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shred - Overwrite the specified FILE(s) repeatedly, in order to make it harder for even very expensive hardware probing to recover the data.
To permanently delete all files within a folder (e.g. Documents) and subfolders, use the following command:
find Documents/ -type f -exec shred -uvz {} \;
After the command has been executed, all files are irretrievably deleted. Only the (sub)folders remain. To delete the empty (sub)folders, use the follwoing command:
rm -r Documents/
You can also use shred to permanently delete one file only:
shred -uvz example.txt
Default overwrites file always three times; u - deallocate and remove file after overwriting; v - show progress; z - add a final overwrite with zeros to hide shredding
Use the following command to display the serial number in cmd (Windows 10 or older):
wmic bios get serialnumber
Use the following command to display the serial number in PowerShell (Windows 11 or later):
Get-WmiObject win32_bios | select Serialnumber
To securely erase HDDs, overwrite them completely with zeros. However, this doesn't work with an SSD/NVMe. To do that, you boot from an live-Linux-ISO/-USB-stick and execute the following command:
sudo hdparm -I /dev/sda
This command shows you specific information about the SSD/NVMe. The importend pieces are under the section Security - not enabled, not locked, not frozen.
If the SSD/NVMe is frozen you can use the command sudo systemctl suspend to suspend your PC/Notebook. Then restart your PC/Notebook and run the command sudo hdparm -I /dev/sda again to check whether the entry is set to not frozen.
To enable secure erase execute the following commmand:
sudo hdparm --user-master u --security-set-pass PASSWORD /dev/sda
PASSWORD = can be chosen freely. Please run the command sudo hdparm -I /dev/sda again to check whether the entry is set to enabled.
If everything looks fine, run the following command:
sudo time hdparm --user-master u --security-erase-enhanced PASSWORD /dev/sda
It may take a few seconds for the command to be executed. After successful deletion, the security function of the SSD/NVMe should be automatically deactivated again. Run the command sudo hdparm -I /dev/sda again to check whether the entry is set to not enabled.