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I have several similarly configured macs, osx/macos 10.12.3, used as Jenkins followers.

In checking out another issue, I noticed Jenkins' report of its hardware status, claims there are 0 bytes of swap space free. From Jenkins forums/bugs I learned that Jenkins is getting that information from the bash top command's summary, and the 0 bytes free is show in the command line, see below, "Swap: 0B + 0B free."

$ top -o cpu -O +rsize -S -l1 -n 1 
Processes: 373 total, 2 running, 371 sleeping, 1313 threads  2017/03/20 09:32:55 Load Avg:
1.72, 1.78, 1.71  CPU usage: 10.29% user, 25.0% sys, 64.70% idle  SharedLibs: 202M resident, 44M data, 52M linkedit. MemRegions: 92722
total, 4174M resident, 149M private, 955M shared. PhysMem: 10G used
(1847M wired), 6186M unused. VM: 1001G vsize, 621M framework vsize,
0(0) swapins, 0(0) swapouts. Swap: 0B + 0B free. Purgeable: 131M
67381(0) pages purged. Networks: packets: 25600359/10G in,
28183278/28G out. Disks: 24966156/317G read, 13958561/455G written.

PID COMMAND  %CPU TIME   ## etc

However in the machine's activity monitor, it claims the opposite, that memory pressure is nil, green, and that there are no swap bytes used at all.

enter image description here

Which is right?

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    This message may have further details for you. They're both saying the same thing: you have no swap space, so even though there's no pressure at the moment, Jenkins still may require swap because of Java requirements.
    – phyrfox
    Commented Mar 20, 2017 at 15:00
  • @phyrfox I wasn't sure if that IOException info applied to Mac OSX since Mavericks 10.9? That's when mac switched to compressing memory and an Ars reviewer said OSX is now very loathe to use swap. Additionally, if it applies, there does not seem to be a way to change it. arstechnica.com/apple/2013/10/os-x-10-9/17/#compressed-memory
    – AnneTheAgile
    Commented Mar 20, 2017 at 15:09
  • I don't know what the "rules" are for that. What sort of erratic behavior are you seeing? I didn't see anything like that in the question.
    – phyrfox
    Commented Mar 20, 2017 at 15:26
  • @phyrfox 1.I rewrote question to clarify on one thing. The erratic part is less important than grokking top. 2.I think I don't understand, I thought potential swap space could be almost the entire HD if needed? 3.From what I've read, I have no way as a user/admin on OSX to increase swap. Am I wrong?
    – AnneTheAgile
    Commented Mar 20, 2017 at 17:25
  • @phyrfox I think I get it now, so you mean that the terminal result showing "Swap: 0B + 0B free" means that zero bytes were requested, so clearly it makes sense there are also zero bytes free. Is that right? I had thought swap space started as a positive number always, but in contrast, here swap starts at zero and can fluctuate. Did I get it right?
    – AnneTheAgile
    Commented Mar 22, 2017 at 0:08

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