First Aid on macOS Base system reports:

"Volume could not be unmounted.
Using live mode.
Performing fsck_apfs -n -l -x/dev/rdisk4s1" 
Then after checking the container superblock, EFI jumpstart record, space manager, free queue trees, object map, volume, APFS volume superblock reports 4 warnings:

"warning: apfs superblock  at index 0:apfs_unmount_time (1673423888397739670) is greater than current time (1672554063021003000)

warning apfs superblock at index 0:apfs_last_mod_time (167342388839264383) is greater than current time(1672554063021003000)

warning:apfs superblock at index 0:apfs_formatted_by.timestamp (1673423844666815818) is greater than current time

warning:apfs superblock at index 0:apfs_modified_by[0]. timestamp (1673423888397737482) is greater than current time (1672554063021003000)"

Then checks object map, snapshot metadata tree, metadata, extent ref tree, fsroot tree,verifies allocated space and reports volume/dev/rdisk4s1 appears ok, system check code is 0, restores original state as mounted and "Operation successful"

Any help on how to resolve and eliminate the warnings which is allowing recurrence of problems after booting with a fresh installer and replacing the Nvme SSD.

Thank you.

  • 2
    What model of Mac is this? The presence of 'Base System" suggests you're booting to Recovery. Is that right? Are then you're running First Aid on the Recovery volume? What problems after booting are recurring?
    – benwiggy
    Commented Feb 19 at 17:15
  • MacBook Pro running Big Sur. I am booting in recovery mode using an installer and having initialised the SSD and formatted as APFS and GUID partition shows the new SSD, installer and Apple disk image media, container disk4 and macOS Base System. The first aid was to the recovery volume and showed the warnings stated. After an apparently successful recovery files are changed and added and access to the wireless card sought and got. The system reports showed time changes when the MacBook was powered off which concealed changes and new files. Commented Feb 19 at 18:11
  • So is all working now? I wouldn't worry about problems with the Recovery volume itself, if it's up and running. Presumably this is a pre-2018 MBP....?
    – benwiggy
    Commented Feb 19 at 18:16
  • It is a pre-2018 MBP the recovery volume is the only remaining common link with 2 previous SSDs from which a string of issues arose and the o/s starts to slow, inexplicable files appear and eventually freezes and crashes. Commented Feb 19 at 18:21
  • Wireshark was set up to monitor traffic and was disabled repeatedly after being reinstalled repeatedly and initially functioning perfectly. Etrecheck was also used and disabled Commented Feb 19 at 18:23

1 Answer 1


When booted into recovery, with a clean SSD and using a bootable installer on a flashdrive, the boot process was not solely by the bootable installer. An additional volume had been created next to the base system, the 2 volumes entitled "MACOS Base System". The extra volume included a preboot and could not be deleted, even in single user mode for a string of reasons.

Repeated reinstallation of macOS did not cure issues with installer files always reappearing and masquerading as base system files. This was caused by remote access a third party clearly had. The installation log reported that the recovery drive was not a Disk Image, as the label stated, and files within it were obviously not base system type files. The SSD was being required to be unlocked too early than should be the case.

This was solved by connecting a SSD from another Macbook via a USB port, with the bootable installer in another USB and upon a recovery boot, the base system from the attached SSD was utilised without any operator input and disk utility showed the base system as "OS X base system", the correct label and content. It was a genuine disk image.

The bootable installer provided the rest of the macOS and a clean installation of macOS achieved. I believe the booting issue was an issue identified in 2011 by Jorge Jenderek and is the subject of a number of articles by others since and affects Unix and other systems - thank you Jorge.

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