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Commands.Wiki

Networking

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Create a dummy networking interface

This command creates a dummy network interface and assigns it an IP address.

Terminal window
ip link add <interface_name> type dummy &&
sudo ip addr add <cidr> brd + dev <interface_name> label <interface_name>:0
  1. ip link add <interface_name> type dummy: Creates a new dummy network interface named <interface_name>. Replace <interface_name> with the name you want for the interface, one example being vip0.
  2. sudo ip addr add <cidr> brd + dev <interface_name> label <interface_name>:0: Assigns the cidr <cidr> to the interface <interface_name>, the cidr should be in the format of <ip>/<subnetmask>. Please replace the <cidr> with the one that fits your network. The brd + option sets the broadcast address to the default value. The label <interface_name>:0 option assigns a label to the interface.

Figure Out What Is Using A Specific Port

Prints out all applications running on a certain port

Terminal window
sudo lsof -i :<PORT>

  • sudo: This runs the following command with root privileges, which are often required to inspect network activity.

  • lsof -i :<PORT>: lsof is a command meaning ‘list open files’, and the -i option tells it to list files using Internet addresses. :<PORT> should be replaced with the port number you’re interested in. For example, :80 would list all processes using port 80.

Check the certificate of a smtp server

Connects to a smtp server using openssl

Terminal window
openssl s_client -connect <ip/hostname>:587 -starttls smtp

  • openssl s_client: This starts the OpenSSL client.

  • -connect <ip/hostname>:587: This tells the client to connect to the SMTP server at the specified IP address or hostname on port 587. Replace <ip/hostname> with the actual IP address or hostname of the server.

  • -starttls smtp: This tells the client to use the STARTTLS command to upgrade a plaintext connection to an encrypted (TLS or SSL) connection before issuing any SMTP commands.

Generate a standalone certificate

Generates a standalone certificate using certbot.

Terminal window
sudo certbot certonly --standalone -d <dns-name>
  • certbot certonly --standalone: Runs Certbot in standalone mode, which means it will temporarily start a web server for the certificate validation process.
  • -d <dns-name>: Specifies the domain name for which the certificate should be issued. Replace <dns-name> with your domain name.