iso image with systemd stage1 fails to boot due to nonexistent /dev/root

[anna328p]

Describe the bug

An iso image built with systemd stage1 (initrd.systemd.enable = true) fails to boot due to nonexistent /dev/root.

/etc/fstab:

overlay /nix/store overlay x-initrd.mount,lowerdir=/nix/.ro-store,upperdir=/nix/.rw-store/store,workdir=/nix/.rw-store/work 0 0

bash-5.2# systemctl status sysroot-iso.mount |cat
× sysroot-iso.mount - /sysroot/iso
     Loaded: loaded (/nix/store/4kazmgs52j4zp0kr3h5y9vdpmv6kc00d-initrd-fstab; generated)
     Active: failed (Result: exit-code) since Sun 2024-07-14 19:16:40 UTC; 1min 7s ago
      Where: /sysroot/iso
       What: /dev/root
       Docs: man:fstab(5)
             man:systemd-fstab-generator(8)
        CPU: 1ms

Jul 14 19:16:40 localhost systemd[1]: Mounting /sysroot/iso...
Jul 14 19:16:40 localhost systemd[1]: sysroot-iso.mount: Mount process exited, code=exited, status=1/FAILURE
Jul 14 19:16:40 localhost mount[172]: mount: /sysroot/iso: no valid filesystem type specified.
Jul 14 19:16:40 localhost systemd[1]: sysroot-iso.mount: Failed with result 'exit-code'.
Jul 14 19:16:40 localhost systemd[1]: Failed to mount /sysroot/iso.

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

• system: "x86_64-linux"
• host os: Linux 6.7.10, NixOS, 24.05 (Uakari), 24.05.20240317.f471be9
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.23.1
• nixpkgs: /nix/store/xb5p9kg3gy00q7c8s638jf15j6qqj473-source

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[nvmd]

Experiencing the same issue but via nix-community/nixos-images#258.

full contents of fstab:

tmpfs / tmpfs x-initrd.mount,mount=0755 0 0
/dev/root /iso auto x-initrd.mount 0 0
/iso/nix-store.squashfs /nix/.ro-store squashfs x-initrd.mount,loop 0 0
tmpfs /nix/.rw-store tmpfs x-initrd.mount,mode=0755 0 0
overlay /nix/store overlay x-initrd.mount,lowerdir=/nix/.ro-store,upperdir=/nix/.rw-store/store,workdir=/nix/.rw-store/work 0 0

[anna328p]

I have no idea why I'd only ended up posting the last line, I swear I copied the whole thing lol

[ElvishJerricco]

#291750, which is blocked by #309190

[nvmd]

Also, almost a duplicate of this issue, with some background information on root= kernel command line option handling #217173