Hello,
Is there any way to share a folder which is located on the seafile server itself ?
The easiest way would be to use the FUSE extension I think, but that would be read-only. You could leverage Webdav but that really doesn’t correspond to a folder existing on the server itself. Aside from those two options, the only other thing I can think of is syncing 
UPDATE 1: Added syncing.
syncing on the same machine using seaf-cli ?
Hello!
Don’t think using that utility would work as it merges the contents and I’m not sure that’s what you want. It sounds like you want to essentially make a folder local to the server available as a share in the Seafile interface. I think I got it working but I essentially had to have two separate folders on the Seafile server synced with each other, using something like rsync or unison with something like inotify.
Hi,
My concern is that I can export a data folder, from a PC in a secure network, using rsync on the seafile server, but I am not able to directly sync the PC folder to the seafile server.
Then I want to share this data with several users of the seafile server.
What I have done is to use seaf-cli on the server itself to sync the data folder with the seafile server. This work, but has the effect of duplicating the data on the server machine (once in the rsync-ed folder and once in the data structure of seafile).
That works, but if anyone has a more efficient solution, I am interested. Maybe, as you mentioned, FUSE could help there, I will investigate that.
Hello!
Yes the duplication is something I tried to avoid on my test servers but I didn’t have any luck. Any solution that did work involved duplication. Using something like bindfs also could be a part of a solution. Still, again it wouldn’t be an elegant solution 
I did briefly try it however, attempting to bind-in the local folder to the Seafile data folder but I couldn’t get around the fact that I couldn’t remount due to write-protection.
Of course, I think the source is available, and perhaps a custom version of seadrive could also be a solution but of course that really isn’t a trivial task, nor would it be supported.
Best of luck!