Enabling Maintenance Mode in 11i

Enabling the Maintenance Mode through the script

$AD_TOP/patch/115/sql/adsetmmd.sql sending the parameter 'ENABLE' or 'DISABLE' :

When adsetmmd.sql runs, it sets the Profile Option 'Applications Maintenance Mode' (APPS_MAINTENANCE_MODE) to 'MAINT' to Enable 'Maintenance Mode' and to 'NORMAL' to Disable it.
Query to find the status of the maintenance mode

select fnd_profile.value('APPS_MAINTENANCE_MODE') from dual;

sqlplus <APPS_Schema name>/<APPS Password>@adsetmmd.sql ENABLE | DISABLE

    ENABLE  -   Enable Maintenance Mode .
    DISABLE -   Disable Maintenance Mode.

Otherwise you can run the ADADMIN for enabling the maintenace mode which inturn calls the same script.