Anatomy of a simple Linux utility
What really happens when you enter a program's name in a terminal window? This article is a journey into the workings of a commonly used program – the ubiquitous ls file listing command. This journey starts with the Bash [1] shell finding the ls program in response to the letters ls typed at the terminal, and it leads to a list of files and directories retrieved from the underlying filesystem [2].
To recreate these results, you'll need some basic understanding of standard debugging techniques using the GNU debugger (gdb), some familiarity with the SystemTap system information utility [3] [4], and an intermediate-level understanding of C programming code. SystemTap is a scripting language and an instrumentation framework that allows you to examine a Linux kernel dynamically. If you don't have all these skills, following along will still give you some insight into the inner workings of a program on Linux.
This article assumes you are running Linux kernel 3.18 [5] with the debug symbols for Bash installed, that a local copy of the 3.18 kernel source is available, and that SystemTap is set up properly. In the next section, I will describe how to configure your system to follow this article.
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