On Linux, I would like to to set up a user account in such a way that the user would have to enter 2 passwords to log in. Is this possible, and what would be the implications of this?
Reading between the lines, what you want to configure is two-factor authentication. This will require an additional "piece of information" in addition to the password for the user to log in.
There are a multitude of ways of implementing it, but a few popular options are:
- The open source Google Authenticator.
- Using a third party product like YubiKey - see this guide for more information.
In both cases, PAM modules are available so all system logins (console,
ssh, etc) can be configured to use two-factor authentication.
A quick search turned up Two Factor SSH Setup which is a simple walkthrough of the steps required for setup.