Ok, then I agree with your last paragraph. Here's the current version, with semantic newlines: In Linux kernels up to 5.4, flock() is not propagated over SMB. A file with such locks will not appear locked for remote clients. Since Linux 5.5, flock() locks are emulated with SMB byte-range locks on the entire file. Similarly to NFS, this means that fcntl(2) and flock() locks interact with one another. Another important side-effect is that the locks are not advisory anymore: a write on a locked file will always fail with EACCES. This difference originates from the design of locks in the SMB protocol, which provides mandatory locking semantics. Remote and mandatory locking semantics may vary with SMB protocol, mount options and server type. See mount.cifs(8) for additional information. Cheers, -- Aurélien Aptel / SUSE Labs Samba Team GPG: 1839 CB5F 9F5B FB9B AA97 8C99 03C8 A49B 521B D5D3 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg, DE GF: Felix Imendörffer, Mary Higgins, Sri Rasiah HRB 247165 (AG München)