Save defaults before any changes

attrLog = Log // Attributes;

ClearAttributes[Log, Listable]

Log // Attributes



  {NumericFunction, Protected}


Restore defaults

Attributes[Log] = attrLog



  {Listable, NumericFunction, Protected}


How to restore function attributes to default
i want to generate 4 unique digit each time from 1 to 12. For example: [1,3,4,6] or [1,3,10,6] or [1,2,3,4]... but not like [1,2,8,1] or [2,2,4,5]
because in last two chunk 1 comes twice and so as 2 in second chunk. Again i need to generate those unique chunk of numbers randomly.

Any help will be appreciated. Big thanks in advance...:) 
