Memory Overview
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Video Transcription
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>> Hey Cybrarians and welcome back to
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the Linux+ course here at Cybrary.
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I'm your instructor Rob Gills,
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and in today's lesson we're going to be
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talking about memory monitoring.
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Upon completion of this lesson,
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you're going to be able to understand
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the importance of memory monitoring.
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We're going to see where we can locate
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memory information,
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and we're going to explain the purpose of
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the buffer cache and the OOM killer.
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Memory monitoring is at least as
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important as CPU Monitoring.
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Because a well tuned CPU is not
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super-helpful if the system runs out of memory.
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Now we are going to cover
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memory monitoring tools over the next few lessons.
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But before we get into that,
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before going into troubleshooting,
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let's look at where we can find that memory information.
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We're going to do the same thing like we did
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with the CPU in the previous lesson,
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and just like we saw with the CPU,
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the proc directory also holds memory information.
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For our purposes, we're going to be looking in
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the proc mem info file
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to find information about our memory.
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Now just like we saw with proc CPU info,
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the proc mem info file is viewable directly.
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We can just cut it out or do it less,
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and tools that we're going to cover later in this module,
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we'll use this information in the file.
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Now, processes use memory for
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quicker data retrieval over going to the disk,
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and this process is known as disk buffering.
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It can improve disk read performance.
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In this buffering, the data is
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read from the disk and stored in the buffer cache,
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which is actually just memory system memory,
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and then subsequent access to
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that data gets read from
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memory instead of going to the disk.
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That provides a significant performance improvement
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versus going to the disk,
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it's much faster to read from memory.
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Now another thing we should cover when we're
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talking about memory concepts before we
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move forward into memory troubleshooting is
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the concept of memory over commitment.
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Because in Linux,
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memory is allowed to be over committed to processes.
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Not every process is being used and ran at the same time.
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Linux can sometimes give
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a little bit more memory than
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actually exists on the system,
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and that can improve efficiency
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and performance of the system but it can
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also cause the system to run critically law and
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memory because it's standing out
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memory doesn't actually have.
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In this situation, Linux will try and reclaim
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old memory pages that are no longer in use,
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and if it doesn't get the system out of danger,
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Linux uses something called the out of
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memory or OOM killer.
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The OOM killer will scan
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through processes and it's going to create
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a score based on total memory that's
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used by the process and any of its children,
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and it's going to look at the smaller number
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of processes or smallest number of
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processes that can be killed to get
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out of the critically low memory state.
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Now kernel processes or root and
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crucial processes are given an intentionally low score,
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and that is because the higher the score,
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the more likely a process is to be killed off.
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It's going to look at all the other processes that
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aren't kernel root or crucial processes.
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Look for the highest score and then it's
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going to sacrifice that process to try
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and get the system out of
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that critically low memory state
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and get it back operating normally.
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With that, in this lesson,
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we cover the importance of memory monitoring.
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We talked about using the proc amendment
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full file to view memory information,
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and then we talked a little bit about the purpose
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of the buffer cache and OOM Killer.
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Thanks so much for being here and I look
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forward to seeing you in the next lesson.
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