[Bug 2119012] Re: Ubuntu Studio CD image build failure

Tue Aug 19 07:56:36 UTC 2025

I cannot test this with an ubuntustudio livefs, it doesn't seed the
lowlatency-kernel package in Plucky. Instead, I created a Plucky chroot
and manually installed the lowlatency-kernel package from release (to
confirm the issue) and then from proposed to verify the fix.

1. Confirm the issue with lowlatency-kernel from plucky-release:

# sudo debootstrap plucky plucky
# sudo chroot plucky
# apt-get download lowlatency-kernel
Get:1 http://archive.ubuntu.com/ubuntu plucky/main amd64 lowlatency-kernel amd64 1.2 [1928 B]
Fetched 1928 B in 0s (4680 B/s)

# dpkg --force-all -i lowlatency-kernel_1.2_amd64.deb 
Selecting previously unselected package lowlatency-kernel.
(Reading database ... 12785 files and directories currently installed.)
Preparing to unpack lowlatency-kernel_1.2_amd64.deb ...
Unpacking lowlatency-kernel (1.2) ...
dpkg: lowlatency-kernel: dependency problems, but configuring anyway as you requested:
 lowlatency-kernel depends on kernel-supports-lowlatency-bootargs; however:
  Package kernel-supports-lowlatency-bootargs is not installed.

Setting up lowlatency-kernel (1.2) ...

Configuration file '/etc/default/grub.d/99-lowlatency.cfg', does not exist on system.
Installing new config file as you requested.
/var/lib/dpkg/info/lowlatency-kernel.postinst: line 13: update-grub: command not found
dpkg: error processing package lowlatency-kernel (--install):
 installed lowlatency-kernel package post-installation script subprocess returned error exit status 127
Errors were encountered while processing:
 lowlatency-kernel

2. Verify the lowlatency-kernel from plucky-proposed

# Uninstall broken lowlatency-kernel
# Add plucky-proposed to apt sources.list
# apt-get download lowlatency-kernel/plucky-proposed
Get:1 http://archive.ubuntu.com/ubuntu plucky-proposed/main amd64 lowlatency-kernel amd64 1.3~25.04.1 [2122 B]
Fetched 2122 B in 0s (17.3 kB/s)            

# dpkg --force-all -i lowlatency-kernel_1.3~25.04.1_amd64.deb 
Selecting previously unselected package lowlatency-kernel.
(Reading database ... 12859 files and directories currently installed.)
Preparing to unpack lowlatency-kernel_1.3~25.04.1_amd64.deb ...
Unpacking lowlatency-kernel (1.3~25.04.1) ...
dpkg: lowlatency-kernel: dependency problems, but configuring anyway as you requested:
 lowlatency-kernel depends on kernel-supports-lowlatency-bootargs; however:
  Package kernel-supports-lowlatency-bootargs is not installed.

Setting up lowlatency-kernel (1.3~25.04.1) ...

Configuration file '/etc/default/grub.d/99-lowlatency.cfg', does not exist on system.
Installing new config file as you requested.

** Tags removed: verification-needed-plucky
** Tags added: verification-done-plucky

** Tags removed: verification-needed-noble
** Tags added: verification-done-noble

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https://bugs.launchpad.net/bugs/2119012

Title:
  Ubuntu Studio CD image build failure

Status in livecd-rootfs package in Ubuntu:
  Confirmed
Status in lowlatency-kernel package in Ubuntu:
  Fix Released
Status in livecd-rootfs source package in Noble:
  Fix Released
Status in lowlatency-kernel source package in Noble:
  Fix Released
Status in livecd-rootfs source package in Plucky:
  Won't Fix
Status in lowlatency-kernel source package in Plucky:
  Fix Committed
Status in livecd-rootfs source package in Questing:
  Confirmed
Status in lowlatency-kernel source package in Questing:
  Fix Released

Bug description:
  [ Impact ]

  Ubuntu Studio uses the lowlatency kernel. With 6.14, the lowlatency
  kernel is just the generic kernel with some bootargs to make it
  lowlatency. This breaks the Ubuntu Studio livefs and CD image builds.

  https://launchpad.net/~ubuntu-
  cdimage/+livefs/ubuntu/noble/ubuntustudio

  Problem 1)

  The postinst hook of the lowlatency-kernel package calls update-grub
  unconditionally which fails if the package is installed in a chroot.

  From a livefs build log:

  Processing triggers for dbus (1.14.10-4ubuntu4.1) ...
  Processing triggers for libgtk-3-0t64:amd64 (3.24.41-4ubuntu1.3) ...
  Processing triggers for shared-mime-info (2.4-4) ...
  Processing triggers for libgtk2.0-0t64:amd64 (2.24.33-4ubuntu1.1) ...
  Processing triggers for desktop-file-utils (0.27-2build1) ...
  Processing triggers for initramfs-tools (0.142ubuntu25.5) ...
  Processing triggers for hicolor-icon-theme (0.17-2) ...
  Processing triggers for libc-bin (2.39-0ubuntu8.5) ...
  Processing triggers for man-db (2.12.0-4build2) ...
  Processing triggers for dictionaries-common (1.29.7) ...
  Processing triggers for linux-image-6.14.0-24-generic (6.14.0-24.24~24.04.3) ...
  /etc/kernel/postinst.d/initramfs-tools:
  update-initramfs: Generating /boot/initrd.img-6.14.0-24-generic
  cryptsetup: ERROR: Couldn't resolve device overlay
  cryptsetup: WARNING: Couldn't determine root device
  cryptsetup: ERROR: Couldn't resolve device /dev/vdb
  Errors were encountered while processing:
   lowlatency-kernel

  Problem 2)

  The kernel flavor name changed from 'lowlatency' to 'generic'. This
  breaks livecd-rootfs.

  [2025-07-30 21:10:37] No catalog entry template for standard.live
  [2025-07-30 21:10:38] P: Begin unmounting filesystems...
  [2025-07-30 21:10:38] P: Saving caches...
  [2025-07-30 21:10:38] No kernel output for lowlatency!
  [2025-07-30 21:10:38] P: Begin unmounting filesystems...
  [2025-07-30 21:10:38] P: Saving caches...
  [2025-07-30 21:10:38] Build failed

  Problem 3)

  The ISO kernel is the generic kernel now so needs additional boot args
  to make it lowlatency. Otherwise 'Try Ubuntu Studio' will run the
  generic kernel which is likely not what we want.

  [ Test Plan ]

  1. Trigger an Ubuntu Studio livefs build and watch it succeed.
  2. Boot a resulting CD image and verify the running kernel is lowlatency.
  3. Install Ubuntu Studio and verify the running kernel is lowlatency.

  [ Where Problems Could Occur ]

  Other consumers of livecd-rootfs could fail, i.e., other livefs builds
  might fail due to livecd-rootfs changes.

  Machines that have the lowlatency-kernel package installed might not
  update grub.cfg and hence not switch the kernel to lowlatency but
  continue to run with generic settings.

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