Troubleshoot Compute

Common problems for Compute typically involve misconfigured networking or credentials that are not sourced properly in the environment. Also, most flat networking configurations do not enable ping or ssh from a compute node to the instances that run on that node. Another common problem is trying to run 32-bit images on a 64-bit compute node. This section shows you how to troubleshoot Compute.


Move the sections below into sub-pages for readability.

Compute service logging

Compute stores a log file for each service in /var/log/nova. For example, nova-compute.log is the log for the nova-compute service. You can set the following options to format log strings for the nova.log module in the nova.conf file:

  • logging_context_format_string

  • logging_default_format_string

If the log level is set to debug, you can also specify logging_debug_format_suffix to append extra formatting. For information about what variables are available for the formatter, see Formatter Objects.

You have two logging options for OpenStack Compute based on configuration settings. In nova.conf, include the logfile option to enable logging. Alternatively you can set use_syslog = 1 so that the nova daemon logs to syslog.

Guru Meditation reports

A Guru Meditation report is sent by the Compute service upon receipt of the SIGUSR2 signal (SIGUSR1 before Mitaka). This report is a general-purpose error report that includes details about the current state of the service. The error report is sent to stderr.

For example, if you redirect error output to nova-api-err.log using nova-api 2>/var/log/nova/nova-api-err.log, resulting in the process ID 8675, you can then run:

# kill -USR2 8675

This command triggers the Guru Meditation report to be printed to /var/log/nova/nova-api-err.log.

The report has the following sections:

  • Package: Displays information about the package to which the process belongs, including version information.

  • Threads: Displays stack traces and thread IDs for each of the threads within the process.

  • Green Threads: Displays stack traces for each of the green threads within the process (green threads do not have thread IDs).

  • Configuration: Lists all configuration options currently accessible through the CONF object for the current process.

For more information, see Guru Meditation Reports.

Common errors and fixes for Compute

The site offers a place to ask and answer questions, and you can also mark questions as frequently asked questions. This section describes some errors people have posted previously. Bugs are constantly being fixed, so online resources are a great way to get the most up-to-date errors and fixes.

Credential errors, 401, and 403 forbidden errors


Missing credentials cause a 403 forbidden error.


To resolve this issue, use one of these methods:

  1. Manual method

    Gets the novarc file from the project ZIP file, saves existing credentials in case of override, and manually sources the novarc file.

  2. Script method

    Generates novarc from the project ZIP file and sources it for you.

When you run nova-api the first time, it generates the certificate authority information, including openssl.cnf. If you start the CA services before this, you might not be able to create your ZIP file. Restart the services. When your CA information is available, create your ZIP file.

Also, check your HTTP proxy settings to see whether they cause problems with novarc creation.

Live migration permission issues


When live migrating an instance, you may see errors like the below:

libvirtError: operation failed: Failed to connect to remote libvirt URI
qemu+ssh://stack@cld6b16/system: Cannot recv data: Host key verification
failed.: Connection reset by peer


Ensure you have completed all the steps outlined in Configure SSH between compute nodes. In particular, it’s important to note that the libvirt process runs as root even though it may be connecting to a different user (stack in the above example). You can ensure everything is correctly configured by attempting to connect to the remote host via the root user. Using the above example once again:

$ su - -c 'ssh stack@cld6b16'

Instance errors


Sometimes a particular instance shows pending or you cannot SSH to it. Sometimes the image itself is the problem. For example, when you use flat manager networking, you do not have a DHCP server and certain images do not support interface injection; you cannot connect to them.


To fix instance errors use an image that does support this method, such as Ubuntu, which obtains an IP address correctly with FlatManager network settings.

To troubleshoot other possible problems with an instance, such as an instance that stays in a spawning state, check the directory for the particular instance under /var/lib/nova/instances on the nova-compute host and make sure that these files are present:

  • libvirt.xml

  • disk

  • disk-raw

  • kernel

  • ramdisk

  • console.log, after the instance starts.

If any files are missing, empty, or very small, the nova-compute service did not successfully download the images from the Image service.

Also check nova-compute.log for exceptions. Sometimes they do not appear in the console output.

