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LINUX An Introduction

LINUX An Introduction. Wan Ahmad Tajuddin Wan Abdullah Universiti Malaya KL ACGRID-II 2009. Operating Systems (OS). System software that abstracts the interface to various resources provided by low-level system hardware and software; and that manages these resources. user. OS.

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LINUX An Introduction

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  1. LINUXAn Introduction Wan Ahmad Tajuddin Wan Abdullah Universiti Malaya KL ACGRID-II 2009

  2. Operating Systems (OS) System software that abstracts the interface to various resources provided by low-level system hardware and software; and that manages these resources. user OS machine • distinct resources can be shared effectively • the programmer can use system resources easily [user provided with a virtual machine] * file management * error handling * reliability * security * monitoring * accounting * system management * user interface * process management and scheduling * job and session management * device management * timing management * memory management

  3. independent task units which are executed e.g. a batch job, the shell of a login session, a program run OS: Processes The execution of processes is controlled by the kernel and is interlaced – this part of the kernel is known as the despatcher or low-level scheduler when a process ends, or uses up its scheduled time, or cannot be continued because an interrupt occurred or the process is waiting for something or the error trap suspends the execution of the process while an error is handled the despatcher executes the next process in the process queue according to priority

  4. most basic layer of operating system, which communicates with hardware OS: Kernel • provides environment where processes can exist: • handling of interrupts • changing processor usage from process to process • implements mechanisms for communication and coordination between processes (semaphores, shared memory, message passing, input/output redirection, pipes,…), including deadlock avoidance and recovery Thread – flow of control between processes; a process can spawn daughter processes and so on shares process resources

  5. Files are contained in directory and subdirectory (which is also a kind of file) structure which is tree-like. Uppermost directory – main file directory or root directory (‘/’ or ‘\’). OS: File structure / /C /A /B /C/h /A/b /A/a /B/D /B/g /B/E /B/D/c /B/D/e /B/D/f

  6. implement open specifications adequately for interfaces, services, and support formats which allow application software built appropriately to be ported onto various types of systems with minimal change, to interoperate with other applications on local and remote systems, and to interact with users in a style which facilitates user mobility portability, interoperability, non-dependency, flexibility, integrability Open specification a public specification maintained by an open public consensus process, to include current new technology and which is consistent with standards. increased consultation with respect to system and application provider due to advantage from clear description of system needs Example of open operating system: UNIX System V Example of open specifications: POSIX (Portable Operating System Interface) Open Systems

  7. UNIX-like OS initially for PCs LINUX • Open source – free, standards, community, modifiable • Monolithic kernel – single standard system calls • Distribution suites (Red Hat, Ubuntu, Scientific Linux, …) - together with other open source (esp GNU) applications • CLI: shells (c-shell, Bourne again, ...) • GUI: based on X-Windows • Desktop environments (KDE, Gnome, ...)

  8. programmers environment simple user interface many, simple utilities that can be combined to perform powerful functions hierarchical file system simple interface to devices consistent with file format, supports I/O redirection and piping multi-user, multi-process system architecture independent and transparent to the user. Written in C – close to C, portable Legacy of UNIX

  9. LINUX User Interface Command Line Interface – shells (processes) Line commands: command –flags arguments Arguments can be e.g. filenames stdin (standard input – keyboard), stdout (standard output – monitor), device drivers (e.g. /dev/lp) are treated like files Graphics User Interface – based on X Windows (processes)

  10. LINUX File system Hierachical tree-like structure of (sub)directories and files Root directory: / Subdirectories usually e.g.: Filenames have extensions after a dot, usually describing type of file e.g. prog.c, files.tar, files.tar.gz

  11. File can be link to other file or (sub)directory File protection mode: defines priviledges for owner, group (of users where owner is in), (the rest of the) world, e.g. rwxr-x--x : owner can read, write, execute; group can read, execute; world can execute only (binary: 111101001) Superuser (root) have all priviledges to all files

  12. Networking Protocol: TCP/IP Hosts: domain name address (host.domain), IP address (number: xxx.xxx.xxx.xxx) Services: • Remote terminal – telnet, ssh • File transfer – ftp, scp • Web – http • Mail – smtp • etc

  13. Hands on • Introduction • GUI, tools and scripts • [System: processes and threads] • [Network programming]

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