Unison

Revision as of 06:07, 25 November 2008

Unison File Synchronizer

Unison is a file-synchronization tool for Unix and Windows. See the manual for a detailed look at it's capabilities.

Unison comes in two flavors:

• Text mode only version (debian package name: unison)
• GTK-based graphical version (debian package name: unison-gtk)

Unison can sync

• between two directory trees on the same computer or
• between directory trees on two separate machines.

For syncing desktop machine and Neo we use the latter. The recommended way to do this is the remote shell method: We start unison or unison-gtk on the desktop PC. The program will connect to the Neo via ssh and start a text-only instance of unison on the Neo to retrieve new files or deltas and to modify files on the Neo.

For this to work, ssh may not output any text itself, because unison parses the first line of console output to determine the version of unison on the remote computer. So we setup ssh for public key authentication:

• Create a key pair on the desktop PC
• Configure the desktop PC for public key authentication
• Add the public key of the desktop PC to ~/.ssh/authorized_keys on the Neo

We need to install the text version of unison on the neo. Since there's no native opkg file available currently, we take the debian package. Extract the file unison-2.27.57 and copy it to /usr/bin on neo. Create a symlink by the name of unison.

A unison configuration on the desktop PC (~/.unison/Openmoko.prf) might look like this

# Unison preferences file

label      = Syncing Openmoko

# the directories on the desktop and on the neo
root       = /home/user/Openmoko/data
root       = ssh://root@192.168.0.202//media/mmc4

# common options
include Common.opt


# Do not compare modification time
times      = false

########### Music ##############
path       =      music

########### GPS Data ###########
path       =      gps
ignore     = Path gps/Maps/*
ignorenot  = Path gps/Maps/OSM
ignore     = Path gps/log/*

On first execution of unison on the desktop, unison will create hashes for the entire directory tree. This may take a while.

Unison supports various preferences to interactively include programs for comparing and merging files during synchronization (see the manual).