Introduction to Process

Definition of a Process

A process in Unix is an instance of a running program. It represents the execution of a program in a specific state. It contains the program code and its current activity.

Process States (Running, Ready, Blocked)

• Running State: A process is actively executing instructions on the CPU.
• Ready State: A process is loaded into the main memory and is awaiting execution.
• Blocked State (or Waiting State): A process is temporarily inactive, often because it’s waiting for some event (e.g., I/O operation completion).

Process Control Block (PCB)

The Process Control Block (PCB) is a data structure that contains information about a process in the operating system. It includes:

• Process state
• Program counter
• CPU registers
• CPU scheduling information
• Memory management information
• I/O status information
• Accounting information
• Unique Process ID (PID)

Process ID (PID)

A Process ID (PID) is a unique numerical identifier assigned to each running process in a Unix-like operating system. It helps the system keep track of and manage individual processes.

Parent and Child Processes

• Parent Process: A process that creates another process (child process). The parent process may wait for the child process to terminate or continue its own execution.
• Child Process: A process created by another process (parent process). It inherits attributes, file descriptors, and environment variables from its parent.

Process Hierarchy

Processes are organized in a hierarchical structure, often referred to as a process tree. The root of this tree is typically the init process with PID 1. Child processes are spawned by their parent processes, creating a parent-child relationship.

Commands and Explanations

1. ps Command:

• The ps command is used to display information about active processes.

ps -ef

• The option -e selects all processes, and -f provides full format listing.

2. top Command:

• The top command provides a dynamic view of system processes, continuously updating in real-time.

top

• It displays a list of active processes with details like PID, CPU usage, memory usage, etc.

3. pstree Command:

• The pstree command displays the processes in a tree format, showing their hierarchical relationship.

pstree

• This command provides a visual representation of the parent-child relationships among processes.

4. pgrep Command:

• The pgrep command allows you to search for processes by their name.

pgrep <process-name>

• It returns the PID(s) of processes that match the specified name.

5. pkill Command:

• The pkill command is used to send signals to processes based on their name.

pkill <process-name>

• This command sends a signal to all processes whose names match the specified pattern.

These commands and explanations should provide a practical understanding of the topics related to the introduction of processes.