error: snap_metadata_val object (): invalid extentref_tree_oid (0x0)

I have the same error as you. In my case it turned out to be a dateless time machine local snapshot.

To check for it, open a Terminal and list local time machine snapshot by running the
command "tmutil listlocalsnapshots /"

It will show entries like "com.apple.TimeMachine.YYYY-MM-DD-HHMMSS"

If you see dateless snapshot, delete it use "sudo tmutil deletelocalsnapshots YYYY-MM-DD-HHMMSS"
with the actual date of the dateless entry. You will need to enter your user password.

# tmutil listlocalsnapshots /

com.apple.TimeMachine.2017-10-04-014927 (dataless)

com.apple.TimeMachine.2017-10-04-024750

com.apple.TimeMachine.2017-10-04-024752

com.apple.TimeMachine.2017-10-04-024835

com.apple.TimeMachine.2017-10-04-024852

# sudo tmutil deletelocalsnapshots 2017-10-04-014927

Password:

Deleted local snapshot '2017-10-04-014927'

# tmutil listlocalsnapshots /

com.apple.TimeMachine.2017-10-04-024750

com.apple.TimeMachine.2017-10-04-024752

com.apple.TimeMachine.2017-10-04-024835

com.apple.TimeMachine.2017-10-04-024852

First of all, thanks a lot for trying to help.

I have run the disk utility. Here are the results;

And I tried to thin the localsnapshot too. That seems not working for me as well. Here is the output:

Last login: Sun Apr 1 20:38:57 on console

Buraks-MacBook-Pro:~ Burak$ tmutil listlocalsnapshots /

com.apple.TimeMachine.2018-03-25-021312

Buraks-MacBook-Pro:~ Burak$ tmutil thinlocalsnapshots / 1000000000

Thinned local snapshots:

Buraks-MacBook-Pro:~ Burak$ tmutil thinlocalsnapshots / 1000000000 1

Thinned local snapshots:

Buraks-MacBook-Pro:~ Burak$

I ALMOST formatted my SSD to resolve this error, but I'm glad I saw your answer first! The error is resolved!

Just one quick bit of feedback... you might want to edit your response to replace the word "dateless" with the correct word, "dataless." While it's somewhat insignificant, there might be pepo[le honing in on that one keyword, and if they searched for "dataless," your solution might not show up for them in Google.

Anyhow, thanks again for taking the time to share!

I suggest you run disk utility on the volume first before this.

see Verify a disk using Disk Utility on Mac - Apple Support

If there is huge amount of disk space used for localsnapshots, you can try thinlocalsnapshots verb of the tmutil.

TMUTIL(8) BSD System Manager's Manual TMUTIL(8)

NAME

tmutil -- Time Machine utility

...

thinlocalsnapshots mount_point [purge_amount] [urgency]

Thin local Time Machine snapshots for the specified volume.

When purge_amount and urgency are specified, tmutil will attempt (with urgency level 1-4) to reclaim purge_amount in bytes by thinning snapshots.

If urgency is not specified, the default urgency will be used.

Google thinlocalsnapshots for suggestion.

Hi, all -

I tried a couple of things, but they didn't work:

• I tried adding the prefix com.apple.[etc] to the snapshot name when using sudo tmutil delete, but it didn't help. Same errors.
• On the hunch that maybe the "idle sleep power assertion" error I got had something to do with the fact that my laptop wasn't plugged in at the time, I tried doing the commands again after having attached the power supply and rebooting. No change. Same errors. I just realized that there was a typo in my first post, though. Here's the correct number:

  IOPMAssertionCreateWithName returned -536870199

Any suggestions?

Thanks mate. I was facing this issue, but the strange thing I had found thread where the listlocalsnapshots was with cammel case and found me, that I don’t have any. I used yours, without cammel case and it worked like a charm. Thanks.

Hello everybody.

I was suffering this error and I fixed it deleting the dataless snapshot.

But the next day a new dataless snapshot appeared and with it the first aid error.

Any clue? What can I do to avoid these dataless snapshots?

Best regards.

Thanks! This fixed my problem — I should add that I repeated the command for every snapshot, and freed up several hundred GB of unusable drive space while I was at it. (There were several older snapshots listed in mine)

TLDR: THANK YOU HEAPS DARLING

I had this same problem, preventing me from installing the 10.13.1 OS update (which failed silently whilst looking like it had worked, grrrr).

I rebooted to recovery, applied disk first aid and saw the error in the title of this thread, which is how I found this thread.

Followed the instructions here and lo and behold, removing a dataless local time machine backup solved the problem.

I regularly switch my laptop between GMT and GMT+1. I wonder whether there’s any commonality there? I also back up to two separate time machines in the different time zones, so at any one time I always have one time machine backup failing whilst the other succeeds.

Thanks for your tips. Have the same problem and google led me here.

I followed your steps, but it just doesn't work in my case.

$ tmutil listlocalsnapshots /

com.apple.TimeMachine.2017-11-22-071811 (dataless)

com.apple.TimeMachine.2017-11-24-112803

com.apple.TimeMachine.2017-11-24-125246

$ sudo tmutil deletelocalsnapshots 2017-11-22-071811

Error parsing argument 2017-11-22-071811

Is there any other way to delete these snap shots files?

Any advice?

Thank for your help.

Unfortunately "su -l" gave me su: Sorry.

Google it and use "sudo su" but still get "Error parsing argument 2017-11-22-071811"

In the end I did a clean install from scratch and have the time machine off at the moment.

I am dealing with this error and also cannot delete the dateless snapshot.

root# tmutil listlocalsnapshots /

com.apple.TimeMachine.2017-11-27-194607 (dataless)

com.apple.TimeMachine.2017-12-06-120144

root# tmutil delete com.apple.TimeMachine.2017-11-27-194607

com.apple.TimeMachine.2017-11-27-194607: No such file or directory (error 2)

Total deleted: 0B

Thanks very much for the help. This totally solved the problem I was getting. Just one minor thing: you mentioned "If you see dateless snapshot" and "with the actual date of the dateless entry". I believe these should both say "dataless", not "dateless". Thanks again.

Believe it or not, it is correct in the way it was written.

The item in the backups is marked “(dateless)” even though you have to delete it using the date shown for the “(dateless)” line item.

Perhaps the backup is out “on a date” “without a date”?