Hello

I talked about systemTap for about 15 minutes at tonight's meeting.   I
figured it was worth while to give people some links:

Home page:  http://sourceware.org/systemtap/
Wiki:  http://sourceware.org/systemtap/wiki


I installed it on my Ubuntu 8.04 beta system,  it required that I
install a few  packages that are not listed as a prereq for systemTap.
 The webpage:
http://sourceware.org/systemtap/wiki/SystemtapOnUbuntu describes what is
needed.

It seems to be an interesting, if somewhat complex tool that can really
let you see what's happening on your system.   From the Intoduction on
the systemTap tutorial:

Systemtap is a tool that allows developers and administrators to write
and reuse simple scripts to deeply examine the activities of a live
Linux system. Data may be extracted, filtered, and summarized quickly
and safely, to enable diagnoses of complex performance or functional
problems.

The essential idea behind a systemtap script is to name events, and to
give them handlers. Whenever a specified event occurs, the Linux kernel
runs the handler as if it were a quick subroutine, then resumes. There
are several kind of events, such as entering or exiting a function, a
timer expiring, or the entire systemtap session starting or stopping. A
handler is a series of script language statements that specify the work
to be done whenever the event occurs. This work normally includes
extracting data from the event context, storing them into internal
variables, or printing results.

Systemtap works by translating the script to C, running the system C
compiler to create a kernel module from that. When the module is loaded,
it activates all the probed events by hooking into the kernel. Then, as
events occur on any processor, the compiled handlers run. Eventually,
the session stops, the hooks are disconnected, and the module removed.
This entire process is driven from a single command-line program, stap.



Jim

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