VCB basic usage - debugging

During the series of articles about VCB usage I supposed that all the presented VCB command examples are running smoothly and without errors. But this is not always true. There can  be a lot of reason why it is not working as expected, e.g. wrong permissions assigned to VCB backup user, misconfigured SAN which doesn't allow to access VMFS volumes or  unspecified problem with creating virtual machine snapshot.

If something goes wrong all VCB commands can be run in more verbose mode with command line switch -L and verbosity level from 0 to 6. The next example illustrates it. We want to perform a full backup of a virtual machine named vcb-backup and it seems the provided user vcbadmin doesn't have required permissions to do it:

vcbmounter -h host -u vcbadmin -p pass -a name:vcb-backup -r c:\mnt\vcb-backup -t fullvm -m nbd -L4

[2010-06-15 13:15:12.843 'vcbMounter' 360 info] Connected using API Namespace vim25.
[2010-06-15 13:15:12.843 'vcbMounter' 360 info] Authenticating user vcbadmin
[2010-06-15 13:15:12.859 'vcbMounter' 360 info] Logged in!
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Got VM MoRef
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Got access method
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Got coordinator object
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Attempting data access.
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Creating mount directory
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] No snapshot info for this VM, nothing to do.
[2010-06-15 13:15:12.890 'vcbMounter' 360 info] Creating snapshot
[2010-06-15 13:15:19.296 'vcbMounter' 360 info] Snapshot created, ID: snapshot-579
[2010-06-15 13:15:19.296 'vcbMounter' 360 info] Mount operation created snapshot.
[2010-06-15 13:15:19.312 'vcbMounter' 360 info] Mount operation obtained backupinfo.
[2010-06-15 13:15:19.312 'vcbMounter' 360 info] Performing SearchIndex find.
[2010-06-15 13:15:19.328 'vcbMounter' 360 info] Successfully obtained instance lock.

[2010-06-15 13:15:24.359 'vcbMounter' 360 error] Error: No permission to perform this action.

[2010-06-15 13:15:24.359 'vcbMounter' 360 error] An error occurred, cleaning up...
[2010-06-15 13:15:24.359 'vcbMounter' 360 info] Performing SearchIndex find.
[2010-06-15 13:15:24.359 'vcbMounter' 360 info] Successfully obtained instance lock.
[2010-06-15 13:15:29.437 'vcbMounter' 360 info] Remove clone disks successful.
Deleted directory c:\vcb\vcb-backup

The bold line helps us to identify the cause of the problem.

YUM download only mode

How many times I was in a situation I needed to update a server with RHEL installed but I wasn't at site and I didn't have a way how to reboot the server after installing a new kernel or glibc package on it reliably? Yes, I have a test environment and I'm testing the updates on it but many installations are too critical to just run yum update -y and then shutdown -r now. On top of that, there are well known Murphy's laws which are able to damage more than we are able to imagine.

Instead of remote resolution of why the server is suddenly unresponsive I'm trying to prepare some offline update archive (if there isn't an update server available but this is another situation) and then during a site visit to apply it.

As I'm talking about RHEL I'm using YUM or Yellowdog Updater Modified for it. This tool is able to download updates locally without installing them if we have RHEL 5.x system. It only requires to install a download plugin which is part of yum-downloadonly package. Try to install it with


yum install yum-downloadonly

The next lines contain common commands that I use for downloading updates:

yum install PACKAGE_NAME.rpm -y --downloadonly
yum update -y --downloadonly


If we have a RHEL 4.x server we don't have this package and we need to install another package called yum-tools which contains similar tool yumdownloader.


yum install yum-tools -y

Here it is how to use the tool

yumdownloader PACKAGE_NAME.rpm


If we wan't to download all the available updates with yumdownloader we need to get a list of all packages with yum check-update and then to pass it to yumdownloader. You can do it from shell with sed, cut or awk commands or what would you prefer:

for PKG in `yum check-update | cut -d' ' -f1`; do
   yumdownloader $PKG
done

For more detailed description of the tools and their parameters have a look at their man pages.

Time to continue

After almost a whole year, I would like to awake my blog from a sleep and begin to publish articles more regularly. During the previous period I was too busy at work and I couldn't afford to take care of it as I would like. On the other hand, I had an opportunity to participate on some interesting projects and I needed to solve many unusual tasks. Everything was written down and now it is waiting for readers and comments.

I hope the new articles will be interesting and helpful for you as the previous ones.