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After installing do the following steps:
# Deleting Hyper-v BIS driver names
   sed -i "" '/Loader labels for Hyper-v BIS driver/d' /boot/loader.conf
   sed -i "" '/hv_vmbus_load/d' /boot/loader.conf
   sed -i "" '/hv_utils_load/d' /boot/loader.conf
   sed -i "" '/hv_storvsc_load/d' /boot/loader.conf
   sed -i "" '/hv_netvsc_load/d' /boot/loader.conf
   sed -i "" '/hv_ata_pci_disengage_load/d' /boot/loader.conf

   #Hyper-v driver names
   echo  "# Loader labels for Hyper-v BIS drivers -do not modify" >> /boot/loader.conf
   echo  'hv_vmbus_load="YES"' >> /boot/loader.conf
   echo  'hv_utils_load="YES"'  >> /boot/loader.conf
   echo  'hv_storvsc_load="YES"'  >> /boot/loader.conf
   echo  'hv_netvsc_load="YES"'  >> /boot/loader.conf
   echo  'hv_ata_pci_disengage_load="YES"'  >>/boot/loader.conf
When deinstalled, restore /boot/loader.conf
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