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Is it mandatory to have the name of the makefile as 'Makefile'
Yes, make will go for "Makefile" or "makefile".
If you want to keep the original Makefile,
you will have rename it temporarily,
while using your own Makefile.
'mv Makefile Makefile.orig'
'mv Makefile.2.6 Makefile'
And rename back after compiling.
( Suggest : keep backup copies of both,
if something goes wrong .. overwriting, etc.)