Posts By The Tall Dane

Flyer position for entry to bird

Are you aware of where you position yourself (as a flyer) when you enter bird? Do you want to help your base give you a smooth entry? Check out this little tip 🙂

Linux homedir encryption



I recently decided to install Ubuntu Focal Fossa (currently in beta) and test it out. I use my computer(s) a lot – both home and professionally – and I enjoy getting new software installed. It is always exciting to discover new features (and bugs 😖 ) and see what’s been changed.

ZFS features (excerpt)
  • Snapshots and clones. Useful for e.g. docker and system backups.
  • Copy-on-write (making snapshots initially zero-cost).
  • Raid.
  • Encryption.
  • SSD caching.
See more on the ZFS wiki page (features) or this reddit post.

One of the new features in Focal Fossa is improved ZFS support; it is now possible to use it / enable it right from the installation of Ubuntu. Great ✋. I wanted to give it a go (looking forward to features such as built-in raid support and snapshots) but unfortunately it clashed a little bit with my wish to encrypt my home directory.

While this post is about home directory encryption in a setting of ZFS (and its built-in support of encryption), the general approach may also be of interest to you if you run ext4 and/or other disk encryption tools.

But Why?

Why would you want to encrypt your home directory? Do you have something to hide? Why go through the troubles?

Well… there are a couple of reasons why I chose to do it1And I am sure there are more…:

  • I work as a consultant in IT and it is mandatory (for several reasons) for us to encrypt our data on-disk. E.g. Customer NDAs comes readily to mind.
  • While we don’t have private key files for our net banking and government related sites any-more2But have a mobile app for it instead. Perhaps we should pay a bit of attention to security on those devices as well…!, I still have SSH-keys for technical accounts on the net, and for my personal server. And who knows what a skilled hacker could gather of personal information from my web browser cache!?!?
  • If my laptop got stolen, I would also like to know that the thief could not readily browse through my personal data (mails, photos, documents, etc.). I believe it is similar to when burglars breaks in to homes: It is not a nice feeling to know that some random stranger has been rummaged through your personal belongings.
  • Lastly: Why not? I’m a geek and it’s fun 🙂

Overview – What is the challenge?

The main challenge is two fold:

Ubuntu 20.04 did not provide an option to encrypt your home directory when using ZFS

Ubuntu did previously provide this option, but it used eCryptfs which was considered buggy, under-maintained, [and] not fit for main anymore and has thus been removed.

When enabling encryption manually (after installation) the decrypt action is performed before user login

The issue arises because ZFS is configured (on Ubuntu 20.04) to automatically mount all file systems on the system at boot time – including encrypted home directories. GDM has support for asking for passwords, and hence a prompt appears at boot time. This is great for system wide storage, but not so great for user directories.

PAM to the rescue

PAM is a authentication system that allows programs that rely on authentication to be written independent of the underlying authentication scheme. I.e. if GDM need to authenticate me as a user, it (GDM) can be agnostic about whether my password is in a file on the hard drive or is validated against an AD on the network.

PAM is the Pluggable Authentication Module system in *nix world. If you don’t know it, don’t worry. Neither do I. It is a complex system and I have not had the time (or urge) to really dig in to it other than what I needed here:

We can use PAM to get a hold of the user password when logging in, and in turn use the password to unlock our home directory storage.

So… what we are going to do is:

  1. Migrate the home directory from an unencrypted home directory to an encrypted one.
  2. Write a small Bash script to assist us in unlocking our home directory.
  3. Set up PAM to use the Bash script.
  4. Configure properties (used in the unlock script) on our ZFS volume.

Warning – Here Be Monsters

This is the computer-nerdiest post I have written on this site up until now, so if you have not heard of ZFS before, nor are you considering encrypting your home directory, then I am surprised that you got this far in the text 😀

If you continue on this journey with me, then I will assume that you

  • Know your way around your Linux system.
  • Have the basic knowledge of ZFS (at least read the ZFS man page. Or skimmed it. Or… you know… have heard of it).
  • Know your way around Bash scripting.

Here Be Monsters. Messing around your filesystem may lead to data loss. Do back up your data. Proceed at own risk.

Step 1: Migrating the data

It is not possible to encrypt an existing dataset (filesystem) in ZFS once it has been created. Instead one has to make a little (fairly straight-forward) dance to create a new dataset (encrypted right from the beginning) and then move the data.

The command snippets below are examples from my own system; remember that you need to adapt the paths as you go.

  1. Create a temporary admin user.
  2. Log out of your normal user and log in with the temporary admin user.
  3. Move the mount point of your normal user homedir:
    sudo zfs set mountpoint=/home/jvc_nonenc rpool/USERDATA/jvc_tdssc
    Note, here rpool/USERDATA/jvc_tdssc is the existing un-encrypted dataset for my home directory, created by the Ubuntu installation.
  4. Creat a new encrypted home directory:
    sudo zfs create -o encryption=aes-256-gcm -o keyformat=passphrase -o keylocation=prompt rpool/USERDATA/jvc_enc -o mountpoint=/home/jvc
    Important: Use your normal user password for this encryption, otherwise you won’t be able to decrypt the storage automatically when you log in.
  5. Set ownership of new home directory: sudo chown jvc:jvc /home/jvc
  6. Copy data from old home directory to new: sudo -u jvc rsync -ar /home/jvc_noenc/ /home/jvc/
  7. Make a mental note to clean up (remove) the temporary user and old home directory when all is set and done.

