The following information describes how to manually load DTrace kernel modules. If you plan to use DTrace kernel modules that are automatically loaded, you can skip this section of the tutorial. See Section 1.4.1, “Using Automatically Loaded DTrace Modules”.
To use DTrace providers, their supported kernel modules must be loaded each time the kernel is booted.
If the dtrace
kernel module is not already
loaded, when the dtrace command is run, the
dtrace
module and all of the modules that are
listed in /etc/dtrace-modules
are all loaded
automatically. However, if the dtrace
kernel
module is already loaded, the automatic kernel module loading
mechanism is not triggered.
You can load modules manually by using the
modprobe command. For example, to use the
fbt
kernel module if it is not in the default
list, you would run the following command:
# modprobe fbt
The modprobe action also loads the
dtrace
kernel module as a dependency so that
a subsequent dtrace command does not drive
automatic loading of other dtrace
modules
until the dtrace
kernel module is no longer
loaded. The drace
kernel module will no
longer be loaded upon another boot of the system or after the
manual removal of the dtrace
kernel modules.
The suggested practice is to use the dtrace
-l command to trigger automatic module loading and
thereby also confirm basic dtrace
functionality. Then, use the modprobe command
to load additional modules that are not in the default list,
such as fbt
, as needed.