As I've mentioned before, the TOTP specification is a stagnant wasteland. But it does have this to say about the secret:

The secret parameter is an arbitrary key value encoded in Base32 according to RFC 3548.

The Base32 alphabet is pretty simple. The upper-case letters A - Z, and the numbers 3 - 7.

But that's only half the problem.

How long should the secret be?

This is an area where the official spec is silent. Around the web, you'll find people saying things like:

The length in bytes of generated shared secrets. The minimum is 20 (or 160 bits), and the default is 32 (or 256 bits). In most use cases 32 is sufficient. Though some authenticators may have issues with more than the minimum. Our minimum is the recommended value in RFC4226, though technically according to the specification 16 bytes (or 128 bits) is the minimum. Authelia

Although that's for the HOTP algorithm, rather than TOTP.

Looking through my 49(!) different TOTP codes, the shared secret ranges from 16 characters to 52 characters. No consistency whatsoever.

The Code

Run this on your command line.

cat /dev/urandom | LC_ALL=C tr -dc 'A-Z3-7' | fold -w 24 | head -n 1

That generates a random-enough⁰ string using the correct alphabet and truncated to a sensible length.

Let's go through each part of it.

cat /dev/urandom spits out random data from your machine. You may wish to use /dev/random if you feel like it.

LC_ALL=C sets the Locale to by ANSI bytes.

tr is "Translate, squeeze, and/or delete characters.".

-dc 'A-Z3-7' is delete the complement (i.e. delete anything which isn't in the following string).

fold -w 24 is wrap the input text with a line length of 24.

head -n 1 displays the first line of the file.

Next Steps

Now... How do I locally generate a QR code without anything else being installed...?

Here's a partial list of everything I cannot do on a Mac, but I can do on Ubuntu.

These are all objective facts. These are things which either are impossible, or require adding unsupported 3rd party software - sometimes at a cost.

• Resize the system font
  • I find the menu bar at the top too small. The only way to do this on MacOS is to lower the resolution of the entire screen!
• Change the system font
  • I know you like Helvetica San Francisco - but I find it a bit too thin to read.
• Focus Follow Mouse
  • I have multiple screens and multiple windows. I want to be able to hover over a new one and start interacting with it without clicking.
• Change my mouse button order
  • On Linux, this is a complex command-line incantation. On MacOS it is impossible. I use a vertical mouse and use my thumb to click. RSI FTW!
• Read files from MTP devices
  • If I stick a USB cable between my phone and Linux laptop, I can see the Android files on my laptop. I can open them, move them around, etc. On a Mac I need to install some shonky 3rd party software which rarely works.
• Always on top windows
  • Sometimes I want to keep the calculator on screen while I type an email. Is that too much to ask?
• No way to remove UI elements.
  • I don't want a notification icon in the top right of my screen. I prefer having the clock on the left. Trivial in Linux, static in MacOS.
• Window snapping
  • On Ubuntu, I drag a window to the side or to a corner, and it snaps into position. Vital when using multiple windows at once. On Mac there's a half-hearted splitscreen view which only supports horizontal splitting. Useless on a vertical monitor.
• See tooltips
  • I can't see them on Mac when I have a larger cursor. Weird!
• Mount an SSH or NFS drive
  • In Ubuntu, I get a nice little GUI for picking network shares. Impossible on Mac.
• Wobbly Windows!
  • Seriously MacOS. Where's the fun?

I know you're going to be tempted to reply with "you're using it wrong" - but I'm not. This is how I like to use my computer. And it is clear that the MacBook isn't my computer - it is Apple's. (OK, OK! It belongs to my employer!)

I like having a large mouse cursor. I find it easier to see on my large monitor, especially when sat at a safe distance. But, if I use a large cursor - I can't see the tool-tips underneath it.

Annoyingly, Apple don't include the larger cursor sizes when taking a screenshot. So you get the joy of me pointing a camera at my screen like some kind of troglodyte sharing memes on your neighbourhood's Facebook group.

Broken Behaviour

What does this tool-tip say?

That's from "Finder" the default Mac file system app.

Expected Behaviour

With the "normal" size icon, I can see what the text says.

Usability pervasiveness

OK, it's impossible to test every combination that a user might choose. But it really feels like bits of MacOS are hostile to accessibility changes.

It is impossible to change the system font size. That top menu is fixed at a tiny size. If you want a more readable font - tough.

