Unless Lucee is doing some serious magic, UNC isn't going to work on Linux. Using UNC on windows is leveraging a core OS feature, not a Lucee or Java feature. UNC doesn't exist on Linux. (further, what credentials would it use to connect? Do you have kerberos configured?) Even on windows, it would only work if your Lucee process were not running as LocalSystem, but a domain user with appropriate access to the file share.
Drive mappings will work. You could use cifs to mount your document_root to a known file path, and access that (with static credentials).
Or you can leverage the JCIFS java library or similar to make calls against SMB shares.
That said, I see Lucee depends on jCIFS.jar, so it's entirely possible Lucee has some built in support for it and I'm wrong. But I'd fully expect you'd at least need username and password.
If Lucee did support it, it's probably be at the VFS layer, so since you can do things like file:/// and ram:/// in various parts of Lucee, there's probably a prefix for SMB. Try smb://host/path or cifs://host/path . and you might have to set jcifs.smb.client.username and jcifs.smb.client.password properties, or do a url like smb://user:pw@host/path
-G