Here I document my setup of networked Time Machine backups to my linux server over Samba (SMB), which should be faster than AFS (photographylife.com). The data is stored on a USB disk connected to the server formatted with zfs.

Ideally I would be able to backup over network, and unplug the disk from the server to directly restore from it, however the networked Time Machine backup is of different structure than a backup to a directly connected disk, so that’s still on the wishlist.

Setup ¶

• ZFS to protect against bitrot (not sure if this works on encrypted disk images, but let’s try anyway) and because we can
• 2 MacOS clients, one will get 1.2TB quota (MacBook Pro, mbp), the other 0.3TB (MacBook Air, mba).
• 1 Ubuntu 20.04 LTS server

Installation ¶

1. Prepare disk
   1. Install ZFS on Ubuntu (ubuntu.com)
   2. Partition disk (linuxhint.com) – NB ensure you use static labels (archlinux.org) or else your pools might disappear (benjaminrampe.de)! (If they did disappear, you debug sudo zdb, search sudo zpool import and import them again (stackexchange.com): zpool import -d /dev/disk/by-id <pool-name>)

      blkid
      parted /dev/disk/by-id/
      mklabel GPT
      q
      

   3. Create pool sudo zpool create pool0 /dev/disk/by-id/
   4. Create datasets (arstechnica.com)

      sudo zfs create pool0/timemachinembp
      sudo zfs set quota=1200G pool0/timemachinembp
      sudo zfs create pool0/timemachinemba
      sudo zfs set quota=300G pool0/timemachinemba
      zfs list
      

   5. Automatic spin-down of USB disk (openmediavault.org) (old hd-idle (sourceforge.net), new hd-idle (github.com)), run at reboot from crontab, tell logrotate we want the log files to rotate.

      sudo hd-idle -t disk/by-id/wwn-0x3e41415851524c4a # optionally test once
      

      1. Either run via system service

         cat << EOF | sudo tee --append /etc/default/hd-idle
         # TvW 20210313 Setting up hd-idle for USB disk
         HD_IDLE_OPTS="-i 0 -a disk/by-id/wwn-0x3e41415851524c4a -i 3600 -l /var/log/hd-idle.log"
         START_HD_IDLE=true
         EOF
         sudo service hd-idle start
         grep hd-idle /var/log/syslog
         

      2. Or run via crontab

         (sudo crontab -l 2>/dev/null; echo "@reboot hd-idle -a disk/by-id/wwn-0x3e41415851524c4a -i 3600 -l /var/log/hd-idle.log";) | sudo crontab -
         

      3. In both cases, set-up logrotate for hd-idle:

         cat << EOF | sudo tee /etc/logrotate.d/hd-idle
         /var/log/hd-idle.log {
           missingok
           notifempty
           compress
           delaycompress
         }
         EOF
         

2. Create backup users
   1. No new homedir, point to datasets instead. Don’t allow shell login. No password needed on system level.

      sudo useradd --no-create-home --home-dir /pool0/timemachinembp --shell /usr/sbin/nologin backupmbp
      sudo useradd --no-create-home --home-dir /pool0/timemachinemba --shell /usr/sbin/nologin backupmba
      

   2. Set zfs dataset permissions & umask

      sudo chown backupmbp:backupmbp /pool0/timemachinembp
      sudo chown backupmba:backupmba /pool0/timemachinemba
      sudo chmod o-rx /pool0/timemachine{mbp,mba}
      

3. Set-up file server using Samba v3 (photographylife.com)
   1. Install Samba >4.8.0 (kirb.me) for file serving and avahi-daemon for discovery sudo apt install samba avahi-daemon
   2. Allow users

      openssl rand -base64 20
      sudo smbpasswd -a backupmbp
      sudo smbpasswd -e backupmbp
      openssl rand -base64 20
      sudo smbpasswd -a backupmba
      sudo smbpasswd -e backupmba
      

   3. Configure Samba in /etc/samba/smb.conf:

      [timemachinembp]
          comment = Time Machine MBP
          path = /pool0/timemachinembp
          valid users = backupmbp
          browseable = yes
          writeable = yes
          create mask = 0600
          directory mask = 0700
          spotlight = yes
          vfs objects = catia fruit streams_xattr
          fruit:aapl = yes
          fruit:time machine = yes
      [timemachinemba]
          comment = Time Machine MBA
          path = /pool0/timemachinemba
          valid users = backupmba
          browseable = yes
          writeable = yes
          create mask = 0600
          directory mask = 0700
          spotlight = yes
          vfs objects = catia fruit streams_xattr
          fruit:aapl = yes
          fruit:time machine = yes
      

   4. Disable printing (serverfault.com) (because we don’t serve printers)

      load printers = no
      printing = bsd
      printcap name = /dev/null
      disable spoolss = yes
      

   5. Restart Samba and check if all OK

      sudo systemctl restart smbd
      tail -n 50 /var/log/samba/log.smbd
      

      should show

      daemon_ready: daemon 'smbd' finished starting up and ready to serve connections
      

   6. Check if stuff is working with sudo smbstatus, check users known to samba with sudo pdbedit -L -v (from stack (askubuntu.com))
4. Debugging zfs in case something goes wrong, I still don’t really get how zfs works :p. Also see here (askubuntu.com).

   zpool status
   sudo zpool import -c /etc/zfs/zpool.cache
   sudo zpool import <id>
   sudo zpool import pool0
   sudo zpool status
   sudo zfs umount pool0
   

   1. See also https://superuser.com/questions/685882/zpool-pool-i-o-is-currently-suspended (superuser.com)

Configuration on Mac ¶

Based on this (kirb.me) this (macworld.com) and this (lifehacker.com) guides.

1. Create sparse encrypted disk image using Disk Utility on network (Samba) share, naming as NAME_MACADDRESS.sparsebundle (NAME from scutil --get ComputerName and MACADDRESS from ifconfig en0 | grep ether sans colons), with fixed size to constrain Time Machine disk use.
2. Mount said disk image, store password in Keychain to allow MacOS Time Machine to mount/unmount by itself (maybe this is not necessary)
3. Tell Time Machine to use the network volume: sudo tmutil setdestination -a /Volumes/{network-drive}
4. Enter network share credentials & disk image password

If you accidentally delete the Time Machine destination ¶

1. Tell Time Machine to use the network volume again: sudo tmutil setdestination -a /Volumes/{network-drive}
2. Tell Time Machine to use the existing backup.