C Programming Fundamentals Quiz

Introduction

• This document contains notes on the presentation of programming systems, specifically focusing on processes.

Processes

• A process is the memory image of a program currently running. It has a life cycle. It begins, runs, and then ends.
• A program launched twice creates two distinct processes.
• Every process is identified in memory by a unique number assigned by the operating system called the PID (Process ID).

Process Tree in a Unix System

• The init process is the parent of all other processes in a Unix system.
• init assigns the machine name, initializes the date and time, and ensures the system has been properly shut down.
• It starts the "getty" process which displays "login" prompt on a terminal and waits for input.
• It also launches the "inetd" process for network monitoring.
• Processes ending in "d" are called "daemon" processes that are server processes which work in continuous loops to provide consistent service to clients.

Process States

• Initial: newly created, in transition.
• Active: the process is executing.
• Waiting: the process is paused and relinquishes the CPU to another process.
• Terminating: the process has finished execution.

Process Concepts

• A processor executes one task at a time.
• The process has various states, such as "Ready," "Running," "Blocked," and "Terminated." These states depict the behavior of the process.
• Transitions happen between states on event occurrence. For instance, a process can transition to 'ready' from 'blocked' or 'terminated' on completion.

Process Creation

• User processes are launched by a command interpreter (shell). They can also create further processes.
• Processes need to interact among each other.
• The creator process is termed a "Parent" process.
• Processes created are referred to as "Children" processes.

Process Termination

• Process termination can be done in 3 ways:
• Normal Termination: Finishing its operations
• Permitted Termination: By the parent process executing a suitable command
• Abnormal Termination: By the system, such as exceeding execution time or insufficient memory.

Implementation

• The operating system maintains a process table, or table of processes, to track individual processes.
• Each entry contains information about the process, including its status, instruction address, stack pointer, open files, and the allocated memory.

Process Structure

• An operating system process comprises various elements such as PID (Process ID), UID (User ID), GID (Group ID), open files, maximum file size, and priority.
• The Terminal is the terminal from which a command was executed.

Priorities

• Under Linux, processes have a priority of -20 to 19 to control execution order.
• Higher values indicate lower priority.
• The nice command is used to adjust process priority

Example: Structure of a Unix Process

• Processes have unique IDs.
• Processes have sets of open files and a current directory.
• Processes have a certain priority, and execution time.

The ps command

• Shows information about running processes.
• Provides a list of processes linked to a specific terminal, along with CPU utilisation data.
• Useful for viewing processes that aren't linked with terminals.

The kill command

• Sends a signal to a process to perform an action.
• Accepts a signal number.

Signals

• A signal in an operating system is an asynchronous event that can interrupt the running of a program.
• Signals can be generated by hardware events (e.g., a signal to inform a process that an interrupt has occurred), the operating system itself, another process, or an error condition within the process.
• Example Signals: SIGINT, SIGQUIT, SIGKILL, etc.

Job Management

• A job is a collection of one or more commands.
• Commands, including programs, can be made into a job.
• Launch jobs in the background via the '&' character.
• The "jobs" command displays all running jobs.
• Use the 'bg' command to resume the execution of a stopped job.
• Use the 'fg' command to bring a job into the foreground.

Linux Management of Services

• The "service" command manipulates machine services.
• Shows status of all running services.
• Useful for managing processes.

Concepts and Tools.

• General information about Linux development.
• Information for developers on interaction between application and the machine.
• Information about system calls.

Development in Linux

• There are three basic steps in Linux development:
  • Editing the source code.
  • Compiling the source code into an executable file.
  • Linking the object files with the required libraries into a single executable file.

Compiling and Linking

• The compiler/linker (gcc) converts source code into machine language.
• Different options are used during compilation, like ‘-g’ for debugging and ‘-Wall’ to display warnings.

Execution

• An example of how to run C code.
• How to compile, execute programs in Linux.

Example

• Illustrative examples for various program execution scenarios.

Compilation in C

• Explains the compilation process in C programs using gcc.

The Makefile

• Managing multiple source files and dependencies within a C project.
• Using a makefile to automate compilation for large projects.
• Ways to write the different rules to automate compilation.
• Ways to define rules to automate compilation.
• Ways to define variables within a makefile for reuse.
• A guide on how to write, read and correctly interpret a makefile.

Parameters to "main()"

• Explanation of parameters in the main() function in a C program, including argc, argv, and envp.
• Explains what each parameter represents and how they are used within the program.
• Gives some example implementations in order to better understand their usage.

The PATH Variable

• The value of PATH is a set of paths.
• The executables are searched at all the paths defined within the PATH value.

Access to Environment

• How to access environment variables in code.
• Example usage and retrieval of values.

System Calls C

• Methods for creating and manipulating processes in C.
• Explanation of the system calls and their use in controlling process behavior.
  • Description of the 'fork' system call.

The fork System Call

• Usage: Creation of child processes, and how processes can communicate with each other after using fork().

Process Presentation

• Explains how processes are presented.
• Clarifies the parent-child relationship between two processes, and illustrates how the system deals with the parent process after the creation of a child process.

The wait System Call

• How to wait for a child process's status after the fork system call is used.
• This call is used to ensure the parent process stops till the child process ends, therefore allowing processes to complete in sequence.

Displaying the Date with the Child Process

• Demonstrates an example of using the fork and execv system calls to run a command, and capture its output to display within the current application.

Implementing Files

• Describes the various methods for interacting with files.
• Explains how raw file manipulation can differ from the standard input and output operations.

File Descriptors

• Discusses the concept of file descriptors for identifying files in a C program
• Explains the importance of understanding file descriptors in performing file operations.

stat Structure

• How to access file details using stat.
• Describes the contents of the struct stat to indicate file information like permissions, creation, modification, and access times.

File Writing

• Explanation of writing operations on files in C using the write system call.

File Reading

• Explanation of reading operations on files in C using the read system call.

File Management

• Various methods for managing and manipulating files in C, including creating, writing, reading, closing, and renaming files.

File Buffering

• Explains file buffering and its relationship with file I/O operations.

File Operations

• A summary of file operations and the necessary headers.

Standard POSIX

• Summary of the POSIX standard and its relevance to file operations.

Named Pipes

• Explanation of named pipes for inter-process communication.
• Showing how named pipes can persist across process terminations.

Signal Handling

• Introduction to signals and how they can be handled in C programs to make applications more robust.
• Illustrates how signal handling can be managed in processes to handle errors, or to perform some task when an error is encountered.

Signals : CTRL-C & CTRL-Z

• Illustrates how the CTRL+C and CTRL+Z commands can be used to interrupt a program.

Signal Handling

• Explains different ways to handle signals.
• Explanation of how to handle signals including the use of signal(), pause(), and alarm().
• Explains the structure, role, handling of signals.
  • Includes code examples, to help to understand the different signal handling.

Signal Interface

• Explains the interface for managing signals in C programs.

Signal Values in Unix

• Explains the different signal values in Unix-like systems (Linux).