How can I add Ubuntu to a windows domain?

I'm not sure, but you also need to edit /etc/nsswitch.conf and change "host" line like this:

hosts:    wins files mdns4_minimal [NOTFOUND=return] dns mdns4

At least, it helped me

Have you checked the DC to see if the computer object already exists? If it does - delete it - then try to rejoin. If you have more problems you can try running the following command listed below to get some more verbose logging:

> domainjoin-cli --loglevel verbose
> --log /tmp/domainjoin.log join domain fqdn AD account

After searching a lot, i just find the way myself. The steps i have followed in ubuntu 10.10 to join windows domain are as follows,

• Open up the Ubuntu Software Center.
• Search for “centrify” (No quotes).
• Click Install.
• Type your sudo password and press Enter.
• Once the installation is finished you can then close out the Ubuntu Software Center.

Configure nsswitch file:

• Open the terminal and type the following,

  sudo editor /etc/nsswitch

• Search for the line that says

  hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4

• Put # infront of that line and add a new line

  hosts: files dns

• So that the file will look like

• Also edit the following file, sudo editor /etc/centrifydc/group.ignore

You need to add the group “admin” (no quotes) to this list. If you do not do this your sudo users will not longer have sudo privileges. Without sudo privileges your users will not be able to install applications or run anything that needs administrative permissions. Once you have configured that file, save it. You are now ready to join the domain.

Now its time to join the domain. Type the following in your terminal,

sudo adjoin -w DOMAIN -u USERNAME

You will get the following confirmation.

    karthick@karthick:~$ sudo adjoin -w XXX.XX.COM -u Administrator
    Administrator's Active Directory password: 
    Using writable domain controller: xxxxxx.xxx.xx.com
    Join to domain:XXX.XX.COM, zone:Auto Zone successful

    Centrify DirectControl started.
    Loading domains and trusts information


    You have successfully joined the Active Directory domain: XXX.XX.COM
    in the Centrify DirectControl zone: Auto Zone

    You may need to restart other services that rely upon PAM and NSS or simply
    reboot the computer for proper operation.  Failure to do so may result in
    login problems for AD users.