vagrant-coreos image drops shared folders in virtualbox 4.3.2 in OS X on reboot

Question

Running this CoreOS image inside of Vagrant on Mac OS X, leveraging version 4.3.2 of VirtualBox.

When I start the image up I get the following error:

[default] No guest additions were detected on the base box for this VM! Guest
additions are required for forwarded ports, shared folders, host only
networking, and more. If SSH fails on this machine, please install
the guest additions and repackage the box to continue.

This is not an error message; everything may continue to work properly,
in which case you may ignore this message.

This is despite the fact that I am running VirtualBox on OS X, which doesn't appear to support guest additions.

Nonetheless, I am able to add shared folders manually via Settings -> Shared Folders, though these do not persist on image reboot even if I select Auto-mount and Make permanent.

This CoreOS image includes random reboots as part of its security policy, so I lose shared folders after the reboot, and am unable to regain it without nuking the image entirely and repaving.

Why is this happening?

Answer 1

@fox

CoreOS doesn't actually support the Virtualbox guest additions. Using these requires not only an additional Kernel module, but one which is not upstreamed into the Linux Kernel. We (CoreOS) worked with one of the Kernel developers to try and have this put into the staging kernel tree but there was too many problems with the code for this to be feasible.

The shared folder support that you are seeing is through a Kernel module provided by the Plan 9 filesystem (9pfs) which emulates a squashfs filesystem.

The reason that these are not persisting is the version of the CoreOS image that you are using at the moment. In your Vagrantfile, change the string amd64-generic to amd64-usr. This is a new development image that we are working on.

Additionally, make sure you run a git pull on the repository to ensure you have the most up to date copy of the files. There have been a number of changes since you posted the question and we would hate to see you miss out on them.

Answer 2

The VirtualBox guest additions must be installed in the guest OS, not on the host. My guess is that the warning comes after the CoreOS has been automatically upgraded with a new kernel, and the guest additions are not recompiled/reinstalled.

After the guest additions are reinstalled, you can just vagrant reload to remount the shared folders based on Vagrantfile.