The root file systems for enigma2 fta receivers are packaged in several different ways. A common compression method used in the 4K receivers is .tar.bz2. An image is downloaded in a compressed form which usually contains a folder, then a sub-folder with a group of files in it as seen in this screencap.
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The rootfs.tar.bz2 package contains all the root file system folders that are seen in the receiver's image or file system when viewed through FileZilla or other ftp program. Extracting or decompressing the rootfs.tar.bz2 package is easy to do, and can be done using the Zero 4K receiver. Once extracted, the files can be adjusted. You may add custom files or you may delete items such as pre-installed channels or satellite files. It is also very easy to compress the root files system back into the rootfs.tar.bz2 format and load your changes or modifications into the receiver.

Disclaimer:
Enigma2 receivers have been very generous for many years when it comes to downloading or installing bad or corrupted files. About the only way to make an enigma2 receiver useless is to destroy the bootloader, which I have seen maybe a handful of people do over a 5 year period. I can say with confidence that you will not harm your enigma2 receiver by loading a bad or corrupted rootfs.tar.bz2 file. A corrupted or bad rootfs.tar.bz2 file will cause the receiver to fail on boot, but reloading a good rootfs.tar.bz2 file after the receiver fails to boot will correct it. I am not responsible for any receiver failures by providing the information in this thread . Always load files at your own risk!

The rootfs.tar.bz2 file is found in many different brands or models of receivers. I will demonstrate using the Vu+ Zero 4K receiver, but the exact same or similar methods can be used on Octagon SF4008 and other receivers that have the same file format. It is a good idea to use a receiver that the image was created for. You do this so the file permissions will be set correctly. Modifying or decompressing the rootfs.tar.bz2 file outside of the intended receiver will work, but you may have some permissions that will need to be changed or modified. It is easiest to use the receiver, and only modify images for that particular receiver model.

Here is what you need:
(1) Vu+ Zero 4K receiver.
(2) Computer with telnet capability.
(3) FileZilla or other ftp program.

Pay Attention to details: Little things matter the most!