How to set up TimeMachine drive on your NAS (but inefficient, slow).

README.md

• Login to your SMB with Finder, and save the password to Keychain.
• Create timemachine-macbook.sparsebundle under the SMB root directory.
  • You need to choose "Mac OS Extended (Journaled)", not "APFS", even if your MachintoshOS drive is APFS.
  • Because such a buckup cannot be encrypted by TimeMachine, I recommend to set up disk encryption at this timing.
  • If you set password, save the password as accountName = TimeMachineSparseBundlePass in your login keyring.
  • ref. https://blog.fosketts.net/2015/07/22/how-to-use-mac-os-x-sparse-bundle-disk-images/
• Mount it to /Volumes/TimeMachine.
• Run tmutil setdestination /Volumes/TimeMachine as root (with sudo).
• Allow security command to access your keyring to automate mounting TimeMachine drive.
  • security find-generic-password -wa TimeMachineSparseBundlePass
  • security find-internet-password -ws ***SMB HOSTNAME***
  • If you are prompted, always allow security to access these passwords.
• Save the attached mounttm.plist and mkmountpoint.plist to local.
• Rename ***xxx*** points according to your environment.
• Place mkmountpoint.plist at /Library/LaunchDaemons/mkmountpoint.plist.
  • This file creates mount point for SMB under /Volumes.
  • Execution of this command requires root permission.
• Place mounttm.plist at ~/Library/LaunchAgents/mounttm.plist.
  • This file creates mount point for SMB under /Volumes.
  • Execution of this command requires root permission.
• Reboot the machine and check everything works.

mkmountpoint.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>com.tomykaira.mkmountpoint</string>
        <key>ProgramArguments</key>
        <array>
            <string>/bin/sh</string>
            <string>-c</string>
            <string>mkdir -p /Volumes/timemachine-smb && chown ***YOUR MAC USER NAME*** /Volumes/timemachine-smb</string>
        </array>
</dict>
</plist>

mounttm.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>com.tomykaira.mounttm</string>
        <key>ProgramArguments</key>
        <array>
            <string>/bin/sh</string>
            <string>-c</string>
            <string>mount_smbfs "//***Windows UserName***:$(security find-internet-password -ws ***HOSTNAME***)@***HOSTNAME***/***FOLDER NAME***" /Volumes/timemachine-smb && printf '%s\0' "$(security find-generic-password -wa TimeMachineSparseBundlePass)" | hdiutil attach -encryption AES-128 -stdinpass -mountpoint /Volumes/TimeMachine /Volumes/timemachine-smb/timemachine-macbook.sparsebundle</string>
        </array>
</dict>
</plist>