updated second chapter, added info about root and no-root user and other commands used

02-folder-structure/README.md

@@ -3,13 +3,15 @@
 ### Explanation of System Directories
 
 ### **Symbolic Links (Less Significant)**
+
 | Directory | Description |
 |-----------|-------------|
 | `/sbin -> /usr/sbin` | System binaries for administrative commands (linked to `/usr/sbin`). |
 | `/bin -> /usr/bin` | Essential user binaries (linked to `/usr/bin`). |
 | `/lib -> /usr/lib` | Shared libraries and kernel modules (linked to `/usr/lib`). |
 
 ### **Important System Directories**
+
 | Directory | Description |
 |-----------|-------------|
 | `/boot` | Stores files needed for booting the system (not relevant in containers). |
@@ -18,6 +20,7 @@
 | `/etc` | Stores system configuration files. |
 
 ### **User & Application-Specific Directories**
+
 | Directory | Description |
 |-----------|-------------|
 | `/home` | Default location for user home directories. |
@@ -26,6 +29,7 @@
 | `/root` | Home directory for the root user. |
 
 ### **Temporary & Volatile Directories**
+
 | Directory | Description |
 |-----------|-------------|
 | `/tmp` | Temporary files (cleared on reboot). |
@@ -35,8 +39,208 @@
 | `/dev` | Contains device files (e.g., `/dev/null`, `/dev/sda`). |
 
 ### **Mount Points**
+
 | Directory | Description |
 |-----------|-------------|
 | `/mnt` | Temporary mount point for external filesystems. |
 | `/media` | Mount point for removable media (USB, CDs). |
-| `/data` | Likely your **mounted volume** from Windows (`C:/ubuntu-data`). |
+| `/data` | Likely your **mounted volume** from Windows (`C:/ubuntu-data`). |
+
+# SSH Terminal Prompt and Linux Commands
+
+## Understanding the Terminal Prompt
+
+When you SSH into a terminal, you typically see a prompt like this:
+
+```
+username@hostname:~$
+```
+
+This prompt provides important information about your current session:
+
+- **username** - The account you're logged in as
+- **hostname** - The name of the machine you're connected to
+- **:** - Separator between hostname and current directory
+- **~** or **/** - Your current working directory location
+- **$** - Indicates a regular user (root users see `#` instead)
+
+### Current Directory Indicators
+
+#### The Tilde Symbol (~)
+
+The tilde `~` represents your **home directory**.
+
+```
+username@hostname:~$
+```
+
+This means you are currently in your home directory, which is typically:
+
+- `/home/username` for regular users
+- `/root` for the root user
+
+#### The Forward Slash (/)
+
+The forward slash `/` represents the **root directory** of the filesystem.
+
+```
+username@hostname:/$
+```
+
+This means you are currently in the root directory, which is the top-level directory of the entire Linux filesystem hierarchy.
+
+## Switching Between Root and Home Directory
+
+### Going to Home Directory
+
+There are multiple ways to navigate to your home directory:
+
+**Method 1: Using cd with tilde**
+
+```bash
+cd ~
+```
+
+**Method 2: Using cd without arguments**
+
+```bash
+cd
+```
+
+All three commands will take you to your home directory.
+
+### Going to Root Directory
+
+To navigate to the root directory of the filesystem:
+
+```bash
+cd /
+```
+
+### Quick Navigation Examples
+
+```bash
+# Currently in home directory
+username@hostname:~$ cd /
+# Now in root directory
+username@hostname:/$ cd ~
+# Back to home directory
+username@hostname:~$
+```
+
+## The ls -ltr Command
+
+The `ls -ltr` command is a combination of the `ls` command with three flags that modify its behavior.
+
+### Breaking Down ls -ltr
+
+- **ls** - List directory contents
+- **-l** - Long format (detailed view)
+- **-t** - Sort by modification time
+- **-r** - Reverse order
+
+### What Each Flag Does
+
+#### -l (Long Format)
+
+Displays detailed information about each file/directory in columns:
+
+```
+-rw-r--r-- 1 user group 1234 Jan 15 10:30 file.txt
+```
+
+The columns show:
+
+1. **Permissions** - `-rw-r--r--`
+2. **Number of links** - `1`
+3. **Owner** - `user`
+4. **Group** - `group`
+5. **Size in bytes** - `1234`
+6. **Modification date/time** - `Jan 15 10:30`
+7. **Filename** - `file.txt`
+
+#### -t (Sort by Time)
+
+Sorts files by modification time, with the newest files first.
+
+#### -r (Reverse Order)
+
+Reverses the sort order. When combined with `-t`, it shows oldest files first.
+
+### Combined Effect of ls -ltr
+
+The `ls -ltr` command shows:
+
+- **Long detailed format** (permissions, owner, size, etc.)
+- **Sorted by modification time**
+- **In reverse order** (oldest files first, newest files last)
+
+### Example Output
+
+```bash
+username@hostname:~$ ls -ltr
+total 32
+drwxr-xr-x 2 user group 4096 Jan 10 09:15 old_folder
+-rw-r--r-- 1 user group 1024 Jan 12 14:20 document.txt
+-rw-r--r-- 1 user group 2048 Jan 15 16:45 script.sh
+drwxr-xr-x 3 user group 4096 Jan 18 11:30 new_folder
+-rw-r--r-- 1 user group  512 Jan 20 13:00 recent_file.log
+```
+
+In this example, files are listed from oldest (Jan 10) to newest (Jan 20).
+
+### When to Use ls -ltr
+
+This command is particularly useful when you want to:
+
+- Find the most recently modified files (they appear at the bottom)
+- Track chronological changes to files
+- Debug issues by identifying when files were last modified
+- Monitor file creation/modification patterns
+
+### Alternative: ls -lt
+
+If you want the newest files at the top instead, use:
+
+```bash
+ls -lt
+```
+
+This omits the `-r` flag, showing newest files first.
+
+## Quick Reference
+
+| Command | Description |
+|---------|-------------|
+| `cd ~` or `cd` | Go to home directory |
+| `cd /` | Go to root directory |
+| `pwd` | Print current working directory |
+| `ls -ltr` | List files in long format, sorted by time (oldest first) |
+| `ls -lt` | List files in long format, sorted by time (newest first) |
+| `ls -la` | List all files including hidden ones in long format |
+
+## Directory Navigation Tips
+
+```bash
+# Go to home directory
+cd ~
+
+# Go to root directory
+cd /
+
+# Go back to previous directory
+cd -
+
+# Go up one directory level
+cd ..
+
+# Go to specific directory
+cd /var/log
+
+# Check where you are
+pwd
+```
+
+---
+
+**Note**: The `$` symbol in the prompt indicates a regular user, while `#` indicates the root user. Always be cautious when operating as root, as you have unrestricted access to the system.