Prepping Used Laptops for Resale (Might As Well Post My SSN on the Darkweb)

Lately, I’ve been selling off stuff I no longer need because I am broke and live in my parents’ basement. Among these items for sale are some older laptops I don’t use anymore (there simply isn’t enough time in the day to complete every single side project you start, right?). At least I learned what I could from the devices while I had them; that is, an Acer Chromebook 15 and a MacBook Air 11. Neither operating system was really my cup of tea (we all know there’s nothing quite like Linux), but they were definitely each worth the initial purchase. Enabling developer mode on Chrome OS is where most of the fun is; and despite what they may say, you really can do a lot with macOS by installing HomeBrew and using the Terminal as much as possible. But alas, neither of them is receiving updates any longer from Google or Apple, respectively, nor are they eligible for an upgrade. I could install Linux on the Chromebook (it would definitely be a fun project, as the process for this particular hardware is fairly involved), but I already have my hands full with a Debian and a Rocky laptop. I briefly had openSUSE Tumbleweed on the MacBook, but I installed Lubuntu on it for resale purposes.

As an IT and cybersecurity enthusiast, I need to be paranoid about information security. But as a testament to just how absent-minded of a ~tech professional~ I am, I hadn’t really thought about doing a secure erase (the process is explained in more detail below) on the drives. Then, as I was prepping the laptops, the thought popped into my head and it wouldn’t stop nagging me after that. At least I had the sense to stop using the devices after the security patches stopped coming in, and I have informed my prospective buyers of the situation. It blows my mind how little some people care about cybersecurity, even if they are fairly tech-savvy; they’ll just keep using Windows 7 for years after Microsoft has dropped support for it, while still downloading pirated movies and shows. Hmm…

Wiping the drive on the Chromebook and MacBook can be done with one of my favorite Linux tools: dd (data duplicator). It is one of the very first Linux (and to be fair, Unix, as it is also built into macOS) tools I learned to use, since I needed a way to create my Linux thumb-drive installers. You just download the ISO for whatever distro you want from the official website, then run some variation of the below command to write it to your thumb drive. In goes the ISO, out it goes to your device, recommended block size is usually 4 MBs, and you will see the progress in the terminal output:

sudo dd if=./ubuntu-is-basic-69.iso of=/dev/sdz bs=4M status=progress

On the other hand, the command to just write a bunch of random numbers to your target drive is slightly different. /dev/urandom is a file in Unix-like systems used for generating random data. /dev/sda is usually the native hard disk on Linux systems, though it often has a different name especially on other systems such as Chrome OS (e.g. /dev/mmcblk0):

sudo dd if=/dev/urandom of=/dev/sda bs=4M status=progress

Theoretically, to run this command on Chrome OS, I will only need to enable developer mode first (see what I meant about dev-mode being fun?). Then I can reinstall Chrome OS from a thumb drive. On the MacBook, I plan on just using a Tails OS thumb drive and running the command in the Tails terminal; Tails runs entirely in RAM, so there shouldn’t be any issues with erasing a disk that is currently in use, etc.

Hopefully this information has been useful to you. It’s very difficult to make your data completely unrecoverable, but if you do find yourself in a situation where you have to sell or give away your old devices, by taking a few precautions such as these you can prevent most attacks. I prefer using the terminal, but I’m certain there are many GUI tools available for people who feel more comfortable with that. And don’t worry, if you do end up becoming the target of advanced computer forensic techniques, my data will be on the darkweb right next to yours! We may even find ourselves in the same bundle deal :)