Скачать или смотреть Understanding the argv Variable: The Connection to /proc/ pid /cmdline in Linux

Explore how the `argv` variable relates to the `/proc/ pid /cmdline` file in Linux, revealing the inner workings of process command line arguments.
---
This video is based on the question https://stackoverflow.com/q/63442034/ asked by the user 'pottea' ( https://stackoverflow.com/u/7021510/ ) and on the answer https://stackoverflow.com/a/63443636/ provided by the user 'Milag' ( https://stackoverflow.com/u/10304821/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How is /proc/ pid /cmdline related to the argv variable of a process?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Connection Between argv and /proc/<pid>/cmdline in Linux

When working with processes in Linux, you might have come across the argv variable, which holds command line arguments passed to a program. But have you ever wondered how this is connected to /proc/<pid>/cmdline, a special file in the proc filesystem? If so, you're not alone. This question often sparks curiosity among developers and system enthusiasts alike. In this guide, we will delve into this intriguing relationship, clarifying how these two components interact within the Linux environment.

What is /proc/<pid>/cmdline?

The directory /proc is a virtual filesystem in Linux that provides an interface to kernel data structures. It contains information about running processes and system resources. Within this directory, each process has a subdirectory named after its process ID (pid). One of the key files in this directory is cmdline. This file contains the command line arguments that were used to start the process.

Accessing the cmdline File

To view the command line arguments for your current shell process, you can use the following command:

[[See Video to Reveal this Text or Code Snippet]]

In this command, $$ refers to the current shell's process ID, making it easy to see the command that started it.

How Does It Relate to argv?

The argv variable in C (and many programming languages) is an array of strings (character pointers) representing the command line arguments passed to a program. Specifically, argv[0] typically holds the name of the executable, while the subsequent indices hold the additional arguments passed to the command.

Interaction Between argv and /proc/<pid>/cmdline

Content Consistency: The content of /proc/<pid>/cmdline is closely linked to the argv array. Whenever a process is executed, the arguments supplied at the command line are stored in the argv variable. This data is then represented in the /proc filesystem's corresponding cmdline file.

Kernel Underpinnings: Internally, the Linux kernel manages command line arguments and process information through various data structures. The saved_command_line variable is a global variable in the kernel that captures this information. When a process is created, the kernel fills out this variable with the values from argv, thereby enabling the /proc/<pid>/cmdline file to reflect the command line used to initiate the process.

Reading the Command Line: The function proc_pid_cmdline_read() is responsible for reading the command line arguments from the saved_command_line variable and making them accessible via the /proc/<pid>/cmdline file. This ensures that you can query the command line used to start any user process running on the system.

Notes on Compatibility

It is worth mentioning that the symbols and implementations may vary across different releases of the Linux kernel, which can sometimes complicate the understanding of this relationship. Thus, it’s essential to consider the version of the kernel you are working on for accurate interpretations.

Conclusion

The connection between the /proc/<pid>/cmdline file and the argv variable provides valuable insights into how command lines are processed within the Linux operating system. By understanding this relationship, users and developers can gain a clearer view of process management and manipulation in Linux, leading to more effective programming and debugging practices. Whether you're developing software or simply curious about how processes work under the hood, knowing how to navigate this system can prove incredibly beneficial.

Happy coding, and may your argv always reflect the command lines you intended!