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I would like the know in what cpus % can be considered in save range and also load average? Which indication will give signal something is wrong with the server?

top - 22:55:51 up 3 days,  6:39,  1 user,  load average: 0.53, 0.43, 0.37
Tasks: 229 total,   2 running, 227 sleeping,   0 stopped,   0 zombie
Cpu0  : 16.2%us,  0.7%sy,  0.0%ni, 82.8%id,  0.0%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu1  : 10.5%us,  0.7%sy,  0.0%ni, 88.5%id,  0.0%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu2  :  9.0%us,  0.0%sy,  0.0%ni, 91.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  :  0.3%us,  0.3%sy,  0.0%ni, 99.4%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu4  :  1.0%us,  0.0%sy,  0.0%ni, 99.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu5  : 44.8%us,  2.6%sy,  0.0%ni, 37.0%id,  0.0%wa,  9.4%hi,  6.2%si,  0.0%st
Cpu6  :  3.0%us,  0.0%sy,  0.0%ni, 96.7%id,  0.0%wa,  0.0%hi,  0.4%si,  0.0%st
Cpu7  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  16468596k total,  2423908k used, 14044688k free,   200172k buffers
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Well, that just shows that about everything at your server is idle at the moment. You need to be way more detailed to get any answers. –  Janne Pikkarainen Mar 28 '12 at 15:05
    
I want to know which values will tell me that my server is busy or getting slower. –  user111196 Mar 28 '12 at 15:08
    
That involves more than just looking at cpu utilization, that's for sure. –  adaptr Mar 28 '12 at 15:09
    
@adpatr what does it involve beside cpu is it the i/o? please help me as I would like to master this too to help me in debug the root cause of system becoming slow. –  user111196 Mar 28 '12 at 15:37

3 Answers 3

up vote 1 down vote accepted

Do not focus on individual cpu % numbers so much, but rather take note of the load average. These numbers will give you an idea if your system is 'overloaded'.

The load average's 3 values indicate what percentage of your system has been utilized over the last 1, 5 and 15 minutes. For example, a load average value of 1.0 on a single cpu system, means that is is utilizing 100% of its cpu resources and processes will need to queue and wait for free resources before they can be processed. For systems with more than one cpu, divide the load average number by the number of processors in your system. For example, a value of 8.0 would mean your system is 100% utilized.

The load average: 0.53, 0.43, 0.37 in your example, states that your system has been utilizing 6.6% of its cpu resources over the last one minute, 5.3% over the last 5 minutes, and 4.6% over the last 15 minutes (which is pretty low).

What number freaks you out is relative, but generally you would not want to run at 75%+ sustained utilization if possible. I say this simply because around that number and higher, the temps in your server will rise and your fans will start running at full speed, more load will be put on your power system, and the hotter the room the server is in will be (which can affect the cooling of other systems and AC costs). Also, the life of your system may be shortened as well due to the increase use of the fans and higher temps over long periods.

Keep in mind that your system is capable of going over 100% utilization, and in fact can go quite high if under heavy load. Spikes are not uncommon (backups for example, spikes in internet traffic, system updates, etc), and should generally only concern you if it is affecting your customers, sites or services, or your system is running under heavy load for extended periods as I stated above.

You can quickly use the uptime command to see the load times.

Hope this helps!

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yes this what I was looking for the freaking number. How about memory usage what the freaking numbers I must look out for too? –  user111196 Mar 29 '12 at 5:20
    
I think we're all saying the same thing but just to be crystal clear: The load averages differ from CPU percentage in two significant ways: 1) Load averages measure the trend in CPU utilization not only an instantaneous snapshot, as does percentage, and 2) load averages include all demand for the CPU not only how much was active at the time of measurement. (As per linuxjournal.com/article/9001). –  Mike B Mar 29 '12 at 16:01
    
@mike if you notice the comments by symbcbean he is not quite agreeing that metrics give us the indication on the server performance so what is your say then? –  user111196 Mar 30 '12 at 16:38
    
@user111196 Unfortunately the extent of my knowledge on load averages is already covered in that article. I'd suggest reviewing it and posting more questions if something doesn't make sense. –  Mike B Mar 30 '12 at 17:37
    
@mike so in short can I say that load average is how much task is awaiting to be completed or it be simplified as the amount of work completed. The more load average can I say is more waiting time? –  user111196 Mar 31 '12 at 13:51

What a "safe" range is depends entirely on what this server is used for, and what you are prepared to accept with respect to high load.

There is no ready answer; some companies want their servers to never reach above 50% total utilization, some don't care as long as everything is done on time.

You start with the intended purpose of this box, and work your way across from that.

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I am going to run a web server and also java listner to receive socket connection but the db server is going to be another different server. So what will typical safe range be for this sort of server. –  user111196 Mar 28 '12 at 15:34

I think you've bought the idea that these metrics show how your server is performing - that's not the case, high values will indicate how the performance is constrained which is something very different.

I see nothing in the data you've provided here to suggest that the performance of this server is constrained by CPU, disk I/O nor memory.

If you want to know if the services provided by this box are being adversely affected by performance then measure the time taken to service requests

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@symbcbean you are quite rite I want to know is the server doing its job in optimised time or is getting delayed due to heave traffic or too many connection from many clients. –  user111196 Mar 28 '12 at 15:36
    
@symbcbean any help on this then? –  user111196 Mar 29 '12 at 15:46
    
So you already suspect that specific things (heavy traffic", number of connections) may affect performance - then you need to measure these as well as the speed of the transactions. BTW you've not said what this server is serving. –  symcbean Mar 29 '12 at 22:22
    
The server is going to server both http connection and customised sockect connection on specified ports. –  user111196 Mar 30 '12 at 5:35

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