Q:

How to disable on the Clearcase Server for RESERVED CHECKOUT within VOB? 

How to disable on the server side across VOB any form of RESERVED CHECKOUT for any element within CLEARCASE irrespective of CLIENT side SETUP configuration? 

A:

As detailed in the "About reserved and unreserved checkouts" page, you can make a trigger which would immediatly "unreserve" and reserved checkout:
UNIX and Linux:

cleartool mktrtype -element -all -post checkout -exec '/opt/rational/clearcase/bin/cleartool unreserve -nc $CLEARCASE_PN' <Tigger_Name>

Microsoft Windows:

cleartool mktrtype -element -all -post checkout -exec "cleartool unreserve -nc \"%CLEARCASE_PN%\"" <Tigger_Name>

The other approach (in this thread) is a script which tests the environment variable "CLEARCASE_RESERVED".  If this is 1, then it's a reserved checkout and you can exit to prevent the checkout. 

A Perl Script example would be like this. 

if ($ENV{CLEARCASE_RESERVED} == 1)
{
  print "A reserved checkout is not allowed.  Please do an
  unreserved checkout.\n";
  exit 1;
}

