# Red Hat Certified System Administrator ## **Day 1: Introduction to RHCSA & Installation** ### **What is RHCSA?** **RHCSA** stands for **Red Hat Certified System Administrator**. ### **Why RHCSA is Important** * Industry-recognized Linux certification * Required for **Linux system administration jobs** * Builds strong foundation in: * Linux OS * Users & permissions * Filesystems * Networking * Services & processes * Useful for **DevOps, SysAdmin, Cloud, and Server roles** ### **How We Install Linux for Practice** We do **not** install Linux directly on our main system. Instead, we use **Virtualization**. ### **Virtual Machine (VM)** * We use **VMware** (or VirtualBox) * A VM allows us to run an **OS inside another OS** * Example: * Host OS: Windows * Guest OS: RHEL / CentOS / Rocky Linux ### **Installation Steps (High Level)** 1. Install VMware 2. Create a new Virtual Machine 3. Attach Linux ISO file 4. Allocate: * RAM * CPU * Disk 5. Install Linux OS inside VM ✅ **This method is safe and widely used for learning and testing** --- ## **Day 2: Linux Directory Structure & Basic Commands** ### **Root Directory** `/` Linux has a **single root directory** `/`. Everything starts from here. ### **Important System Directories** | Directory | Purpose | | --- | --- | | `/` | Root of the filesystem | | `/root` | Home directory of **root user** | | `/home` | Home directories of normal users | | `/bin` | Essential user commands (ls, cp, mv) | | `/sbin` | System/admin commands | | `/etc` | Configuration files | | `/var` | Logs, mail, variable data | | `/tmp` | Temporary files | | `/boot` | Bootloader & kernel files | --- ### **Basic Commands Learned** ```plaintext whoami ``` ➡ Shows **current logged-in user** ```plaintext ls ``` ➡ Lists files and directories ```plaintext cd ``` ➡ Changes directory Examples: ```plaintext cd /etc cd .. cd ~ ``` --- ### **Linux Terminal Prompt Explained** Example: ```plaintext hassan@server1:/home/hassan$ ``` | Part | Meaning | | --- | --- | | `hassan` | Username | | `server1` | Hostname | | `/home/hassan` | Current directory | | `$` | Normal user | | `#` | Root user | ✅ **Correction:** * `$` → normal user * `#` → root (admin) user --- ## **Day 3: How Linux OS Boots + File Commands** ### **How Operating System Works (Boot Process)** Correct boot order: 1. **BIOS / UEFI** * Initializes hardware 2. **Bootloader (GRUB2)** * Loads the kernel * Allows selecting different OS 3. **Kernel** * Core of OS * Manages CPU, memory, devices 4. **init / systemd** * Starts services 5. **Login Screen** * OS is ready to use ✅ **Correction:** * BIOS **does not load the OS directly** * BIOS/UEFI loads the **bootloader** * Bootloader loads the **kernel** * Kernel starts the OS ### **Multiple OS Concept** * If multiple OS are installed * GRUB menu allows choosing which OS to boot # 🧠 One-Line Memory Trick * **Linux:** `UEFI → GRUB → Kernel → systemd → Services → Ready` * **Windows:** `UEFI → Boot Manager → Kernel → Services → Login → Ready` --- ### **File Commands** ```plaintext cp source destination ``` ➡ Copy files or directories Examples: ```plaintext cp file1 file2 cp -r dir1 dir2 ``` ```plaintext mv source destination ``` ➡ Move or rename files Examples: ```plaintext mv file1 /tmp mv oldname newname ``` --- ### **Change Hostname** Temporary: ```plaintext hostname newname ``` Permanent (Recommended): ```plaintext hostnamectl set-hostname newname ``` --- ## **Day 4: BIOS vs UEFI, Editors & Practice Tasks** ### **BIOS vs UEFI** | BIOS | UEFI | | --- | --- | | Old technology | Modern | | Slow boot | Fast boot | | MBR partition | GPT partition | | Limited disk size | Supports large disks | | Text-based | GUI support | ✅ **UEFI is used in modern systems** --- ### **Text Editors** Linux has command-line editors. #### **Nano (Easy)** ```plaintext nano file.txt ``` * Easy to use * Shortcuts shown at bottom * Save: `CTRL + O` * Exit: `CTRL + X` #### **Vim (Advanced)** ```plaintext vim file.txt ``` Modes: * **Normal mode** (default) * **Insert mode** → `i` * **Command mode** → `:` Common commands: ```plaintext i # insert mode :w # save :q # quit :wq # save and quit :q! # quit without saving ``` --- ### **Practice Tasks** * Create files * Edit files using nano & vim * Copy and move files * Rename files * Change hostname * Navigate directories --- ## ✅ Summary You learned: * RHCSA basics and importance * Linux installation using VMware * Linux directory structure * Basic Linux commands * Boot process (BIOS → GRUB → Kernel → OS) * BIOS vs UEFI * File operations * Nano & Vim editors # **RHCSA – Class Notes (Day 5 & 6)** --- ## **Day 5: File and Directory Management** ### **Copying Directories** ```plaintext cp -r source_directory destination_directory ``` * `-r` → recursive (copy directory and all its contents) * Example: ```plaintext cp -r /home/hassan/docs /home/hassan/backup_docs ``` --- ### **Deleting Files** ```plaintext rm filename ``` * Removes a file ```plaintext rm -i filename ``` * Asks **confirmation** before deletion --- ### **Deleting Directories** ```plaintext rmdir directory_name ``` * Removes **empty directories only** ```plaintext rm -r directory_name ``` * Removes **directory and all contents recursively** ```plaintext rm -rf directory_name ``` * Removes **directory and contents without warning** * ⚠️ **Use carefully**! Can delete important data --- ### **Wildcard** `*` * `*` is used to represent **all files or directories** * Example: ```plaintext rm *.txt ``` * Deletes all `.txt` files in current directory --- ### **Command Structure** ```plaintext command [options] [arguments] ``` * **Command** → what to do (`ls`, `cp`, `rm`) * **Options** → modify behavior (`-l`, `-r`, `-f`) * **Arguments** → files or directories to operate on **Example:** ```plaintext ls -l /home/hassan ``` --- ### **Hidden Files** * Files starting with `.` are hidden * Create a hidden file: ```plaintext touch .hiddenfile ``` --- ### **Clear Terminal** ```plaintext clear ``` * Clears the screen --- ### **Creating Directories** ```plaintext mkdir folder_name ``` #### **Nested Directories** ```plaintext mkdir -p parent_folder/child_folder ``` * `-p` → create parent directories if they don’t exist #### **Creating Multiple Folders** ```plaintext mkdir folder{1..10} ``` * Creates `folder1`, `folder2`, … `folder10` #### **Creating Multiple Files** ```plaintext touch file{1..10}.txt ``` * Creates `file1.txt` → `file10.txt` --- ### **Viewing Directory Tree** ```plaintext tree directory_name ``` --- ## **Day 6: Reading File Content & Searching** ### **View File Content** #### **cat** ```plaintext cat /etc/services ``` * Displays **entire file content** #### **more** ```plaintext more /etc/fstab ``` * Shows file **page by page** (use space to scroll) #### **less** * Better alternative to `more` * Scroll forward/backward ```plaintext less /etc/fstab ``` #### **head** ```plaintext head -n 10 /etc/services ``` * Shows first **10 lines** of file #### **tail** ```plaintext tail -n 10 /etc/services ``` * Shows last **10 lines** of file #### **nl** ```plaintext nl /etc/services ``` * Shows file content with **line numbers** --- ### **Search Inside Files –** `grep` ```plaintext grep "pattern" filename ``` * Search for **specific text** in a file * Example: ```plaintext grep "ftp" /etc/services ``` #### **With options** * `-i` → ignore case * `-c` → show **count** of matching lines * `-v` → show **non-matching lines** * `-n` → show **line numbers** Example: ```plaintext grep -i "ftp" /etc/services grep -c "ssh" /etc/services ``` --- ### **Word Count –** `wc` ```plaintext wc filename ``` * Shows lines, words, characters Options: * `-l` → number of lines * `-w` → number of words * `-c` → number of bytes * `-m` → number of characters Example: ```plaintext wc -l /etc/services wc -w /etc/services ``` --- ### **Redirection & Operators** * **Redirect output to a file** ```plaintext ls > file.txt ``` * Overwrites `file.txt` with output of `ls` * **Append output to a file** ```plaintext ls >> file.txt ``` * Adds output to the **end** of `file.txt` * **Pipes** (send output of one command to another) ```plaintext cat /etc/services | grep ftp ``` ✅ **Correction:** * `>` → overwrite * `>>` → append * `|` → pipe (send output to another command) --- ### **Summary – Day 5 & 6** You learned: * Copying, moving, deleting files and directories * Wildcards `*` for multiple files * Command structure (command → options → arguments) * Hidden files and creating them * Creating folders/files in bulk * Reading files (`cat`, `more`, `less`, `head`, `tail`, `nl`) * Searching in files (`grep` with options) * Word count (`wc`) * Redirection (`>`, `>>`) and pipes (`|`) ## **Day 7: Operators in Linux** Linux allows combining commands and controlling execution flow using **operators**. --- ### **1️⃣ Semicolon** `;` * **Purpose:** Run multiple commands **sequentially**, **regardless of whether previous commands succeed or fail** * **Syntax:** ```plaintext command1; command2; command3 ``` * **Example:** ```plaintext echo "Hello"; ls; pwd ``` * Output: 1. Prints “Hello” 2. Lists files 3. Shows current directory ✅ **Note:** Commands run **one by one** even if one fails. --- ### **2️⃣ Single Pipe** `|` * **Purpose:** Sends output of first command as input to second command * **Syntax:** ```plaintext command1 | command2 ``` * **Example:** ```plaintext cat /etc/services | grep ftp ``` * `cat` prints file → `grep` filters only lines containing “ftp” --- ### **3️⃣ Double AND** `&&` * **Purpose:** Run **second command only if the first command succeeds** * **Syntax:** ```plaintext command1 && command2 ``` * **Example:** ```plaintext mkdir test && cd test ``` * Only enters `test` folder if folder creation **succeeds** --- ### **4️⃣ Single AND** `&` * **Purpose:** Run command in **background** * **Syntax:** ```plaintext command & ``` * **Example:** ```plaintext gedit file.txt & ``` * Opens `gedit` in background, so terminal is **free to use** --- ### **5️⃣ Double Pipe** `||` * **Purpose:** Run **second command only if the first command fails** * **Syntax:** ```plaintext command1 || command2 ``` * **Example:** ```plaintext cd nonexistfolder || echo "Folder does not exist" ``` * If `cd` fails, prints warning --- ### **Summary of Operators** | Operator | Purpose | | --- | --- | | `;` | Run commands sequentially, ignore errors | | `&&` | Run next command only if previous succeeds | | \` | | | `&` | Run command in background | | \` | \` | --- ## **User and Group Management** Linux manages **users and groups** for **access control** and **permissions**. --- ### **Types of Users** | User Type | Description | UID | | --- | --- | --- | | **Root user** | Super admin, full privileges | `0` | | **System user** | Used by OS services, limited login | `1–999` | | **Regular user** | Normal human user, limited privileges | `1000+` | --- ### **Types of Groups** | Group Type | Description | | --- | --- | | **Root group** | Associated with root user, admin group | | **System group** | For OS processes and services | | **Regular group** | For normal users, sharing resources | --- ### **Commands (Basics)** * **View current user** ```plaintext whoami ``` * **View groups of a user** ```plaintext groups username ``` * **View all users** ```plaintext cat /etc/passwd ``` * **View all groups** ```plaintext cat /etc/group ``` --- ✅ **Corrections / Clarifications** 1. UID ranges for system vs regular users: * System: 1–999 * Regular: 1000+ 2. Background operator: single `&` runs **command in background**, not a chain. 