Installation guide

Chapter 2.

The proc File System

The Linux kernel has two primary functions: to control access to physical devices on the computer

and to schedule when and how processes interact with these devices. The /proc/ directory contains

a hierarchy of special ﬁles which represent the current state of the kernel — allowing applications and

users to peer into the kernel’s view of the system.

Within the /proc/ directory, one can ﬁnd a wealth of information about the system hardware and

any processes currently running. In addition, some of the ﬁles within the /proc/ directory tree can

be manipulated by users and applications to communicate conﬁguration changes to the kernel.

2.1. A Virtual File System

Under Linux, all data are stored as ﬁles. Most users are familiar with the two primary types of ﬁles:

text and binary. But the /proc/ directory contains another type of ﬁle called a virtual ﬁle. It is for

this reason that /proc/ is often referred to as a virtual ﬁle system.

These virtual ﬁles have unique qualities. Most of them are listed as zero bytes in size and yet when one

is viewed, it can contain a large amount of information. In addition, most of the time and date settings

on virtual ﬁles reﬂect the current time and date, indicative of the fact they constantly changing.

Virtual ﬁles such as interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions pro-

vide an up-to-the-moment glimpse of the system’s hardware. Others, like /proc/filesystems and

the /proc/sys/ directory provide system conﬁguration information and interfaces.

For organizational purposes, ﬁles containing information on a similar topic are grouped into virtual

directories and sub-directories. For instance, /proc/ide/ contains information for all physical IDE

devices. Likewise, process directories contain information about each running process on the system.

2.1.1. Viewing Virtual Files

By using the cat, more, or less commands on ﬁles within the /proc/ directory, you can immedi-

ately access an enormous amount of information about the system. For example, if you want to see

what sort of CPU your computer has, type cat /proc/cpuinfo and you will see something similar

to the following:

processor : 0

vendor_id : AuthenticAMD

cpu family : 5

model : 9

model name : AMD-K6(tm) 3D+ Processor

stepping : 1

cpu MHz : 400.919

cache size : 256 KB

fdiv_bug : no

hlt_bug : no

f00f_bug : no

coma_bug : no

fpu : yes

fpu_exception : yes

cpuid level : 1

wp : yes

flags : fpu vme de pse tsc msr mce cx8 pge mmx syscall 3dnow k6_mtrr

bogomips : 799.53