I did the dance and rebooted my computer, and got (as expected) this:

So yes, my home directory was encrypted. Great. But as expected, I now have to enter my password twice: Once during boot for unlocking the storage, and then once more for logging in to the system. This is an issue for me in two ways:

  1. I just dislike having to enter my password twice.
  2. If my girlfriend should use my computer, then she would not be able to do so without me entering my password at boot time.

Fair enough… most of the time I don’t shut down my computer but only suspends it (like everyone else)… but still…

Step 2: Writing the unlock-mount script

I will just show the script I use here. Assuming that you know how to read Bash, the content is fairly clear (and comments are provided in the code). The properties canmount and dk.talldanestale.automount:user will be explained in step 4.

Save the script to /sbin/mount-zfs-homedir and remember to set the executable bit:


set -eu

# Password is given to us via stdin, save it in a variable for later
PASS=$(cat -)

# List all zfs volumes, listing the *local* value of the property canmount.
zfs get canmount -s local -H -o name,value | while read line; do
    # Filter on canmount == 'noauto'. Filesystems marked 'noauto' can be mounted,
    # but is not done so automatically during boot.
    canmount=$(echo $line | awk '{print $2}')
    [[ $canmount = 'noauto' ]] || continue

    # Filter on user property dk.talldanestale.automount:user. It should match
    # the user that we are logging in as ($PAM_USER)
    volname=$(echo $line | awk '{print $1}')
    user=$(zfs get dk.talldanestale.automount:user -s local -H -o value $volname)
    [[ $user = $PAM_USER ]] || continue

    # Unlock and mount the volume
    zfs load-key "$volname" <<< "$PASS" || continue
    zfs mount "$volname" || true # ignore erros

Debug tip: You can change set -eu to set -eux to make Bash print out all commands as it is executing the script. In order to see the output, you also need to enable debug output in PAM. See next step.

Note: The use of here-string (the <<< operator) instead of echo "$PASS" | ... prevents your password from being written to the log.

Step 3: Set up PAM to use the Bash script.

The approach is to use the PAM module to pass on the user password to an unlock-script.

The PAM configuration is a set of files residing in /etc/pam.d/. Some files are service specific3i.e. named after the service it is relevant to while others are shared (included) by the other files. On my Ubuntu system there is a file named /etc/pam.d/common-auth that is included from other services that enable users to login4console login, gdm, ssh etc.. This is the place to add the hook:

  1. Edit the file /etc/pam.d/common-auth:
  2. Add the line:
auth optional expose_authtok /sbin/mount-zfs-homedir

This line can be read as:

  1. Set up a hook for user authentication (auth) …
  2. that is allowed to fail (optional) …
  3. to run a command (pam_exec) …
  4. that exposes the password through stdin (expose_authtok).
  5. The command to run is mount-zfs-homedir.

That is it for PAM configuration.

Debug tip: If you need to debug things, then adding debug log=/tmp/file.log will help you. Example:

auth optional expose_authtok debug log=/tmp/file.log /sbin/mount-zfs-homedir

Step 4: Configure properties on our ZFS volume.

The unlock script used two properties, which we will explain and configure here:

Property canmount

The first (substantial) line of the script lists datasets in the zfs pool along with the canmount property. We filter on values noauto. The noauto value indicates to the system that it should not be auto-mounted during boot (which is the trigger for the password prompt at boot).

In other words: We need to mark our home directory not to be auto-mounted at boot:

sudo zfs set canmount=noauto rpool/USERDATA/jvc_enc

Property dk.talldanestale.automount:user

Next, the script is filtering on a custom property dk.talldanestale.automount:user which I use to indicate to which user this dataset (filesystem) belongs. I do not want to attempt to mount my girlfriend’s home directory using my password.

The property is one I created. The ZFS states that user properties must contain a ‘:’, but otherwise is free to choose. I like the concept of prepending (semi) global properties with organization identifier. Hence the dk.talldanestale.

To set the property, execute:

sudo zfs set dk.talldanestale.automount:user=jvc rpool/USERDATA/jvc_enc

That’s it. I hope it helps you on your journey.

Addendum: zsys automatic snapshots

One of the really nice features of ZFS is the snapshot feature. It enables you to, well, take a snapshot on the fly of the filesystem for later use. Later use could be…

  • mounting (read-only) for retrieving lost files.
  • rolling back system after a failed upgrade or install of a driver.
  • a precautionary backup when you are about to perform actions that could potentially result in data loss.

On Ubuntu there is a hook set up in the apt/dpkg configuration that (via zsys) creates a snapshot of the machine just before installing packages. Unfortunately something broke when I created my new home directory and now I would get the error Couldn't find any association for the user dataset ....

