What are the checks Done When a Tcode is Called in SAP

When a transaction is called, a system program makes various checks to
ensure that the user has the appropriate authorization.

1. Is the transaction code valid? (table TSTC check).


2. Is the transaction locked by the system administrator? (table
   TSTC check).


3. Is the user authorized to call the transaction?



4. The authorization object S_TCODE (call transaction) contains the
   field TCD (transaction code).


5. The user must have an authorization with a value for the selected
   transaction code.


6. Does the transaction code have an authorization object? If so, a
   check is made that the user has authorization for this authorization
   object.

Then there are check at ABAP program level and if these checks
are succesful the the authorization checks are successful. If any one
of the checks fail, the user cannot execute the tcode.