Is RAM cleared after a warm reboot?

By rodion15
Jun 10, 2015
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  1. A warm reboot restarts a computer without loss of power to the motherboard. If it's a forced reboot (not sure this is the right way to call it), that is: a reboot produced by a kernel panic, BSOD or by pressing the reset button, what happens to memory?.

    During a warm reboot (for example the reboot produced by a BSD, kernel panic or pressing the reset button): is the RAM emptied then refilled again?. I say because, since the motherboard isn't powered off in any moment, does the RAM keep data?. I heard that sometimes it's necessary to actually do a cold reboot to clear memory after a warm boot.
  2. jobeard

    jobeard TS Ambassador Posts: 9,160   +599

    BOOT never clears ram - - while hibernate and shutdown can be so configured.
    This is a security exposure if/only if the intruder has physical access to the machine, strips the chips from the box and proceeds to examine the content.

    Consider what you know of the difference between HD Quick Format and a Low Level format.
    • Quick format only writes the free and allocated lists and gives up, assuming the actual sectors are present from the initial Low Level
    • A Low Level fmt, writes every block in the partition with a sector number, rereads it to verify and if bad, places that sector on the bad list.
    Boot does as little memory management as possible - - akin to the hd quick fmt.

    Your concern that leftover information in memory contaminates the boot process implies that memory IS being read without ever being written first - - Not during boot!

    Just to complete this saga, there is a software bug known as Use After Free, where
    1. a program allocates a block of memory for dynamic use,
    2. saves the pointer to it,
    3. uses it for awhile, usuallin in subroutines
    4. and then gives it back but,
    5. forgets to zero the pointer to it, and being non-zero,then attempts to reuse that same block again. Frequently that block is in-use elsewhere.

    Use After Free is nasty to find and the consequences are indeterminable - - corruption of data and/or program failure are typical.

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