How To Securely And Permanently Delete Your Data In Linux

Securely And Permanently Delete Your Data In Linux

As you may know already, the deleted data from your hard drive can be recovered using some data recovery software, with little bit of effort. However, some times you don’t want your private data to be recovered or you simply wanted to make it very hard to recover your personal data. Some people might recover your data and misuse them for their own benefit. So, it is very important that you must remove all personal, official, or any kind of important data before selling or exchanging your old hard drive. This brief tutorial describes how to securely and permanently delete your data in Linux.

Securely And Permanently Delete Your Data In Linux

While there are many tools and methods are available to delete your important files or folders in Unix-like operating systems, we are going to see only one tool called secure-delete. It provides four useful utilities that helps you to securely and permanently erase your data from your system, so that it would be very hard to recover those data by using any data recovery software.

A word of caution: Please remember that it is very hard to recover after deleting your files or folders using secure-delete. So, double check before using secure-delete utilities. Also, all of these are both unnecessary and dangerous on SSD drives or other flash based media. SSDs store data differently from hard disk drives. I recommend you to use the manufacturer utilities to erase SSDs. For HDDs, this method will just work fine as described below.

Install secure-delete

secure-delete is available in the default repositories of DEB and RPM based systems.

In Debian, Ubuntu, Linux Mint, you can install it using command:

sudo apt-get install secure-delete

In Fedora:

sudo dnf install secure-delete

In RHEL, CentOS:

sudo yum install secure-delete

In Arch Linux, you can install it from AUR using yaourt or packer as shown below.

yaourt -S secure-delete

Or,

packer -S secure-delete

Usage

secure-delete package provides the following four utilities to securely erase file/folder, disk, swap, and memory of your Linux system.

  1. srm – secure remove
  2. sfill – Secure free disk and inode space wiper
  3. sswap – Secure swap wiper
  4. smem – secure erase memory

Let us discuss the usage of each command.

1. srm – securely remove files and folders

srm is used to erase your files and folders securely and permanently, so the data can’t be recovered by data recovery softwares, law enforcement or any other threats.

The typical syntax of this command is:

srm [-d] [-f] [-l] [-l] [-r] [-v] [-z] files

Here,

  • -d – Ignore the two special dot files . and .. on  the  command line.
  • -f – fast and insecure mode. no /dev/urandom, no synchronize mode.
  • -l – lessens the security. If you use this option for second time, it lessens the security even more.
  • -r – Recursive mode (Deletes all sub-directories and its contents)
  • -v – Verbose mode
  • -z – Wipes the last write with zeros instead of random data

srm usage is pretty same as rm command.

The following command will recursively delete a folder called ostechnix.

sudo srm -r ostechnix

This command will delete a file called sk.txt.

sudo srm sk.txt

Please note that srm will not completely delete NFS shares (remote file systems), RAID systems, and swap file system.


Also read: How To Find And Delete Files Older Than X Days In Linux


2. sfill – Secure free disk and inode space wiper

sfill will scan the specified partition or directory and look for space marked as free or available. If there is any free space, it will fill it up with some random data ensuring that there are no more recoverable data on the specified partition.

The syntax for this command is:

sfill [-f] [-i] [-I] [-l] [-l] [-v] [-z] directory/mountpoint

The following command will fill some random data on the empty space in the /home partition.

sudo sfill /home

3. sswap- securely remove files and folders

Swap partition can be used when the RAM is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. To securely erase this data (inactive pages), you need sswap utility. As the name implies, sswap command will securely erase the data from swap partition.

The syntax of sswap command is:

sswap [-f] [-l] [-l] [-v] [-z] swapdevice

First, find the swap partition using command:

cat /proc/swaps

Sample output of the above command in my Arch Linux is:

Filename Type Size Used Priority
/dev/sda3 partition 2097148 25144 -1

As you see above, my swap partition is /dev/sda3.

Disable swap partition using command:

sudo swapoff /dev/sda3

Now, securely wipe the swap partition’s data with command:

sudo sswap /dev/sda3

After securely erasing the Swap partition’s data, enable it back:

sudo swapon /dev/sda3

4. smem – Secure memory wiper

semem command is used to securely erase the contents of the RAM which contains the state of running programs.

The Syntax for the above command is:

smem [-f] [-l] [-l] [-v]

To securely clear the RAM which could contain any sensitive data of running programs, enter the following command:

sudo smem

You might want to protect some important files and directories from accidental deletion or modification. Here are the two simple ways to protect your important files from accidental deletion.


And, that’s all. Now, you know how to delete files and folders securely and permanently from your Linux box. If you find our guides useful, please share them on your social, professional networks, so that others also can benefit from them. I will be soon here with another interesting and useful guide. Until then, stay tuned with OSTechNix.

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  • Larry Gagnon

    I thought the utility “shred” comes by default with almost every Linux distro I know of. That utility by itself is sufficient to securely remove any file.