Working with the Unix OS

Introduction to kernel
UNIX Internals
Kernel Basics - system calls & interrupts
File System - directory, regular, device files
Process management - share CPU & memory
Input/Output - terminal I/O
Interprocess Communication IPC
Kernel Basics
Kernel is part of UNIX OS
- share CPU & memory between competing processes
- processes system calls
- handles peripherals
- loaded into RAM on power on
- runs until turned off or system crashes
File management
Input/Output
Peripherals
IPC
Process management
Memory management
CPU + RAM
Talking to Kernel
Processes access kernel facilities via system call interface & peripherals communicate with kernel via hardware
interrupts.
Peripherals ======= KERNEL ======= Processes
Hardware Interrupts System Calls
System Calls
- interface to kernel
- open/close files
- perform I/O read/write
- send signals - kill
- create pipes/sockets
- duplicate process - fork
- overlay a process - exec
- terminate a process - exit
- input/output
- interprocess communication
- process management
User Mode & Kernel Mode
The kernel contains data structures, which are essential to functioning of the system
e.g. process table - one entry for each process
open file table - one entry for each open file
- reside in kernel's memory space
- protected from user processes by a memory management system
- system calls can directly manipulate kernel data structures
- when a user process is running, it operates in a special mode called “user mode”
- user mode prevents a process from executing privileged machine instructions
- the only way for a user process to enter kernel mode is to execute a system call
e.g.
User Process
user code
...
result = open (" file", O_RDONLY);
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