unhinge

@unhinge@programming.dev

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unhinge, (edited )

Between btrfs filesystem usage / and btrfs filesystem du -s / there’s nearly 11GiB difference for used space. I have checked btrfs du -hs <path/to/subvolume> for all subvolume in the filesystem, and total seems to be 72 GiB, hence the confusion. Still I don’t know if I’m using the tools properly or something else is at fault here.

To correct myself, 11GiB is additional space used by snapshot probably used space difference between btrfs fi usage and btrfs fi du -s / is because of diff between snapshot and parent volume (didn’t consider that while adding all used GiB of subvolumes). So btrfs filesystem usage works well to check used/free space.

edit: fix incorrect args; additional space is not diff

unhinge, (edited )

Thanks that helped. I have one snapshot of home. Size of diff between btrfs subvolume and Additional space used by snapshot is 11GiB (probably) and btrfs fi du -s / is 72GiB, making 83GiB (closer to btrfs fi df /).

unhinge,

just comparing the subvolume with its snapshot with btrfs send -p /example/subvol /snapshot/of/example/subvol >examplediff.btrfs.

From man btrfs-send

generate a stream of instructions that describe changes between two subvolume snapshots

Thanks for btdu, it seems useful as ‘btrfs fi du’ probably doesn’t account for compression, will check it out sometime.

unhinge,

You are right. I shouldn’t have used diff. I’ll fix that

Also, incremental changes from subvolume to its snapshot might be incorrect as that will be new data added to subvolume, rather that old data deleted from subvolume while still present in snapshot. I’ll have to check carefully.

Encrypted hard drive asking for password every time

I recently switched to Linux (Zorin OS) and I selected “use ZFS and encrypt” during installation. Now before I can log in it asks me “please unlock disk keystore-rpool” and I have to type in the encryption password it before I’m able to get to the login screen....

unhinge,

Assuming you want:

  1. Single password prompt instead of auto-decrypt with tpm
  2. User’s files to be encrypted

There are several ways to achieve this:

  1. autologin (recommended for single user system):/ is encrypted using luks or zfs native encryption and user’s home needs to be unencrypted. User’s password may be same as encryption password for convenience, though they still are two passwords used for different purposes.
  2. pam mount:/ is unencrypted or auto-decrypted and user’s home is encrypted independently from / using zfs,luks,fscrypt,etc. In this case, user’s login password must be same as user’s home encryption password. It’s suitable for multi-user system. NOTE: It cannot be used with autologin since user’s home needs to be decrypted to log in.

WARNING: For tpm usage, using secure boot is highly recommended to prevent unauthorized user from accessing key stored in tpm.

To prevent auto-decrypt with tpm, tpm-pin can be used (with autologin for requirement #1).

  1. **systemd-cryptenroll with/without tpm:**As far as I know it can be only used to unlock disk encrypted with luks2. It can be used without tpm with pkcs11-token (e.g. YubiKey) or fido2-device. It also uses parameter encryption while key is unsealed, so safe from key sniffing via communication bus. This is easy if secure boot is enabled and luks2 is used for encryption.
  2. **clevis with tpm:**It can be used in place of systemd-cryptenroll. May be used with zfs native encryption. Though I’m not sure if it uses parameter encryption (correct me).
  3. **unencrypted keyfile on usb:**Not sure about zfs, but you can use keyfile on a usb drive to decrypt luks containers.

NOTE: I’m not a forensic/security expert. I listed a brief overview of methods I could think of to keep user’s files encrypted while providing single password till login.

unhinge,

I have no idea what TPM is

Read Skull giver’s reply or look it up.

Re-reading your post, I take you want to avoid typing long and tedious password? And that’s why you want to auto-decrypt?

  1. (Recommended) You could use strong memorable passwords that are not difficult to type and enable autologin. Related xfcd comic:

https://imgs.xkcd.com/comics/password_strength.png

  1. systemd-cryptenroll: For TPM usage, I highly recommend using secure boot. Though not sure if you can easily do that. A less secure alternative using systemd-cryptenroll would be use tpm2-pin and bind key to no pcrs (discouraged). But then you’ll have to use luks2 for encryption. Notice from man systemd-cryptenroll regarding tpm2-pin:

Note that incorrect PIN entry when unlocking increments the TPM dictionary attack lockout mechanism, and may lock out users for a prolonged time, depending on its configuration. The lockout mechanism is a global property of the TPM, systemd-cryptenroll does not control or configure the lockout mechanism. You may use tpm2-tss tools to inspect or configure the dictionary attack lockout, with tpm2_getcap(1) and tpm2_dictionarylockout(1) commands, respectively Also tpm2-pin is not disk encryption password and short alphanumeric password needed so tpm decrypts the device; so encryption password should be secured in a safe place. Also check if your distro supports systemd-cryptenroll.

  1. usb drive: read previous comment
  2. clevis: It probably isn’t as simple as systemd-cryptenroll but I guess you can use zfs and combine that with tpm2-pin if not using secure boot (discouraged).

You’ll have to make a compromise somewhere between security and convenience. Even if you use pam mount, you’ll have to enter the password, biometrics won’t do.

Edit: remove unnecessary user tag and add img uri

unhinge,

oh, I forgot. Thanks for mentioning that :)

unhinge,

user’s password can be totally different from luks password if you’re using autologin. You can keep it same but that’s totally optional. You can login without entering any password at all if not using luks (or using autodecrypt), you can see that in live isos.

unhinge,

oh shit I forgot to set up subvolumes

lol

I’m also planning on using its subvolume and snapshot feature. since zfs also supports native encryption, it’ll be easier to manage subvolums for backups

unhinge,

that sounds good.

Have you used luks integrity feature? though it’s marked experimental in man page

unhinge,

afaik openzfs provides authenticated encryption while luks integrity is marked experimental (as of now in man page).

openzfs also doesn’t reencrypt dedup blocks if dedup is enabled Tom Caputi’s talk, but dedup can just be disabled

unhinge,

if you happen to find the comparison, could you link it here

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