jftuga/00_Unison_Configuration.md

## 00_Unison_Configuration.md

      
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              00_Unison_Configuration.md
            
          
    Cross Platform Unison Setup: One Way, Immutable File Mirroring


Server: desktop - a windows PC
Client: macbook
Unison: version 2.53.5

Concept

I need to run KeePassXC on both my Windows desktop and MacBook.  I consider the desktop to be the source of truth.
If I want to update an entry, then I will modify KeePassXC only on my Windows box.  I am restricting myself to this
self-imposed limitation, because I don't trust two-way file synchronization.  The is my own unfounded, unreasonable
mind-set as I don't want to have to deal with file synchronization conflicts. By using the -force option, this effectively changes unison from a synchronizer into a mirroring utility.  Consider this to be immutable mirroring.
Since Windows 10 now has a built in SSH server, I can run ssh-keygen on both systems to configure an authorized_keys
file on both systems to allow for password-less, key-only SSH access to each system.
You probably only need to allow the Macbook to authenticate to the Windows system without a password.

I have not tested this as I use ssh from my Windows system to connect to my Macbook via a key file and therefore need both ways.
In order to allow the macbook to log into the windows desktop without using a password, I appended the contents of the macbook's ~/.ssh/id_rsa.pub file onto the windows desktop file: ~/.ssh/authorized_keys.  Note: On the macbook, this file might also be named: ~/.ssh/id_ed25519.pub.
Once that is done, I can use a MacOS LaunchAgent
to launch my unison shell script at User Login.
This also has the advantage that the script will automatically relaunch if the unison binary crashes and/or stops.
Files on MacBook


~/.ssh/config - defines the Windows server address
~/Library/LaunchAgents/local.john.unison.plist - the LaunchAgent definition file
~/bin/unison_to_desktop.sh - a simple wrapper with all of the necessary unison command line options
~/bin/unison - a sym link to  /opt/homebrew/bin/unison
~/bin/unison-fsmonitor - built from https://github.com/benesch/unison-fsmonitor


This is not included the the unison homebrew formulae.


/tmp/local.unison.out
/tmp/local.unison.err


STDOUT and STDERR streams of the unison binary


Directory Locations


macbook: ${HOME}/unison
windows desktop: $env:USERPROFILE\unison
These locations can be changed by modifying the unison_to_desktop.sh script, which resides on the macbook.

Behavior


Any files residing in the unison folder on the authoritative Windows server can not be modified by the Macbook.
Any files residing in the unison folder on the Windows server are copied to the Macbook.
If you try to add a new file in the Macbook unison folder, it will be immediately deleted.
If you try to modify an existing file in the Macbook unison folder, the changes will not be saved.
On the MacBook, these KeePassXC settings are disabled:


Remember database key files and security dongles


Automatically save after every change


Automatically save when locking database


Automatically save non-data changes when locking database


On the MacBook, these KeePassXC settings are enabled:


Automatically reload the database when modified externally


If KeePassXC is simultaneously opened on both systems and a change is made on the Windows side, this change will immediately get synced to KeePassXC running on the MacBook.


On the macbook, both /tmp/local.unison.out and /tmp/local.unison.err will be deleted upon a system reboot.

Limitations


Using this setup will only allow synchronization to occur while the two systems are on the same LAN.


This could be overcome by editing the ~/.ssh/config file and then allowing external SSH access to the Windows server, but I don't want to do this.


I'm OK with having to wait until both systems are on the same LAN before a file sync can occur.


## config
Host desktop
    HostName 192.168.1.105
    User john
    Port 22
#   Compression yes

## local.john.unison.plist
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>local.john.unison</string>

        <key>Program</key>
        <string>/Users/john/bin/unison_to_desktop.sh</string>

        <key>RunAtLoad</key>
        <true/>

        <key>KeepAlive</key>
        <true/>

        <key>StandardErrorPath</key>
        <string>/tmp/local.unison.err</string>

        <key>StandardOutPath</key>
        <string>/tmp/local.unison.out</string>
    </dict>
</plist>


## unison_to_desktop.sh
#!/bin/zsh
exec ${HOME}/bin/unison -repeat watch -batch -silent -force ssh://desktop/unison ${HOME}/unison ssh://desktop/unison
# you may need to include something like this: -servercmd /Users/jftuga/bin/unison
	Host desktop
	HostName 192.168.1.105
	User john
	Port 22
	# Compression yes
	<?xml version="1.0" encoding="UTF-8"?>
	<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
	<plist version="1.0">
	<dict>
	<key>Label</key>
	<string>local.john.unison</string>

	<key>Program</key>
	<string>/Users/john/bin/unison_to_desktop.sh</string>

	<key>RunAtLoad</key>
	<true/>

	<key>KeepAlive</key>
	<true/>

	<key>StandardErrorPath</key>
	<string>/tmp/local.unison.err</string>

	<key>StandardOutPath</key>
	<string>/tmp/local.unison.out</string>
	</dict>
	</plist>
	#!/bin/zsh
	exec ${HOME}/bin/unison -repeat watch -batch -silent -force ssh://desktop/unison ${HOME}/unison ssh://desktop/unison
	# you may need to include something like this: -servercmd /Users/jftuga/bin/unison