procfs

The proc filesystem (procfs) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized method for dynamically accessing process data held in the kernel than traditional tracing methods or direct access to kernel memory. Typically, it is mapped to a mount point named /proc at boot time. The proc file system acts as an interface to internal data structures in thekernel. It can be used to obtain information about the system and to changecertain kernel parameters at runtime (sysctl). Many Unix-like operating systems support the proc filesystem, including Solaris, IRIX, Tru64 UNIX, BSD, Linux, IBM AIX, QNX, and Plan 9 from Bell Labs. OpenBSD dropped support in version 5.7, released in May 2015. The Linux kernel extends it to non–process-related data. The proc filesystem provides a method of communication between kernel space and user space. For example, the GNU version of the process reporting utility ps uses the proc file system to obtain its data, without using any specialized system calls. Tom J. Killian implemented the UNIX 8th Edition (V8) version of /proc: he presented a paper titled 'Processes as Files' at USENIX in June 1984. The design of procfs aimed to replace the ptrace system call used for process tracing. Detailed documentation can be found in the proc(4) manual page. Roger Faulkner and Ron Gomes ported V8 /proc to SVR4, and published a paper called 'The Process File System and Process Model in UNIX System V' at USENIX in January 1991. This kind of procfs supported the creation of ps, but the files could only be accessed with functions read(), write(), and ioctl(). Between 1995 and 1996, Roger Faulkner created the procfs-2 interface for Solaris-2.6 that offers a structured /proc filesystem with sub-directories. Plan 9 implemented a process file system, but went further than V8. V8's process file system implemented a single file per process. Plan 9 created a hierarchy of separate files to provide those functions, and made /proc a real part of the file system. 4.4BSD cloned its implementation of .mw-parser-output .monospaced{font-family:monospace,monospace}/proc from Plan 9. As of February 2011, procfs is gradually becoming phased out in FreeBSD. It was removed from OpenBSD in version 5.7, which was released in May 2015, because it 'always suffered from race conditions and is now unused'.