If a Unix application separate from Samba tries to update a file that Samba has oplocked to a Windows client, it will likely succeed (depending on the operating system) and both Samba and the client will never be aware of it. However, if the local Unix operating system supports it, Samba can warn it of oplocked files, which can suspend the Unix process, notify the client via Samba to write its copy back, and only then allow the open to complete. Essentially, this means that the operating system kernel on the Samba system has the ability to handle oplocks as well as Samba.
You can enable this behavior with the
kernel
oplocks option, as follows:
[global]
kernel oplocks = yes
Samba can automatically detect kernel oplocks and use them if present. At the time of this writing, this feature is supported only by SGI Irix 6.5.2f and later. However, Linux and FreeBSD support are expected in the near future. A system without kernel oplocks will allow the Unix process to update the file, but the client programs will notice the change only at a later time, if at all.
