systemtap (Linux trace/probe tool)

SystemTap provides free software (GPL) infrastructure to simplify the
gathering of information about the running Linux system. This assists
diagnosis of a performance or functional problem. SystemTap eliminates
the need for the developer to go through the tedious and disruptive
instrument, recompile, install, and reboot sequence that may be
otherwise required to collect data.

SystemTap provides a simple command line interface and scripting
language for writing instrumentation for a live running kernel plus
user-space applications. We are publishing samples, as well as
enlarging the internal "tapset" script library to aid reuse and
abstraction.

Among other tracing/probing tools, SystemTap is the tool of choice for
complex tasks that may require live analysis, programmable on-line
response, and whole-system symbolic access. SystemTap can also handle
simple tracing jobs.