3. Pipes and logical operators (`&&`, `||`) are different: * `|` → sends **output to input** * `&&` / `||` → controls **execution flow** --- ### **Examples** ```plaintext # Sequential execution echo "Start"; ls; echo "End" # Logical AND mkdir demo && cd demo # Logical OR cd nofolder || echo "Folder not found" # Background process gedit file.txt & # Pipe cat /etc/services | grep ftp ``` --- This covers **Day 7 operators + intro to user & group management**. # **RHCSA Day 8 – User and Group Management** User and group management is a **core topic in RHCSA** and very important for real-world Linux administration. On Day 8, we focused on creating users, managing passwords, understanding user IDs (UIDs), group IDs (GIDs), and how Linux stores user and group information internally. --- ## 1\. Adding a New User To create a new user in Linux, we use the `useradd` command. ```bash useradd username ``` Example: ```bash useradd ali ``` This command: * Creates the user * Assigns a UID automatically * Creates a home directory `/home/ali` * Assigns a default shell > ⚠️ By default, the user does **not** have a password yet. --- ## 2\. Setting or Changing User Password To set or change a password, use: ```bash passwd username ``` Example: ```bash passwd ali ``` You will be prompted to enter and confirm the password. --- ## 3\. Checking User ID and Group Information ### Check UID and GID ```bash id username ``` Example: ```bash id ali ``` Output shows: * UID (User ID) * GID (Primary Group ID) * Secondary groups ### Check Current Logged-in User ```bash whoami ``` --- ## 4\. Types of Users in Linux Linux has **three main types of users**: | User Type | Description | UID Range | | --- | --- | --- | | Root User | Superuser with full access | 0 | | System User | Used by services and processes | 1–999 | | Regular User | Normal human users | 1000+ | --- ## 5\. Modifying a User (User Management) The `usermod` command is used to modify user properties. ### Example: Set Account Expiry Date ```bash usermod -e 2026-12-31 ali ``` ### Lock a User Account ```bash usermod -L ali ``` ### Unlock a User Account ```bash usermod -U ali ``` --- ## 6\. Password Aging and Expiry We can control password policies using `chage`. ```bash chage username ``` Example: ```bash chage ali ``` To view password aging info: ```bash chage -l ali ``` You can: * Set password expiry * Force password change * Set warning days --- ## 7\. Users vs Groups ### What is a User? * An individual account * Has its own UID * Can log in ### What is a Group? * Collection of users * Used to manage permissions easily * Identified by GID > Groups make permission management easier instead of assigning permissions user by user. --- ## 8\. Adding Groups ```bash groupadd groupname ``` Example: ```bash groupadd developers ``` --- ## 9\. Primary and Secondary Groups ### Primary Group * Each user has **one primary group** * Assigned at user creation * Used by default when creating files ### Secondary Groups * Additional groups a user belongs to * Used for extra permissions ### Add User to a Secondary Group ```bash usermod -aG groupname username ``` Example: ```bash usermod -aG developers ali ``` > ⚠️ `-a` is very important. Without it, existing groups will be removed. --- ## 10\. Checking User and Group Files Linux stores user and group information in `/etc` directory. ### `/etc/passwd` ```bash cat /etc/passwd ``` Contains: * Username * UID * GID * Home directory * Shell > Passwords are **not stored here**. --- ### `/etc/shadow` ```bash cat /etc/shadow ``` Contains: * Encrypted passwords * Password expiry info > Only readable by **root user**. --- ### `/etc/group` ```bash cat /etc/group ``` Contains: * Group name * GID * Group members --- ## 11\. Summary (Day 8) On Day 8, we learned: * How to add users and set passwords * How to check UID, GID, and group membership * Difference between users and groups * Primary vs secondary groups * How to add users to groups * User modification and password expiry * Internal Linux files: `/etc/passwd`, `/etc/shadow`, `/etc/group` This topic is **very important for RHCSA exam and real Linux administration**.