UNIX for Dummies Questions & Answers

When I exeute vmstat (e.g. vmstat 30 2),
in some machines I get some wierd result as the first line.
like: -117% or 208% for CPU idle percentage.
But the second line is alright.
Could someone explain this please.

Thanks !
Chaadana

vmstat obtains some counters from the kernel. Then it waits a second, then it obtains the counters again. At this point, it can tell you what happened over the past second. When it prints that first line, it doesn't have any previous history. So many of the values on the first line are useless. Some versions of vmstat suppress that first line.

thanks for the clarification.

This could be better: (To avoid the first line)

vmstat 5 3|awk '!NR==3'

Maybe, but some of the stuff isn't computed by subtracting the previous values. And now you have to wait 5 seconds to see anything.

Also, the previous history was supposed to initialed to zero. So that first line was supposed to be an "average" since the system was booted. Today's systems are fast so those 32 bit counters wrap around too much for that. And when one counter wraps and another didn't, calculations involving multiple counters get screwy. I still see references to the first line serving as an average since boot, but this doesn't work anymore.