On Oracle Solaris hosts, the Oracle VM VirtualBox watchdog service daemon is integrated into the SMF framework. You can change the parameters, but do not have to if the defaults already match your needs:

svccfg -s svc:/application/virtualbox/balloonctrl:default setprop \
  config/balloon_interval=10000
svccfg -s svc:/application/virtualbox/balloonctrl:default setprop \
config/balloon_safetymargin=134217728

also applies for Oracle Solaris. The parameter names must be changed to lowercase and a prefix of config/ has to be added. For example: config/user or config/balloon_safetymargin. If you made any change, do not forget to run the following command to put the changes into effect immediately:

svcadm refresh svc:/application/virtualbox/balloonctrl:default

If you forget the above command then the previous settings will be used when enabling the service. Check the current property settings with the following command:

svcprop -p config svc:/application/virtualbox/balloonctrl:default

When everything is configured correctly you can start the Oracle VM VirtualBox watchdog service with the following command:

svcadm enable svc:/application/virtualbox/balloonctrl:default

For more information about SMF, please refer to the Oracle Solaris documentation.