How to make any file in a TemplateBasedVM persistent using bind-dirs

What is bind-dirs.sh?

With bind-dirs.sh you can make arbitrary files or folders persistent in TemplateBasedVMs.

What is it useful for?

For example, it is useful for Whonix, sys-whonix, where Tor's data dir /var/lib/tor has been made persistent in the TemplateBased ProxyVM sys-whonix. So sys-whonix does not require to be a StandaloneVM. And therefore can benefit from the Tor anonymity feature 'persistent Tor entry guards' without the overhead of a StandaloneVM.

Minimum Qubes Version

bind-dirs.sh works with Qubes R3.2 and above.

How to use bind-dirs.sh?

Make sure folder /rw/config/qubes-bind-dirs.d exists.
```
sudo mkdir -p /rw/config/qubes-bind-dirs.d
```
Create a file /rw/config/qubes-bind-dirs.d/50_user.conf with root rights inside a VM.
Append a folder or file to the binds variable. In the following example we are using folder /var/lib/tor. You can replace that folder with a folder or file of your choice.
```
binds+=( '/var/lib/tor' )
```
Save.
Reboot the VM.
Done.

Other Configuration Folders

/usr/lib/qubes-bind-dirs.d (lowest priority, for packages)
/etc/qubes-bind-dirs.d (intermediate priority, for template wide configuration)
/rw/config/qubes-bind-dirs.d (highest priority, for per VM configuration)

Limitations

Files that exist in the TemplateVM root image cannot be made deleted in the TemplateBasedVMs root image using bind-dirs.sh.
Does not work if the file / folder in question does not already exist in the root image. I.e. a file that does not exist in the root image cannot be bind mounted in the TemplateBasedVM.
Re-running sudo /usr/lib/qubes/bind-dirs.sh without previous sudo /usr/lib/qubes/bind-dirs.sh umount does not work.
Running 'sudo /usr/lib/qubes/bind-dirs.sh umount' after boot (before shutdown) is probably not sane and nothing can be done about that.

How to remove binds from bind-dirs.sh?

binds is actually just a bash variable (an array) and the bind-dirs.sh configuration folders are sourced as bash snippets in lexical order. Therefore if you wanted to remove an existing entry from the binds array, you could do that by using a lexically higher configuration file. For example, if you wanted to make /var/lib/tor non-persistant in sys-whonix without manually editing /usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf, you could use the following.

/rw/config/qubes-bind-dirs.d/50_user.conf

binds=( "${binds[@]/'/var/lib/tor'}" )

(Editing /usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf directly is recommended against, since such changes get lost when that file is changed in the package on upgrades.)

Discussion

TemplateBasedVMs: make selected files and folders located in the root image persistent- review bind-dirs.sh

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