I run Ubuntu 16 Desktop as host and on VirtualBox running Ubuntu 16 Server as guest which is using raw partition on another disk different from the one used by the host.I am searching for a solution which will allow me to have safe read-write access to the guest's FS (or at least to some directory on the guest partition!). I'd like to know for each opportunity even if it will sacrifice some ext4 features (security/performance) and will result in actually unsafe FS on the guest side.I am not experienced in the Unix environment but I guess that it is achievable trough proper mounting configuration for the host partition (from fstab) and proper root mounting on the guest side.I have tried by mounting on both sides with defaults option but when I create file from the host it is not showing on the guest FS, however it is read-write accessible from the host! When file is edited it is not actually reflecting on the guest.
How to get read-write access (safe) to ext4 filesystem used by second OS running from virtualbox
virtualbox;ext4;read write
Don't do this...If two operating systems try to access the same raw block device at the same time then you should expect to see data corruption.  Even if one of them is read-only, that read-only instance will cache data (eg directory contents, file contents) and won't know that the underlying data blocks have changed.  At best this may result in perceived corruption inside the OS; at worst this may cause the OS to treat the filesystem as bad.  If both OSes have write access to the device then the worst case scenerio is that you can expect the filesystem itself to be corrupted.(There are some filesystems that will allow multi-server access, but they are not common).Instead you should have one OS access the block device and then NFS export this to the other OS, which can then mount the filesystem over the network.