• System calls in UNIX
  • Interesting signals in UNIX
  • Memory
  • UNIX Memory Management Policies
    		•

    Types of Processes in UNIX




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    Unix

    Types of Processes in UNIX


    Mainly 3 types
    • User process
    • Daemon process
    • Kernel process
    • Daemon process
    • Performs the function in a system wide basis. The function can be of any auxiliary kind but they are vital in controlling the computational environment of the system.
    • Example Print spooling, Network Management.
    • Once created Daemon process can exist throughout the life time of the Operating System.

    System calls in UNIX

    • Fork(): -This system call create new process.
    • Exec(): -This system call used after a fork to replace the process memory space with a new program.
    • Wait():-This system call moves a process off the ready queue until the

      • termination of the child.

    Interesting signals in UNIX

    • SIGCHLD
    • SIGFPE
    • SIGILL
    • SIGINT
    • SIGKILL
    • SIGSEGV
    • SIGSYS
    • SIGXCPU
    • SIGXFSZ

    Child process died or suspended Arithmetic fault
    Illegal instruction
    tty interrupt (Control C) Kill process Segmentation fault Invalid System call Exceeds CPU limit Exceeds file size limit

    Memory

    • Primary memory is a precious resource that frequently cannot contain all active processes in the system
    • The memory management system decides which processes should reside (at least partially) in main memory
    • It monitors the amount of available primary memory and may periodically write processes to a secondary device called the swap device to provide more space in primary memory
    • At a later time, the kernel reads the data from swap device back to main memory

    UNIX Memory Management Policies

    • Swapping
      • Easy to implement
      • Less system overhead
    • Demand Paging
      • Greater flexibility

    Swapping

    • The swap device is a block device in a configurable section of a disk
    • Kernel allocates contiguous space on the swap device without fragmentation
    • It maintains free space of the swap device in an in-core table, called map
    • The kernel treats each unit of the swap map as group of disk blocks
    • As kernel allocates and frees resources, it updates the map accordingly

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