I'm setting up a Synology NAS running DSM 6.1. I only have SMB enabled (up to SMB 3) and enabled Bonjour for Time Machine discovery. I've setup my shares, set quotes, granted appropriate user read/write access and when I configure the workstation to backup to the NAS, I see the backup targets.

However, when the backup starts, I immediate get an error that reads:

The network backup disk could not be accessed because there was a problem with the network username or password. You may need to re-select the backup disk and enter the correct username and password.

I've verified the username and password are correct and have read/write access to the share, so I'm not sure what's wrong.

Workstations are running High Sierra. Others have had this problem too, with no solution.

One thing I've noticed while trying to to connect from multiple Macs is I am never asked for a username or password and end up getting another error that the machine cannot be found (after it shows up via Bonjour). If I first connect via Finder, enter the username and password, then select the Time Machine backup target will I get the error above.

Since posting this question I tried turning off SMB and enabling AFP only on the Synology NAS. In addition I enabled the Bonjour services for AFP. I connected to the NAS from the Mac using Time Machine and and the backups working just fine. Therefore, the problem appears to be SMB related.

Any one know what the issue is?

3 Answers 3


Remove the drive as your backup disk in Time Machine, then open your terminal and run. beware that running this command will remove any other existing time machine destination disks!

sudo tmutil setdestination smb://uruser:urpass@NAS_IPADDRESS/TimeMachineName

If you don't want to remove all the existing destinations, you can pass the -a argument.

sudo tmutil setdestination -a smb://uruser:urpass@NAS_IPADDRESS/TimeMachineName



I use AFP. The Synology article referenced below, which is what I followed, uses AFP. My personal experience is that in general I have less trouble with Apple equipment when I use their own software for connectivity.

  • 1
    Thanks Al. Like I said, AFP works but Apple is getting away from AFP in favor or SMB. My goal is to only use SMB. Commented Jun 2, 2018 at 17:30
  • Update: that article now states: "For macOS Sierra (10.12) and later, Time Machine uses SMB as the default protocol. We recommend you to perform Time Machine backups via SMB."
    – Ian Dundas
    Commented Apr 12, 2022 at 12:22

The cause for me was using a password with symbols.

Try setting the timemachine user's password to alphanumeric characters only.

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