ADPATCH with "options=prereq" - what really happens there?

With adpatch utility we have a possibility to ask for a prerequisite check prior to running patch driver files.
Actually, some patches must apply with prerequisite check before applying them.

The adpatch command should look like: adpatch option=prereq
This flag indicate to adpatch to check prerequisite before applying patch.

adpatch checks the prerequisite based on information from patch files and current snapshot on APPL_TOP.

When running adpatch with "prereq" flag, we might get an error message like:
Analyzing prerequisite patch information...
AutoPatch error: This patch has some prerequisites specified, but a "snapshot" of this APPL-TOP's file-system has never been taken, thereby rendering it impossible to check for the prerequisites.
Please take a "snapshot" of this APPL-TOP using "AD Administration" first.

This error message will show up if a snapshot on current APPL_TOP doesn't exists.

To create such snapshot on APPL_TOP:
1) run adadmin
2) Select "Maintain Applications Files menu"
3) Select "Update current view snapshot"
4) Rerun adpatch

**It might take couple of hours depends on your hardware and APPL_TOP size.


So how adpatch check the prerequisites?

1) Check if a snapshot on current APPL_TOP exist.
using sql script - adbkflsn.sql (if not, will terminate with above error message.....)

2) adpatch uploads a ldt file with FNDLOAD utility into system (bug-fixes).
ldt file name is: b[PATCH_NUMER].ldt - comes from patch root directory.

3) Execute the UMS analysis engine based on the snapshot and bug-fixes to check if all prerequisites exists.