Time Machine backup on macOS Sequoia cannot be completed

My Time Machine backs up fine until my iMac goes to sleep. Upon waking, I see the error message that it could not complete the backup. Then it backs up fine. More of an annoyance for me than anything, but something I hope Apple fixes. 24" M1 2021 running MacOS 15.0.1

This continues to be an issue for me and I have opened a support ticket with Apple. It has been escalated to their engineers. I have reinstalled the OS, the new 15.1 didn't resolve the issue, reformatted the drives, uninstalled the antivirus software I was using, and still have the issue. Interestingly, the backups were working again for the first few days of upgrading to 15.1 and then have stopped again.

I get no specific errors other than Backup Not Completed: Time Machine couldn't back up to....

I'll update this thread with any updates.

All of these posts about deleting the default nsmb.conf file are completely irrelevant as backups fail whether backing up to a remote drive over SMB or over a local drive.

The problem is happening because Time Machine is being refused access to certain locked files. The specific files can be viewed by searching the logs for the last 24 hours or so:

log show --info --style compact --predicate '(subsystem == "com.apple.TimeMachine")' --last 24h

Time Machine should have full disk access so this is a bug in MacOS.

Just to follow up. I'm still working with Apple engineers on this. There were a couple weeks of ghosting me but eventually they replied and last week logs were taken and I'm waiting for my rep to get back to me on next steps/conclusions, etc. I also updated the firmware of my Samsung T5 and T7 drives which was a challenge in itself, but did not resolve the issue so hopefully that eliminates them saying it's Samsung's issue. ;-)

More to follow when I hear back.

It’s not the cables.

start a backup running and then lock the screen and leave it to finish. It won’t.

the problem is very simple - Time Machine is denied access to some files while the machine is locked and so cannot complete the backup until the machine is unlocked.

the problem is not hardware related as it happens with external disks -and- network storage.

Yes - the problem is very much related to Time Machine losing permissions to certain files when the machine sleeps. I've worked around this (until it's fixed) by making the following changes to power management:

sudo pmset -b hibernatemode 0

sudo pmset -b standby 0

sudo pmset -b disksleep 1

What this does is prevent the machine from fully hibernating. This will affect battery life a little if it's a laptop you regularly take about the place, but in general terms this is how MacOS -used- to operate.

3) An earlier suggestion was to "forget" the backup drive (a Synology NAS drive) in TimeMachine, reboot, and then reselect the drive. This has not solved the problem. I then took it a step further, I actually deleted the backup and the NAS share partition, rebooted, recreated the share and started a brand new TM set. After successfully completing the initial full backup, the backups failed (while I was under macOS 15.1) during unattended sessions. I then replicated this process when 15.1.1 came out (after trying the two suggestions above), and again after 15.2 came out. In all instances, TM fails to backup when the computer is unattended.

4) Someone suggested it was a firewall problem and to disable the macOS built-in firewall. I have never had the macOS firewall enabled, so that suggestion did not help. Instead, I use the firewall built into my Ubiquiti router. Even though TM worked just find under macOS 14 and macOS 15.0, once 15.1 came out, TM started failing while unattended. Even though nothing changed in my firewall rules, I explicitly created a rule allowing all connections between my 3 Macintosh computers (with known IP and MAC addresses) and my Synology NAS drive (with known IP and MAC address). This did not solve my problem either.

I appreciate all the comments on this thread, even though none that I have tried has solved my particular situation, and apparently not for many other people as well.

So, at this point I am at a loss. It definitely seems like a bug in macOS 15.1 and later. Apple needs to get more serious about identifying and fixing this bug.

Just tagging in to say "same". Only when sleep. When awake again is fine. So would appear to be some state change in something(s) somewhere that blocks some process.

FWIW, this is to a Fantom Thunderbolt drive, not finding specs at the moment, APFS. Info shows as Bootable=No, Journaled=No, SMART=Not Supported,not encrypted,Ejectable=Yes. Looks like I have it hanging off a OWC Thunderbolt Hub USB4.

• I had no success backing up to my Western Digital (MyCloudEX2Ultra) since upgrading to Sequoia. Updated to 15.0.1 with same problems.
• I found an old post that suggested running this command in Terminal: sudo rm -f /etc/nsmb.conf (note: you may need to provide the password used to sign into Sequoia before Terminal will run the command)
• Since doing so, Time Machine has passed the prior errors and appears to be completing a backup on my MyCloudEX2Ultra via wireless network. As of this post, it reports 5 hours remaining (took <45 minutes to back up to a standard USB drive)
• Hope this helps

I have nothing but issues with Time Machine since upgrading to MacOS 15.0 - was hoping it would be resolved under 15.0.1. Removing and re-adding the two APFS drives I have attached sometimes resolves the issues but eventually the error continues.

Time machine occasionally fails to complete its backup operations due to files unavailable error. Interestingly, it completes once I am active on the MBP M1 16" running 15.0.1. Not sure what I can do next to avoid the issue.

Glad it worked for you. Unfortunately, I did the same thing you did but still have the problem. I did remove my NAS drive from Time Machine, delete the partition on the NAS and create a new differently-named one, go into Safe Mode, added the new partition and successfully did a full initial backup. I then rebooted into "normal" mode and successfully did a 2nd backup.

But from that point on, if I am "actively" using my Mac, TM completes successfully. However, if I walk away and my Mac is idle, TM always fails to complete a backup, regardless of any energy, screensaver, "put my disk to sleep" settings.

An update: I have followed with interest the many comments posted. I am glad several people have "fixed" the issue by deleting their TM backups, or deselecting and reselecting their TM destinations, etc. But clearly, many of us are still having issues of TM failing to backup when their computers have gone to sleep/hibernating, but works just fine while the computer and display are active. Many posts suggest this is an actual bug in Sequoia. I concur.

User Zoid85 suggested using a 3rd party app from the App Store called Coca, which I downloaded. When one of its preferences, allow display to sleep is checked, TM fails to backup. But when that preference is unchecked (thus preventing the display to sleep), TM successfully backed up several times over the past 24 hours, thus appearing to confirm the many posts that say that the issue is within Sequoia and permissions issues.

I plan to do some further testing to confirm. 1) I plan to check the Coca setting to allow the display to sleep and see if once again TM starts failing, and then subsequently unchecking it to see if TM backups normally again.

2) I missed a post by Chewbury who listed 3 terminal commands affecting power management. After I complete testing Coca, I will test his commands. Specifically, I will test all three as a group, then test them individually, one-by-one.

sudo pmset -b hibernatemode 0

sudo pmset -b standby 0

sudo pmset -b disksleep 1

I resolved the issue after working with an Apple support person. I have an MBP M1 Pro with MacOS 15.1.1. and I had failures with TM both on NAS and hard wired backups. My workaround, as per the boards, was to to turn off the MacOS Firewall to let the backups work to completion.

However, I also have a cyber security software which includes a firewall of its own. There is a conflict between its firewall and the MacOS one starting with Sequoia 15.x. After I turned off the security software firewall and left the Mac OS one active, all TM backups work without error. The 3rd party cyber security software firewalls need to be updated for Sequoia.

On my M2 Macmini Pro after upgrading to 15.2 I also got the extremely annoying notifications every time I woke the machine. I noticed that after upgrading to 15.2 from 15.1 the firewall seems to now be enabled by default - it was off previously. I added /System/Library/CoreServices/TimeMachine/TMHelperAgent.app to the apps listed in firewall Options… settings and that seems to have resolved the problem.