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Monitor & Management of Linux Processes using Top Command

February 10, 2024
Monitor & Management of Linux Processes using Top Command

In Linux environments, managing system processes efficiently is crucial for optimal performance and resource utilization. The top command serves as a powerful tool for real-time process monitoring, providing insights into CPU, memory, and overall system performance.

Introduction to Top Command

The top command is a versatile utility that offers a dynamic, real-time overview of system processes. When executed, it presents a continuously updated list of processes, sorted by various criteria such as CPU usage, memory consumption, and more.

Understanding the Display

Upon running the top command, the display is divided into several sections:
- Header: Provides summary information about system uptime, total number of processes, CPU usage, memory usage, and more.
- Process List: Displays a list of running processes, sorted by default based on CPU usage.
- Command Bar: Offers interactive commands for managing processes, such as sorting, filtering, and killing.
Changing Display Modes

The top command allows users to customize the display according to specific monitoring requirements. Here are some common display modes:

Memory Usage Mode

To view processes sorted by memory usage:
```
top -o RES
    
```
This command sorts the process list based on the amount of memory (RES) each process is utilizing.

CPU Usage Mode

To display processes sorted by CPU usage:
```
top -o CPU
    
```
Using this command, processes are sorted based on their CPU consumption, with the most CPU-intensive processes listed at the top.

Filtering Processes by User ID

To filter processes by a specific user ID:
```
top -u username
    
```
Replace username with the desired user’s username. This command displays only the processes associated with the specified user.

Killing Processes

To terminate a process using the top command:
1. Run top.
2. Identify the PID (Process ID) of the process you want to terminate.
3. Press k to enter PID mode.
4. Enter the PID of the process.
5. Press Enter.
6. Confirm the action by pressing y.
This process termination method provides a safe and controlled way to stop misbehaving or unnecessary processes.

Keyboard Shortcuts

While running the top command, users can utilize various keyboard shortcuts for enhanced functionality:
- m: Toggle memory usage mode.
- p: Toggle CPU usage mode.
- k: Kill a process by entering its PID.
- Shift + M: Sort processes by memory usage.
- Shift + P: Sort processes by CPU usage.
- Shift + U: Filter processes by user ID.
- Shift + T: Sort processes by cumulative CPU time.
- Shift + R: Reverse the sort order of processes.
- Shift + H: Toggle thread display.
Examples

Let’s delve into practical examples of utilizing the top command:

Example 1: View Memory Usage
```
top -o RES
    
```
This command sorts processes based on their memory utilization, allowing administrators to identify memory-intensive processes.

Example 2: View CPU Usage
```
top -o CPU
    
```
With this command, users can monitor CPU-intensive processes, helping in troubleshooting performance issues related to CPU utilization.

Example 3: Filter Processes by User ID
```
top -u myusername
    
```
By specifying a username, this command filters and displays processes associated with the specified user only.

Example 4: Kill a Process

To terminate a process with PID 1234:
```
top
k
1234
    
```
By entering the PID and confirming the action, the selected process is safely terminated, freeing up system resources.

Watch Video Tutorial

Conclusion

The top command is an invaluable tool for Linux system administrators, offering real-time insights into system processes and resource utilization. By leveraging its various display modes, keyboard shortcuts, and functionalities, administrators can effectively manage and optimize system performance.
Authenticating with Password in Apache and Nginx on Raspberry Pi OS

February 9, 2024
Authenticating with Password in Apache and Nginx on Raspberry Pi OS

In this guide, we’ll learn how to set up password authentication in both Apache and Nginx on Raspberry Pi OS (Debian).

Prerequisites

Before you begin, make sure you have:
- A Raspberry Pi running Raspberry Pi OS (Debian).
- Apache and Nginx installed and configured.
Setting Up Password Authentication in Apache

Step 1: Create a Password File

First, create a password file using the htpasswd utility. Replace username1 and username2 with the desired usernames:
```
htpasswd -c /etc/apache2/.htpasswd username1
htpasswd /etc/apache2/.htpasswd username2
    
```
Step 2: Configure Apache

Edit the Apache configuration file:
```
sudo nano /etc/apache2/sites-available/000-default.conf
    
```
Add the following lines inside the <VirtualHost> section:
```
        <Directory "/var/www/html">
            Options Indexes FollowSymLinks
            AllowOverride All
            Require all granted
            AuthType Basic
            AuthName "Restricted Content"
            AuthUserFile /etc/apache2/.htpasswd
            Require valid-user
        </Directory>
    
```
Step 3: Restart Apache

Restart the Apache service to apply the changes:
```
sudo systemctl restart apache2
    
```
Step 4: Access Restricted Content

Now, when you access your website, you’ll be prompted to enter the username and password you created in Step 1.

Setting Up Password Authentication in Nginx

Step 1: Create a Password File

Similar to Apache, create a password file using the htpasswd utility:
```
sudo htpasswd -c /etc/nginx/.htpasswd username1
sudo htpasswd /etc/nginx/.htpasswd username2
    
```
Step 2: Configure Nginx

Edit the Nginx configuration file:
```
sudo nano /etc/nginx/sites-available/default
    
```
Add the following lines inside the server block:
```
        location / {
            auth_basic "Restricted Content";
            auth_basic_user_file /etc/nginx/.htpasswd;
        }
    
```
Step 3: Restart Nginx

Restart the Nginx service to apply the changes:
```
sudo systemctl restart nginx
    
```
Step 4: Access Restricted Content

Now, accessing your website in Nginx will prompt you to enter the username and password you created in Step 1.

