Systemtap 允许开发者写一些简单的脚本来观察活动着的 linux 系统。能够检查一些复杂的系统以及函数问题。
一般默认是不会装 systemtap 的。可以通过下面这一条来安装
yum install systemtap
安装好了之后，就可以有一个命令 stap。试试下面这个简单的脚本hello-world.stp。
probe begin
{
print ("Hello World.")
exit ()
}
在命令行中运行
# stap hello-world.stp
Hello World.
非常的简单。
probe 可以放在下面这些地方：
begin The startup of the systemtap session.
end The end of the systemtap session.
kernel.function(“sys_open”)The entry to the function named sys_open in the kernel.
syscall.close.return The return from the close system call.
module(“ext3”).statement(0xdeadbeef)The addressed instruction in the ext3 filesystem driver.
timer.ms(200)A timer that fires every 200 milliseconds.
timer.profileA timer that fires periodically on every CPU.
perf.hw.cache_missesA particular number of CPU cache misses have occurred.
procfs(“status”).readA process trying to read a synthetic file.
*process(“a.out”).statement(“*@main.c:200”) *Line 200 of the a.out program.
这完全像一个 debugger。只要你能确定是哪里都能放一个probe。举些例子：
probe kernel.function("*@net/socket.c") { }
probe kernel.function("*@net/socket.c").return { }
放了probe呢。当然是想知道可以输出什么有用的信息了。如下：
tid()The id of the current thread.
pid()The process (task group) id of the current thread.
uid()The id of the current user.
execname()The name of the current process.
cpu()The current cpu number.
gettimeofday_s()Number of seconds since epoch.
get_cycles()Snapshot of hardware cycle counter.
pp()A string describing the probe point being currently handled.
ppfunc()If known, the the function name in which this probe was placed.
$$varsIf available, a pretty-printed listing of all local variables in scope.
print_backtrace()If possible, print a kernel backtrace.
print_ubacktrace()If possible, print a user-space backtrace.
systemtap 还支持一些基础的控制语句，例如 if-else-if，比较等。支持一些函数，嵌入 C 的代码。功能非常强大，希望以后可以带来一些实战吧。