Week 2

VL 3 - 23.04.25

• os api’s:
  • a quick exmaple: system calls in windows, reading a data.
  • API’s in Windows vs Posix
  • Windows Subsystem for Linux (WSL)

Processes

• Process: an active, executing program
• a programm becomes a process when the OS loads the program code to the memory => same program can be started many times => multiple processes of the same program
• Memory of a process:
  • stack: function calls, return addresses, variables local to the stack
  • heap: dynamically allocated memory for objects and arbitrarily large data structures.
  • data: global variables, constants.
  • program code.
• stack and heap grow towards each other.
• Process Control Block (PCB): the way OS managemes processes (process bookkeeping) (implemented as struct in C.)
• Process management: creation, deletion, etc
  • fork(): creates an identical child-process.
  • execve(): replace the memory contents of a process.
  • waitpid(): wait for the ending of a child-process.
  • _exit(): end the process
• example: a (very) mimimal, toy shell - application of fork()
• init() in Posix
• process creation in windows.
• process management

fork

• parent and child processes can be synchonozied with a wait() command in conjunction with fork().

## Tutorial

• overview of bash

  greeting="Hello, world!"
  echo "$greeting"