Requirements:

Go language must be installed in your kali machine

If it’s not installed, then install it by following the commands

apt-get install golang-go

Now let’s install subfinder

Step 1:  run this command in your terminal

go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest

or you can install it by using this simple command

apt get install subfinder

Step 2: Now check if subfinder is installed or not using this command

subfinder

Subfinder is successfully installed in your machine

Step 3: Now there are various flags that are available in subfinder. So, you will have to enter subfinder -h command to see other flags

Step 4: Now choose one target URL on that you want to find subdomains

For example, I’m choosing Starbucks as a target

After choosing the target enter this command to find subdomains of Starbucks

subfinder -d starbucks.com

As you can see subfinder found 4113 subdomains of Starbucks

We can save this subdomains in text file using the -o flag

subfinder -d starbucks.com -o starbucks.txt