Linux os
- 2. Submitted to Dipok Chandra Das Lecturer Of IIT,NSTU Prepared By Abdullah An Noor(ASH1825001M) Fazle Rabbi(ASH1825004M) MD Mynuddin(ASH1825007M)
- 3. Contents ■ Linux History ■ Design Principles ■ Kernel Modules ■ Process Management ■ Scheduling ■ Memory Management ■ File Systems ■ Input and Output ■ Interprocess Communication ■ Network Structure ■ Security
- 4. Linux History ■ Linux is a modern, free operating system based on UNIX standards ■ First developed as a small but self-contained kernel in 1991 by Linus Torvalds, with the major design goal of UNIX compatibility ■ Its history has been one of collaboration by many users from all around the world, corresponding almost exclusively over the Internet ■ It has been designed to run efficiently and reliably on common PC hardware, but also runs on a variety of other platforms ■ The core Linux operating system kernel is entirely original, but it can run much existing free UNIX software, resulting in an entire UNIX-compatible operating system free from proprietary code ■ Many, varying Linux Distributions including the kernel, applications, and management tools
- 5. The Linux Kernel ■ Version 0.01 (May 1991) had no networking, ran only on 80386- compatible Intel processors and on PC hardware, had extremely limited device-drive support, and supported only the Minix file system ■ Linux 1.0 (March 1994) included these new features: ● Support for UNIX’s standard TCP/IP networking protocols ● BSD-compatible socket interface for networking programming ● Device-driver support for running IP over an Ethernet ● Enhanced file system ● Support for a range of SCSI controllers for high-performance disk access ● Extra hardware support ■ Version 1.2 (March 1995) was the final PC-only Linux kernel
- 6. ■ Released in June 1996, 2.0 added two major new capabilities: ● Support for multiple architectures, including a fully 64-bit native Alpha port ● Support for multiprocessor architectures ■ Other new features included: ● Improved memory-management code ● Improved TCP/IP performance ● Support for internal kernel threads, for handling dependencies between loadable modules, and for automatic loading of modules on demand ● Standardized configuration interface ■ Available for Motorola 68000-series processors, Sun Sparc systems, and for PC and PowerMac systems ■ 2.4 and 2.6 increased SMP support, added journaling file system, preemptive kernel, 64-bit memory support Linux 2.0
- 7. The Linux System ■ 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 min 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
- 8. ■ Linux is a multiuser, multitasking system with a full set of UNIX compatible tools ■ Its file system adheres to traditional UNIX semantics, and it fully implements the standard UNIX networking model ■ Main design goals are speed, efficiency, and standardization ■ Linux is designed to be compliant with the relevant POSIX documents; at least two Linux distributions have achieved official POSIX certification ■ The Linux programming interface adheres to the SVR4 UNIX semantics, rather than to BSD behavior Linux Design Principles
- 9. ■ Like most UNIX implementations, Linux is composed of three main bodies of code; the most important distinction between the kernel and all other components ■ The kernel is responsible for maintaining the important abstractions of the operating system ● Kernel code executes in kernel mode with full access to all the physical resources of the computer ● All kernel code and data structures are kept in the same single address space ■ The system libraries define a standard set of functions through which applications interact with the kernel, and which implement much of the operating-system functionality that does not need the full privileges of kernel code ■ The system utilities perform individual specialized management tasks Components of a Linux System
- 10. ■ A kernel module may typically implement a device driver, a file system, or a networking protocol ■ Kernel modules allow a Linux system to be set up with a standard, minimal kernel, without any extra device drivers built in ■ Three components to Linux module support: ● Module Management : is split into two separate sections: Managing sections of module code in kernel memory Handling symbols that modules are allowed to reference ● Driver Registration : Allows modules to tell the rest of the kernel that a new driver has become available Registration tables include the following items: ● Conflict Resolution : Device drivers File systems Network protocols Binary format A mechanism that allows different device drivers to reserve hardware resources and to protect those resources from accidental use by another driver. It aims to: Prevent modules from clashing over access to hardware resources Prevent autoprobes from interfering with existing device drivers Resolve conflicts with multiple drivers trying to access the same hardware Linux Kernel Modules
- 11. Process Management ■ UNIX process management separates the creation of processes and the running of a new program into two distinct operations. ● The fork system call creates a new process ● A new program is run after a call to execve ■ Under UNIX, a process encompasses all the information that the operating system must maintain t track the context of a single execution of a single program ■ Under Linux, process properties fall into three groups: Process Identity Process Environment Process Context
- 12. Processes and Threads Linux uses the same internal representation for processes and threads; a thread is simply a new process that happens to share the same address space as its parent ■ A distinction is only made when a new thread is created by the clone system call ● fork creates a new process with its own entirely new process context ● clone creates a new process with its own identity, but that is allowed to share the data structures of its parent ■ Using clone gives an application fine-grained control over exactly what is shared between two threads
