Error in Migrating VM's from one host machine to another. i am using Openstack Juno on CentOs 7.

asked 2015-03-13 06:09:08 -0600

HK gravatar image

When Trying to migrate VM's from one host to another host. I get the following error:

Error: Failed to launch instance "XYZ": Please try again later [Error: Unexpected error while running command. Command: ssh 172.16.32.* mkdir -p /var/lib/nova/instances/520c189a-d14d-4e31-8364-2f88648d7089 Exit code: 255 Stdout: u'' Stderr: u'Host key verification failed.\r\n'].

I am using openstack juno and CentOs 7 and have configured Controller on one host machine and Compute on another host machine.

Please suggest why this error is coming and how can it be resolved. Please elaborate as i m relatively new to openstack.

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Someone please help !! I am migrating instances using OpenStack Dashboard.

HK gravatar imageHK ( 2015-03-13 06:10:55 -0600 )edit

Can the user nova ssh between controllers and compute nodes without being asked for a password?

lnxslck gravatar imagelnxslck ( 2015-03-13 06:16:47 -0600 )edit

Also check the admin_password in the nova files configuration. They must be the same in all controllers and computes.

lnxslck gravatar imagelnxslck ( 2015-03-13 06:19:05 -0600 )edit

Inxslck.. can u please elaborate on your answer. I am quite new to this and really not getting how to proceed with fixing of the above error. On the broader picture ... Can you figure out what this error is due to ? Is it due to some key-pair issues ?

HK gravatar imageHK ( 2015-03-13 13:15:41 -0600 )edit

How to switch to nova user to test ssh between compte nodes ?

HK gravatar imageHK ( 2015-03-22 07:48:26 -0600 )edit

3 answers

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answered 2015-03-13 13:59:27 -0600

Access the destination host & confirm if the instance directory exists, it should be:


if the directory doesn't exist create it (mkdir) and update the ownership to nova (chown -R nova:nova) then start the vm again and it should work.

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This changes the error but it does not resolve the problem of migration. Also will i need to manually add this directory for every instance that i create and wish to migrate. It isn't working. Please suggest some other solution.

HK gravatar imageHK ( 2015-03-16 11:05:31 -0600 )edit

you shouldn't have to do this manually every time. What kind of file system are you using and what do you have in the nova.conf file under live_migration_flag=

raul.flores gravatar imageraul.flores ( 2015-03-24 10:59:02 -0600 )edit

In nova.conf file, live_migration_flag is commented


what to do next?

HK gravatar imageHK ( 2015-03-25 01:06:53 -0600 )edit

Ok, that is the default. Have you reviewed the Configure Migrations document to ensure everything is correctly configured?

What error are you seeing now?

raul.flores gravatar imageraul.flores ( 2015-03-25 09:58:22 -0600 )edit

answered 2015-09-15 03:30:17 -0600

fifieldt gravatar image


It sounds like you might need to perform some additional steps to configure your cloud for live migrations. Particularly, you need to set up SSH so your hypervisor hosts can log into each other (if you google "Host Key Verification Failed" you will find some techniques to deal with this, such as distributing a known_hosts file).

Further information about migrations can be found in the Admin Guide at

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answered 2015-07-10 00:18:09 -0600

liyahua gravatar image

updated 2015-07-10 00:38:27 -0600

I have also met this problem , from my point of view ,there is something wrong with the authentication. my error is like this : 错误: Unexpected error while running command. Command: ssh mkdir -p /var/lib/nova/instances/f5340ef9-2a8a-48ff-a55c-a6716abbb67f Exit code: 255 Stdout: u'' Stderr: u'Host key verification failed.\r\n'].

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Asked: 2015-03-13 06:09:08 -0600

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Last updated: Sep 15 '15