While the Oracle Linux kernel can dynamically load and unload kernel modules, for fbt probes, the fbt kernel module must be loaded to support the instrumentation. For more information about loading kernel modules, see the note in Section 1.1, “Getting Started With DTrace”. If fbt is not listed in /etc/dtrace-modules, or if the dtrace -l command lists no fbt probes, use the following command:

# modprobe fbt

Conversely, you can unload the fbt instrumentation with the following command:

# modprobe -r fbt

When the fbt module is loaded, FBT automatically provides probes to instrument all other loaded modules, including any new modules that are dynamically loaded. If a loaded module has no enabled FBT probes, the module might be unloaded and the corresponding probes are destroyed as the module is unloaded. If a loaded module has enabled FBT probes, the module is considered busy and cannot be unloaded.