Linux Essentials – The Big Picture

• Linux has three major layers
  • Hardware:
    • Includes all the hardware components of the computer
  • Kernel:
    • Kernel is software which will reside in RAM (memory) and tells other hardware components like CPU, Disks etc what has to be done
    • It manages the hardware and acts as interface between the hardware and running program
  • User Space:
    • the running programs that kernel manages – collectively make up the system’s upper level called user space.

The Kernel

• The kernel is in charge of managing taks in four general system areas
  • Process:
    • Kernel is responsible for describes the starting, pausing, resuming and terminating of process.
  • Memory:
    • Kernel keeps track of all the memory which is currently allocated to particular process, what might be shared between process and what is free
  • Device drivers:
    • Kernel acts as interface between hardware (such as disk, usb’s etc) and processes.
  • System calls and support:
    • Processes use system calls to communicate with the kernel

User Spaces and User

• The main memory allocated for user processes is called user space.
• Linux kernel supports the traditional concept of the Unix user. User is an entity that can run processes and own files. Each User is associated with username, However kernel doesn’t manage the username; instead it identifies users by simple identifiers called as userids
• Users exist to support permissions and boundaries