[Bug 2150675] Re: /etc/default/grub found empty (0 bytes) after unattended upgrade on Ubuntu 26.04 while updating to kernel 7.0.0-15

[Julian Andres Klode]

Probably update-grub would need to restore that; but also sed may want
to fsyncdata() the temporary file before renaming it (and sync the
directory after) to be safe.

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Title:
  /etc/default/grub found empty (0 bytes) after unattended upgrade on
  Ubuntu 26.04 while updating to kernel 7.0.0-15

Status in grub2 package in Ubuntu:
  New

Bug description:
  System Context:
  I have two identical Intel 13th Gen i7 NUCs running Ubuntu 26.04.

  The Issue:
  Following an unattended-upgrade which updated the kernel from 7.0.0-14 to 7.0.0-15 involving the grub2 package, one machine became unresponsive/stuck, requiring a hard reboot. After rebooting, the system defaulted to a verbose boot (no splash screen) and showed a GRUB menu timeout.

  Upon inspection, /etc/default/grub on the affected machine was
  completely empty (0 bytes). The second identical machine updated
  successfully without wiping the file.

  Impact:
  Loss of critical boot parameters including quiet splash, zswap settings, and USB power management overrides (usbcore.autosuspend).

  Steps to Resolve:
  Manually restoring the content of /etc/default/grub from the healthy machine and running sudo update-grub resolved the issue.

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