On Oracle Solaris hosts, the 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 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.