Anatomy of a simple Linux utility
How ls Works
© racorn, 123RF
A simple Linux utility program such as ls might look simple, but many steps happen behind the scenes from the time you type "ls" to the time you see the directory listing. In this article, we look at these behind-the-scene details.
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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