How Do I Resize A BitLocker Filesystem?


New Member
Esteemed Colleagues:

Perhaps this is a Linux question and not a Microsoft Windows question, but I don't know whether the people who can answer it are Linux people or Microsoft Windows people, so I am posting it to this forum. I hope one of you can answer my question.

One of my clients has sent me a laptop with Microsoft Windows on it, and I am resolved to turn it into a multiboot machine, which is what I always do whenever I get a computer with Microsoft Windows on it. The first step is to boot it into Linux. I have an external USB disk on which I copied LinuxMint 20 (LinuxMint because it comes with ntfsresize, whereas there are some other Linux distributions that do not) and I booted from it. The lsblk command reports that /dev/sda is partitioned into four slices, and that /dev/sda1, /dev/sda2 and /dev/sda4 all have less than 1G, and that the major part of the storage is /dev/sda3 with 464G.

The goal is to reduce the size of /dev/sda3 with ntfsresize, and then render the freed-up storage accessible by removing /dev/sda3 with gdisk, and then recreating it smaller (restoring the original partition UUID, in case secure boot depends on it -- I actually don't know whether it does or not, but I once did this without noting or restoring the original partition UUID, and I ended up with a Microsoft Windows system that I could not boot). The first step is to find out how small I can ntfsresize the filesystem by mounting it and then asking df how much disk storage it is really using. I have done this before countless times. This time the first step failed. The mount command says "/mnt: unknown filesystem type 'BitLocker'". When I explicitly specify "-t ntfs", the mount command says "The device /dev/sda3 doesn't seem to have a valid NTFS". When I invoke ntfsresize anyway (which I prefer not to do, because I don't know what --size= argument to give it, but I figured 180G would be safe), it says "NTFS signature is missing".

BitLocker, I have found out, is some kind of encryption scheme for Microsoft Windows filesystems. But the encryption has not been set up. I know this to be true, because when I boot into Microsoft Windows, I am not asked for a decryption key. When I go to the control panel, or whatever it's called, and look at the BitLocker item, it says that BitLocker is ready to be set up, but is not yet set up, or words to that effect. So the filesystem is still in plaintext. How, then, do I resize it, so I can free up some disk storage into which to install some other operating systems? As always, I thank you in advance for any and all replies.

jay at m5 dot chicago dot il dot us


Windows Forum Team
Staff member
If the computer has a TPM the key is stored there. You'll need to run the command manage-bde -status to make sure bit locker is not enabled but it sounds like it is enabled, if it is and it's a requirement I don't recommend making it a multi boot system. If it is encrypted you will need to decrypt the drive. In addition I don't know that bitlocker will work with grub as the boot loader. Is there some reason you're trying to make it dual boot? Do they need Linux and why not just host a Linux distro in as a VM?