rdisp/shutdown/disable_login is a SAP Parameter attribute which is used to control Disable login during shutdown 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 .
You can use this parameter to prevent logons during shutdown. This is
valid irrespective of user roles or authorizations.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.