Thanks...
I put away the Linux versions.
Within Windows 2 lines of source-code is efficiënt to block a second and more startup:
Go with me in TApplication:
var
hMutex : THandle; //run once
// RUN ONCE
// ========
hMutex:=CreateMutex(nil,True,'//programma naam');
if GetLastError=ERROR_ALREADY_EXISTS then Halt(255);
// START PROGRAMMA
// =============
// Next/eigen code//