Next, check the log file for the instance in the /var/log/libvirt/qemu directory to see if it exists and has any useful error messages in it.

Finally, from the /var/lib/nova/instances directory for the instance, see if this command returns an error:

# virsh create libvirt.xml

Empty log output for Linux instances


You can view the log output of running instances from either the Log tab of the dashboard or the output of nova console-log. In some cases, the log output of a running Linux instance will be empty or only display a single character (for example, the ? character).

This occurs when the Compute service attempts to retrieve the log output of the instance via a serial console while the instance itself is not configured to send output to the console.


To rectify this, append the following parameters to kernel arguments specified in the instance’s boot loader:

console=tty0 console=ttyS0,115200n8

Upon rebooting, the instance will be configured to send output to the Compute service.

Reset the state of an instance


Instances can remain in an intermediate state, such as deleting.


You can use the nova reset-state command to manually reset the state of an instance to an error state. You can then delete the instance. For example:

$ nova reset-state c6bbbf26-b40a-47e7-8d5c-eb17bf65c485
$ openstack server delete c6bbbf26-b40a-47e7-8d5c-eb17bf65c485

You can also use the --active parameter to force the instance back to an active state instead of an error state. For example:

$ nova reset-state --active c6bbbf26-b40a-47e7-8d5c-eb17bf65c485

Injection problems


Instances may boot slowly, or do not boot. File injection can cause this problem.


To disable injection in libvirt, set the following in nova.conf:

inject_partition = -2


If you have not enabled the config drive and you want to make user-specified files available from the metadata server for to improve performance and avoid boot failure if injection fails, you must disable injection.

Cannot find suitable emulator for x86_64


When you attempt to create a VM, the error shows the VM is in the BUILD then ERROR state.


On the KVM host, run cat /proc/cpuinfo. Make sure the vmx or svm flags are set.

Follow the instructions in the Enable KVM section in the Nova Configuration Reference to enable hardware virtualization support in your BIOS.

Failed to attach volume after detaching


Failed to attach a volume after detaching the same volume.


You must change the device name on the nova-attach command. The VM might not clean up after a nova-detach command runs. This example shows how the nova-attach command fails when you use the vdb, vdc, or vdd device names:

# ls -al /dev/disk/by-path/
total 0
drwxr-xr-x 2 root root 200 2012-08-29 17:33 .
drwxr-xr-x 5 root root 100 2012-08-29 17:33 ..
lrwxrwxrwx 1 root root 9 2012-08-29 17:33 pci-0000:00:04.0-virtio-pci-virtio0 -> ../../vda
lrwxrwxrwx 1 root root 10 2012-08-29 17:33 pci-0000:00:04.0-virtio-pci-virtio0-part1 -> ../../vda1
lrwxrwxrwx 1 root root 10 2012-08-29 17:33 pci-0000:00:04.0-virtio-pci-virtio0-part2 -> ../../vda2
lrwxrwxrwx 1 root root 10 2012-08-29 17:33 pci-0000:00:04.0-virtio-pci-virtio0-part5 -> ../../vda5
lrwxrwxrwx 1 root root 9 2012-08-29 17:33 pci-0000:00:06.0-virtio-pci-virtio2 -> ../../vdb
lrwxrwxrwx 1 root root 9 2012-08-29 17:33 pci-0000:00:08.0-virtio-pci-virtio3 -> ../../vdc
lrwxrwxrwx 1 root root 9 2012-08-29 17:33 pci-0000:00:09.0-virtio-pci-virtio4 -> ../../vdd
lrwxrwxrwx 1 root root 10 2012-08-29 17:33 pci-0000:00:09.0-virtio-pci-virtio4-part1 -> ../../vdd1

You might also have this problem after attaching and detaching the same volume from the same VM with the same mount point multiple times. In this case, restart the KVM host.

