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107 lines
5.0 KiB
Markdown
107 lines
5.0 KiB
Markdown
---
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lang: en
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layout: doc
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permalink: /doc/bind-dirs/
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redirect_from:
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- /en/doc/bind-dirs/
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ref: 186
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title: How to Make Any File Persistent (bind-dirs)
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---
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## What are bind-dirs? ##
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With [bind-dirs](https://github.com/QubesOS/qubes-core-agent-linux/blob/master/vm-systemd/bind-dirs.sh)
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any arbitrary files or folders can be made persistent in app qubes.
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## What is it useful for? ##
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In an app qube all of the file system comes from the template except `/home`, `/usr/local`, and `/rw`.
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This means that changes in the rest of the filesystem are lost when the app qube is shutdown.
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bind-dirs provides a mechanism whereby files usually taken from the template can be persisted across reboots.
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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)
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In this way sys-whonix can benefit from the Tor anonymity feature 'persistent Tor entry guards' but does not have to be a standalone.
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## How to use bind-dirs.sh? ##
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In this example, we want to make `/var/lib/tor` persistent.
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Inside the app qube.
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1. Make sure folder `/rw/config/qubes-bind-dirs.d` exists.
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```
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sudo mkdir -p /rw/config/qubes-bind-dirs.d
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```
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2. Create a file `/rw/config/qubes-bind-dirs.d/50_user.conf` with root rights.
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3. Edit the file 50_user.conf to append a folder or file name to the `binds` variable.
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```
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binds+=( '/var/lib/tor' )
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```
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4. Save.
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5. Reboot the app qube.
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6. Done.
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From now on any files within the `/var/lib/tor` folder will persist across reboots.
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You can make make many files or folders persist, simply by making multiple entries in the `50_user.conf` file, each on a separate line.
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For example, if you added the file `/etc/tor/torrc` to the `binds` variable, any modifications to *that* file will persist across reboots.
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```
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binds+=( '/var/lib/tor' )
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binds+=( '/etc/tor/torrc' )
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```
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## Other Configuration Folders ##
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* `/usr/lib/qubes-bind-dirs.d` (lowest priority, for packages)
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* `/etc/qubes-bind-dirs.d` (intermediate priority, for template wide configuration)
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* `/rw/config/qubes-bind-dirs.d` (highest priority, for per VM configuration)
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## How does it work? ##
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bind-dirs.sh is called at startup of an app qube, and configuration files in the above configuration folders are parsed to build a bash array.
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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.
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Creation of the files and folders in `/rw/bind-dirs` should be automatic the first time the app qube is restarted after configuration.
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If you want to circumvent this process, you can create the relevant file structure under `/rw/bind-dirs` and make any changes at the same time that you perform the configuration, before reboot.
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Note that you must create the full folder structure under `/rw/bind-dirs` - e.g you would have to create `/rw/bind-dirs/var/lib/tor`
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## Limitations ##
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* Files that exist in the template root image cannot be deleted in the app qubes root image using bind-dirs.sh.
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* Re-running `sudo /usr/lib/qubes/init/bind-dirs.sh` without a previous `sudo /usr/lib/qubes/init/bind-dirs.sh umount` does not work.
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* Running `sudo /usr/lib/qubes/init/bind-dirs.sh umount` after boot (before shutdown) is probably not sane and nothing can be done about that.
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* 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.
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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`.
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* Some files are altered when a qube boots - e.g. `/etc/hosts`.
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If you try to use bind-dirs on such files you may break your qube in unpredictable ways.
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You can add persistent rules to `/etc/hosts` using [`/rw/config/rc.local`](/doc/config-files)
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## How to remove binds from bind-dirs.sh? ##
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`binds` is actually just a bash variable (an array) and the bind-dirs.sh configuration folders are sourced as bash snippets in lexical order.
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Therefore if you wanted to remove an existing entry from the `binds` array, you could do that by using a lexically higher configuration file.
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For example, if you wanted to make `/var/lib/tor` non-persistent in `sys-whonix` without manually editing `/usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf`, you could use the following in:
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`/rw/config/qubes-bind-dirs.d/50_user.conf`
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~~~
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binds=( "${binds[@]/'/var/lib/tor'}" )
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~~~
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(Editing `/usr/lib/qubes-bind-dirs.d/40_qubes-whonix.conf` directly is strongly discouraged, since such changes get lost when that file is changed in the package on upgrades.)
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## Discussion ##
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[app qubes: 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)
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