The /proc File System And ProcMeter

The /proc file system is a part of Linux that most people have not investigated deeply—perhaps may have never heard of. Like the kernel itself, it is a vital part of a Linux system. Yet its contents and its function are a mystery to most users. If the kernel is the brain of the operating system then the /proc file system is its personal organizer.

In this article I will describe the /proc file system—what it is, and how it can be used. There is also a description of the program ProcMeter that uses the /proc file system to display useful information.

First of all, the /proc file system is not a real file system; it is a virtual file system without the physical presence that a disk or a tape has. The most common file system you use is the collection of files on the disk. The disk stores the data without regard to meaning, and the file system (e.g., the Linux ext2fs system) makes sense of the data. The file system organizes the data as directories and files for the user. Another common file system is the Network File System (NFS), which makes files on remote computers accessible.

All file systems are managed by the Linux kernel, which maps the data on the device into a usable form. The user-level programs that access the file system do not need to know how or where the data is actually stored. When a program reads from a file, the kernel manipulates the appropriate device to obtain the data. When a program accesses one of the /proc files there is no device; instead, the kernel supplies the information from its internal state. The files exist only while there is a program actually looking at them.

The /proc file system is a feature which Linux inherited from one of its Unix ancestors. There are two main dialects of Unix in popular usage: System V and BSD. The history of these two are not important here, except that System V contains a /proc and BSD does not.

Everything that is happening in Linux. Every single program that is running, the entire contents of memory, the internal workings of the kernel—all the processes currently running on the system are contained in the /proc file system. proc is an abbreviation for process.

The most interesting files in /proc are listed below. This list was compiled from kernel version 1.2.13; other versions will be different. This is not a complete list, but contains only those files whose contents are obvious to casual browsers. A full description of the files can be read in the Linux kernel source code—a task not for the faint-hearted.

The contents of /proc are completely dependent on the processor architecture. (For example, the file /proc/cpuinfo is available only for ix86 processors.) The different types of hardware with which the kernel must communicate can also add files (e.g., /proc/pci on PCI bus computers). There are also files that are present or not, depending on which kernel options are compiled. (My /proc/modules is empty, because I did not compile in modules support.)

You can look at the contents of these files yourself. Just type:

cat /proc/meminfo

and you will see something like:

    total:  used:  free:  shared: buffers:
Mem: 11423744 8753152 2670592 2670592 2764800
Swap: 25800704 5328896 20471808