Nixos-rebuild switch does not update boot entries

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1

Hello!

I discovered some time ago that running sudo nixos-rebuild switch does not update the entries in /boot/loader/entries. When I boot, I always see the same invariant 66 entries last modified on October of 2020.

The symptoms are very much like this:

But my configuration of the boot partition seems to be correct as far as I can tell, and I haven’t changed the configuration of bootloaders or the mount points ever since.

$ mount | grep boot
/dev/nvme0n1p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)

$ grep boot /etc/nixos/configuration.nix
  boot.loader.grub.enable = true;
  boot.loader.grub.device = "/dev/nvme0n1";
  boot.loader.grub.configurationLimit = 100;

The configuration in /etc/nixos/hardware-configuration.nix looks correct as well

  fileSystems."/boot" =
    { device = "/dev/disk/by-uuid/98B0-E4F6";
      fsType = "vfat";
    };

Any advice on debugging this is appreciated.

Thanks!

2

Is your boot partition full? 66 entries sounds like a lot.

Could you post the full output of nixos-rebuild boot?

3

The fact that your /boot is vfat makes me assume that you are on EFI, while at the same time your configuration screams for legacy boot. Which of these is true?

4

The boot partition is not full

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        794M     0  794M   0% /dev
tmpfs           7.8G  211M  7.6G   3% /dev/shm
tmpfs           3.9G   11M  3.9G   1% /run
tmpfs           7.8G  432K  7.8G   1% /run/wrappers
/dev/dm-0       219G  158G   51G  76% /
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/nvme0n1p1  549M  209M  341M  39% /boot
tmpfs           1.6G  244K  1.6G   1% /run/user/1000

I think I’m using efi since /sys/firmware/efi is present

$ ls /sys/firmware/efi
config_table  efivars  esrt  fw_platform_size  fw_vendor  runtime  runtime-map  systab  vars

Happy to do more checks.

Thanks for your thoughts.

5

And here’s the output of nixos-rebuild boot

$ sudo nixos-rebuild boot
building Nix...
building the system configuration...
updating GRUB 2 menu...
6

I discovered today that I can boot into the latest generations if I change the firmware to boot in legacy mode. For some reason, nixos stopped updating efi entries and only updates the legacy configuration. I wonder if there is some way to have both configurations updated.

7

I think that’s probably what @NobbZ meant. You need to set boot.loader.grub.efiSupport for, well, efi support.

Looking at the grub install script, it looks like there’s some support for doing both: https://github.com/NixOS/nixpkgs/blob/4c560cc7ee57e1fb28e6fd7bdacdf01f948f8a91/nixos/modules/system/boot/loader/grub/install-grub.pl#L607. ~~I’m not sure it’s possible to hit that condition though, since grubTarget is what propagates there, and that can only be one or the other: https://github.com/NixOS/nixpkgs/blob/4c560cc7ee57e1fb28e6fd7bdacdf01f948f8a91/pkgs/tools/misc/grub/2.0x.nix#L132~~ nevermind, I think both is the “default” if you set efi support? This script is hard to read without actually testing it.

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8

Not only this, but for grub one needs to also set boot.loader.grub.device = "nodev" or something like that.

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