The /proc File System

Werner Klauser

The /proc file system (procfs) is an example of a virtual file system used by several UNIX operating systems, including Sun's Solaris, Linux, OpenBSD, and AT&T's UNIX on an NCR system. No official standards regulate the /proc file system. This article provides a brief history of /proc and its implementation on Sun's Solaris 2.5 and Solaris 2.6 operating systems, as well as a few hints about how /proc can be used to solve various system administration problems.

History

The concept of /proc was first introduced by Tom Killian in the research Eight Edition UNIX system and was first written up in a paper: "Process as Files" in the Proceedings of the USENIX Association Summer Conference held in Salt Lake City, June 1984. The early version was essentially a ptrace(2) replacement with the important advancement that the address space of the process could be examined and modified using the read(2) and write(2) system calls rather than the clumsy ptrace(2) one-word-at-a-time interface.

Roger Faulkner and Ron Gomes ported the research version of /proc to SVR4 and provided an easier viewing and access method of the active processes. They presented their work in another USENIX paper: "The Process File System and Process Model in UNIX System V" in the Proceedings of the USENIX Association Winter Conference held in Dallas, TX, January 1991. At that time, Roger Faulkner was with Sun Microsystems and Ron Gomes with AT&T Bell Laboratories. As described in that paper, future work was intended to restructure /proc from a flat file system into a directory hierarchy describing a process.