what command will prevent all unencrypted passwords from displaying in plain text in a configuration file?

The command you’re looking for is:

(config)# service password-encryption

Quick Scoop

On Cisco IOS devices, running service password-encryption tells the device to encrypt all currently configured, plain-text passwords in the running configuration. This includes things like console, VTY, and line passwords so they no longer appear in clear text when you do a show running-config.

Think of it as flipping a switch: all those readable passwords get converted into type 7–style encrypted strings, which are at least not human-readable at a glance. It’s not strong cryptography by modern standards, but it does prevent casual viewing in plain text, which is exactly what the question is asking.

Why this specific command?

• Other options like enable secret Secret_Password or enable secret Encrypted_Password only protect the enable password, not all passwords in the config.

• service password-encryption applies to all unencrypted line passwords already configured on the device.

• This is a classic CCNA / networking exam-style question, and the officially accepted correct answer is always service password-encryption.

Mini example

1. You configure a console password:
   line console 0
password cisco123
login

2. Before encryption, show running-config will show password cisco123 in plain text.

3. After you run:
   config terminal
service password-encryption

4. That same section will now show a scrambled, non-plain-text value instead of cisco123.

Final exam-style answer:
(config)# service password-encryption

Note: Information gathered from public forums or data available on the internet and portrayed here.