How to Securely Delete Files So They Can't Be Recovered

Your file:   [●●●●●●●●●●●●●●●●]
File system: [················]  (marked as "free space")
Data on disk:[●●●●●●●●●●●●●●●●]  (still there until overwritten)

# Download from Microsoft
# sdelete.exe [options] file-or-folder

# Delete a file (3 passes)
sdelete sensitive.docx

# Delete a folder (recursive)
sdelete -s C:\path\to\folder

# Wipe free space (slow, but overwrites deleted files)
sdelete -c C:

# Wipe free space on C: drive (takes hours)
cipher /w:C:\

- File Shredder (free)
- Eraser (free, open source)
- BCWipe (paid)
- CCleaner Drive Wiper (free, built-in)

Applications → Utilities → Disk Utility
Select drive → Erase → Security Options

# Overwrite a file with random data before deleting
srm sensitive.docx

# srm options:
# -s  (simple: 1 pass of random data)
# -m  (medium: 7 passes) - default
# -z  (zero: overwrite with zeros)

# Remove recursively
srm -r /path/to/folder

# Wipe free space
# Create a large file to fill remaining space, then delete it
dd if=/dev/zero of=~/tempfile bs=1m
rm ~/tempfile

# Overwrite a file (3 passes by default)
shred sensitive.docx

# Verify by reading back
shred -v sensitive.docx

# Remove after overwriting
shred -u sensitive.docx

# More passes (for paranoia)
shred -n 10 -u sensitive.docx

# Shred entire partition
sudo shred -v /dev/sda1

# Install
sudo apt install wipe

# Wipe a file or directory
wipe sensitive.docx
wipe -r /path/to/folder

# Overwrite with zeros (fast)
sudo dd if=/dev/zero of=/dev/sda bs=4M status=progress

# Overwrite with random data (slower but more secure)
sudo dd if=/dev/urandom of=/dev/sda bs=4M status=progress

# Multi-pass
for i in 1 2 3; do
  sudo dd if=/dev/urandom of=/dev/sda bs=4M status=progress
done

# Create a file to fill all free space
dd if=/dev/zero of=~/tempfile bs=1M
rm ~/tempfile

# Install hdparm
sudo apt install hdparm

# Check if drive supports secure erase
sudo hdparm -I /dev/sda | grep -i "secure erase"

# Set a password (temporary)
sudo hdparm --user-master u --security-set-pass p /dev/sda

# Issue the secure erase command
sudo hdparm --user-master u --security-erase p /dev/sda

- Degaussing (magnetically erase HDDs)
- Drilling holes through the platters (HDD)
- Crushing with a hydraulic press
- Shredding (industrial shredders)
- Incineration