Encrypted disks and/or filesystems are nothing new on Linux; most distributions, these days, allow you to encrypt some or all your disk partitions, so that they can only be accessed with a password. In this tutorial, however, we’re going to add a new encrypted partition to an existing system, using only the command line. I’ve found that tutorials on the web seem to make this issue more complex than it actually is, so here’s mine — hopefully it’ll be easier than most.
In this guide, we’ll be making a few assumptions. First, as said above, it’ll be an existing system, to which we’ve just added a new disk, /dev/sdb . Adapt to your situation, of course. If you’re not using an entire disk, just create a new partition with fdisk (e.g. /dev/sdb1) and use it instead. Second, we’ll have the machine boot with the disk unmounted, then use a command to mount it (asking for a passphrase, of course), and another to dismount it when you don’t need it. The obvious usage of such a partition is for storing sensitive/private data, but theoretically, you could run software on it — as long as you don’t automatically attempt to start it on boot, and don’t mind keeping it mounted most or all of the time, which perhaps defeats its purpose: if it’s mounted, it’s accessible.
So, without further ado…
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