[CentOS] Windows 2003 AD, Winbind, Kerberos and NFSv4

Fri Jul 2 18:27:35 UTC 2010
James A. Peltier <jpeltier at fas.sfu.ca>

Hi All,

I'm having a bit of difficulty getting a CentOS 5.5 Kerberized NFSv4 
server working.  This server is configured as a Winbind client to a 
Windows 2003 Active Directory.  I've successfully bound it to AD and I am 
able to authenticate.  I've successfully created a NFSv4 entry in 
/etc/exports to export the /exports directory and I can successfully mount 
a non-Kerberized NFSv4 mount on a client machine.  I now want to take it 
to the next step and add Kerberos and it doesn't seem to be working for 
me.  Below are my configurations and the steps I performed.

Fresh install of CentOS 5.5. Non-Kickstarted.  Wanted to get it working 
manually first.

Used the First Boot Authentication Wizard to configure Winbind Support for 
User Information.

Configured Winbind and Kerberos under the Authentication Tab

Checked Local auth is sufficient and Create home directories under options

The computer successfully joins the domain and appears in the Computer 
container in AD.  Below is the extract from /etc/samba/smb.conf for 
authconfig plus what I changed, everything else is stock.

I disabled the firewall and SELinux is running in permissive mode on both 
the test server and test client.

#======================= Global Settings =====================================


# Generated by authconfig on 2010/07/01 18:32:54
# DO NOT EDIT THIS SECTION (delimited by --start-line--/--end-line--)
# Any modification may be deleted or altered by authconfig in future

    workgroup = MY.AD.NAME
    password server = MY.AD.SERVER
    realm = MY.AD.NAME
    security = ads
    idmap uid = 16777216-33554431
    idmap gid = 16777216-33554431
    template shell = /bin/bash


#-- my additions/changes-start --
    template homedir = /home/%U
    winbind use default domain = true
    winbind offline logon = true
    winbind nested groups = true
    winbind refresh tickets = true
    use spnego = yes
    use kerberos keytab = yes
#-- my additions/changes-end --

It also created an appropriate, I believe, /etc/krb5.conf to which I 
removed only the .example.com stuff resulting in the following file.

  default = FILE:/var/log/krb5libs.log
  kdc = FILE:/var/log/krb5kdc.log
  admin_server = FILE:/var/log/kadmind.log

  default_realm = MY.AD.NAME
  dns_lookup_realm = false  # with and without true tried for these
  dns_lookup_kdc = false
  ticket_lifetime = 24h
  forwardable = yes

  MY.AD.NAME = {
   kdc = MY.AD.SERVER
   admin_server = MY.AD.SERVER
   kdc = MY.AD.SERVER

  my.ad.name = MY.AD.NAME
  .my.ad.name = MY.AD.NAME
  pam = {
    debug = false
    ticket_lifetime = 36000
    renew_lifetime = 36000
    forwardable = true
    krb4_convert = false

If I log into this host I am properly issued a Kerberos ticket from AD so 
it would appear that Kerberos is working properly

[jpeltier at oak ~]$ ssh aconite klist
jpeltier at aconite's password:
klist: You have no tickets cached
Ticket cache: FILE:/tmp/krb5cc_16777216_ltvWwy
Default principal: jpeltier at MY.AD.NAME

Valid starting     Expires            Service principal
07/02/10 10:46:43  07/02/10 20:46:43  krbtgt/MY.AD.NAME at MY.AD.NAME
         renew until 07/02/10 20:46:43

Kerberos 4 ticket cache: /tmp/tkt16777216
[jpeltier at oak ~]$

Now I configured NFSv4 exports on the server

/exports	*(rw,fsid=0)

Edited /etc/sysconfig/nfs to change

# Set to turn on Secure NFS mounts.


# Set to turn on Secure NFS mounts.

restarted NFS service and it appears as an export

[root at aconite ~]# /etc/init.d/nfs restart
Shutting down NFS mountd:                                  [  OK  ]
Shutting down NFS daemon:                                  [  OK  ]
Shutting down NFS quotas:                                  [  OK  ]
Shutting down NFS services:                                [  OK  ]
Shutting down RPC svcgssd:                                 [  OK  ]
Starting RPC svcgssd:                                      [  OK  ]
Starting NFS services:                                     [  OK  ]
Starting NFS quotas:                                       [  OK  ]
Starting NFS daemon:                                       [  OK  ]
Starting NFS mountd:                                       [  OK  ]

[root at aconite ~]# exportfs
/exports        <world>
[root at aconite ~]#

To support NFSv4 with Kerberos security, we also need to generate service 
principal for NFS:

[root at aconite ~]# net -U administrator ads keytab add nfs

which then looks like this

[root at aconite ~]# klist -k
Keytab name: FILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
    3 host/aconite.my.ad.name at MY.AD.NAME
    3 host/aconite.my.ad.name at MY.AD.NAME
    3 host/aconite.my.ad.name at MY.AD.NAME
    3 host/aconite at MY.AD.NAME
    3 host/aconite at MY.AD.NAME
    3 host/aconite at MY.AD.NAME
    3 nfs/aconite.my.ad.name at MY.AD.NAME
    3 nfs/aconite.my.ad.name at MY.AD.NAME
    3 nfs/aconite.my.ad.name at MY.AD.NAME
    3 nfs/aconite at MY.AD.NAME
    3 nfs/aconite at MY.AD.NAME
    3 nfs/aconite at MY.AD.NAME

Test on the client

[root at celastrina ~]# showmount -e aconite
Export list for aconite:
/exports *
[root at celastrina ~]# mount -t nfs4 aconite:/ /mnt
[root at celastrina ~]# mount |grep -i nfs4
aconite:/ on /mnt type nfs4 (rw,addr=
[root at celastrina ~]#

So as you can see everything is now working *without* Kerberos.  However, 
if I change the /etc/exports file on aconite to

[root at aconite ~]# cat /etc/exports
/exports        gss/krb5(rw,fsid=0)
[root at aconite ~]# exportfs
/exports        gss/krb5

and then try to mount with the -o sec=krb5 on the client

[root at celastrina ~]# mount -t nfs4 -o sec=krb5 aconite:/ /mnt
mount.nfs4: Permission denied

and the entry in /var/log/messages on celastrina is

Jul  2 11:21:57 celastrina rpc.gssd[3302]: Using keytab file 
Jul  2 11:21:57 celastrina rpc.gssd[3302]: WARNING: Failed to obtain 
machine credentials for connection to server aconite.my.ad.name

nothing appears in the logs on aconite.

If you've been kind enough to read this entire thread could you be kind 
enough to let me know what I am missing or doing wrong?  It seems so close 
now that I can taste it, but this one last piece doesn't seem to want to 
fall into place. :(

James A. Peltier
Systems Analyst (FASNet), VIVARIUM Technical Director
HPC Coordinator
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.fas.sfu.ca | http://vivarium.cs.sfu.ca
MSN     : subatomic_spam at hotmail.com

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