Check which Debian install you have:

lsb_release -a

echo $var             # is the same as...
printf '%s\n' "$var"

echo -n $var          # is the same as...
printf '%s' "$var"

Basic Syntax:

find /path/to/search/ -name searchTerm

If you get a bunch of garbage on the screen, send it all to /dev/null:

find /path/to/search/ -name searchTerm 2>/dev/null

tar xvzf filename

# x - extract
# v - verbose
# z - zip / gnuzip
# f - file (name follows)

How to Install VirtualBox on Debian 11 (Bullseye)

Several of these steps require you to be root or have root permissions. So, either su - to become root (and then exit when we're all finished) or preface all the required commands with sudo. I prefer su - so that's what follows (and, yes, that space and the hyphen are going to be necessary because are going to want all of root, including his path, not just his superman powers to break things).

Make sure you have the required packages installed :

apt install build-essential linux-headers-amd64

Find a happy, safe place to put your new file:

cd ~/Downloads/

Open a browser and go to: virtualbox.org/wiki/Linux_Downloads

Right-click on “All distributions” at the bottom of the VirtualBox for Linux files. This is a script file (so it's just text; if you click on it, your browser will open it up for you to read). If you want to just download it (make sure you pull the filename from the “All distributions” link mentioned above!):

wget -v https://download.virtualbox.org/virtualbox/6.1.14/VirtualBox-6.1.14-140239-Linux_amd64.run

You need to execute that file so change the perms:

chmod 755 VirtualBox-6.1.14-140239-Linux_amd64.run

Run that script file (type a few of the beginning letters of the file and hit the tab key):

./VirtualBox[tab]

If all went well you should see a message saying, “Virtualbox has been installed successfully.” Now we want the extension pack… Go here and click into the version number you just downloaded (e.g., 6.1.14; it should be almost at the bottoms since it should be the newest version):

https://download.virtualbox.org/virtualbox/

That takes us to:

https://download.virtualbox.org/virtualbox/6.1.14/

Find the Extension Pack file that bears the same version number of the .run file you downloaded above. NOTE: You may have a -##### number suffix after your version number (like above: 6.1.14-140239). If there is an Extention Pack file that matches that full version number, right click it and save it to your ~/Downloads/ subdir. If not, just grab the one with the standard version number. The file to download for the above version number is:

https://download.virtualbox.org/virtualbox/6.1.14/Oracle_VM_VirtualBox_Extension_Pack-6.1.14-140239.vbox-extpack

Install that Extension Pack (replace the filename below with the one you downloaded):

VBoxManage extpack install --replace Oracle_VM_VirtualBox_Extension_Pack-6.1.14-140239.vbox-extpack

If all went well you should get a happy message saying, “Successfully installed…”

Now we just need to add users (regular users, not root) to the vboxusers group:

cat /etc/group | grep vbox  ## this will show you the group name
usermod -a -G vboxusers [username]  ## plug in whatever username you want

Reboot and you should be good to go.