Kinda what it says on the tin. I try doing minikube mount /some/dir:/home/docker/other_dir &, and it fails with the following error:

Mounting /some/dir into /home/docker/other_dir on the minikube VM
This daemon process needs to stay alive for the mount to still be accessible...
ufs starting
ssh command error:
command : 
sudo mkdir -p /home/docker/other_dir || true;
sudo mount -t 9p -o trans=tcp,port=38902,dfltuid=1001,dfltgid=1001,version=9p2000.u,msize=262144 192.168.99.1 /home/docker/other_dir;
sudo chmod 775 /home/docker/other_dir;
err     : exit status 1
output  : chmod: changing permissions of '/home/docker/other_dir': Input/output error

Then, when I do a minikube ssh and ls -l inside /home/docker, I get this:

$ ls -l
ls: cannot access 'other_dir': Input/output error
total 0
d????????? ? ?   ?   ?            ? other_dir

UPDATE:

After some experimenting, it looks like the problem arises when /some/dir has a user other than the current user. Why this is the case is unclear.