ownCloud is a very nice tool for syncing and sharing files and folders in a workgroup or even company, basically it’s an open source replacement for Dropbox or Google Drive that runs on your own infrastructure.
A problem that may occur is when user Alice shares a folder „SHARED“ to a group „everybody“ (all the other users are members of this group).
Then user Bob clicks on the Recycle bin icon to „Unshare“ this folder for him/herself (he opts-out of this group-share even if he continues to be member of group „everybody“). Bob does not see this folder anymore but all the others do. Bob has no way of ever reverting this action and cannot opt-in again.
Alice, the owner of the folder „SHARED“ has no idea that the folder is shared to „everybody“ but user Bob opted-out (and perhaps even forgot he did this at some point). Alice expects everybody will see files inside the folder. Alice expects wrong.
Detecting this issue is complicated. Basically Alice must sit next to Bob, show to Bob that she shared folder SHARED to „everybody“, yet Bob does not see such folder in his folders. This indicates that such an opt-out happened.
Unfortunately ownCloud UI has no tool to do anything with it, except for Alice to unshare the entire folder completely (which may wreak havoc, as it gets deleted on all the other computers of all users, re-sharing, link sharing etc. may break), and then share it again with the group „everyone“, and hope that Bob will not opt-out again. (There is also no way of preventing users from such opting-out.)
Fortunately there exists a database hack I would not be able to find by myself, but Vincent Petry (PVince81), one of ownCloud developers, helped me via #owncloud IRC channel:
log-in to the SQL as the user having access to owncloud database
- to show you the „opted-out“ shares, enter SQL command:
select * from oc_share where permissions=0 and share_type=2
if you delete the undesired entry, the share will be visible again for the user from the „share_with“ column