It really isn’t. The threat model is someone who can watch you type a sudo command, and has physical access to your computer to try to brute force combinations, or a way to access a backup of your hard drive or passwords file.
Knowing the length narrows down the search space some, but a meaningfully long password basically makes that knowledge useless, and again, it’s only useful if the approach they take is to try to physically possess your computer or obtain an encrypted backup.
A far more likely effort is going to be a spear fishing email, especially since if they have physical access to you they probably know a lot about you, and what services to spoof to get you to give them passwords, and so on.
Knowing the length narrows down the search space some, but a meaningfully long password basically makes that knowledge useless, and again, it’s only useful if the approach they take is to try to physically possess your computer or obtain an encrypted backup.
A far more likely effort is going to be a spear fishing email, especially since if they have physical access to you they probably know a lot about you, and what services to spoof to get you to give them passwords, and so on.