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Old 02-05-2015, 04:19 PM   #1
chass
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Unhappy Silly Memory Question


Hello,

So I'm not sure if this is a real issue, my understanding is that when a system reboots the virtual memory is dumped in the process. Is there some configuration that would keep the memory intact after rebooting? I'm on RedHat 6 enterprise server, and I just need to make sure that virtual memory is cleared upon reboot. I'm not sure where to look to make sure this is happening.

thank you.
 
Old 02-05-2015, 10:02 PM   #2
jefro
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Ram in most systems should clean/clear based on loss of power. They don't always fully do that.

Generally you use a full cold boot to help prevent issues resulting from a reboot.

I assume this is what you mean.
 
Old 02-05-2015, 11:23 PM   #3
veerain
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I you want to loose program memory from physical ram then you should power off the system for atleast 10 seconds.

A simple restart/reboot would not wipe away ram bytes.

You can also run memtest after reboot/restart it would wipe most of the ram.

There are other programs to do same thing. Do web search.
 
Old 02-06-2015, 07:46 AM   #4
jpollard
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On most systems, a linux reboot causes the BIOS to redo the memory check - which will wipe the memory if it is allowed to complete.

I don't have an EFI system to see, but I think it does the same there.

A cold reboot is aimed more at getting strange devices to fully reset than it is about clearing memory. For instance there were some old ethernet devices that would not reset unless they were powered down, and back up. Without that power cycle they had a tendency to have ROM checksum errors reported and not work.

Last edited by jpollard; 02-06-2015 at 07:48 AM.
 
Old 02-06-2015, 11:04 AM   #5
rtmistler
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What you're talking about would not be a reboot, but rather S3-Hibernate where RAM is suspended to disk in a low power state.

Whether or not the BIOS, a bootloader, or kernel initialization ends up clearing memory versus not, it's a horrifically bad idea to attempt to rely on memory content to be anything meaningful after a reboot. One of the main reasons a good OS boots reliably is that they're typically written to never assume that volatile resources are in any form of set state, excepting uninitialized at startup, whether that startup be cold or warm.
 
Old 02-06-2015, 02:34 PM   #6
chass
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Thanks very much for your replies, yes I was referring to a full reboot or power down and then pushing the power button again. I'm following a checklist of to dos that call for this to be verified.

Thanks again.
 
Old 02-06-2015, 10:53 PM   #7
veerain
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Newer kernel have memtest parameter that you can supply to kernel via bootloader. It uses it to check memory befor booting.

memtest=1

where 1 means test memory with one pattern.
 
  


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