Update Linux Notes: Expanded System Information and User Management Sections

- **System Information**:
  - Added detailed commands for hardware and software information, including `lscpu`, `lshw`, `hwinfo`, and more.
  - Included commands for finding binary paths, counting words and lines in files.

- **User Management**:
  - Introduced new sections for managing user information, super user management, and switching users.
  - Added commands for listing users, disabling root login via SSH, managing sudo permissions, and switching users with sudo or root privileges.

This update provides a more comprehensive overview of system and user management tasks.

notes/linux.md

@@ -4,20 +4,156 @@
 
 - [Linux](#linux)
   - [Table of Contents](#table-of-contents)
-  - [Basic Commands](#basic-commands)
+  - [System Information](#system-information)
+    - [Hardware Information](#hardware-information)
+    - [Software Information](#software-information)
+  - [User Management](#user-management)
+    - [User Information](#user-information)
+    - [Super User Management](#super-user-management)
+    - [Switch User](#switch-user)
   - [USB Devices](#usb-devices)
     - [Test USB Key](#test-usb-key)
 
-## System information
+## System Information
 
-## Basic Commands
+### Hardware Information
+
+To gather detailed information about your hardware, use the following commands:
+
+- **`lscpu`**: Displays information about the CPU architecture, including details about cores, threads, and CPU family.
+- **`lshw`**: Provides a comprehensive listing of hardware components. Use `lshw -short` for a more concise view.
+- **`hwinfo`**: Offers detailed information about hardware components and can be more verbose than `lshw`.
+- **`lsscsi`**: Lists SCSI devices, including disks and other SCSI-attached hardware.
+- **`lsusb`**: Shows information about USB devices connected to your system.
+- **`lsblk`**: Lists block devices such as hard drives and their partitions.
+- **`df -H`**: Displays disk space usage in a human-readable format.
+- **`fdisk -l`**: Lists all partitions on the system.
+- **`dmidecode`**: Retrieves hardware information from the BIOS. Use:
+  - `dmidecode -t processor` for CPU details
+  - `dmidecode -t memory` for RAM details
+  - `dmidecode -t bios` for BIOS information
+
+### Software Information
+
+**Finding Path to Binary**
+
+To find the location of an executable binary, use:
+
+```bash
+type composer
+```
+
+This command will show the path to the `composer` executable if it's available in your `PATH`.
+
+**Number of Words in a File**
+
+To count the number of words in a file, use:
+
+```bash
+wc filepath
+```
+
+This command will show the number of words along with other details like lines and characters.
+
+**Number of Lines in a File**
+
+To count the number of lines in a file, use:
+
+```bash
+wc -l filepath
+```
+
+This command will display the number of lines in the specified file.
+
+## User Management
+
+### User Information
+
+**List Users**
+
+To list all users from the `/etc/passwd` file, use:
+
+```bash
+awk -F':' '{ print $1}' /etc/passwd | sort
+```
+
+This command extracts the usernames from the `/etc/passwd` file and sorts them in alphabetical order.
+
+### Super User Management
+
+**Disable Root Login**
+
+To disable root login via SSH, perform the following steps:
+
+1. **Edit the SSH Configuration File:**
+
+   ```bash
+   nano /etc/ssh/sshd_config
+   ```
+
+   Comment out the line containing `PermitRootLogin` by adding a `#` at the beginning of the line.
+
+2. **Change Shell for Root User:**
+
+   ```bash
+   nano /etc/passwd
+   ```
+
+   Find the line starting with `root` and change `/bin/bash` to `/sbin/nologin` to disable login for the root user.
+
+   Save and close the file. Restart the SSH service for changes to take effect:
+
+   ```bash
+   systemctl restart ssh
+   ```
+
+**Sudo Management**
+
+**Add User to Sudo Group**
+
+```bash
+adduser fabrice sudo
+```
+
+**Update Sudoers File to Remove Password Requirement**
+
+Edit the sudoers file:
+
+```bash
+visudo
+```
+
+Add the following line to allow the user to execute commands without a password:
+
+```bash
+fabrice     ALL=(ALL) NOPASSWD:ALL
+```
+
+### Switch User
+
+**Switch to Another User as Sudoer**
+
+```bash
+sudo -i -u postgres
+```
+
+This command switches to the `postgres` user with sudo privileges.
+
+**Switch to Another User as Root**
+
+```bash
+su - postgres
+```
+
+This command switches to the `postgres` user with root privileges.
 
 ## USB Devices
 
 ### Test USB Key
 
 **Device Information**
-Check if the system recognizes the device and show the latest system messages related to USB devices being connected.
+
+Check if the system recognizes the device and show the latest system messages related to USB devices being connected:
 
 ```bash
 lsusb
@@ -25,7 +161,8 @@ dmesg | tail -n 20
 ```
 
 **Find Mount Points and Device Information**
-Identify mount points, partitions, and other relevant details of mounted devices.
+
+Identify mount points, partitions, and other relevant details of mounted devices:
 
 ```bash
 lsblk -f
@@ -35,73 +172,90 @@ mount | grep /dev/sd
 ```
 
 **Print Detailed Information About the USB Key**
-View detailed partition and disk information.
+
+View detailed partition and disk information:
 
 ```bash
 fdisk -l /dev/sdc
 ```
 
 **Test the File System**
-Check and repair the filesystem on the USB key.
+
+Check and repair the filesystem on the USB key:
 
 ```bash
 fsck /dev/sdc1
 ```
 
 **Test Data Integrity**
-Perform read/write tests to ensure the integrity of the USB key.
+
+Perform read/write tests to ensure the integrity of the USB key:
 
 1. **Unmount the USB Key** (if mounted):
+
    ```bash
    umount /media/fabrice/BD48-F8BB
    ```
+
 2. **Write Test**:
+
    ```bash
    dd if=/dev/zero of=/dev/sdc bs=4M count=256 status=progress
    ```
+
 3. **Read Test**:
+
    ```bash
    dd if=/dev/sdc of=/dev/null bs=4M count=256 status=progress
    ```
 
 **Check for Bad Blocks**
-Identify any bad sectors on the USB key.
+
+Identify any bad sectors on the USB key:
 
 - **Read-only test**:
+
   ```bash
   badblocks -v /dev/sdc
   ```
+
 - **Non-destructive read-write test**:
 
   ```bash
   badblocks -nsv /dev/sdc
   ```
 
-- The -n option performs a non-destructive read-write test.
+  - The `-n` option performs a non-destructive read-write test.
-- The -s option shows progress.
+  - The `-s` option shows progress.
-- The -v option is for verbose output.
+  - The `-v` option is for verbose output.
 
 **Perform a SMART Test**
-Run SMART diagnostics to test the health of the USB key.
+
+Run SMART diagnostics to test the health of the USB key:
 
 1. **Start a short SMART test**:
+
    ```bash
    smartctl -t short /dev/sdc
    ```
+
 2. **View test results**:
+
    ```bash
    smartctl -a /dev/sdc
    ```
 
 **Benchmark the Speed**
-Measure the read speed of the USB key.
+
+Measure the read speed of the USB key:
 
 ```bash
 hdparm -t /dev/sdc
 ```
 
 **Unmount and Safely Remove**
-Unmount the USB key and safely remove it from the system.
+
+Unmount the USB key and safely remove it from the system:
 
 ```bash
 umount /mnt/usb