System Information /proc

System Information /proc

A wealth of information is provided by the /proc file system for the Linux kernel, from information about each process to system-wide information about CPU, memory, file systems, interrupts, and partitions. This article covers the /proc file system to help you see the overall information that a running system can provide. The two different types of information in the /proc file system are read-only and writeable. The writeable information can be changed on-the-fly. If you change the

value of a /proc entry, the system feature could perform in a different way.

 The /proc file system is a special window into the running Linux kernel. Each file under /proc is tied to a kernel that provides the file's information on-the-fly when the file is read. Many utilities rely on /proc to gather system-type information. Some of the utilities that use /proc entries include iostat, sar, lsdev, lsusb, lspci, vmstat, and mpstat. This chapter covers each of these utilities.

 What Is /proc?

The /proc file system is a reflection of the system in memory. It can be used as a hierarchal view of the system. The goal of the /proc file system is to provide an easy view of the kernel resources and components. You also can use /proc to view information about the processes that are currently running on the system. A second goal of /proc is to present information about the system in a readable way instead of getting this type of information through API system calls.

 There is a close relationship between /proc and sysctl functions. In general, all sysctl functions are also represented under /proc/sys/ as a proc file system entry. The /proc file system entries are not stored on a nonvolatile medium such as a file system; the entries are generated on-the-fly. In other words, every time the read method for the associated file is invoked, the entries are provided. This results in much freedom in how output is represented to the user. The /proc file system is a file system in the sense that it provides an interface to the user that resembles the normal file system interface of any other file system, allowing access via open, read, write, and close.

 /proc has two basic interface types: binary and character-based. Most interfaces are text-mode. In cases where binary interfaces are used, usually both types are implemented at the same time. For user-space applications, it is generally simpler to interface with the binary version rather than with text mode, since in the latter case parsing (or at least scanning fixed-format input lines) would be required. On the other hand, binary interfaces are not well-suited for direct interpretation by humans.