service/hardkillonshutdown is a SAP Parameter attribute which is used to control Kill instance processes during start service stop (Windows only) information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
If this parameter is activated, the start service does not stop the
instance processes belonging to its instance in an orderly way using a
SIGINT signal, but rather hard kills them.
The parameter should not be activated in general, but can be useful in
HA configuration.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.