added apt doc

Linux/LPIC1/1-runlevels.md

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+# 🐧 Linux Runlevels Guide
+
+This guide provides a concise overview of traditional **runlevels** in Linux systems, particularly for **Red Hat** and **Debian**-based distributions. Runlevels define specific states of system operation, historically managed by the `init` system.
+
+---
+
+## 🔄 System Boot Sequence
+
+```plaintext
+BIOS → Bootloader → Kernel → init
+```
+
+* **BIOS**: Performs hardware checks via **POST** (Power-On Self Test).
+* **Bootloader**: Loads the kernel.
+* **Kernel**: Initializes system and mounts the root filesystem.
+* **init**: Launches system processes based on the selected runlevel.
+
+---
+
+## 📊 Runlevels Comparison
+
+| Runlevel | Description                         | Red Hat          | Debian          |
+| -------- | ----------------------------------- | ---------------- | --------------- |
+| 0        | Halt / Shutdown                     | ✅ Supported      | ✅ Supported     |
+| 1        | Single-User Mode                    | ✅ Supported      | ✅ Supported     |
+| 2        | Multi-User (No Network)             | ❌ (Includes Net) | ✅ Supported     |
+| 3        | Multi-User (Network, No GUI)        | ✅ Supported      | ✅ Supported     |
+| 4        | User-Defined / Custom               | ✅ Supported      | ✅ Supported     |
+| 5        | GUI Mode / *(Halt on some systems)* | ✅ GUI Mode       | ⚠️ Custom/Halt? |
+| 6        | Reboot                              | ✅ Supported      | ✅ Supported     |
+
+> 💡 **Notes**:
+> • **Runlevel 5** on Red Hat typically launches a full graphical environment (GUI).
+> • On Debian, runlevels 2–5 are often configured identically and can be customized.
+> • Runlevel behavior is configurable via `/etc/inittab` (SysVinit systems).
+
+---
+
+## 🔧 Useful Commands
+
+### ✅ Check Current Runlevel
+
+```bash
+runlevel
+```
+
+### 🔁 Change Runlevel
+
+```bash
+telinit <runlevel>
+```
+
+or
+
+```bash
+init <runlevel>
+```
+
+> ⚠️ **Caution**: Switching runlevels may stop services or terminate user sessions. Use carefully on production systems.
+
+---
+
+## 🚀 Modern Systems: systemd Targets
+
+Most modern Linux distributions use **systemd**, which replaces runlevels with **targets**.
+
+| Runlevel | systemd Target      |
+| -------- | ------------------- |
+| 0        | `poweroff.target`   |
+| 1        | `rescue.target`     |
+| 3        | `multi-user.target` |
+| 5        | `graphical.target`  |
+| 6        | `reboot.target`     |
+
+### 📌 Common systemd Commands
+
+```bash
+# Show default target
+systemctl get-default
+
+# Change to graphical mode
+systemctl isolate graphical.target
+```
+

Linux/LPIC1/3-package-managers.md

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+# 📦 Linux Libraries & Package Management
+
+This guide provides a quick overview of **library types**, **package sources**, and **Debian-based package management** commands using `apt`.
+
+---
+
+## 📚 Library Types
+
+Linux supports two main types of libraries:
+
+1. **Static Libraries (`.a`)**  
+   - Linked at **compile-time**  
+   - Included in the final binary  
+   - Larger file size, faster execution
+
+2. **Shared Libraries (`.so`)**  
+   - Linked at **run-time**  
+   - Saved separately from the binary  
+   - Saves space and allows updates without recompiling
+
+---
+
+## 📦 Package Sources
+
+### ✅ Official Packages  
+Provided and maintained by the distribution (e.g., Debian, Ubuntu, Red Hat).
+
+### 🌐 Third-Party Packages  
+Created by external developers or organizations. Use with caution and verify trustworthiness.
+
+---
+
+## 🏬 Linux Package Managers
+
+### 📦 Debian-based Systems
+- **Package Manager**: `apt`
+- **Low-level Tool**: `dpkg`
+- **Package Format**: `.deb`
+
+### 📦 Red Hat-based Systems
+- **Package Manager**: `yum` or `dnf` (newer)
+- **Low-level Tool**: `rpm`
+- **Package Format**: `.rpm`
+
+---
+
+## 🌍 Package Mirrors
+
+Mirrors are alternative download sources for package repositories, often closer geographically for faster updates.
+
+To sync with package mirrors and get the latest updates:
+
+```bash
+sudo apt update
+```
+
+---
+
+## 🔧 Common `apt` Commands
+
+| Command                  | Description                           |
+|--------------------------|---------------------------------------|
+| `apt update`             | Refresh package lists                 |
+| `apt upgrade`            | Upgrade all installed packages        |
+| `apt list`               | List packages                         |
+| `apt show <package>`     | Show details of a package             |
+| `apt install <package>`  | Install a new package                 |
+| `apt reinstall <package>`| Reinstall an existing package         |
+| `apt remove <package>`   | Remove a package (keep config files)  |
+| `apt purge <package>`    | Remove package **and** config files   |
+| `apt-cache search <term>`| Search for a package                  |
+| `apt autoremove`         | Remove unused dependencies            |
+
+> 🔐 Use `sudo` before these commands when required.
+

Linux/LPIC1/runlevels.md

@@ -1,59 +0,0 @@
-# Linux Runlevels Guide
-
-This document outlines the standard runlevels for **Red Hat** and **Debian**-based systems. Runlevels are used by `init` systems to define different states or modes of operation for the system.
-
----
-
-## 📊 Runlevels Overview
-
-| Runlevel | Description                          | Red Hat      | Debian          |
-| -------- | ------------------------------------ | ------------ | --------------- |
-| 0        | Halt                                 | ✅ Supported  | ✅ Supported     |
-| 1        | Single User Mode                     | ✅ Supported  | ✅ Supported     |
-| 2        | Multi-user (No Network)              | ❌ (HaveNet)  | ✅ Supported     |
-| 3        | Multi-user (Network, No GUI)         | ✅ Supported  | ✅ Supported     |
-| 4        | Custom/User Defined                  | ✅ Supported  | ✅ Supported     |
-| 5        | Multi-user (GUI Mode) / Halt *(err)* | ❌ (GUI Mode) | ❌ (Halt/Error?) |
-| 6        | Reboot                               | ✅ Supported  | ✅ Supported     |
-
-> 💡 **Note**:
->
-> * On **Red Hat**, runlevel 5 typically starts the system with a graphical user interface (GUI).
-> * On **Debian**, runlevel 5 is often unused or reserved for custom setups.
-> * Runlevel behavior can be customized depending on system configuration.
-
----
-
-## 🔧 Commands
-
-### Check Current Runlevel
-
-```bash
-runlevel
-```
-
-### Change Runlevel
-
-```bash
-telinit <runlevel>
-```
-
-or
-
-```bash
-init <runlevel>
-```
-
-> ⚠️ Changing runlevels may stop or restart services. Use with caution, especially on production systems.
-
----
-
-## 📚 Additional Tips
-
-* Modern Linux systems (especially systemd-based) may not rely on traditional runlevels. Instead, they use *targets*. Example:
-
-  ```bash
-  systemctl get-default
-  systemctl isolate graphical.target
-  ```
-