if I setup a Linux Dubian instance, how easy is it to back up. I would like to use a USB drive that I have laying around.
It seems like you meant to type Debian instead of Dubian. Assuming you want to back up a Debian Linux instance, here are the steps to back up your system using a USB drive.

1. Connect the USB drive: Plug the USB drive into the system you want to back up.
2. Identify the USB drive: To find the device name of your USB drive, you can use the **`lsblk`** or **`fdisk -l`** command. This will list all the connected drives, and you should be able to identify your USB drive by its size.
3. Mount the USB drive: Create a mount point for your USB drive by running **`sudo mkdir /mnt/usb`** and then mount the USB drive by running **`sudo mount /dev/sdXY /mnt/usb`**, where **`/dev/sdXY`** is the device name of your USB drive. Replace X with the appropriate letter and Y with the appropriate partition number.
4. Install **`rsync`**: If you don't have **`rsync`** installed, install it using the command **`sudo apt install rsync`**.
5. Back up your system: You can use the **`rsync`** command to back up your system to the USB drive. Here's an example command:

```jsx
sudo rsync -aAXv --exclude={/dev/*,/proc/*,/sys/*,/tmp/*,/run/*,/mnt/*,/media/*,/lost+found} / /mnt/usb/backup/
```

This command will create a directory named backup on your USB drive and copy your entire system to it, excluding some directories that should not be backed up. You can customize the excluded directories and destination folder as needed.

1. Unmount the USB drive: After the backup process is complete, unmount the USB drive by running **`sudo umount /mnt/usb`**.
2. Safely remove the USB drive: To ensure there is no data loss, you can run **`sudo sync`** before physically disconnecting the USB drive from your system.

Keep in mind that the backup process may take some time, depending on the size of your system and the speed of your USB drive. Additionally, you can automate this process by creating a script or scheduling a cron job to perform the backup regularly.
Can you write a cron job for me and explain where to put it?
Sure! Here's an example cron job that will run the backup command every day at midnight:

Open a terminal window on your Debian system.
Type the command crontab -e to open the crontab file in your default text editor.
Add the following line to the end of the file:
0 0 * * * sudo rsync -aAXv --exclude={/dev/,/proc/,/sys/,/tmp/,/run/,/mnt/,/media/*,/lost+found} / /mnt/usb/backup/
Save and close the file. This will install the cron job.
This cron job will execute the backup command every day at midnight. You can modify the scheduling to match your needs by changing the values in the first four columns of the line (in order, minute, hour, day of month, month).

Keep in mind that you'll need to have permission to edit the crontab file, and that this example command assumes you've mounted the USB drive to /mnt/usb. Be sure to adjust the command to match your system configuration.