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Using Google Authenticator To Provide Two-Factor Authentication For ESXi

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Last year, I came across an interesting open source project called Google Authenticator, which provides two-factor authentication by using both a PAM (Pluggable Authentication Module) module and a mobile application for generating one-time passcodes. This project sparked my curiosity and I wanted to see if I could get Google Authenticator to run on ESXi to provide additional security by requiring two-factor authentication when attempting to login to the ESXi Shell. After several attempts, I failed to get Google Authenticator working on ESXi and eventually gave up. I reported the behavior I saw in my environment in the Issues section of the project which did not yield any responses and I thought that was the end of that experiment.

Almost eight months later, I received a surprising email from two VMware engineers who were also interested in the Google Authenticator project and were able to figure out how to get Google Authenticator to work on ESXi. In sharing their findings, it turns out that the solution was actually quite simple and it just required commenting out three lines of C Macros in the Google Authenticator source code (tweak is documented in this blog post here). I was able to confirm the engineers findings in my home lab and was also able to build a custom Google Authenticator VIB for ESXi to help with the setup.

Disclaimer: This is not officially supported by VMware, use at your own risk

Installing Google Authenticator Custom VIB / Offline Bundle

Prerequisite:

  • Ensure that your ESXi host's clock is in sync with a proper time source (skew should be < 4minutes)
  • Keep a separate SSH connection open to your ESXi host, in case something goes wrong you can easily revert the changes else you can potentially lock yourself out

Step 1 - Download either the Google Authenticator VIB vghetto-google-auth.vib or offline bundle vghetto-google-auth.zip and upload it to the datastore of your ESXi host

Step 2 - You will need to change the acceptance level of your ESXi host to Community Supported as this is a requirement for any custom VIBs created. Run the following ESXCLI command:

esxcli software acceptance set --level CommunitySupported

Step 3 - To install Google Authenticator VIB, you will need to run the following ESXCLI command and specify the full datastore path of the VIB:

esxcli software vib install -v /vmfs/volumes/mini-local-datastore-1/vghetto-google-auth.vib -f

To install the Google Authenticator offline bundle, you will run the same command but instead of using the -v argument, you will specify the -d

Step 4 - You can verify the Google Authenticator was installed successfully by running the following ESXCLI command:

esxcli software vib get -n vGhetto-goog-auth

 

Configuring Google Authenticator & ESXi Configurations

Step 1 - Download the Google Authenticator app for your mobile phone. In this example, I am using the iPhone's Google Authenticator mobile app.

Step 2 - Next you will need to configure Google Authenticator for the ESXi host, run the google-authenticator command in the ESXi Shell which will start the setup.

You should see a URL as well as the secret key which you will need to enter into your Google Authenticator mobile app. You can either manually add your ESXi host into the mobile app by entering the secret key OR copy and paste the URL into a web browser which provides a QRC code that the mobile app can just read.

For all the prompted questions, you can use yes for the defaults.

Step 3 - You will need to add the following configuration to your SSHD configuration under /etc/ssh/sshd_config

ChallengeResponseAuthentication yes

Step 4 - You will also need to add the following entry to the following PAM configuration files /etc/pam.d/login and /etc/pam.d/sshd

auth   required   pam_google_authenticator.so

To add the entry into both files on the ESXi Shell, run the following two commands:

sed -i -e '3iauth       required     pam_google_authenticator.so\' /etc/pam.d/login
sed -i -e '3iauth       required     pam_google_authenticator.so\' /etc/pam.d/sshd

Note:  To ensure the above configuration persists after a reboot, you will need to add the two sed commands to /etc/rc.local.d/local.sh for ESXi 5.1 or /etc/rc.local for ESXi 5.0 hosts which will automatically add the entries upon bootup. 

Finally, you will need to restart the SSH daemon for the changes to go into effect by running the following command:

/etc/init.d/SSH restart

Step 5 - To validate that everything was configured correctly, open a new SSH session to your ESXi host. Instead of seeing the usual password prompt, you should now see a verification code prompt. Open up your Google Authenticator mobile app and enter the code that is displayed for your ESXi host and then enter the root password.

If everything was correct, you should now be authorized and logged into your ESXi host

Though the configuration could be a bit more automated including adding each ESXi host to your mobile application, this is a pretty nifty and free solution to provide two-factor authentication for your ESXi hosts. I am curious to see if others are interested in such functionality within ESXi or if this would be useful? Feel free to leave a comment.

Big thanks to VMware engineers who helped me get this solution to work!

How To "Pause" (Not Suspend) A Virtual Machine In ESXi?

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Last week I received a very interesting question from a fellow blogger asking whether it was possible to "pause" (not suspend) a virtual machine running on ESXi. Today ESXi only supports the suspend operation which saves the current memory state of a virtual machine to disk. With a "pause" operation, the memory state of the virtual machine is not saved to disk, it is still preserved in the physical memory of the ESXi host. The main difference with a "pause" operation is the allocated memory is not released and this allows you to quickly resume a virtual machine almost instantly at the cost of holding onto physical memory.

