In a TemplateBasedVM all of the file system comes from the template except /home and /usr/local.
This means that changes in the rest of the filesystem are lost when the TemplateBasedVM is shutdown.
bind-dirs provides a mechanism whereby files usually taken from the template can be persisted across reboots.
For example, in Whonix, [Tor's data dir /var/lib/tor has been made persistent in the TemplateBased ProxyVM sys-whonix](https://github.com/Whonix/qubes-whonix/blob/8438d13d75822e9ea800b9eb6024063f476636ff/usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf#L5).
In this way sys-whonix can benefit from the Tor anonymity feature 'persistent Tor entry guards' but does not have to be a StandaloneVM.
3. Edit the file 50_user.conf to append a folder or file name to the `binds` variable. (In the following example we are using folder `/var/lib/tor`. You can replace that name with a folder or file name of your choice.)
If you added for example folder `/var/lib/tor` to the `binds` variable, from now any files within that folder would persist reboots. If you added for example file `/etc/tor/torrc` to the `binds` variable, from now any modifications to that file would persist reboots.
bind-dirs.sh is called on startup of a TemplateBasedVM, and configuration files in the configuration folders above are parsed to build a bash array.
Files or folders identified in the array are copied to /rw/bind-dirs if they do not already exist there, and are then bind mounted over the original files/folders.
Creation of the file and folders in /rw/bind-dirs should be automatic the first time the TemplateBasedVM is restarted after configuration.
If you want to circumvent this process, you can create the relevant filestructure under /rw/bind-dirs and make any changes at the same time that you perform the configuration, before reboot.
* Many editors create a temporary file and copy it over the original file. If you have bind mounted an individual file this will break the mount.
Any changes you make will not survive a reboot. If you think it likely you will want to edit a file, then either include the parent directory in bind-dirs.rather than the file, or perform the file operation on the file in /rw/bind-dirs.
* Some files are altered when a qube boots - e.g. /etc/hosts. If you try to use bind-dirs on such files you may break your qube in unpredictable ways.
`binds` is actually just a bash variable (an array) and the bind-dirs.sh configuration folders are `source`d 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`](https://github.com/Whonix/qubes-whonix/blob/master/usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf), you could use the following.
(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.)
[TemplateBasedVMs: make selected files and folders located in the root image persistent- review bind-dirs.sh](https://groups.google.com/forum/#!topic/qubes-devel/tcYQ4eV-XX4/discussion)
