5

During today's ssh session to my amazon ec2 instance I got the following notice on log in:

System information disabled due to load higher than 1.0

Reading this:

   System load averages is the average number of processes that are either
   in a runnable or uninterruptable state.  A process in a runnable  state
   is  either  using the CPU or waiting to use the CPU. A process in unin‐
   terruptable state is waiting for some I/O access, eg waiting for  disk.
   The  averages  are  taken over the three time intervals.  Load averages
   are not normalized for the number of CPUs in a system, so a load  aver‐
   age  of 1 means a single CPU system is loaded all the time while on a 4
   CPU system it means it was idle 75% of the time.

I understood that this is due to CPU reached 100% (I am using micro instance with ubuntu 13.10 installed). The problem is that looking at my aws monitor, I can see that for the last 20 minutes it has not reached even 20% bar and there was a spike that was close to 75% half an hour ago when I installed a lot of updates.

Can anyone clarify what is the problem?

5

First, CPU percentage != load average. You probably ought to read up on what the difference is.

Now, to your question. If the load average spikes right on login, even for a few seconds, that is enough to push it over 1.00, which will disable Ubuntu's system information display. Short spikes like this frequently get "averaged out" when displayed in long-time duration graphs, so you won't see them. Additionally, the AWS cloudwatch graphs cannot know what your system load average is. Only the kernel in your instance can know that. Cloudwatch can only see how much CPU you're using, which is only one small component that goes into load average.

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