I was disappointed to find the syncing feature was not available on the Ubuntu version. I did find a work-around tho. You need a windows shared drive (I used a server). You basically create an auto-mount so the .mnemosyne directory is really on the smb server. This is really nice because you can use a server that's always on so you can always get your files! If you don't know how do do this ill explain. I recommend watching this you tube video http://youtu.be/HNKNFwskz3A, but ill give a written tutorial below.
First, you open the terminal and type " sudo nano .smbcred " This will create a hidden text file and you will be taken to the text editor. Type and replace whats in quotes with your credentials:
username="your username on the smb server"
password="your password on the smb server"
Now hit ctrl+x, hit y and you should be back at the command prompt. The next step is to type "sudo nano /etc/fstab" you should now be in a text editor and the file looks like this:
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
# / was on /dev/sda5 during installation
UUID=0eb03022-3bb0-49c3-a159-bad24166dc96 / ext4 errors=remount-ro 0 1
# swap was on /dev/sda6 during installation
UUID=d4cbb36a-113a-4176-8418-7e8c535748d3 none swap sw 0 0
Now under the # <file system> line add
//"yourserverip"/"thedirectorytosyncto" /home/"yourusername"/.mnemosyne cifs uid="yourusername",Credentials=/home/"yourusername"/.smbcred,iocharset=utf8,sec=ntml 0 0
Just copy and paste what I typed above, and replace whats in quotes with your information (remove the quotes). Your almost done! Now hit ctrl+x then hit y and your back at the command line. Only three more things to do! Type:
sudo apt-get install cifs-utils
Hit enter and do whatever it asks. Now you need to type:
sudo mount /home/"username"/.mnemosyne
Hit enter and if no errors pop up your almost done! Open the .mnemosyne folder (use file viewer and hit ctrl+h to show hidden folders), open the backups folder (or use previous backups) and open the most recent folder and extract the .xml file to the .mnemosyne directory. Go into mnemosyne and restore the backup and your done.