synchronizationunison

Unison: sync only in one direction

If I have folder A and B, is it possible to sync the new files from A to B and to not erase in B files erased in A?

That is to say, I would like to use B as a big container for any file, including the one that I once synchronized from A and than erased. I think is considered kind of "one way syncing".

Solution

  • I understand that you are having these two requirements on Unison

    Mirroring

    According to the Unison manual, the -force xxx option "effectively changes Unison from a synchronizer into a mirroring utility". The force option takes the folder that is to be favored as argument. Unison will resolve all changes in favor of this folder.

    The commandline to mirror, e.g., folder /src/dir to /dest/dir would be

    unison /src/dir /dest/dir -force /src/dir

    Preserving

    Use the option -nodeletion xxx to prevent Unison from recommending any deletion on the folder xxx as default action.

    The commandline to preserve files on /dest/dir after they have been deleted from /src/dir would be

    unison /src/dir /dest/dir -nodeletion /dest/dir

    Sum up

    So in total you want to run Unison with these two options to satisfy your requirements:

    unison /src/dir /dest/dir -force /src/dir -nodeletion /dest/dir

    Notes

    Until you have set up Unison to run in batch mode, I recommend to run Unison in interactive mode using the graphical UI. Working with the graphical UI is more convenient as you see all pending changes including the default actions Unison suggests.

    When you are satisfied with the default actions, you can run unison in batch mode (option -batch) using the textual UI. In batch mode, changes with default actions will accepted, changes without default action (due to conflicts) will be skipped.

    Remember, these options can be overridden in interactive mode by the user. They are in no way an absolute protection against deletion, they just provide guidance to Unison about how to decide on the default action. In interactive mode, the user can always override the default action, i.e., press "<" to propagate the change to the source folder (the direction which you do not want).