Author: Roo

Using a OSX recovery key on a Macbook M1

Passwords are annoying, but also a critical part of your security posture. Strong passwords are important, and many organizations have policies which require you to regularly change those passwords. This will eventually lead to you changing your password – and then forgetting it – locking you out of your machine.

The Apple Macbook Pro M1 has some great hardware security, this is good to keep the bad guys out, but it’ll also keep you out if you’ve forgotten your password.

Use pass phrases. Long passwords are better passwords. Use a password manager – like 1Password or Bitwarden. When you change a key password – make sure to put aside time to practice entering that password. I find if I can spend a few hours the afternoon after I change a password – I can lock it into my muscle memory. I tend to keep it written down for those first few hours, but then make sure to securely delete/dispose of that record of the password once it’s baked into my brain/fingers.

For the first time in many years, I blew it. Thankfully my work provides a way with the serial number of the device to get a recovery key if I reach out to our IT support folks. If you don’t have this safety net – make sure you take the time to create a recovery key and then store it somewhere very safe and secure.

The key will look something like this:

RECOVERY KEY: GE62-3HW1-Y7ER-QZCT-2JJ1-6SNK

Of course, in the heat of the moment you’ll be trying to surf the web on your phone to figure out how to do these steps – and there are lots of options. Let me lay out the very simple steps you need to do to recover using this key on an M1.
  1. Boot into recovery. From a powered off state, press and hold the power button until you boot into recovery mode.
  2. Connect to a network.
  3. Open a terminal from the Utilities menu.
  4. Run the resetpassword command – follow the prompts which is where you will use that recovery key.
That’s it. Easy, but make sure you have the recovery key available to you – future you will be thankful.

PSA: DNS servers have no priority order

It is a common misconception that DNS servers that your system uses are managed in a priority order. I had this misunderstanding for years, and I’ve seen many others with the same.

The problem comes from the router or OS setup where you can list a “Primary” and “Secondary” DNS server. This certainly gives you the impression that you have one that is ‘mostly used’ and a ‘backup one’ that is used if the first one is broken, or too slow. This is false, but confusingly also sometimes true.

Consider this stack exchange question/answer. Or this serverfault question.  If you go searching there are many more questions on this topic.

Neither DNS resolver lists nor NS record sets are intrinsically ordered, so there is no “primary”. Clients are free to query whichever one they want in whichever order they want. For resolvers specifically, clients might default to using the servers in the same order as they were given to the client, but, as you’ve discovered, they also might not.

Let me also assure you from my personal experience, there is no guarantee of order. Some systems will always try the “Primary” first, then fall back to the “Secondary”. Others will round-robin queries. Some will detect a single failure and re-order the two servers for all future queries. Some devices (Amazon Fire Tablets) will magically use a hard coded DNS server if the configured ones are not working.

Things get even more confusing to understand because there is the behaviour of the individual clients (like your laptop or phone), and then the layers of DNS servers between you and the authoritative server. DNS is a core part of how the internet works, and there is lots of information on the different parts of DNS out there.

The naming “Primary” and “Secondary” come from the server side of DNS. When you are hosting a system and configure the domain name to IP mapping, you set up your DNS records in the “Primary” system. The “Secondary” system is usually an automated replica of that “Primary”. This really has nothing to do with what the client devices are going to do with those addresses.

Another pit-fall people run into when they think there is an ordering, is when they setup a pi-hole for ad-blocking. They will use their new pi-hole installation as the “Primary” and then use a popular public DNS server (like 8.8.8.8) as the “Secondary”.  This configuration sort of works – at least some of the time, your client machine will hit your pi-hole and ad-blocking will work. Then, unpredictably it will not block an ad – because the client has used the “Secondary”.

Advice: Assume all DNS servers are the same and will return the same answer. There is no ordering.

I personally run two pi-hole installations. My “Primary” handles about 80% of the traffic, and the “Secondary” about 20%. This isn’t because 20% of the time my “Primary” is unavailable or too slow, but simply that about 20% of the client requests are deciding to use the “Secondary” for whatever reason (and that a large amount of my traffic comes from my Ubuntu server machine). Looking deeper at the two pi-hole dashboards, the mix of clients looks about the same, but the “Secondary” has fewer clients – it does seem fairly random.

If your ISP hands out IPv6 addresses, you may find that things get even more interesting as you’ll also have clients assigned an IPv6 DNS address, this adds yet another interface to the client device and another potential DNS server (or two) that may be used for name lookups.

