dm-linear like target which provides discard, but replaces it with write of erase pattern data to a discarded region. Thus, discarded data is securely deleted (sanitized). Because of abstract nature, it could support many file-systems which support discard (such as ext3, ext4, xfs, btrfs).

Operation notes:

Create a mapped device with secdelsetup tool. Make sure file-system is mounted from that device and not from the underlying device. Make sure file-system is mounted with -o discard option. Do not enable data journaling (such as -o data=journal do not enable it). Note, that when you rm files discards will be sent (and, thus, erasing will performed) asynchronously, so, to make sure data is already erased issue sync or remount file-system with -o sync option before rm. If you wish that filenames are wiped too, first, make sure file-system is created completely without journaling (such as mkfs.ext4 -O ^has_journal, and second, delete the directory itself, so its blocks are discarded and erased. If you issue fstrim all free blocks of file-system will be discarded and thus erased too (make sure that file-system is still mounted with -o discard though.)

Usage:

secdelsetup /dev/sda5 [/dev/mapper/secdel5]

• will map sda5 to secdel5. (With default erase more which is single pass of (crng) random data). Alternatively:

secdelsetup /dev/sda5 [/dev/mapper/secdel5] 1R0

• Will work same as above but with with three pass overwriting: first pass of 1-bits, second pass of (crng) random bits, and third pass of 0-bits.

Then, file-system on secdel5 should be mounted with -o discard.

secdeltab --all or secdeltab --list

• show current maps.

secdelsetup --save

• save current maps to /etc/secdeltab which will be automatically activated after reboot (by secdeltab.service systemd unit).

secdeltab --detach-all

• detach all active maps.

Based on the code of dm-linear from Linux kernel of their respective authors. (C) 2018,2019 vt@altlinux.org; License GPL-2.0-only.