The Linux System

The Linux System

1. Tecnológico de Costa Rica, Carrera: Ingeniería en Computación, Sede: Cartago, Curso: Principios de sistemas operativos, Profesor: Esteban Arias Méndez, Estudiante: Jason David Espinoza Siles, Carné: 201223941, II semestre, 2016, Libro: Operating System Concepts 9th.pdf capítulo 18

2. Linux uses many tools developed as part of Berkeley’s BSD operating system, MIT’s X Window System, and the Free Software Foundation's GNU project  The main system libraries were started by the GNU project, with improvements provided by the Linux community  Linux networking-administration tools were derived from 4.3BSD code; recent BSD derivatives such as Free BSD have borrowed code from Linux in return  The Linux system is maintained by a loose network of developers collaborating over the Internet, with a small number of public ftp sites acting as de facto standard repositories  File System Hierarchy Standard document maintained by the Linux community to ensure compatibility across the various system components  Specifies overall layout of a standard Linux file system, determines under which directory names configuration files, libraries, system binaries, and run-time data files should be stored

3. Virtual Memory

   • The VM system maintains the address space visible to each process: It creates pages of virtual memory on demand, and manages the loading of those pages from disk or their swapping back out to disk as required.  The VM manager maintains two separate views of a process’s address space:  A logical view describing instructions concerning the layout of the address space  The address space consists of a set of non-overlapping regions, each representing a continuous, page-aligned subset of the address space  A physical view of each address space which is stored in the hardware page tables for the process

4. The Linux Proc File System

   • The proc file system does not store data, rather, its contents are computed on demand according to user file I/O requests  proc must implement a directory structure, and the file contents within; it must then define a unique and persistent inode number for each directory and files it contains  It uses this inode number to identify just what operation is required when a user tries to read from a particular file inode or perform a lookup in a particular directory inode  When data is read from one of these files, proc collects the appropriate information, formats it into text form and places it into the requesting process’s read buffer

5. Input and Output

   • The Linux device-oriented file system accesses disk storage through two caches:  Data is cached in the page cache, which is unified with the virtual memory system  Metadata is cached in the buffer cache, a separate cache indexed by the physical disk block  Linux splits all devices into three classes:  block devices allow random access to completely independent, fixed size blocks of data  character devices include most other devices; they don’t need to support the functionality of regular files  network devices are interfaced via the kernel’s networking subsystem

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