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Chapter 13

Chapter 13. Processes. What is a process?. A process is a program in execution A process is created whenever an external command is executed Whenever the execution of the external command is completed, the process is terminated. CPU Scheduling.

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Chapter 13

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  1. Chapter 13 Processes

  2. What is a process? • A process is a program in execution • A process is created whenever an external command is executed • Whenever the execution of the external command is completed, the process is terminated

  3. CPU Scheduling • CPU scheduling is the process of assigning the CPU to different processes • CPU scheduling takes into consideration many factors: • Whether the process is interactive or batch • The priority of the different processes • Process state of readiness • Past behavior of process

  4. Figure 13.1 LINUX process state diagram

  5. Table 13.1 A Brief Description of the LINUX Process States

  6. Figure 13.2  Process creation via the fork system call

  7. Figure 13.3  Steps for execution of a binary program sort by a LINUX shell

  8. Figure 13.3  Steps for execution of a binary program sort by a LINUX shell

  9. Figure 13.4  Steps for execution of a shell script by a LINUX shell

  10. Figure 13.5  Execution of commands under the child shells (also called subshells)

  11. Process Attributes • The system keeps track of several process attributes • The description of the current processes including their attributes can be displayed using the ps command • Syntax • ps [options] • Option syntax varies with SYS V (-), BSD ( ), GNU (--)

  12. ps Command Syntax ps [options] Option syntax varies with • SYS V (-l, -a, -N, -u ulist, …) • BSD ( l, a, U ulist, f, …) • GNU (--l, --a, …) • l long listing • a all processes (not just users) • N negate selection • U ulist info about other users’ processes • f ASCII art tree format

  13. Table 13.2 Some Process States and Their Meaning

  14. Table 13.3 Various Fields of the Output of the commandps -l

  15. Table 13.3 Various Fields of the Output of the commandps -l

  16. Process Control Commands • nice • kill • Running commands in the background using & • Suspending process using CTRL-Z • fg • bg • ps • top • pstree • jobs

  17. Daemons • Daemons are system processes running in the background in order to handle a variety of system services • Daemon examples: • mail daemon • print daemon • internet daemon

  18. Specifying Multiple Commandsin a Single Command Line • Several commands separated by “;” in a single command are executed sequentially • Several commands separated by “&” in a single command are executed in parallel

  19. Forced Termination • Foreground processes can be terminated using CTRL-C • Background processes can be terminated by: • Using kill • Bringing them to the foreground then using CTRL-C

  20. Figure 13.6  LINUX process hierarchy

  21. Process Hierarchy • The current process hierarchy can be displayed using the pstree command • The ulimit command can be used to determine the maximum number of simultaneous processes that can berun by the user

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