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TOPIC: who is invoking fsck on otherwise 'idle' computer?

who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 14:25 #11319

Just curious. I run latest Mojave with TechTool Pro 11 and Checkmate and notice fsck_hfs sometimes running on external HDs.
Although some of the Micromat utilities may invoke fsck, it does not appear that Micromat products are involved.

Does MacOS periodically invoke fsck? Although some UNIX configurations may run fsck on reboot, is it common to run periodically or when an external disk is mounted?

Just curious who is doing this.....
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who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 14:40 #11320

I know that fsck_hfs runs after a restart or reboot following an abnormal shutdown. It may also run if a volume is not properly unmounted, and is later remounted.

I think Activity Monitor shows what process launched another process, calling the one doing the launching the "parent" process.

How to use Activity Monitor on your Mac
MicroMat Inc
Makers of TechTool
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who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 18:39 #11321

Thanks.

I find from the fsck_hfs.log that it is being run sporadically frequently only my TimeMachine partition.
Have run Disk Utility "First Aid" on this partition and see that settles it down. In case others are interested, I plan to post if I ever discover why this is happing.

Did notice a quick fsck_hfs run when the "First Aid" mounted the volume, but I cannot find any logs of volumes getting mounted to see if that could explain the frequent runs from fsck on this volume....
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who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 18:54 #11322

I suggest you post a topic about your observations at the Apple Support Forums. Someone may have already explored the issue.

I would not be surprised if the operating system periodically checked the Time Machine volume with fsck_hfs or fsck_apfs. If you have forty backups in your Time Machine volume, the disk directory is roughly forty times as complex as the one on a typical source volume. Time Machine has a reputation for eventually getting directory corruption. In my experience, this is less likely to happen if backups are made manually rather than automatically.

Time Machine should not be your only type of backup, as this impolitely-titled but still useful article makes clear:

11 Stupid Backup Strategies
MicroMat Inc
Makers of TechTool
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who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 19:43 #11323

I have posted requested query to the Apple support MacOS Mojave community.

I have some circumstantial evidence indicating MacOS TM is responsible. This old exchange would indicate that it can invoke fsck_hfs in some fashion back in the Lion days:
superuser.com/questions/153828/why-has-m...hfs-for-two-days-now
but the mentioned ""Skip verification" appears to be gone in Mojave. I use TimeMachineEditor to schedule the backups only twice a day, but apparently the "verification" happens more often.

Although I do not have proof, the explanation is consistent with the calling sequence I found: launchd, diskmanagementd, fsck_hfs and the fact that fsck_hfs was run right after a Time Maching backup was done.

BTW, I also schedule backup 'important' data to a separate HD (not just partition) using Carbon Copy Cloaner.

Thanks again for quick and informative replies....
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who is invoking fsck on otherwise 'idle' computer? 16 Aug 2019 22:08 #11324

You are welcome, and thanks for the clear description of what you have learned to date.

I have a 4 TB external G-Technology rotational drive that I use for my Time Machine backups. I have it excluded from Spotlight, and from the File Structures test in TechTool Pro and Checkmate. I have sometimes wondered, at the conclusion of a backup, why the disk activity light is blinking rapidly, when I am not aware of any reason why the drive should be busy. It may be that fsck_hfs is running, and that may explain why I am sometimes not able to properly unmount the Time Machine volume and turn off the drive. Activity Monitor shows no open files on the Time Machine volume. If the volume Time Machine volume is in use by fsck+hfs, that would explain why it cannot be unmounted without forcing it.
MicroMat Inc
Makers of TechTool
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who is invoking fsck on otherwise 'idle' computer? 17 Aug 2019 03:35 #11325

Perhaps not, if you use the Apple-default TM schedule. The fsck runs in question stopped when I turned off my 'twice-daily' TimeMachineEditor control and enabled the normal hourly backups from the Time Machine Preferences. I am currently doing a test with TimeMachineEditor set to have the backups every two hours. If the fsck runs in question do not re-appear, I'll live with 12 backups a day instead of two.

Unfortunately, none of these 'reverse engineering' tests are definite, what we really need is an answer from someone with knowledge of how these things are scheduled and if infrequent TM backups could trigger an fsck run in an attempt to recover the TM automatically.... (implicit assumption that Apple controls the frequency)
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who is invoking fsck on otherwise 'idle' computer? 17 Aug 2019 11:59 #11326

Thanks for your additional comments.

I stopped using any automatic or scheduled backups on Time Machine after I noticed that it always developed directory corruption after around eight months of use. I make the backups manually now, turning the drive on, doing the backup, unmounting the Time Machine volume, and turning the drive off. This approach works only for people who remember to perform the backups. My oldest Time Machine backup has this time stamp: 2016-08-07-220623.

I also keep a Super Duper clone onsite, and one offsite backup.
MicroMat Inc
Makers of TechTool
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