Working with the Unix OS

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Introduction to kernel
Programs & Processes
A program is a collection of instructions & data that are kept in an ordinary file on disk
the file is marked executable, the contents have to obey rules
text file --------> object file -----> bind with libraries
compile linker
To run program, the kernel has to create a new process (environment in which program executes)
A process consists of
- instruction segment
- userdata segment
- system data segment
A process's system data includes attributes such as
- current directory,
- open file descriptors,
- CPU time,
A process uses system calls to access & modify attributes
A process is created by the kernel on behalf of a currently executing process, which becomes the parent of the new
child process.
The child inherits most of the parents system data attributes.
The UNIX
Kernel
User Level
Kernel Level
traps
The system calls for controlling processes are:
user programs
libraries
system call interface
file subsystem
process control subsystem
interprocess communication
buffer cache
scheduler
memory management
character block
device drivers
hardware control
Kernel Level
Hardware Level
hardware
System calls interact with the file subsystem and process control system.
The file subsystem manages files, allocating file space, administrating free space, controlling access to files,
retrieving data for users.
The file subsystem accesses file data using a buffering mechanism that regulates data flow between the kernel and
secondary storage devices.
Block I/O devices are random access storage devices, raw devices are called character devices.
The process control subsystem is responsible for process synchronization, interprocess communication, memory
management, and process scheduling.
Processes interact with file subsystem via systems calls:
open, close, read, write, stat, chown, chmod.
fork, exec, exit, wait, brk, signal.
Memory management - swapping and demand paging
Scheduler
- allocates the CPU to processes
IPC - asynchronous signaling of events to synchronous transmission of messages between processes
Hardware control is responsible for handling interrupts and communicating with the machine.