Essential Linux Commands and Concepts

Commands to Access Documentation and View Processes

man: Displays the manual for any Linux command. For example:
```
  man ls
```
This opens the manual for the ls command, explaining its usage and options.
ps -aux: Lists all running processes along with details such as:
- Process ID (PID)
- CPU and RAM usage
- Command that initiated the process
top: Provides a dynamic, real-time view of system resources including:
- CPU usage
- RAM usage
- Process priorities
- Automatically refreshes at regular intervals.
htop: A more user-friendly and interactive version of top, offering better visualization and easier navigation.

Managing Process Priorities

nice: Assigns priority to a new process. Lower values indicate higher priority. Example:
```
  nice -n 10 my_process
```
renice: Adjusts the priority of an already running process. Example:
```
  renice -n 5 -p <PID>
```
This changes the priority of the process identified by <PID>.

Memory Management Commands

free -m: Displays memory usage in megabytes, including:
- Total memory
- Used memory
- Free memory
Cache: Memory occupied by previously used processes that still resides in RAM. To view or clear cache:
```
  cat /proc/sys/vm/drop_caches
```

Viewing CPU Information

lscpu: Displays detailed CPU information such as:
- Number of cores
- CPU architecture
- Clock speed

Shell Scripting Essentials

Shell scripting automates repetitive tasks using Linux commands.

Key Commands and Techniques

echo: Prints text or variables to the terminal.
```
  echo "Hello, World!"
```

Setting Variables:

  x=5
  echo $x  # Prints the value of x

read: Accepts user input during script execution.
```
  read var
  echo $var
```
Backticks (`): Executes commands within a script.
```
  echo `date`  # Prints the current date
```

Escape Sequences (-e): Enables special characters in echo.

  echo -e "Line1\nLine2"  # Prints with a newline

Example Script

Here’s a simple script to demonstrate these concepts:

#!/bin/bash
# A simple script to demonstrate Linux commands

# Set a variable
name="User"

# Print a welcome message
echo "Hello, $name!"

# Display current date and time
echo "Current date and time: `date`"

# Ask for user input
read -p "Enter your favorite Linux command: " cmd

# Display the manual for the entered command
man $cmd

Summary

These Linux commands and shell scripting basics provide a foundation for managing processes, system resources, and automation. Mastery of these tools empowers users to optimize and streamline their workflows efficiently.