How can a backend admin tell all the ECTR frontend clients to shut down?
In SAP add an entry into the table /DSCSAG/PREF:
NAME = SAP.PLM.FORCE.SHUTDOWN VALUE = TRUE
You can use transaction SE37 FM /DSCSAG/IMPORT_PREF to add this line into the table.
This will popup a dialog to the front-end user and ask him to shut down ECTR.
Important: don't forget to remove the setting or set value to "FALSE" after performing the backend maintaining tasks.