The Linux virtual file system or virtual file system generally is a layer that sits on the top of your actual file system which allows the user to access different types of file systems, you can think of virtual file system as an interface between the kernel and the actual file system.

That means you will not find any entries for those Linux virtual filesystems in your /etc/fstab file. Yet, you will still find them listed in the output of the mount command.

https://likegeeks.com/linux-virtual-file-system/

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