Create timemachine share in TrueNAS

Create timemachine share in TrueNAS

Note: I got issue suddenly after sometimes, and spent hours to fix it. End up, I switched back to Synology NAS as timemachine. Check Update section.

Tried many hours on setting up time machine backup in TrueNAS Scale, encountered many issues. To save time next time, record important steps and parameters for for next setup.

Create dataset

Create a dataset called timemachine under zpool pool1. Set ACL Type of dataset to POSIX.

Create user

Creating new user/group is not a good way if the NAS is also used for other user from same machine at same time. This is because the TrueNAS will use both user to login, which is hard to troubleshoot and confusing. If do not create new user, the ownership/permission of sharing dataset is also hard to decide. To use dedicated user for timemachine, following steps can be used.

Create a new named as user id tm with group tm. It will create a sub-dataset in ZFS under timemachine dataset. Change home directory of tm to the dataset created in Create dataset section.

The Auxiliary Groups have a group named as builtin_users. Beware of this group, it will appear later in this post again.

Note: If the backup folder was copied from other system, change the owner/group to tm:builtin_users, and permission to 775 to avoid permssion issue.

Set permission of dataset

Strip ACL

This is most easy way with lesser headache. Remove ACL if ACL is wong or just use traditional UNIX permission system.


Change owner and group to both tm.

The dataset permission set to POSIX_HOME, this will enable owner and group both have read/write/execute permission, others will be read only.

Create share

In TrueNAS, the actual implementation for time machine done by option in SMB sharing, named Multi-user time machine, so select Multi-user time machine as Purpose, otherwise, Time Machine option will not be set and it is unchangable.

Beware of option Time Machine is selected, and Path Suffix is set to %U, both are unchangable. The %U means, a sub-dataset will be created under shared dataset for each user, they will not share the same view.

The individual host to be backed up will create a folder <hostname>.sparsebundle, which will be shown as disk in MacOS.

File/Folder permission

Remove ACL

If got strange issue on permission, uncheck ACL in SMB sharing, and then restart SMB service.

Note: The error can be verified by using Windows access share drive.

Workable permission

The actual file created in sub-dataset, will be under builtin_users group with permission 770, not tm for unknown reason. Sample output is shown below.

truenas# ls -la /mnt/pool2/timemachine/tm
total 70
drwxrwx---+ 3 tm tm               4 Oct  3 22:32 .
drwxrwxr-x+ 6 tm tm               6 Oct  3 21:23 ..
-rwxrwx---+ 1 tm builtin_users 6148 Oct  3 21:32 .DS_Store
drwxrwx---+ 4 tm builtin_users   10 Oct  3 23:02 shark.sparsebundle


Suddently, timemachine on TrueNAS stopped working, error message shows macOS could not find server.

I tried to manually map SMB drive, but failed too. I could not access the timemachine shared folder, but rest of shared folders are accessible.


During the troubleshooting, found that macOS could not see TrueNAS in Finder, the issue could be related to mDNS missing.

Finial settings

The following settings make timemachine work again.

  • Purpose: Multi-user time machine
  • Enable ACL
  • Browsable to Network Clients
  • Time Machine (Can not change)
  • Legacy AFP compatibility
  • Enable Shadow Copies
  • Enable Alternate Data Streams
  • Enable SMB2/3 Durable Handles

But the the shared folder still requires to be opened before macOS Time Machine can see it. So, mDNS issue is still there.

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