There are numerous posts about how to use Active Directory to authenticate your ssh logins to your ESX servers.

Jason Boche,Travis Laird, Geert Baeke

The idea is pretty simple

1. Configure the ESX server with esxcfg-auth as in the above posts
2. Add the desired users locally on your ESX Server
3. Login away

But….

Once this is enabled  all authentication will be done against Active directory – INCLUDING THE root USER

Jason mentioned this on his post

Warning:  One thing to watch out for would the existance of a root account in AD in which you are not the owner of.  By implementing AD authentication, a root account in AD is going to be granted root level Service Console access on the ESX host!  Take the necessary precautions here.

Travis did as well and provided a solution as well

If you are not using root login through SSH and you want to exclude the root user login from attempting Active Directory authentication, modify the /etc/pam.d/system-auth file and add the parameter minimum_uid=1 to the following line so it reads:

auth sufficient /lib/security/$ISA/pam_krb5.so use_first_pass minimum_uid=1

Geert as well..

A couple of other things to think of:

• If you create a user in AD with account name root, you can logon as root with its AD password.
• If you don't want AD authentication for root, you can edit /etc/pam.d/system-auth. On the line that starts with auth and also includes pam_krb5.so, add this to the end: minimum_uid=1. Authentication for root (uid=0) will now be done locally only.

Now of course ssh login is disabled for root. But when trying to login I saw in the logs /var/log/secure that root was trying to authenticate against the domain.

Feb 17 10:32:08 esx2 sshd[5838]: pam_krb5[5838]: authentication fails for 'root' (root@MAISHK.LOCAL): User not known to the underlying authentication module (Clients credentials have been revoked)

(the root account exists in the domain, but is disabled)

So I wanted to add the solution as published above.

These are the contents of the /etc/pam.d/system-auth file

#%PAM-1.0

account      required pam_per_user.so   /etc/pam.d/login.map
auth         required pam_per_user.so   /etc/pam.d/login.map
password     required pam_per_user.so   /etc/pam.d/login.map
session      required pam_per_user.so   /etc/pam.d/login.map

As you can see, no auth sufficient or /lib/security/$ISA/pam_krb5.so in the file…

Hmmmmm….

So I gather that this has changed for ESX 4.0, session pointed to /etc/pam.d/login.map

These are the contents of the /etc/pam.d/login.map file

vpxuser  : system-auth-local
*        : system-auth-generic

OK. so all users except vpxuser are pointed to /etc/pam.d/system-auth-generic

These are the contents of the /etc/pam.d/system-auth-generic file

#%PAM-1.0
# Autogenerated by esxcfg-auth

account         sufficient      /lib/security/$ISA/pam_krb5.so
account         required        pam_unix.so

auth            required        pam_env.so
auth            sufficient      pam_unix.so         try_first_pass nullok
auth            sufficient      /lib/security/$ISA/pam_krb5.so              use_first_pass
auth            required        pam_deny.so

password        required        /lib/security/$ISA/pam_passwdqc.so          min=8,8,8,7,6 similar=deny match=0
password        sufficient      pam_unix.so         try_first_pass use_authtok nullok shadow md5
password        sufficient      /lib/security/$ISA/pam_krb5.so              use_authtok
password        required        pam_deny.so

session         optional        pam_keyinit.so              revoke
session         required        pam_limits.so
session         sufficient      /lib/security/$ISA/pam_krb5.so
session         [success=1 default=ignore]      pam_succeed_if.so           service in crond quiet use_uid
session         required        pam_unix.so

Yep! There it is!

So added the minimum_uid=1 to the file

auth            sufficient      /lib/security/$ISA/pam_krb5.so       use_first_pass minimum_uid=1

Feb 17 10:58:51 ilesx2 sshd[11906]: pam_unix(system-auth-generic:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=msaidelk-server.xxx.xxxx.com  user=root

And now I see in the log when logging in as root the authentication is
pam_unix(system-auth-generic:auth) and not pam_krb5

My Active Directory Authentication process is complete!!

Update:
Thanks to Armin van Lieshout for pointing this out to me. you can do this all with the command line as well    esxcfg-auth --enforce-local-auth=root

This will force local authentication for the defined user