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Diffstat (limited to 'examples/small_demos/demo_script.txt')
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diff --git a/examples/small_demos/demo_script.txt b/examples/small_demos/demo_script.txt deleted file mode 100644 index f3166a49..00000000 --- a/examples/small_demos/demo_script.txt +++ /dev/null @@ -1,102 +0,0 @@ -> cd /root/systemtap - -A systemtap script can be as simple as a single line. For example, -the following script places a probepoint on the kernel sys_read() -function and prints all callers with the function's arguments. - ->stap -e 'probe syscall.open {printf("%s: %s\n", execname(), argstr)}' - -Most scripts are a bit longer. (show top.stp) -This script sets a probepoint on all kernel functions beginning with "sys_". -When the probepoint is hit, it increments an entry in the map -(or associative array) "syscalls" with the key "probefunc()" which returns -the name of the function that was triggered. For example, "sys_read". - -There is a timer that is triggered every 5000ms or 5 seconds. That timer -calls the function print_top(). print_top() sorts the syscalls map -and prints the top 20 entries. Then it clears the map. - -> ./top.stp - -(after stopping "top" go ahead and enter "./sys.stp". It takes a minute -to load this script. Diplay the source in another window and talk -while it is loading.) - -The "top" script looked only at the functions called. If we want more -detail about the functions, we can use systemtap to examine their local -arguments and variables. However that would be difficult because each -system call has different parameters. The Syscall Tapset solves -this problem. To use it, we set probe points using the syntax "syscall.name" -instead of kernel.function("sys_name"). The Syscall Tapset provides three -defined variables we can use: -name - the name of the function -argstr - on function entry, a formatted string containing the arguments -retstr - on function exit, the return value and possibly error code - -In this example, we filter out programs named "staprun" because this is -part of the systemtap infrastructure. (It may be filtered out -automatically in the future.) - -The next example shows how you can use systemtap to focus on -specific programs or pids. (show prof.stp) - -Like the "top" example, this script places probes on all kernel -functions starting with "sys_". Only the probepoint also checks to see -if the tid/pid matches the one returned by "target()". We'll show how -the target pid is set later. - -Unlike the previous examples, this script sets a probe point on all the -system call returns. When triggered, this probepoint computes the elapsed -time since the function entry. - -To run this script, we must give it a pid to use for the target, or a -program to run, in which case target will be its pid. - -> ./prof.stp -c "top -n5" - --------------------------------- - -Systemtap can also run in an unsafe mode where you can give -it arbitrary C code to run at probepoints, or modify kernel variables -and structures. This is very dangerous so only experts with root access will -ever be permitted to do this. - -(show keyhack.stp) - -The next example will modify the local variable "keycode" in the "kdb_keycode" -function in the kernel driver. We indicate it is a local variable by putting -a dollar sign before the name. - -./keyhack.stp - -(prints error message) - -To tell systemtap we really want to run this script, we must use the "-g" flag. - -./keyhack.stp -g - -(type some keys. "m" should display as "b" in every window) - -This example is not something you would normally want to do. There are -far better ways to remap a keyboard. What it demonstartes is that Systemtap -can modify variables in a running kernel. - -(show kmalloc.stp) -This next script shows the kind of statistics systemtap can collect. -It collects information about kernel allocations. - -> ./kmalloc.stp - -Now we can refine this further -(show kmalloc2.stp) - -Remember in some previous examples, we used maps or associative arrays. Maps can contain -statistics too. So we have enhanced the previous script to collect statistics per -program name. The output might be large so we'll redirect it to a file. - -> ./kmalloc2.stp > out - -(runs for 10 seconds) - -> more out - |