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There was another interesting thread today on the VMTN community forums about disabling an unused vmnic from an ESXi host due to false alarms being generated from HP SIM. Due to the specific hardware version, disabling the vmnic through the BIOS was not an option and there were no alternatives from the discussion.

I decided to dig a bit to see what I could find and stumbled upon a neat little utility called vmkchdev (VMkernel Change Device?) and from what I can tell provides a method passing a particular device to be controlled by either the VMkernel or as a passthrough device to a virtual machine (think VMDirect Path).

Disclaimer: Please note, this is using an undocumented utility. You should test this out in a development/lab environment before using and you may want to also contact VMware support to get their blessings***

~ # vmkchdev
Usage:
-s (scan device)
-v (give device to vmkernel)
-p (give device to passthru/VM)
-l (list device state)
-L (list device state with details)
[0x][seg:[bus[:slot[.func]]]]

What I found while testing the utility is by passing it over as a passthrough device, the vmnic is actually unrepresented to the VMkernel and does not show up under network adapters or even the unused/unlinked adapter list in the vSwitch configurations. It seems that it is just masks the device away from the VMkernel as you can still see the active configuration in esx.conf and you can see the device listed using vmkchdev.

Here is an example of an unused physical nic vmnic1 that we would like to disable and unpresent to an ESXi host.

Here is the output from esxcfg-nics:

First we need to identify the vmnic's PCI slot, we do by running the "-l" or list operation and searching for the particular vmnice device.

~ # vmkchdev -l | grep vmnic1
000:002:01.0 8086:100f 15ad:0750 vmkernel vmnic1

Next we will pass the device from the VMkernel to passthrough/VM using the "-p" flag and specifying the PCI slot, which in this case it is 000:002:01.0. We will also need to refresh the network section so the changes are reflected in the vSphere Client by using vim-cmd.

~ # vmkchdev -p 000:002:01.0
~ # vim-cmd hostsvc/net/refresh

If we list our vmnic again using vmkchdev, you will notice the device is now owned by passthru versus the VMkernel.

~ # vmkchdev -l | grep vmnic1
000:002:01.0 8086:100f 15ad:0750 passthru vmnic1

Now if we check the output of esxcfg-nics and the vSphere Client, you will notice that vmnic1 is no where to be found

If you would like to enable or re-present the disabled vmnic, you just need to pass the device back over to VMkernel by using the "-v" flag.

~ # vmkchdev -v 000:002:01.0
~ # vim-cmd hostsvc/net/refresh

Your vmnic should now re-appear on all your screens and any existing NIC teams that may have exists is automatically restored. This trick actually works on both a used and unused vmnic

If you are trying to do this on ESX, vmkchdev actually has an additional option called "console" for the Service Console.

[root@esx41-1 ~]# vmkchdev
Usage:
-s (scan device)
-c (give device to console)
-v (give device to vmkernel)
-p (give device to passthru/VM)
-l (list device state)
-L (list device state with details)
[0x][seg:[bus[:slot[.func]]]]

I found that you need to pass the vmnic from VMkernel to Console, passing it to passthru/VM will not work and an error is thrown if you do. Again, you can easily re-enable by passing it back to the VMkernel

vmkchdev -c 000:002:01.0

If you would like to automatically persist this change across reboots, specifically for ESXi as changes are not saved. You will need to add the following lines to /etc/rc.local which will execute the disabling of the vmnic's after bootup.

/sbin/vmkchdev -p 000:002:01.0
vim-cmd hostsvc/net/refresh

You will also need to run /sbin/auto-backup.sh to ensure the changes to /etc/rc.local are saved and reloaded upon the next reboot. For ESX, you can place it in /etc/rc.local without having to do anything extra as the changes persists across reboots for classic ESX

Now you can play hide and seek with your vmnic's without resorting to a system reboot or touching the BIOS. Though ideally, if you do have unused devices, you should definitely disable them in the BIOS if you have the option. On a side note, this might be a fun trick to play on one of your co-workers by hiding all vmnics 😉

Earlier this year I created a simple vSphere SDK for Perl script that allows you to update ESXi's DCUI (Direct Console User Interface) banner with multiple lines of text. I originally thought you could not customize the text color or the background color, though recently I found out that was not the case. While doing some testing on ESXi 4.1, I noticed two files (support,welcome) located under /etc/vmware and looking at the contents of support, it made realize we might be able to change the colors.

Here is the contents of /etc/vmware/support, notice the special formatting of the variables including color tags:

I decided to use one of my favorite UNIX utility, "strings" to take at the dcui binary that is located under /sbin in the Busybox Console (Tech Support Mode) and discovered you can control both the font color and background color. There are also special variables that can be used to display information about the ESXi host such as the product version or IP Address.

Here are the supported colors:

white
black
dark-grey
light-grey
yellow

Here are the special variables:

assettag
BIOSversion
BMCversion
CIM_Chassis
CPLDversion
esxproduct
esxversion
hostname
ip
license
memory
OMC_MCFirmwareIdentity
OMC_SMASHFirmwareIdentity
OtherIdentifyingInfo
PLSAversion
serial-number
servicetag
ssl-thumbprint
supportperiod
supportstart
VersionString
VMware_HHRCSoftwareIdentity

There are two ways of updating the DCUI welcome banner: using local or remote esxcfg-advcfg or manually editing /etc/vmware/welcome file.

Here is an example of using vCLI's esxcfg-advcfg:

Here is what that looks like on the DCUI:

As you can see, this is not easy if you want to update multiple lines. You would need to add a lot more spaces to force newlines, but this becomes tedious and pretty much unreadable. The second method is edit the welcome file that is located in the Busybox Console, which requires you to enable ESXi's Tech Support Mode. I wrote a quick Perl script called generateDCUIScreen.pl which accepts an input file and allows a user to customize the output and the script generates the "welcome" file which is uploaded to your ESXi host.

Here is an example of the input file:

The script will parse the input file which will contain definitions for:

bgcolor and color as described above
special variables as described above (must use braces for variables to be translated)
custom text
"=space=" string which is unique to my script which generates the newlines

The script requires that you have Perl, but you do not need to have vSphere SDK for Perl. For ease of use, I executed the script using vMA.

Here is an example execution using the input file from above:

You will need to scp the new"welcome" file to your ESXi host under /etc/vmware which is empty by default. For the changes to take effect, you will need to run the following command at the console:

kill $(ps | grep dcui | awk '{print $1}')

This will kill dcui utility and watchdog process will spawn a new instance causing the change to take effect Note: A reboot will also do the job, but be sure to run /sbin/auto-backup.sh before doing so, that way the change will be backed up.

Here is what DCUI screen looks like:

As you can see, you can control variety of pre-defined variables including hostname and IP Address and custom text for your organization. This is useful for those that do not want to expose all the information that available on the default DCUI screen, which may be a security concern for some organizations. A few things to note, I was not able to fill the entire screen like the default DCUI banner and the "welcome" file is character sensitive and you need to use tabs or white spaces to force the background to get filled. There is also a limit in the number of characters per row before it wraps to the next line.

I am sure there is someone out there that will create some interesting ASCII art, but here is my 5min free hand attempt at it 😉

This can easily be integrated into a scripted install using the new ESXi 4.1 kickstart feature.

How to Disable a vmnic in ESX(i)

How to add a splash of color to ESXi DCUI Welcome Screen