No, it is not safe. Calibre is not multi user.
One way to handle it could be to make a backup copy of the library and treat that as a read only version of the library, to be used by the content server. I run a content server like that. I have configured a Virtual Box to automatically copy the latest backup of the Calibre library, using rsync, when starting.
So I have three copies. One main copy that I add books to, and change. One backup. (Actually several backups.) And one copy of the latest backup used by the content server. This means that I can update and backup the main library at any time, and refresh the content server by restarting it.
It is also very, very bad to switch between Windows and Linux. Linux use case sensitive filenames, but Windows don't. Chaos lurking there...
Last edited by Adoby; 11-29-2012 at 07:35 PM.