I know that this question is old, but because there is no accepted answer and none of these answers solved the issue for me, I am writing how I solved this today:

When running this command, get this error:

$ sudo modprobe vboxdrv
modprobe: ERROR: could not insert 'vboxdrv': Required key not available

The problem is that the module is not signed and therefore not loaded with the kernel. This will happen if your computer has the SecureBoot mode activated, something very common in modern equipment.

That's why I get this error opening any machine in the virtual box

Kernel driver not installed (rc=-1908)

Do the following steps to sign a driver, and it is loaded as a kernel module, on Ubuntu systems and also on Debian 9:

1. Install the mkutil package to be able to do signed.

    sudo apt-get update
    sudo apt-get upgrade
    sudo apt-get install mokutil
   

2. Generate the signature file:

    openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=VirtualBox/"
   

3. Then add it to the kernel:

    sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxdrv)
   

4. Register it for the Secure Boot.

IMPORTANT! That will ask you for a password, put the one you want, you will only have to use it once in the next reboot.

    sudo mokutil --import MOK.der

5. Finally, restart the computer. A blue screen will appear with a keyboard wait, press the key that asks you to interrupt the boot.

When you are inside the blue screen, select

Eroll MOK -> Continue -> and it will ask you for the password

that you have previously entered, you will enter it and you will be informed that the operation has been completed successfully.

Now your operating system will start and you can now use VirtualBox without problem :)

Hope this helps someone.

I know that this question is old, but because there is no accepted answer and none of these answers solved the issue for me, I am writing how I solved this today:

When running this command, get this error:

$ sudo modprobe vboxdrv
modprobe: ERROR: could not insert 'vboxdrv': Required key not available

The problem is that the module is not signed and therefore not loaded with the kernel. This will happen if your computer has the SecureBoot mode activated, something very common in modern equipment.

That's why I get this error opening any machine in the virtual box

Kernel driver not installed (rc=-1908)

Do the following steps to sign a driver, and it is loaded as a kernel module, on Ubuntu systems and also on Debian 9:

1. Install the mkutil package to be able to do signed.

    sudo apt-get update
    sudo apt-get upgrade
    sudo apt-get install mokutil
   

2. Generate the signature file:

    openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=VirtualBox/"
   

3. Then add it to the kernel:

    sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxdrv)
   

4. Register it for the Secure Boot.

IMPORTANT! That will ask you for a password, put the one you want, you will only have to use it once in the next reboot.

    sudo mokutil --import MOK.der

5. Finally, restart the computer. A blue screen will appear with a keyboard wait, press the key that asks you to interrupt the boot.

When you are inside the blue screen, select

Enroll MOK -> Continue -> and it will ask you for the password

that you have previously entered, you will enter it and you will be informed that the operation has been completed successfully.

Now your operating system will start and you can now use VirtualBox without problem :)

Hope this helps someone.

1. Install the mkutil package to be able to do signed.

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install mokutil

2. generate the signature file:

openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=VirtualBox/"

3. Then add it to the kernel:

sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxdrv)

4. Register it for the Secure Boot.

sudo mokutil --import MOK.der

5. Finally, restart the computer. A blue screen will appear with a keyboard wait, press the key that asks you to interrupt the boot.

When you are inside the blue screen, select Eroll MOK > Continue > and it will ask you for the password that you have previously entered, you will enter it and you will be informed that the operation has been completed successfully.

Hope this help someone.

1. Install the mkutil package to be able to do signed.

    sudo apt-get update
    sudo apt-get upgrade
    sudo apt-get install mokutil
   

2. Generate the signature file:

    openssl req -new -x509 -newkey rsa:2048 -keyout MOK.priv -outform DER -out MOK.der -nodes -days 36500 -subj "/CN=VirtualBox/"
   

3. Then add it to the kernel:

    sudo /usr/src/linux-headers-$(uname -r)/scripts/sign-file sha256 ./MOK.priv ./MOK.der $(modinfo -n vboxdrv)
   

4. Register it for the Secure Boot.

    sudo mokutil --import MOK.der

5. Finally, restart the computer. A blue screen will appear with a keyboard wait, press the key that asks you to interrupt the boot.

When you are inside the blue screen, select

Eroll MOK -> Continue -> and it will ask you for the password

that you have previously entered, you will enter it and you will be informed that the operation has been completed successfully.

Hope this helps someone.