Unison

Unison is a utility that allows you to compare two directories and, if they are different, to synchronize them.

You can use it for backup purposes.

Get it

• Download it from http://www.cis.upenn.edu/~bcpierce/unison/
• unpack and build it (example):

# tar xvzf unison-2.32.52.tar.gz
# cd unison-2.32.52/
# make -j4 && make install

Run it

To run Unison to compare two directories on the same computer, start it like this:

unison /directory1 /directory2

TroubleShooting

Inconsistent state

Symptom

Warning: inconsistent state.  
The archive file is missing on some hosts.
For safety, the remaining copies should be deleted.
  Archive ar12953235d4d7106b0880b820546c3ea1 on host tweedleburg is MISSING
  Archive ar6a548e7688b901a571b72c38e13194ff on host scorpio should be DELETED
Please delete archive files as appropriate and try again.

Solution

Go to ~/.unison and delete the archive file