Update 2025-02-07 A few folks in my circle and online pointed me to using nix-collect-garbage -d as a way to clean up my profiles. In my own personal testing, this works BUT I found it was flagging all my profiles. Also when I applied the --delete-older-than flag it was flagging things that were less than the timeframe. For example, I would set it for --delete-older-than 30d but it would have a profile that I created in the past few days. Without digging too deep into things, I have a feeling that the flags are using a different date than my expectation. I was expecting the command to use the date of when I created the profile. I think going forward I will use the nix-collect-garbage command but I think the advice below is great for those who need more control in what gets purged. Again, I am still learning so I might find something better and happy to update.

In my adventures with NixOS, I got carried away in using profiles when I do nixos-rebuild switch for a system upgrade and/or adding new software to the laptop. I love idea of reverting when I screw something up without too much trouble. I had built up a collection about 40 items in my bootloader and realized I could do some pruning since they are there as “oh shit” catchers. However when I began looking around there wasn’t clear advice on how to do this. I discovered a way to do this in case you pulled a me and overused the profile feature.

Standard disclaimer: You are messing with the guts of your NixOS which require root access. While this worked for me, I also keep diligent backups of my data and snapshots of my OS so I could always revert or abandon and start over. The advice might backfire because you failed to backup prior hand. So stop reading, ensure you have backed up and TESTED your restores BEFORE you go any further.

Now that my moral obligation has been met, let’s begin:

1. Backup you data
   • Seriously, I am giving you every chance to avoid calamity here
2. Test that you can recover from your backups
   • My personal favorite method is picking a random document and opening it up
3. If you are using ZFS, take a snapshot of your /nix directory
4. Navigate to your /nix/var/nix/profiles/system-profiles
5. You will notice that the items listed here match what you see in GRUB menu
6. Also there will be two entries:
   • <profile name>
   • <profile name>-1-link
7. Run rm <insert profile name here>
8. Run rm <insert profile name here>-1-link
9. Run nixos-rebuild boot
10. Take a deep breath
11. Restart your computer
12. Upon restart, you will see that the entry is no longer in your GRUB listing

Great, you have a way to clear our profiles and not damage your system! Some things to note:

• Make sure that you don’t blow away a profile you are actively logged into it or a profile that what you system defaults to on bootup
• Do this piecemeal, this is a prime space to footgun your way to victory
• Did I mention backups and doing a test restore from said backups before doing this?
  • Yep, I did. Three times. Cool. The hosts of 2.5 admins would be proud.

Feel free to drop me feedback on mastodon if you found this helpful or see something I didn’t quite get right.