[Bug 2121215] Re: arm64 and arm64+largemem questing installs fail with VFS: Unable to mount root fs on unknown-block(0, 0)
Dan Bungert
2121215 at bugs.launchpad.net
Mon Oct 6 13:40:13 UTC 2025
** Changed in: livecd-rootfs (Ubuntu)
Milestone: ubuntu-25.10 => None
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https://bugs.launchpad.net/bugs/2121215
Title:
arm64 and arm64+largemem questing installs fail with VFS: Unable to
mount root fs on unknown-block(0,0)
Status in livecd-rootfs package in Ubuntu:
Invalid
Bug description:
Logs attached. For over a week now, the arm64 and arm64+largemem ISOs
fail to install, and aren't getting promoted. I'm not entirely sure of
the root cause, I've struggled to dig further. Here's the VM xml:
```
<domain type='kvm' id='32'>
<name>utah-6296-questing-live-server-arm64</name>
<uuid>d3ef32a1-d895-4af9-a245-783acc837857</uuid>
<memory unit='KiB'>1048576</memory>
<currentMemory unit='KiB'>1048576</currentMemory>
<vcpu placement='static'>1</vcpu>
<resource>
<partition>/machine</partition>
</resource>
<os>
<type arch='aarch64' machine='virt-6.2'>hvm</type>
<loader readonly='yes' type='pflash'>/usr/share/AAVMF/AAVMF_CODE.fd</loader>
<nvram template='/usr/share/AAVMF/AAVMF_VARS.fd'>/var/lib/utah/vm/utah-6296-questing-live-server-arm64/nvram.fd</nvram>
<boot dev='cdrom'/>
</os>
<features>
<acpi/>
<gic version='2'/>
</features>
<cpu mode='host-passthrough' check='none'/>
<clock offset='utc'/>
<on_poweroff>destroy</on_poweroff>
<on_reboot>destroy</on_reboot>
<on_crash>destroy</on_crash>
<devices>
<emulator>/usr/bin/qemu-system-aarch64</emulator>
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<source file='/var/lib/utah/vm/utah-6296-questing-live-server-arm64/tmp9vwssl_o/questing-live-server-arm64.iso' index='3'/>
<backingStore/>
<target dev='sdc' bus='scsi'/>
<readonly/>
<alias name='scsi0-0-0-2'/>
<address type='drive' controller='0' bus='0' target='0' unit='2'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' cache='unsafe'/>
<source file='/var/lib/utah/vm/utah-6296-questing-live-server-arm64/disk0.qcow2' index='2'/>
<backingStore/>
<target dev='vda' bus='virtio'/>
<serial>disk-0</serial>
<alias name='virtio-disk0'/>
<address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
</disk>
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='unsafe'/>
<source file='/var/lib/utah/vm/utah-6296-questing-live-server-arm64/tmp9vwssl_o/answers.img' index='1'/>
<backingStore/>
<target dev='vdb' bus='virtio'/>
<serial>disk-1</serial>
<alias name='virtio-disk1'/>
<address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
</disk>
<controller type='scsi' index='0' model='virtio-scsi'>
<alias name='scsi0'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x00' function='0x0'/>
</controller>
<controller type='pci' index='0' model='pcie-root'>
<alias name='pcie.0'/>
</controller>
<controller type='pci' index='1' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='1' port='0x8'/>
<alias name='pci.1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' multifunction='on'/>
</controller>
<controller type='pci' index='2' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='2' port='0x9'/>
<alias name='pci.2'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
</controller>
<controller type='pci' index='3' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='3' port='0xa'/>
<alias name='pci.3'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
</controller>
<controller type='pci' index='4' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='4' port='0xb'/>
<alias name='pci.4'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x3'/>
</controller>
<controller type='pci' index='5' model='pcie-root-port'>
<model name='pcie-root-port'/>
<target chassis='5' port='0xc'/>
<alias name='pci.5'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x4'/>
</controller>
<interface type='network'>
<mac address='52:54:00:4e:a8:2d'/>
<source network='default' portid='7c5ad506-3105-4209-b97f-b08c252cff96' bridge='virbr0'/>
<target dev='vnet31'/>
<model type='virtio'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
</interface>
<serial type='file'>
<source path='/jenkins/servers/platformqa/workspace/ubuntu-questing-live-server-arm64-smoke-default/ARCHVARIANT/default/NODE/iso-testing-arm64/log/utah-6296.syslog.log'/>
<target type='system-serial' port='0'>
<model name='pl011'/>
</target>
<alias name='serial0'/>
</serial>
<console type='file'>
<source path='/jenkins/servers/platformqa/workspace/ubuntu-questing-live-server-arm64-smoke-default/ARCHVARIANT/default/NODE/iso-testing-arm64/log/utah-6296.syslog.log'/>
<target type='serial' port='0'/>
<alias name='serial0'/>
</console>
<audio id='1' type='none'/>
</devices>
<seclabel type='dynamic' model='dac' relabel='yes'>
<label>+64055:+109</label>
<imagelabel>+64055:+109</imagelabel>
</seclabel>
</domain>
```
And the relevant dmesg snippet:
```
[ 1.671218] clk: Disabling unused clocks
[ 1.672280] PM: genpd: Disabling unused power domains
[ 1.673612] md: Waiting for all devices to be available before autodetect
[ 1.673701] md: If you don't use raid, use raid=noautodetect
[ 1.676462] md: Autodetecting RAID arrays.
[ 1.677474] md: autorun ...
[ 1.677540] md: ... autorun DONE.
[ 1.679015] Failed to create /dev/root: -28
[ 1.680198] /dev/root: Can't lookup blockdev
[ 1.681294] VFS: Cannot open root device "" or unknown-block(0,0): error -2
[ 1.681364] Please append a correct "root=" boot option; here are the available partitions:
[ 1.681431] fd00 16777216 vda
[ 1.681506] driver: virtio_blk
[ 1.681565] fd10 1024 vdb
[ 1.681614] driver: virtio_blk
[ 1.681670] 0b00 2214300 sr0
[ 1.681717] driver: sr
[ 1.681772] List of all bdev filesystems:
[ 1.681822] ext3
[ 1.681868] ext2
[ 1.681918] ext4
[ 1.681968] squashfs
[ 1.682017] vfat
[ 1.682067] fuseblk
[ 1.682171]
[ 1.682230] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 1.694047] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.15.0-4-generic-64k #4-Ubuntu PREEMPT(voluntary)
[ 1.695968] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[ 1.697279] Call trace:
[ 1.697762] show_stack+0x38/0xa0 (C)
[ 1.698473] dump_stack_lvl+0x84/0xc0
[ 1.699179] dump_stack+0x1c/0x40
[ 1.699818] panic+0x1a8/0x3e0
[ 1.700409] mount_root_generic+0x204/0x2e8
[ 1.701214] mount_root+0xa8/0xd8
[ 1.701861] prepare_namespace+0x1e0/0x290
[ 1.702648] kernel_init_freeable+0x1a4/0x1e0
[ 1.703481] kernel_init+0x3c/0x190
[ 1.704158] ret_from_fork+0x10/0x20
[ 1.704898] Kernel Offset: disabled
[ 1.705590] CPU features: 0x0000,00000268,01000400,0200021b
[ 1.706663] Memory Limit: none
[ 1.707258] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---
```
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