openstack-manuals/doc/common-rst/support-compute.rst

:orphan:

.. _support-compute:

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 :command:`ping` or :command:`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.


.. _log-files-for-openstack-compute:

Compute service logging
-----------------------

Compute stores a log file for each service in
:file:`/var/log/nova`. For example, :file:`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 :file:`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 http://docs.python.org/library/logging.html#formatter.

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


.. _section_compute-GuruMed-reports:

Guru Meditation reports
-----------------------

A Guru Meditation report is sent by the Compute service upon receipt of the
``SIGUSR1`` signal. This report is a general-purpose error report,
including a complete report of the service's current state, and is sent to
``stderr``.

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

  # kill -USR1 8675

This command triggers the Guru Meditation report to be printed to
:file:`/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 <http://docs.openstack.org/developer/nova/devref/gmr.html>`_.


.. _compute-common-errors-and-fixes:

Common errors and fixes for Compute
-----------------------------------

The `ask.openstack.org <http://ask.openstack.org>`_ 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:

#. Manual method
    Gets the :file:`novarc` file from the project ZIP file, saves existing
    credentials in case of override, and manually sources the :file:`novarc`
    file.

#. Script method
    Generates :file:`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 :file:`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
:file:`novarc` creation.

**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. The fix for this problem is to 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 :file:`/var/lib/nova/instances` on
the ``nova-compute`` host and make sure that these files are present:

* :file:`libvirt.xml`
* :file:`disk`
* :file:`disk-raw`
* :file:`kernel`
* :file:`ramdisk`
* :file:`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 :file:`nova-compute.log` for exceptions. Sometimes they do not
appear in the console output.

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

Finally, from the :file:`/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 :guilabel:`Log` tab of the dashboard or the output of
:command:`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-state:

Reset the state of an instance
------------------------------

If an instance remains in an intermediate state, such as ``deleting``, you
can use the :command:`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
  $ nova delete c6bbbf26-b40a-47e7-8d5c-eb17bf65c485

You can also use the :option:`--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


.. _problems-with-injection:

Injection problems
------------------

If instances do not boot or boot slowly, investigate file injection as a cause.

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

.. code-block:: ini
   :linenos:

   [libvirt]
   inject_partition = -2

.. note:: If you have not enabled the configuration 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.


.. _live-snapshotting-fail:

Disable live snapshotting
-------------------------

If you use libvirt version ``1.2.2``, you may experience problems with live
snapshots creation. Occasionally, libvirt of the specified version fails
to perform the live snapshotting under load that presupposes a concurrent
creation of multiple snapshots.

To effectively disable the libvirt live snapshotting, until the problem
is resolved, configure the ``disable_libvirt_livesnapshot`` option.
You can turn off the live snapshotting mechanism by setting up its value to
``True`` in the ``[workarounds]`` section of the :file:`nova.conf` file:

.. code-block:: ini
   :linenos:

   [workarounds]
   disable_libvirt_livesnapshot = True