If I run software update on a Mavericks Mac it will find a caching server automagically if there are any running locally rather than using the CDN Apple hosts on the internet. I'm not so much concerned about security as just knowing when and if the server is running correctly without having any sort of log in to the server itself.

Is there a log file on the client end or another way to determine this conclusively?

  • As far as I know, this is meant to be invisible to the end user... happy to be proven wrong on this. – pknz Aug 28 '14 at 3:52
  • I'm hoping I don't have to use lsof to record open network ports while the update is running, but hopefully someone has some insight on how this works or perhaps a debug setting to get this logged. We will see in time perhaps. – bmike Aug 28 '14 at 13:29
  • Nothing's 'standing out' in the client logs so far; looking at network traffic would be cumbersome though… – grg Aug 29 '14 at 19:08
  • @GeorgeGarside I wonder if debug mode would help? apple.stackexchange.com/questions/17816/… – bmike Aug 29 '14 at 19:15
  • This is exactly what I was in the process of doing! :) Now to find a VM with a pending update to test… – grg Aug 29 '14 at 19:17

The caching server will print to log when a client requests an update. This log is located at:


The following is the anatomy of a request which was served by the caching server's cache:

  • Client requests update package

    Got request for host = http://swcdn.apple.com/{{REQUEST}}
  • Find cached package in server data

    Initializing asset handler for http://swcdn.apple.com/{{REQUEST}} (path = /Library/Server/Caching/Data/{{UDID}})
  • Check/load asset in cache

    Cached asset length = {{LENGTH}} MD5={{CHECKSUM}} last modified {{DATE/TIME}}
    Extents loaded from disk: {{DATA}}
    Data already cached for asset http://swcdn.apple.com/{{REQUEST}}, issuing If-Modified-Since request
    Info loaded: file length = {{DATA}}, reader = {{DATA}}
  • Serve asset to client from cache

    {{BYTES}} bytes served, {{SERVED_BYTES}} from cache, 0 downloaded

    This 0 downloaded is what shows the update was entirely served by the caching server.

  • Finish

    Outgoing connection finished
  • This would be great except for the "without having any sort of log in to the server itself" requirement. – bmike Aug 26 '14 at 22:16
  • @bmike Totally missed that in the question… I'll look into it again tomorrow (UTC) – grg Aug 26 '14 at 22:21
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    It is worth keeping that answer since for many it will be the ideal solution. If you find another, queue up a second answer :) – bmike Aug 26 '14 at 22:22
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    A simple way to allow access without too much fuss and risks would be to activate "Websites" services and add an alias (eg path /Logs/Server/Caching folder /Library/Server/Caching/Logs)... You may also add "Debug.log" as an Index File... – llange Aug 29 '14 at 19:06

I'm not sure on which version this stat became available, but in version 5.0.15 you can see a graph of the data served by the caching service:

Caching service statistic graph

  • Exactly - the server log is much more detailed than the aggregate graph. The reason I'm asking about determining updates on the client end is to correlate and match the activity I see from the server as well as know when an update happened on the client side when I have no access to the server. – bmike Dec 18 '15 at 14:57

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