Public bug reported:
Ubuntu 26.04 LTS consistently fails to boot when installed on an
external NVMe SSD connected through a USB4 enclosure.
The failure occurs during the early boot (initramfs) stage. The root
filesystem cannot be found because the external NVMe device has not yet
been enumerated.
The problem is reproducible on every boot.
During boot, the early boot environment reports that the root filesystem cannot
be found:
Warning: /dev/disk/by-uuid/<UUID> does not exist
Entering emergency mode.
The emergency shell prompt indicates that the system is running from a
dracut-generated initramfs.
At this point, the external NVMe device is not present under /dev/nvme*, so the
root filesystem cannot be mounted.
From the emergency shell, I found that manually authorizing the
USB4/Thunderbolt device and rescanning the PCI bus immediately causes the NVMe
controller to be enumerated. The following commands consistently make the NVMe
device appear:
echo 1 > /sys/bus/thunderbolt/devices/0-2/authorized
echo 1 > /sys/bus/pci/rescan
After executing these commands, the external SSD becomes visible under
/dev/nvme*.
To further investigate, I embedded the same authorization and PCI rescan
sequence into the early boot environment before the root filesystem is searched
(as dracut script). With only that change, the system boots successfully and
reliably on every attempt.
This strongly suggests that the issue is related to the timing of
USB4/Thunderbolt authorization or PCIe enumeration during early boot.
Expected behavior
When firmware has selected an external USB4 storage device as the boot device,
it should be available before the operating system attempts to locate the root
filesystem.
Actual behavior
During early boot, the external USB4 storage device is not enumerated in time
for the root filesystem to be located.
Introducing an authorization step followed by a PCI rescan earlier in the boot
sequence consistently resolves the issue.
Notes
Based on my investigation, this appears to be an issue in the early boot
initialization sequence. I have not determined whether the root cause lies in
the kernel, the initramfs implementation, or the platform firmware.
Attaching output of boltctl
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-27-generic 7.0.0-27.27
ProcVersionSignature: Ubuntu 7.0.0-27.27-generic 7.0.6
Uname: Linux 7.0.0-27-generic x86_64
ApportVersion: 2.34.0-0ubuntu2
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC1: lukasz 4667 F.... wireplumber
/dev/snd/controlC0: lukasz 4667 F.... wireplumber
/dev/snd/seq: lukasz 4648 F.... pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Sat Jul 4 22:53:45 2026
InstallationDate: Installed on 2026-07-01 (3 days ago)
InstallationMedia: Ubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423.1)
MachineType: ASUSTeK COMPUTER INC. ASUS Zenbook 14 UM3406HA_UM3406HA
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 amdgpudrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-7.0.0-27-generic
root=UUID=1153a0ed-74f0-421b-9d43-2333b4456d66 ro quiet splash
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/23/2025
dmi.bios.release: 5.29
dmi.bios.vendor: American Megatrends International, LLC.
dmi.bios.version: UM3406HA.308
dmi.board.asset.tag: ATN12345678901234567
dmi.board.name: UM3406HA
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: 1.0
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: ASUSTeK COMPUTER INC.
dmi.chassis.version: 1.0
dmi.modalias:
dmi:bvnAmericanMegatrendsInternational,LLC.:bvrUM3406HA.308:bd07/23/2025:br5.29:svnASUSTeKCOMPUTERINC.:pnASUSZenbook14UM3406HA_UM3406HA:pvr1.0:rvnASUSTeKCOMPUTERINC.:rnUM3406HA:rvr1.0:cvnASUSTeKCOMPUTERINC.:ct10:cvr1.0:sku:pfaASUSZenbook14:
dmi.product.family: ASUS Zenbook 14
dmi.product.name: ASUS Zenbook 14 UM3406HA_UM3406HA
dmi.product.version: 1.0
dmi.sys.vendor: ASUSTeK COMPUTER INC.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
** Attachment added: "boltctl.txt"
https://bugs.launchpad.net/bugs/2159575/+attachment/5980135/+files/boltctl.txt
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https://bugs.launchpad.net/bugs/2159575
Title:
External USB4 NVMe boot fails during initramfs until Thunderbolt
device is manually authorized and PCI bus rescanned
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