The use case for this particular request was also quite interesting. The user had an NFS server that housed about 200 virtual machines that needed to be restarted and the goal was to minimize the impact to his virtual machines as much as possible. He opted out from suspending the virtual machines as it would have taken too long and decided on a more creative solution. He filled up the remainder capacity on the datastore which in effect caused all virtual machines to halt their I/O operations. Though not an ideal solution IMHO, this allowed him to restart the NFS server and then run a script for the virtual machines to retry their I/O operation once the NFS server was available again.

Based on the above scenario, he asked if it was possible to "pause" the virtual machines similar to a capability Hyper-V provides today which would have provided him a quicker way to resume the virtual machines. Thinking about the question for a bit, a virtual machine is just a VMX process running in ESXi and I wondered if this process could be paused like a UNIX/Linux process using the "kill" command. Well, it turns out, it can be!

Disclaimer: This is not officially supported by VMware, use at your own risk.

Using the kill command, you can pause the VMX process by sending the STOP signal and to resume the VMX process, you can send the CONT signal. Before getting started, you will need to identify the PID (Process ID) for the virtual machine's VMX process.

There are two methods of identifying the parent VMX PID, the easiest is using the following ESXCLI command:

esxcli vm process list


The PID for the virtual machine will be listed under the "VMX Cartel ID" and in this example I have a virtual machine called vcenter51-1 and on the right I am pinging the system to verify it is up and running. An alternative way of identifying the PID is to use "ps" by running the following command:

ps -c | grep -v grep | grep [vmname]

Note: Make sure you identify the parent PID of the virtual machine if you are using the above command as you will see multiple entries for the different VMX sub-processes.

To pause the VMX process, run the following command (substitute your PID):

kill -STOP [pid]

To resume VMX process, run the following command:

kill -CONT [pid]

Here is a screenshot of pausing and then resuming the virtual machine. You can also see where the pings stop as the virtual machine is paused and then resumed. Once the virtual machine was resumed, it operated exactly where it left off with no issues as far as I can tell.
 
Note: I have found that if you have VM monitoring enabled, there maybe issues resuming the virtual machine. This should only be done if you have VM monitoring disabled as it may not be properly aware that the VMX process being paused on purpose.

Though it is possible to pause a virtual machine, I am not sure I see too many valid use cases for this feature? Are there are use cases where this feature would actually be beneficial, feel free to leave a comment if you believe there are. For now, this is just another neat "notsupported" trick 😉

How To Backup & Restore Free ESXi Host Configuration

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ESXi host configurations can easily be backed up and restored using either the vCLI's vicfg-cfgbackup or PowerCLI's Get-VMHostFirmware cmdlet. These commands along with others that perform "write" operations are only supported when you have a (paid) licensed version of ESXi. If you are using free ESXi, the remote commands are only available for "read-only" operations. For more details, please refer to this article here.

Note: In my personal opinion, it is much quicker and more efficient to re-install ESXi and apply your configurations using either a scripted deployment such as kickstart or a combination along with post configuration scripts. Re-installs become extremely trivial when you centralize your ESXi host configurations, even for small setups.

Having said that, if you are running free ESXi in a small shop or in a home lab and wish to backup your ESXi host configurations, you can still do so by leveraging a neat little tool called vim-cmd found within the ESXi Shell. There is a section under hostsvc/firmware which manages the ESXi host configuration which also uses the same vSphere APIs that both vicfg-cfgbackup & Get-VMHostFirmeware command uses.

Under this section of vim-cmd, there are four commands:

  • backup_config   
  • reset_config    
  • restore_config  
  • sync_config

Prior to actually backing up your ESXi host configuration, run the following command which will flush the ESXi configuration changes:

vim-cmd hostsvc/firmware/sync_config

To backup the ESXi host configurations, run the following command which will generate a file that will be automatically stored in /scratch/downloads and can also be downloaded from a web browser using the URL shown from the output:

vim-cmd hostsvc/firmware/backup_config

Before restoring your ESXi host configurations, you will need to ensure the file is renamed to configBundle.tgz and stored under /tmp directory. You will also need to ensure the ESXi host is placed in maintenance mode by running the following command:

vim-cmd hostsvc/maintenance_mode_enter

To restore the ESXi host configurations, run the following command and specify the backup configuration file which should reside in /tmp/configBundle.tgz:

vim-cmd hostsvc/firmware/restore_config /tmp/configBundle.tgz

Note: Upon completing the restore, it will automatically reboot your ESXi host.

Here is a screenshot using the above commands to backup and then restore ESXi host:

Note: You can not restore an ESXi host using a configuration file backed up from a different host.