sudo vs su (as non-root user)

Question

My computer has user1 and user2, both administrators.

While I'm logged in as user1 I'm trying to:

• "su - user2" -> prompts me for the users2 password, then I can type commands
• "sudo --user=user2 [command]" -> prompts me for the password. If I type user2's password I get a "Sorry, try again." error message as if the password is incorrect. If I type user1's password it runs correctly.

Shouldn't the sudo command require the user's password that I define in the "--user" parameter?

Answer 1

This is expected behaviour.

• The purpose of su is to switch user. It's called the substitute user identity tool. su takes the other user's password since you are switching to that user.

  The su utility requests appropriate user credentials via PAM and switches to that user ID (the default user is the superuser). A shell is then executed.

  ^{Source: Man page}

• The purpose of sudo is to execute a command as another user. The -u or --user option for sudo specifies that user. You're not logging in as that user, just running a command. sudo takes your password to verify your identity for performing such a task.