Kernel zeroes memory?

Question

I am using Debian squeeze and have noticed that memory is always zeroed. Is this new in linux distributions ? Some time ago, I believe I could use puts() and garbage would b

Answer 1

You'll find that memory is zerored on most operating systems that have isolation between processes. The reason is that a process must not be allowed to peek at the memory released by another process, so a memory page must be erased between the time it's freed by some process and the time when it's released by another process. In practice, erased means zeroed, and the memory is usually zeroed at the time it's allocated by the process.

When you call malloc in your toy program, the memory hasn't been used for anything else yet. So it's still fresh from the kernel, full of zeros. If you try in a real program that's already allocated and freed a lot of heap blocks, you'll find that memory that's already been used by your process still contains whatever garbage you (or the memory management system) may have put there.