Failed to attach volume, systool is not installed


This warning and error occurs if you do not have the required sysfsutils package installed on the compute node:

WARNING nova.virt.libvirt.utils [req-1200f887-c82b-4e7c-a891-fac2e3735dbb\
admin admin|req-1200f887-c82b-4e7c-a891-fac2e3735dbb admin admin] systool\
is not installed
ERROR nova.compute.manager [req-1200f887-c82b-4e7c-a891-fac2e3735dbb admin\
admin|req-1200f887-c82b-4e7c-a891-fac2e3735dbb admin admin]
[instance: df834b5a-8c3f-477a-be9b-47c97626555c|instance: df834b5a-8c3f-47\
Failed to attach volume 13d5c633-903a-4764-a5a0-3336945b1db1 at /dev/vdk.


Install the sysfsutils package on the compute node. For example:

# apt-get install sysfsutils

Failed to connect volume in FC SAN


The compute node failed to connect to a volume in a Fibre Channel (FC) SAN configuration. The WWN may not be zoned correctly in your FC SAN that links the compute host to the storage array:

ERROR nova.compute.manager [req-2ddd5297-e405-44ab-aed3-152cd2cfb8c2 admin\
demo|req-2ddd5297-e405-44ab-aed3-152cd2cfb8c2 admin demo] [instance: 60ebd\
6c7-c1e3-4bf0-8ef0-f07aa4c3d5f3|instance: 60ebd6c7-c1e3-4bf0-8ef0-f07aa4c3\
Failed to connect to volume 6f6a6a9c-dfcf-4c8d-b1a8-4445ff883200 while\
attaching at /dev/vdjTRACE nova.compute.manager [instance: 60ebd6c7-c1e3-4\
bf0-8ef0-f07aa4c3d5f3|instance: 60ebd6c7-c1e3-4bf0-8ef0-f07aa4c3d5f3]
Traceback (most recent call last):...f07aa4c3d5f3\] ClientException: The\
server has either erred or is incapable of performing the requested\
operation.(HTTP 500)(Request-ID: req-71e5132b-21aa-46ee-b3cc-19b5b4ab2f00)


The network administrator must configure the FC SAN fabric by correctly zoning the WWN (port names) from your compute node HBAs.

Multipath call failed exit


Multipath call failed exit. This warning occurs in the Compute log if you do not have the optional multipath-tools package installed on the compute node. This is an optional package and the volume attachment does work without the multipath tools installed. If the multipath-tools package is installed on the compute node, it is used to perform the volume attachment. The IDs in your message are unique to your system.

WARNING [req-cac861e3-8b29-4143-8f1b-705d0084e571 \
admin admin|req-cac861e3-8b29-4143-8f1b-705d0084e571 admin admin] \
Multipath call failed exit (96)


Install the multipath-tools package on the compute node. For example:

# apt-get install multipath-tools

Failed to Attach Volume, Missing sg_scan


Failed to attach volume to an instance, sg_scan file not found. This error occurs when the sg3-utils package is not installed on the compute node. The IDs in your message are unique to your system:

ERROR nova.compute.manager [req-cf2679fd-dd9e-4909-807f-48fe9bda3642 admin admin|req-cf2679fd-dd9e-4909-807f-48fe9bda3642 admin admin]
[instance: 7d7c92e0-49fa-4a8e-87c7-73f22a9585d5|instance:  7d7c92e0-49fa-4a8e-87c7-73f22a9585d5]
Failed to attach volume  4cc104c4-ac92-4bd6-9b95-c6686746414a at /dev/vdcTRACE nova.compute.manager
[instance:  7d7c92e0-49fa-4a8e-87c7-73f22a9585d5|instance: 7d7c92e0-49fa-4a8e-87c7-73f22a9585d5]
Stdout: '/usr/local/bin/nova-rootwrap: Executable not found: /usr/bin/sg_scan'


Install the sg3-utils package on the compute node. For example:

# apt-get install sg3-utils

Requested microversions are ignored


When making a request with a microversion beyond 2.1, for example:

$ openstack --os-compute-api-version 2.15 server group create \
  --policy soft-anti-affinity my-soft-anti-group

It fails saying that “soft-anti-affinity” is not a valid policy, even thought it is allowed with the 2.15 microversion.


Ensure the compute endpoint in the identity service catalog is pointing at /v2.1 instead of /v2. The former route supports microversions, while the latter route is considered the legacy v2.0 compatibility-mode route which renders all requests as if they were made on the legacy v2.0 API.