I am using Oracle VirtualBox 4 on CentOS 6 to host some virtual machines. When I am doing a command line export:
VboxManage export <VM> -o /path/outputfile.ova
and there is lack of space on the target disk then that VM becomes unusable. It can't be started or stopped or whatever until the whole machine is restarted. Is there solution to avoid system restart?
Yes.
The solution is "Ensure that you have adequate space on the target drive to complete the export."
(If you would like a different solution I suggest contacting Oracle's support department. It's possible there's a way to resolve this issue without restarting the VM, but I don't know of one.)