Conclusion

Congratulations! You’ve successfully set up password authentication in both Apache and Nginx on Raspberry Pi OS. This adds an extra layer of security to your web servers.
How to Install OpenVPN Server on Windows 10 Pro 22H2

November 22, 2023
How to Install OpenVPN Server on Windows 10 Pro 22H2 (Build 19045.3448)

1. Set up OpenVPN

Set up an OpenVPN connection following this guide

2. Generate a TA key

Generate a TA key and place it in the same folder as the other certificates/keys: openvpn --genkey --secret ta.key

3. Update server.ovpn profile

Append the following lines to your server.ovpn profile:
```
# Route all traffic through VPN
push "redirect-gateway def1"
# Push Google DNS to prevent leak
push "dhcp-option DNS 8.8.8.8"
    
```
4. Update client.ovpn profile

Append the following lines to your client.ovpn profile:
```
# Block DNS leak
block-outside-dns
    
```
Here is my completed configuration file
```
local 1.2.3.4
port 9194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
auth SHA512
tls-crypt tc.key
topology subnet
server 10.8.0.0 255.255.255.0
push "redirect-gateway def1 bypass-dhcp"
ifconfig-pool-persist ipp.txt
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
push "block-outside-dns"
keepalive 10 120
cipher AES-256-CBC
user nobody
group nogroup
persist-key
persist-tun
plugin /usr/lib/x86_64-linux-gnu/openvpn/plugins/openvpn-plugin-auth-pam.so login
client-cert-not-required
username-as-common-name
verb 3
crl-verify crl.pem
explicit-exit-notify
duplicate-cn
```
5. Service Tweaks
1. Open the Services window
2. Find Routing and Remote Access and set it to: Startup type – Automatic
3. Start the service
6. Adapter Tweaks
1. Open the network adapters window
2. Right-click your internet adapter (e.g. Ethernet) and then: Properties -> Sharing -> Allow other network users to connect through this computer’s Internet connection
3. (if applicable) From the drop-down list select your OpenVPN TAP adapter (e.g. Ethernet 2)
4. Note: Only one adapter can be shared at a time, so if you don’t see the Sharing tab, make sure no other adapter is being shared.
7. Registry Tweaks

Key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Value: IPEnableRouter

Type: REG_DWORD

Data: 0x00000001 (1)

8. Configure a Static Route (if behind a router)

You have to route all packets sent to the client’s virtual IP back to the VPN server.

Example using Cisco router:
- 10.8.0.0 – virtual network subnet
- 255.255.255.0 – virtual network subnet mask
- 192.168.1.175 – VPN server internal IP (in the subnet of the router)
9. Issues with ICS (Internet Connection Sharing)

There are a few issues you might encounter when using OpenVPN together with ICS:
- ICS by default automatically assigns a static IP (192.168.137.1) on your LAN adapter, conflicting with OpenVPN IP. To address this, change OpenVPN config to have a consistent IP range or change HKLM\System\CurrentControlSet\services\SharedAccess\Parameters\ScopeAddress to 10.8.0.1.
- On some later Windows versions, ICS might stop working after a reboot. The way to address this is mentioned in this Microsoft support article.
10. Final OpenVPN Tweaks
1. Right-click openvpn-gui.exe and then: Properties -> Compatibility -> Run this program as an administrator
2. (optional) Configure the OpenVPN server to start and connect automatically:
```
"C:\Program Files\OpenVPN\bin\openvpn-gui.exe" --connect server.ovpn
```

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Monitor & Management of Linux Processes using Top Command

Monitor & Management of Linux Processes using Top Command

Introduction to Top Command

Understanding the Display

Changing Display Modes

Memory Usage Mode

CPU Usage Mode

Filtering Processes by User ID

Killing Processes

Keyboard Shortcuts

Examples

Example 1: View Memory Usage

Example 2: View CPU Usage

Example 3: Filter Processes by User ID

Example 4: Kill a Process

Watch Video Tutorial

Conclusion

Authenticating with Password in Apache and Nginx on Raspberry Pi OS

Authenticating with Password in Apache and Nginx on Raspberry Pi OS

Prerequisites

Setting Up Password Authentication in Apache

Step 1: Create a Password File

Step 2: Configure Apache

Step 3: Restart Apache

Step 4: Access Restricted Content

Setting Up Password Authentication in Nginx

Step 1: Create a Password File

Step 2: Configure Nginx

Step 3: Restart Nginx

Step 4: Access Restricted Content

Conclusion

How to Install OpenVPN Server on Windows 10 Pro 22H2

How to Install OpenVPN Server on Windows 10 Pro 22H2 (Build 19045.3448)

1. Set up OpenVPN

2. Generate a TA key

3. Update server.ovpn profile

4. Update client.ovpn profile

5. Service Tweaks

6. Adapter Tweaks

7. Registry Tweaks

8. Configure a Static Route (if behind a router)

9. Issues with ICS (Internet Connection Sharing)

10. Final OpenVPN Tweaks