Not knowing anything about zsys or how this was set up on Ubuntu I went spelunking and found the property com.ubuntu.zsys:bootfs-datasets that was set on my old home dataset but (of course) not on my new. So… copying this property fixed the issue:

VAL=$(zfs get com.ubuntu.zsys:bootfs-datasets rpool/USERDATA/jvc_tdssc -H -ovalue)
sudo zfs set com.ubuntu.zsys:bootfs-datasets=$VAL rpool/USERDATA/jvc_enc

All done. Hope it helped you as well 🙂

Shelters and hiking trips on Fyn

I was planning a small hiking trip with my girlfriend and a couple of friends when I got a little bit frustrated with the availability of map data for Danish hiking routes and sleeping facilities. Yes! We have great resources, but they all (two I will mention here) have some limitations.

Ud-i-naturen is a great overview of *everything* you could need going out into nature. The trouble is: It is a webpage and as such is not a great user experience on a small touch screen (phone) when you are hiking.

The Shelter App fixes that by being a native app, but it has another problem: It is only showing sleeping facilities and thus you need to correlate the map in the app with either another hiking map app, or a paper map.

What do I want instead?

Well, I have been enjoying Skåneleden for some years while living in Copenhagen. At that time, it was possible to download a KML file with all the tracks and shelters. This, I could import in my Locus Map app and vupti, I would have everything I needed in one view, offline (including map tiles).

Today, Skåneleden has changed strategy a bit. Instead of downloading all of the data, they created an online hiking trip planner – including planning of public transportation out and home. Impressive. You select the tracks you plan to hike, can see distances of each track, filter on difficult level and more. And in the end, you download it as a gpsx file to whatever device you like.

I still prefer the “raw” kml file (or gpsx or ???); anything better than a heavy and clumsy webpage. Yes I know… Smartphones are getting more… powerful (not smart) and internet is more ubiquitous, but still… when hiking, I like the idea of being offline – if nothing else, just to save battery life 😉

Hiking trips on Fyn

So, as I said… I was planning my hiking trip and got frustrated with the situation. I stumbled upon Book-en-shelter where you can get a map of hiking routes on Southern Fyn along with mapping of shelters (across all of Fyn) – but again… no download.

The itchy part for we was… the data is there. You can show/hide tracks and click on shelter locations.

So I took a look at the source and extracted the data into two gpx-files. One for the tracks, and one for the shelters. So… if you like me, like to carry your tracks offline, here is to you:

Note: The data was extracted April 2020. They are not updated here on this site. Please check Book-en-shelter for latest info.

Map © OpenStreetMap

Ps.: If you would like more detailed descriptions of the routes, you can find it on VisitFyn.

Pain Free – non-disclaimer

I was browsing through Pete Egoscue’s book Pain Free before lending it out to a friend. I feel upon his non-disclaimer and it just resonated with me (again) that I had to share it 🙂

As he writes:

Health care starts with personal responsibility. Any disclaimer that suggests otherwise does a great disservice.

Pete Egoscue – Pain Free
Pete Egoscue – Pain Free

As a small bonus, here is his Eight Laws of Physical Health:

Pete Egoscue – Pain Free

Cartwheel into eH2H

This is still very much work-in-progress. One could even say that this is still above my level and she’s doing all the work. But still… I am happy that I got the chance to try this 🙂 🙂 🙂

Also… for inspiration… note the couple in the ropes in the background 🙂

Tight Rope Ballerina

Memories from Budapest in September. This video got a little bit more artistic in the cutting and I decided to leave in a couple of fails. You know… just for fun.

Thank you, as always, Anita for playing with me. Hope to see you again soon. ❤️️

And thank you Geri for helping record this, and to Anna for the creational work 🙂

Flyer: Anita Kajor a.k.a. YogAnita
Base: Jørn Christensen
Creators: Anna Biebl, Anita Kajor, and Jørn Christensen
Track: I Wanne Be Loving You by Sam Garbett.

Shower gratefulness

A friend of mine is living in Rotterdam with her old high school friend. One really feel that they enjoy living together, and then – in the shower – one finds this little note block:

Thoughtful moments in the shower

I liked the idea and the thought process – and before I knew it, I found I had filled a page as well:

I may have missed some things… like sitting in (big) windows enjoying a book or just the view 🙂

Hugs ❤

Sticks ‘n’ Sushi

Can’t believe that it has been more than a year since I got to film my last washing machine (The Morning Routine) but now, again thanks to Anita, here it is… Sticks ‘n’ Sushi. Hope you like it 🙂

Flyer: Anita Kajor a.k.a. YogAnita
Base: Jørn Christensen
Creators: Anna Vainö, Anita Kajor, and Jørn Christensen
Track: Paint the Sky by Jeris featuring MissJudged.


I told her to turn around. She did not listen. Now her butt is on the internet 🐝

Double flag

Those guys in Odense know how to hang out ☺

Flyers are Signe and Norberta. Thank you to Lars and René for spotting 🙂