Unmount VMFS volume A general system error occurred: Cannot read the host cache configuration because some other process is modifying it at this time.

I am getting an error when adding a new iscsi volume. The error is

a general system error occured. cannot read the host cache configuation because some other proess is modifying it at this time.

any idea?

I did notice from vdf -h that /tmp is full

Ramdisk                   Size      Used Available Use% Mounted on

root                       32M        3M       28M  11% --

etc                        28M      428K       27M   1% --

tmp                       192M      192M        0B 100% --

hostdstats                803M       23M      779M   2% --

snmptraps                   1M        0B        1M   0% --