- 13. ■ Linux uses two process-scheduling algorithms: ● A time-sharing algorithm for fair preemptive scheduling between multiple processes ● A real-time algorithm for tasks where absolute priorities are more important than fairness ■ For time-sharing processes, Linux uses a prioritized, credit based algorithm ■ Linux implements the FIFO and round-robin real-time scheduling classes; in both cases, each process has a priority in addition to its scheduling class ● The scheduler runs the process with the highest priority; for equal-priority processes, it runs the process waiting the longest ● FIFO processes continue to run until they either exit or block ● A round-robin process will be preempted after a while and moved to the end of the scheduling queue, so that round-robing processes of equal priority automatically time-share between themselves Linux Process Scheduling
- 14. ■ Linux’s physical memory-management system deals with allocating and freeing pages, groups of pages, and small blocks of memory ■ It has additional mechanisms for handling virtual memory, memory mapped into the address space of running processes ■ Splits memory into 3 different zones due to hardware characteristics Relationship of Zones and Physical Addresses on 80x86 Splitting of Memory in a Buddy Heap Memory Management
- 15. ■ 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: Logical View and Physical View ■ The kernel creates a new virtual address space 1. When a process runs a new program with the exec system call 2. Upon creation of a new process by the fork system call ■ The Linux kernel reserves a constant, architecture-dependent region of the virtual address space of every process for its own internal use ■ The VM paging system can be divided into two sections: ● The pageout-policy algorithm decides which pages to write out to disk, and when ● The paging mechanism actually carries out the transfer, and pages data back into physical memory as needed Virtual Memory
- 16. Linux File Systems ■ To the user, Linux’s file system appears as a hierarchical directory tree obeying UNIX semantics ■ Internally, the kernel hides implementation details and manages the multiple different file systems via an abstraction layer, that is, the virtual file system (VFS) ■ The Linux VFS is designed around object-oriented principles and is composed of two components: ● A set of definitions that define what a file object is allowed to look like: ● A layer of software to manipulate those objects The inode-object and the file-object structures represent individual files the file system object represents an entire file system
- 17. ■ 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 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 Linux Input and Output
- 18. ■ Like UNIX, Linux informs processes that an event has occurred via signals ■ There is a limited number of signals, and they cannot carry information: Only the fact that a signal occurred is available to a process ■ The Linux kernel does not use signals to communicate With processes with are running in kernel mode, rather, communication within the kernel is accomplished via scheduling states and wait.queue structures ■ The pipe mechanism allows a child process to inherit a communication channel to its parent, data written to one end of the pipe can be read a the other ■ Shared memory offers an extremely fast way of communicating; any data written by one process to a shared memory region can be read immediately by any other process that has mapped that region into its address space ■ To obtain synchronization, however, shared memory must be used in conjunction with another Interprocess communication mechanis Passing Data Between Processes Interprocess Communication Linux Interprocess Communication
- 19. Shared Memory Object ■ The shared-memory object acts as a backing store for Shared memory regions in the same way as a file can act as backing store for a memory-mapped memory region ■ Shared-memory mappings direct page faults to map in pages from a persistent shared-memory object ■ Shared-memory objects remember their contents even if no processes are currently mapping them into virtual memory
- 20. Network Structure ■ Networking is a key area of functionality for Linux. ● It supports the standard Internet protocols for UNIX to UNIX communications ● It also implements protocols native to nonUNIX operating systems, in particular, protocols used on PC networks, such as Appletalk and IPX ■ Internally, networking in the Linux kernel is implemented by three layers of software: ● The socket interface ● Protocol drivers ● Network device drivers ■ The most important set of protocols in the Linux networking system is the internet protocol suite ● It implements routing between different hosts anywhere on the network ● On top of the routing protocol are built the UDP, TCP and ICMP protocols
- 21. ■ The pluggable authentication modules (PAM) system is available under Linux ■ PAM is based on a shared library that can be used by any system component that needs to authenticate users ■ Access control under UNIX systems, including Linux, is performed through the use of unique numeric identifiers (uid and gid) ■ Access control is performed by assigning objects a protections mask, which specifies which access modes—read, write, or execute—are to be granted to processes with owner, group, or world access ■ Linux augments the standard UNIX setuid mechanism in two ways: ● It implements the POSIX specification’s saved user-id mechanism, which allows a process to repeatedly drop and reacquire its effective uid ● It has added a process characteristic that grants just a subset of the rights of the effective uid ■ Linux provides another mechanism that allows a client to selectively pass access to a single file to some server process without granting it any other privileges Linux Security