title: Understanding Linux top CPU utilisation output
body: <p>I'm using an single core small ARM processor running under Debian and have problems understanding the CPU utilisation output of top, see:</p>
  
  <pre><code>top - 15:31:54 up 30 days, 23:00,  2 users,  load average: 0.90, 0.89, 0.87
  Tasks:  44 total,   1 running,  43 sleeping,   0 stopped,   0 zombie
  Cpu(s): 65.0%us, 20.3%sy,  0.0%ni, 14.5%id,  0.0%wa,  0.0%hi,  0.3%si,  0.0%st
  Mem:     61540k total,    40056k used,    21484k free,        0k buffers
  Swap:        0k total,        0k used,        0k free,    22260k cached
  
    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                    
  26028 root      20   0  2536 1124  912 R  1.9  1.8   0:00.30 top                                                                                        
  31231 root      19  -1 45260  964  556 S  1.9  1.6   1206:15 owserver                                                                                   
      3 root      15  -5     0    0    0 S  0.3  0.0   0:08.68 ksoftirqd/0                                                                                
    694 root      20   0 28640  840  412 S  0.3  1.4 468:26.74 rsyslogd         
  </code></pre>
  
  <p>The column %CPU is very low over all processes, in this example it is all together 4,4% (all other process below had been on 0%)
  But the allover CPU on line 3 shows 65%us and 20%sy, so for both a very high value - and by the way, this is how the system feels: very slow :-(
  The system is almost always in this condition: very low CPU for all processes, but high user+system CPU.
  Can anybody explain why there is such a high inconsistence within the top tool output?
  And what tool can I use to better find out what causes the high user+system CPU utilization - top seems to be useless here.</p>
  
  <p><strong>update</strong>: meanwhile I've found this thread <a href="https://stackoverflow.com/questions/12319894/cpu-column-and-load-in-top">here</a>, which discusses a similiar question, but I can't verify what is written there:</p>
  
  <ul>
  <li>The command <em>uptime</em> shows the average CPU utilization per 1/5/15 minutes</li>
  <li>This is close to what the first line of <em>top</em> outputs as sum of %us+%sy. But this is changing much more, maybe it is an average per 10s?</li>
  <li>Even if looking longer time on the top output, the sum of %us+%sy is always several times higher than the summary of all %CPU  </li>
  </ul>
  
  <p>Thanks
     Achim</p>