Chapter 37. Getting started with SystemTap

Prerequisites

• You have enabled debug repositories as described in Enabling debug and source repositories.

Verification

• If the kernel to be probed with SystemTap is currently in use, test if your installation was successful:

  # stap -v -e 'probe kernel.function("vfs_read") {printf("read performed\n"); exit()}'

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  A successful SystemTap deployment results in an output similar to the following:

  Pass 1: parsed user script and 45 library script(s) in 340usr/0sys/358real ms.
  Pass 2: analyzed script: 1 probe(s), 1 function(s), 0 embed(s), 0 global(s) in 290usr/260sys/568real ms.
  Pass 3: translated to C into "/tmp/stapiArgLX/stap_e5886fa50499994e6a87aacdc43cd392_399.c" in 490usr/430sys/938real ms.
  Pass 4: compiled C into "stap_e5886fa50499994e6a87aacdc43cd392_399.ko" in 3310usr/430sys/3714real ms.
  Pass 5: starting run.
  read performed
  Pass 5: run completed in 10usr/40sys/73real ms.

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  where

• Pass 5: starting run indicates that SystemTap successfully created the instrumentation to probe the kernel and runs the instrumentation.
• read performed indicates that SystemTap detected the specified event, in this example, a VFS read.
• Pass 5: run completed in <time> ms indicates that SystemTap executed a valid handler. It displayed text and closed with no errors.

Procedure

• Run the SystemTap script:

  • From standard input:

    # echo "probe timer.s(1) {exit()}" | stap -

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    This command instructs stap to run the script passed by echo to standard input. To add stap options, insert them before the - character. For example, to make the results from this command more verbose, the command is:

    # echo "probe timer.s(1) {exit()}" | stap -v -

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  • From a file:

    # stap file_name

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