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 the kernel. It can be used to obtain information about the system and to change certain 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. 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.

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