E02:Linux Network and Process Management

 What is a Process?

• A process in Linux is a running program or task. It's an instance of a program that is being executed by the Linux kernel.
• Each process has its own unique Process ID (PID), which is a numerical identifier that distinguishes it from other processes.

Process Characteristics:

• Processes have their own set of resources, including memory, CPU time, file descriptors, and more.
• Each process is isolated from other processes, meaning they can't directly access the memory or resources of another process.

Creation of Processes:

• Processes are typically created in Linux through the fork() system call. This call creates a new process that is a copy of the calling (parent) process.
• The exec() system call can be used to replace the program in the current process with a new one. This is commonly used for running different programs within the same process.

Process Hierarchy:

• Processes in Linux are organized into a hierarchical structure, with a parent-child relationship. Each process, except the initial process (usually PID 1), has a parent process.
• When a parent process spawns a new child process, the child inherits some attributes from the parent, such as environment variables and open file descriptors.
• Monitoring ProcessesThe ps command is used to list currently running processes in the terminal, along with their details such as PID, status, and resource usage.
• The top or htop commands provide a dynamic, real-time view of running processes and system resource usage.
• You can send signals to processes using commands like kill to terminate or interact with them.

Daemon Processes:

• Daemon processes are background processes that run without any user interaction, often providing system services. Examples include web servers, database servers, and printing services.

Process States:

• Processes can be in different states, such as running, sleeping, stopped, or zombie. These states indicate what the process is currently doing.

Process Management

•  ps Command: 
• ps lists running processes.
• ps aux shows detailed process information.
• ps aux | grep username filters processes for a specific user.
• cat /proc//status Command:
• Displays detailed info about a process with a specific PID.
• top Command:
• Real-time process monitor. 
• top -u username shows processes for a specific user. 
• top -u root focuses on root user processes.
• gnome-system-monitor: 
• GUI-based system monitor for a graphical view of processes and system resources.
• kill Command: 
• kill  is used to stop a process by its PID. 
• kill -9  sends a forceful SIGKILL signal to terminate a process.
• systemctl Command:
• sudo systemctl status service_name checks the status of a service.
• sudo systemctl start service_name starts a service.
• sudo systemctl stop service_name stops a service.

Network commands and configurations in Linux:

• Network Interface Commands:
• ifconfig, ip addr, and ip link display network interface information, including names and configurations.
• Routing Information:
• ip route shows routing information for the network your device is connected to.
• Network Configuration File:
• Network configuration files are found in /etc/netplan/.
• The default configuration is in YAML format, and it often uses NetworkManager for network management.
• These commands and locations are useful for managing and configuring network interfaces and connections in Linux.