OpenVZ: Canít umount (unmount) device or resource busy

first check to make sure you donít have any other SSH connections open, or any other connection that may be causing the problem. 99% of the time itís just an SSH connection you still have open.

If that doesnít work, go ahead and login to the container and shutdown:
shutdown -h now

Or from the main node:
vzctl stop 100

Once the container is shutdown, attempt to unmount it and see if it throws any errors:
vzctl umount 100

If you still canít unmount it, try these to see if anything stands out:
ps aux|grep 100

lsof |grep 100

lsof |grep 'root/100'

The final check which ended up being where I found my problem is to run:
cat /proc/mounts |grep 100

Hereís what I ended up finding:
/var/lib/vz/private/100 /var/lib/vz/root/100 simfs ro,relatime 0 0
/var/lib/vz/private/100 \040(deleted)/var/lib/vz/root/100/var/named/chroot/etc/named.rfc1912.zones simfs ro,relatime 0 0
/var/lib/vz/private/100 \040(deleted)/var/lib/vz/root/100/var/named/chroot/etc/named.iscdlv.key simfs ro,relatime 0 0
/var/lib/vz/private/100 \040(deleted)/var/lib/vz/root/100/var/named/chroot/etc/named.root.key simfs ro,relatime 0 0

Turns out it there was still active in read only mode. And the simple way to fix that was:
umount -l /var/lib/vz/root/100

Hope this helps, good luck!


OpenVZ: Error booting containter: Device or resource busy

I had same problem and have no idea to solve it correctly, but here is at least some solution:
You have to change mount point for your VE (example 102) from /var/lib/vz/root/102 to (for example) /var/lib/vz/root/YAHOO/102
mkdir -p /var/lib/vz/root/YAHOO/102
and in the file /etc/pve/openvz/102.conf (or /etc/vz/conf/102.conf) replace string VE_ROOT="/var/lib/vz/root/$VEID" to VE_ROOT="/var/lib/vz/root/YAHOO/$VEID"

It is ugly, but working.