Linux ‘passwd’ command without interactive prompt using ‘stdin’

If you’ve ever tried automating tasks on Linux, you’ve probably run into the interactive nature of the passwd command. By default, it asks for user input, which isn’t great when you’re writing scripts. But don’t worry—there are simple ways to make it work without the hassle. Let’s break it down step by step so you can automate password changes easily.

Why Automate Password Changes?

Automating password updates can save tons of time in situations like:

• Setting up new systems or users: Preloading passwords during system provisioning.
• Resetting passwords for multiple accounts: Handy when managing many users at once.
• Integration with automation tools: Tools like Ansible or Puppet need non-interactive scripts for smooth operation.

With the right approach, you can skip the interactive prompts and get straight to business.

Non-Interactive Password Changes Using chpasswd

One of the easiest ways to automate this is by using chpasswd. It’s built for non-interactive password updates. Here’s what you need to do:

Step 1: Create a User-Password File

Write a file that lists usernames and passwords, separated by a colon. For example:

user1:password123
user2:mysecurepassword

Step 2: Use the chpasswd Command

Run the command below to apply the updates:

sudo chpasswd < user_passwords.txt

This updates the passwords for all users in the file.

Why Use chpasswd?

• It’s simple and works great for bulk updates.
• Keeps passwords out of terminal output for better security.
• It’s fast and reliable.

How to Use passwd Without Interaction

For single-user changes, you can tweak the passwd command using echo. Here’s a quick example:

echo "newpassword" | sudo passwd --stdin username

This pipes the password directly into passwd. Easy, right?

Heads Up for Debian Users

If you’re on a Debian-based system, the --stdin option isn’t available. In that case, you’ll need to use chpasswd or another workaround, like expect.

Automating Password Changes with expect

The expect tool is a lifesaver for automating interactive programs like passwd. It’s perfect for handling prompts. Here’s how to use it.

Example expect Script

This script automates the process:

#!/usr/bin/expect

set timeout -1
set username "user1"
set password "newpassword"

spawn passwd $username
expect "New password:"
send "$password\r"
expect "Retype new password:"
send "$password\r"
expect eof

Save it as change_passwd.exp and run it like this:

sudo ./change_passwd.exp

Why Choose expect?

• Works universally, even when --stdin isn’t supported.
• Can handle any interactive prompts you encounter.

Tips for Keeping It Secure

• Lock down access: Use file permissions to protect scripts and password files. A good rule is chmod 600.
• Avoid plain text passwords: Consider using encrypted vaults or environment variables for storing sensitive info.
• Check your logs: Regularly audit system logs to ensure no sensitive data leaks.

Frequently Asked Questions

Can These Methods Be Used for SSH Key Management?

Not exactly. Managing SSH keys involves tools like ssh-keygen and ssh-copy-id. It’s a different process.

Is expect Preinstalled?

Usually not. You’ll likely need to install it. For instance, on Ubuntu:

sudo apt install expect

What Other Tools Can Manage Users?

You can look into useradd and usermod for broader user management. But for password changes, passwd is the go-to.

Wrapping Up

Automating password updates on Linux doesn’t have to be hard. Whether you’re using chpasswd, passwd with a twist, or the versatile expect, there’s a method that fits your needs. These techniques are perfect for setting up new systems, managing users, or integrating with automation tools. Start streamlining your workflows today and make password management a breeze!