Apple knows best.

Tool tip size

You can increase the font size of tool-tips with this obscure command-line incantation:

defaults write -g NSToolTipsFontSize -int 20

Restart the app and you'll get a larger font!

Which is still obscured by the cursor.

Report this bug

Apple have known about this bug for at least 10 years.

Apple knows best.

Based, in part, from this excellent forum post.

I've always run Linux on my Mac Hardware. I love the physical aspects of the Mac line, but I really can't be bothered with their Play-doh infested software.

Let's assume you have a nice, clean, freshly installed OSX 10.10 Yosemite sat on your MacBook Pro. I'll also assume that you may occasionally want to boot into OSX, so we'll be dual booting with Ubuntu 14.04.

Partition

In OSX, open the Disk Utility, select the main disk. We're going to split this in to two parts. Up to you how much you want to dedicate to OSX. Set the 2nd partition to be "Free Space".

rEFInd

Because Apple is a super-special-snowflake, it's not possible to directly install Ubuntu onto the new partition. We need to first install rEFInd. There are specific instructions for Yosemite.

1. Download rEFInd.
2. Extract it onto your Mac.
3. Open a Terminal and navigate to the directory.
4. Run this command

   sudo ./install.sh --esp

5. We need to edit some files. Still in the Terminal

   mkdir /Volumes/esp

   then

   sudo mount -t msdos /dev/disk0s1 /Volumes/esp

6. Edit the file "/Volumes/esp/EFI/refind/refind.conf". Change the line

   #dont_scan_volumes

   to

   dont_scan_volumes foo,bar

7. Save the file. When you reboot, rEFInd should ask you which OS you want to boot to.

Get Ubuntu

Probably the easiest bit! Download the 64 bit version of Ubuntu. I used another Ubuntu machine to create the Boot Disk on a USB stick.

Install Ubuntu

Turn your MacBook off, insert the USB drive, turn the device on. All being well, rEFInd will give you a choice of devices to boot into. You probably want the one which says something like

/USB/EFI/grub64

You should see a grub style boot screen. Use the cursor keys to move down to "Install Ubuntu". Do NOT press enter! Press "e" to edit the boot options.

If you don't do this - your screen will be blank. And a black screen will make you sad.

Remove the words

quiet nosplash

and replace them with

nomodeset

. Then press the "F10" key to boot.

You'll be taken through the normal Ubuntu installation screen. It's pretty much just clicking "Next" until it is installed.

Partitions

...With the exception of setting up the partitions!

• Create a 130MB empty partion. Macs get sad if OSX is bundled up next to a proper OS.
• Create a 512MB partition and assign it to "/boot"
• At the end of the free space, create a "Swap" parition. Personally, I use as much swap as there is RAM.
• With the remaining free space, create a partition and assign it to "/".
• Which device to you want to boot from? I chose the partition assigned to "/boot" - that way you go straight into Ubuntu when you start the machine. If you ever need to get into OSX, hold down "alt" while turning the machine on.

Keep clicking next! Eventually Ubuntu will be installed and you can reboot!

Setting Up Video

When the grub screen comes up, again you'll need to hit "e" to edit the default boot options.

Scroll down to "load_video" and add these lines below it. I don't know what they mean - it's just magic.

 outb 0x728 1
 outb 0x710 2
 outb 0x740 2
 outb 0x750 0

That should boot you into Linux. Now we need to make those changes permanent. Open a terminal and run

sudo nano /etc/grub.d/10_linux

Press CTRL+W to find the line containing "gzio".

Add these lines before it, so the new section looks like

echo "    outb 0x728 1" | sed "s/^/$submenu_indentation/"
echo "    outb 0x710 2" | sed "s/^/$submenu_indentation/"
echo "    outb 0x740 2" | sed "s/^/$submenu_indentation/"
echo "    outb 0x750 0" | sed "s/^/$submenu_indentation/"
echo "    insmod gzio" | sed "s/^/$submenu_indentation/"

To apply these changes, run the following commands.

sudo update-grub
sudo apt-get update
sudo apt-get dist-upgrade

Fans

For better fan performance...

sudo apt-get install lm-sensors
sudo sensors-detect

Answer yes to all questions. Then:

sudo apt-get install macfanctld

Reboot and enjoy Ubuntu! Everything seems to "just work" - although I'll write another blog post explaining how I've customised it.