Remember, it’s always DNS.

Replacing a ZFS degraded device

It was no surprise that a new RAIDZ array built out of decade old drives was going to have problems, I didn’t expect the problems to happen quite so quickly, but I was not surprised. This drive had 4534 days of power on time, basically 12.5 years. It was also manufactured in Oct 2009, making it 14.5 years old.

I had started to backup some data to this new ZFS volume, and upon one of the first scrub operations ZFS flagged this drive as having problems.

The degraded device, maps to /dev/sdg – I determined this by looking a the /dev/disk/by-id/wwn-0x50014ee2ae38ab42 link.

On one of my other systems I’m using snapraid.it, which I quite like. It has a SMART check that does a calculation to indicate how likely the drive is to fail. I’ve often wondered how accurate this calculation is.

The nice thing is you don’t need to be using snapraid to get the SMART check data out, it’s a read only activity based on the devices. In this case it has decided the failing drive has 100% chance of failure, so that seems to check out.

Well, as it happens I had a spare 1TB drive on my desk so it was a matter of swapping some hardware. I found a very useful blog post covering how to do it, and will replicate some of the content here.

As I mentioned above, you first need to figure out which device it is, in this case it is /dev/sdg. I also want to figure out the serial number.

Good, so we know the serial number (and the brand of drive), but when you’ve got 4 identical drives, which of the 4 is the right serial number? Of course, I ended up pulling all 4 drives before I found the matching serial number. The blog post gave some very good advice.

Before I configure an array, I like to make sure all drive bays are labelled with the corresponding drive’s serial number, that makes this process much easier!

Every install I make will now follow this advice, at least for ones with many drives. My system now looks like this thanks to my label maker

I’m certain future me will be thankful.

Because the ZFS array had marked this disk as being in a FALTED state, we do not need to mark it ‘offline’ or anything else before pulling the drive. If we were swapping an ‘online’ disk we may need to do more before pulling the drive.

Now that we’ve done the physical swap, we need to get the new disk added to the pool.

The first, very scary thing we need to do is copy the partition from an existing drive in the vdev. The new disk is the TARGET, and an existing disk is SOURCE.

Once the partition is copied over, we want to randomize the GUIDs as I believe ZFS relies on unique GUIDs for devices.

This is where my steps deviate from the referenced blog post, but the changes make complete sense. When I created this ZFS RAIDZ array I used the short sdg name for the device. However, as you can see after a reboot the zpool command is showing me the /dev/disk/by-id/ name.

This worked fine. I actually had a few miss-steps trying to do this, and zpool gave me very friendly and helpful error messages. More reason to like ZFS as a filesystem.

Cool, we can see that ZFS is repairing things with the newly added drive. Interestingly it is shown as sdg currently.

This machine is pretty loud (it has a lot of old fans), so I was pretty wild and powered it down while the ZFS was trying to resilver things. When I rebooted it after relocating it to where it normally lives and the noise won’t bug me, it seems that the device naming has sorted itself out.

The snapraid SMART report now looks a lot better too

It took about 9 hours to finish the resilvering, but then things were happy.

Some folks think that you should not use RAIDZ, but create a pool with a collection of vdevs which are mirrors.

About 2 weeks later, I had a second disk go bad on me. Again, no surprise since these are very old devices. Here is a graph of the errors.

The zfs scrub ran on April 21st, and you can see the spike in errors – but clearly this drive was failing slowly all along as I was using it in this new build. This second failing drive was /dev/sdf – which if you look back at the snapraid SMART report, was at 97% failure percentage. It is worth noting that while ZFS and the snapraid SMART have both decided these drives are bad, I was able to put both drives into a USB enclosure and access them still – I certainly don’t trust these old drives to store data on them, but ZFS stopped using the device before it became unusable.

I managed to grab a used 1TB drive for $10. It is quite old (from 2012) but only has a 1.5yrs of power on time. Hopefully it’ll last, but at the price it’s hard to argue. Swapping that drive in was a matter of following the same steps. Having the drive bay labelled with the serial numbers was very helpful.

Since then, I’ve picked up another $10 1TB drive, and this one is from 2017 with only 70 days of power on time. Given I’ve still got two decade old drives in this RAIDZ, I suspect I’ll be replacing one of them soon. The going used rate for 1TB drives is between $10 and $20 locally, amazing value if you have a redundant layout.