"Opening BaseSystem.dmg" box randomly pops up

AlxM

macrumors newbie
Original poster
Mar 21, 2018
25
74
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?
 

splifingate

macrumors 6502
Nov 27, 2013
461
314
ATL
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?
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
 

DarkIcarus

macrumors member
Apr 9, 2016
46
17
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.
 

MSastre

macrumors 6502a
Aug 18, 2014
606
272
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).
 

maxxs

macrumors newbie
May 2, 2018
1
0
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?
 

trevorbsmith

macrumors member
Dec 17, 2007
36
2
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?
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).
 

Neradoc

macrumors newbie
Jun 4, 2018
1
0
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.

Backups.backupdb/.RecoverySets/0/com.apple.recovery.boot/BaseSystem.dmg
Backups.backupdb/.RecoverySets/1/com.apple.recovery.boot/BaseSystem.dmg


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 ?
 
Last edited:

winterquilt

macrumors regular
Feb 18, 2008
166
5
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.

Backups.backupdb/.RecoverySets/0/com.apple.recovery.boot/BaseSystem.dmg
Backups.backupdb/.RecoverySets/1/com.apple.recovery.boot/BaseSystem.dmg


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 ?
I got one yesterday, it happens periodically. This after the latest update for High Sierra users (https://support.apple.com/en-gb/HT201222)
 

MSastre

macrumors 6502a
Aug 18, 2014
606
272
Yes it's a Time Machine thing. I never use it and do not ever get those. I much prefer to have coned drives of my current system as well as a couple OSs back.
 

tanstaafl

macrumors newbie
Jun 9, 2017
7
0
SEATTLE
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.
That exact thing just happened to me, I was not touching my computer at the time, and a time machine backup finished immediately after that message popped up and disappeared. I'm glad I saw your comment, I was worried it was some sort of hack.
 
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