"Opening BaseSystem.dmg" box randomly pops up

Discussion in 'macOS High Sierra (10.13)' started by AlxM, Apr 25, 2018.

  1. AlxM macrumors newbie


    Mar 21, 2018
    North America
    I have a bit of a mystery. Every now and then, as I'm working on my iMac running High Sierra, I occasionally see a box pop up that says "Opening BaseSystem.dmg," then it disappears within a second. I never saw it until installing the latest macOS security update released this week.

    I don't think it's malware. It's a clean system. I don't visit sketchy or nefarious websites, nor do I download things I shouldn't. All my software except for Firefox, Brave Browser, and Capture One are from the official App Store, and the ones listed previously are all from legit developers. MalwareBytes scans come up clean.

    Anyone else run into this? Any ideas or solutions?
  2. splifingate macrumors 6502


    Nov 27, 2013
    Never have seen that (even when I 'intentionally' made-moved on opening BS.dmg) . . . my first thought is that you are getting a QuickLook anomaly (spacebar-activate, etc.).

    Where are you in your System/updates/soft?

    I'm at 10.13.4 (17E202).

    Regards, splifingate
  3. DarkIcarus macrumors member

    Apr 9, 2016
    I have also noticed the pop up box "BaseSystem.dmg" since the security update releasee last week. I am glad someone else has noticed it too. It seems to be happening every time a Time Machine backup is finishing. So if you use Time Machine check next time to see if it happens. It happens for me right at the end of the Time Machine process.
  4. MSastre macrumors 6502


    Aug 18, 2014
    I'm on 10.13.4 and never get that pop up, but also have never ever used Time Machine, so that may be your culprit. I prefer to back up with cloned drives using SuperDuper (Carbon Copy Cloner works well also).
  5. maxxs macrumors newbie

    May 2, 2018
    I also have this "problem" and it also started after the last security update. And also always after finishing a TM backup.

    I would like to note that I did not directly install the update after downloading and waited a few hours, probably done a TM backup in this time frame. I am using a MBP 15" with touchbar. Maybe it is not important but maybe we can find some systematic as it looks like only very few users see this pop up.

    Looks like this happened a few years ago to some people on reddit. However all discussions stoped at some time, maybe it fixed itself with the next update?
  6. trevorbsmith macrumors member

    Dec 17, 2007
    Happening here too. May have happened in the past--not sure. Just did now (prompting my search) and I just installed Mac OS 10.13.5. I also just plugged in my time machine drive after a few days without plugging it in and it is now "cleaning up" (so I assume it was backing up or starting to when I saw the dialog--the delay would have given me time to search, get here, and start posting).
  7. Neradoc, Jun 4, 2018
    Last edited: Jun 4, 2018

    Neradoc macrumors newbie


    Jun 4, 2018
    Hey I had the same thing happen at some point in the past and today, just after updating to 10.13.5, and some research on the web did not really give results. But looking into my Time Machine drives (with the 'find' command line tool) I discovered two "BaseSystem.dmg" files in it, independent of my drives backups.


    Opening them they respectively contain installers for El Capitan and High Sierra (version 10.13.5).

    So my guess is that Time Machine makes a backup of your most recent base system (the High Sierra dmg file weighs 485 MB) and keeps it up to date, which requires "Opening BaseSystem.dmg" whenever there is a system update to backup.

    Seems legit ?

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