Wipe Disks

For HDDs, you need to overwrite everything.
For SSDs, the BIOS can typically invoke a secure erase.

HDDs - Using shred

shred -v -n1 /dev/sda

SATA SSD Secure Erase

https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase

Generally you do not want to write a bunch of zeros or random data to SSDs which would create significant wear. For performance reasons, SSDs typically encrypt data internally. A secure erase on an SSD will just generate a new internal encryption key, taking only a few minutes and avoiding unnecessary wear.

DEVICE=/dev/sdb

# Check if device is frozen
# On Ubuntu live, you may need to sleep and wake the system
sudo hdparm -I $DEVICE

# Set a password to Eins
sudo hdparm --user-master u --security-set-pass Eins $DEVICE
# Check that the master password is enabled
sudo hdparm -I /dev/sda

# Run secure erase (wipes internal encryption key)
sudo hdparm --user-master u --security-erase Eins $DEVICE
# Or for secure erase enhanced (takes longer, wipes multiple times)
sudo hdparm --user-master u --security-erase-enhanced Eins $DEVICE

# After a few minutes, check that the master password is disabled
sudo hdparm -I /dev/sda

NVME - Secure Erase

reference