BTRFS error: could not find root 8

[Thomas Mayer]

I have a KVM guest system which was running for some time now (142 days uptime).

Today, I logged in for the first time since months, and got an error message in syslog (and console):

kernel: BTRFS error (device vda2): could not find root 8

The error happened together with my login (in respect to the date of the log entry).

The system was running with kernel 4.4.0-31-generic when the problem occured.

When googling around, I found some similar results, but nowhere is mentioned that this got fixed somehow.

So far, I could not find anything harmful (I did not reboot yet, however).

I updated the kernel now, eventually that helps.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-31-generic 4.4.0-31.50
ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic x86_64
AlsaDevices:
 total 0
 crw-rw----+ 1 root audio 116, 1 Dec 20 13:00 seq
 crw-rw----+ 1 root audio 116, 33 Dec 20 13:00 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20.1-0ubuntu2.4
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Date: Tue Dec 20 13:40:44 2016
HibernationDevice: RESUME=UUID=419693f3-cd92-4870-a16a-7bede16d9b8a
InstallationDate: Installed on 2016-06-20 (182 days ago)
InstallationMedia: Ubuntu-Server 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.3)
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lsusb:
 Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
 Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
PciMultimedia:

ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB: 0 cirrusdrmfb
ProcKernelCmdLine: BOOT_IMAGE=/@/boot/vmlinuz-4.4.0-31-generic root=UUID=ebfbbec2-f4df-4e40-92a5-3db6b57eb8f5 ro rootflags=subvol=@
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-31-generic N/A
 linux-backports-modules-4.4.0-31-generic N/A
 linux-firmware 1.157.6
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/01/2014
dmi.bios.vendor: SeaBIOS
dmi.bios.version: 1.7.5-20140531_083030-gandalf
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-i440fx-2.1
dmi.modalias: dmi:bvnSeaBIOS:bvr1.7.5-20140531_083030-gandalf:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-2.1:cvnQEMU:ct1:cvrpc-i440fx-2.1:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-2.1
dmi.sys.vendor: QEMU
---
AlsaVersion: Advanced Linux Sound Architecture Driver Version k4.4.0-57-generic.
AplayDevices: Error: [Errno 2] No such file or directory
ApportVersion: 2.20.1-0ubuntu2.4
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/hwC0D2', '/dev/snd/pcmC0D2c', '/dev/snd/pcmC0D1p', '/dev/snd/pcmC0D0c', '/dev/snd/by-path', '/dev/snd/pcmC0D0p', '/dev/snd/controlC0', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
Card0.Amixer.info: Error: [Errno 2] No such file or directory
Card0.Amixer.values: Error: [Errno 2] No such file or directory
DistroRelease: Ubuntu 16.04
InstallationDate: Installed on 2013-08-21 (1229 days ago)
InstallationMedia: Ubuntu-Server 13.04 "Raring Ringtail" - Release amd64 (20130423.1)
IwConfig:
 em1 no wireless extensions.

 lo no wireless extensions.
Lsusb:
 Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Package: linux (not installed)
ProcEnviron:
 TERM=screen.xterm-256color
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-57-generic root=UUID=16120d81-8cde-4e81-87cd-f55f65a4923b ro rootflags=subvol=@ pcie_aspm=force "acpi_osi=!Windows 2012" acpi=force acpi_enforce_resources=lax i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1 i915.semaphores=1
ProcVersionSignature: Ubuntu 4.4.0-57.78-generic 4.4.35
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-57-generic N/A
 linux-backports-modules-4.4.0-57-generic N/A
 linux-firmware 1.157.6
RfKill: Error: [Errno 2] No such file or directory
Tags: xenial
Uname: Linux 4.4.0-57-generic x86_64
UpgradeStatus: Upgraded to xenial on 2016-10-24 (69 days ago)
UserGroups:

_MarkForUpload: True
dmi.bios.date: 03/13/2014
dmi.bios.vendor: Intel Corp.
dmi.bios.version: SWQ6710H.86A.0067.2014.0313.1347
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: DQ67OW
dmi.board.vendor: Intel Corporation
dmi.board.version: AAG12528-309
dmi.chassis.type: 3
dmi.modalias: dmi:bvnIntelCorp.:bvrSWQ6710H.86A.0067.2014.0313.1347:bd03/13/2014:svn:pn:pvr:rvnIntelCorporation:rnDQ67OW:rvrAAG12528-309:cvn:ct3:cvr:

[Brad Figg (brad-figg)]

This change was made by a bot.

[Thomas Mayer (thomas303)]

Reboot worked without issues, now using kernel 4.4.0-53-generic x86_64. I'll see how that works out.

[Joseph Salisbury (jsalisbury)]

Please change the status back to "Confirmed" if the bug happens again.

[Thomas Mayer (thomas303)]

I got the same error using a bare metal system on 16.04.. That system got updated from 14.04 (and is much older). That system got installed completely separate/independent, so there is not much to consider that both systems somehow seem to be similar in terms of configuration.

The kernel of this system is 4.4.0-57-generic, whereas the error happened after a kernel update followed by a reboot.

[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

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[Thomas Mayer (thomas303)]

The bare metal system is a backup server (2x3 Terabytes of disk space), holding a lot of subvolumes from incremental backups).

The report files I just sent are from the bare metal system. Note that btrfs is on top of a Luks encrypted partition which is on top of a md raid. That setup is a lot different from the cloud server which had a btrfs partition, directly used in the kvm image (whereas I don't know how the hoster stores that image).

Tu sum up: Both systems are really different in terms of age, hardware, storage, etc.

The only thing both systems have in common is that they use btrfs and ubuntu 16.04.

So far, I did not notice any problems with both systems (no data loss, etc.).

[DiagonalArg (diagonalarg)]

The same problem in Ubuntu 16.04, with BTRFS Raid-1 on LUKS.

[Cedric Defortis (cedef)]

Same problem here, with Ubuntu 16.04 + BTRFS on a software Raid1

[Tim Edwards (tkedwards)]

Same problem here on Ubuntu 16.04 with BTRFS RAID-1 on LUKS partitions

[Sly_tom_cat (slytomcat)]

The same issue on Ubuntu 16.04.2 with BTRFS on single SHDD disk.

[Sly_tom_cat (slytomcat)]

... it disappears when quota enabled on btrfs

[krishna thapamagar (gongtham)]

OS: Ubuntu 16.04.2 LTS / Disks: btrfs mirror on 2 ssd partitions - /dev/sda4 /dev/sdb4

dmesg shows error every 15 mins

May 7 15:02:22 blade3 kernel: [ 9174.648066] BTRFS error (device sdb4): could not find root 8
...
May 7 21:18:43 blade3 kernel: [31756.490619] BTRFS error (device sdb4): could not find root 8

This error disappeared after enabling quota (just like Sly_tom_cat mentioned).

[jth (jth)]

Hi
According to this it is nothing to worry about.

systemd is probing and if quota disabled as it is by default, this will show.

https://www.mail-archive.com/search?<email address hidden>&q=subject:%22Re%5C%3A+BTRFS%5C%3A+could+not+find+root+8%22&o=newest&f=1