How to Generate Random Passwords in Bash using `/dev/urandom`

Generating random data is a common task in many applications, especially when it comes to creating secure passwords. In this guide, we'll learn how to generate random passwords using Bash and the /dev/urandom file. This method ensures your passwords are both random and secure. We'll build the script step-by-step, explaining each part so you can easily follow along. By the end, you'll have a complete Bash script to generate random passwords.

Step 1: Generate Random Bytes

To start, we'll generate random bytes using the head command to read from /dev/urandom. Then, we'll use base64 to encode these bytes into a readable format.

head -c 16 /dev/urandom | base64

Explanation:

• head -c 16 /dev/urandom: This reads 16 bytes from /dev/urandom, a special file that provides random bytes.
• | base64: This encodes the bytes into a base64 string, making it easy to read.

When you run this command in your terminal, you'll see a random string output, which looks something like this: r8BgD2h+P/QA5FyN.

Step 2: Remove Unwanted Characters

Next, we'll refine the output to include only alphanumeric characters, making the password more user-friendly. We'll use the tr command for this.

head -c 16 /dev/urandom | base64 | tr -dc 'a-zA-Z0-9'

Explanation:

• tr -dc 'a-zA-Z0-9': This removes any characters that are not in the ranges a-z, A-Z, or 0-9, leaving us with a clean alphanumeric string.

Run this command, and you'll get a cleaner output like r8BgD2hPQA5FyN.

Step 3: Putting It All Together

Let's combine everything into a simple script that you can run anytime you need a new random password.

#!/bin/bash

# Generate a random password
PASSWORD=$(head -c 16 /dev/urandom | base64 | tr -dc 'a-zA-Z0-9')

# Display the password
echo "Your random password is: $PASSWORD"

Explanation:

• #!/bin/bash: This line specifies that the script should be run in the Bash shell.
• PASSWORD=$(...): This runs our command and stores the result in the PASSWORD variable.
• echo "Your random password is: $PASSWORD": This prints the generated password to the screen.

Step 4: Running the Script

To run the script, save it to a file (e.g., generate_password.sh), give it execute permissions, and then run it.

chmod +x generate_password.sh
./generate_password.sh

Explanation:

• chmod +x generate_password.sh: This makes the script executable.
• ./generate_password.sh: This runs the script.

When you run the script, you'll see an output like: Your random password is: r8BgD2hPQA5FyN.

Full Script

Here is the complete script for easy reference:

#!/bin/bash

# Generate a random password
PASSWORD=$(head -c 16 /dev/urandom | base64 | tr -dc 'a-zA-Z0-9')

# Display the password
echo "Your random password is: $PASSWORD"

Conclusion

Using /dev/urandom in Bash is a simple and effective way to generate random passwords. This method ensures your passwords are secure and random, which is essential for protecting your data. Now you have a handy script to generate strong passwords anytime you need them!

Feel free to customize the script to suit your needs, and happy coding!

More Reading: Advanced Bash Functions