Purpose of the /proc File System

Answer

The /proc file system is a mounted file system used to trace a process system call, receive signals, and incurred machine faults.

The /proc file system provides access to the state of each active process and thread in the system. The name of each entry in the /proc file system is a decimal number corresponding to the process ID. These entries are subdirectories and the owner of each is determined by the user ID of the process. Access to the process state is provided by additional files contained within each subdirectory. Except where otherwise specified, the term /proc file is meant to refer to a non-directory file within the hierarchy rooted at /proc. The owner of each file is determined by the user ID of the process.

The various /proc directory, file, and field names contain the term lwp (light weight process). This term refers to a kernel thread. The /proc files do not refer to user space pthreads. While the operating system does not use the term lwp to describe its threads, it is used in the /proc file system for compatibility with other UNIX operating systems.

It is known as a "pseudo-filesystem", which means it is not a true filesystem that is consuming storage. The files and directories in /proc are entry points into kernel tables, such as the open file table or the process table. They do not consume space in any filesystem, and should be skipped when backing up the system.

References
IBM Knowledge Center: The proc filesystem
IBM Redbooks: AIX 5L Differences Guide Version 5.2 Edition, Chapter 10.3