes from both replicas will not be merged, all extended
attributes are propagated as a set from one replica to another.
Unison currently supports extended attributes on the following platforms:
unison
process privileges
and is disabled by default. To sync one or more attributes in the security
namespace, for example, you can set the preference
xattrignorenot
to Path !security.*
(for all) or to
Path !security.selinux
(for one specific attribute).
Attributes in system namespace are not synchronized, with the exception of
system.posix_acl_default
and system.posix_acl_access
(also
disabled by default).
Not all filesystems on the listed platforms may support extended attributes.
Caveats:
!
is prepended to the namespace name, except for the
user
namespace; the user.
prefix is stripped from attribute names
instead. This allows syncing extended attributes from Linux to other platforms.
These transformations are reversed when syncing to Linux, resulting in
correct fully qualified attribute names.
The xattrignore
and xattrignorenot
preferences work on the
transformed attribute names. This means that any patterns for the user
namespace must be specified without the user.
prefix and any patterns
intended for other namespaces must begin with an !
.
The xattrignore
preference can be used to filter the names of extended
attributes that will be synchronized. The most useful ignore patterns can
be constructed with the Path
form (where shell wildcards *
and
?
are supported) and with the Regex
form. The
xattrignorenot
preference can be used to override xattrignore
.
Disabling the security and trusted namespaces on Linux is achieved by setting
a default xattrignore
pattern of
Regex !(security|trusted)[.].*.
Disabling the syncing of attributes used to store POSIX ACL on Linux is
achieved by setting a default xattrignore
pattern of
Path !system.posix_acl_*.
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 Ignoring Paths section).
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.
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.
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
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.
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.
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.
This document was translated from LATEX by HEVEA.