what is MD5...
 

when i look at some of the linux versions to download ,i see MD5 ,what does this mean...thanks

MD5 itself is an encryption algorithm, but in your case it's the use of this algorithm to generate a signature for an iso file. basically if you grab "redhat-1.iso" from some site, and it's md5 sum doesn't match the officially decalred one, then it's not the real thing. just a securit measure. you can use the utility "mds5um [isofilehere]" to generate it for your own file and see if it matches.

Thank you for your help....