Active Directory (or AD) is a Microsoft authentication server software.
Small business server trust Edit
The SBS can't normally create a trust relationship with other domains, but there seems to be a workaround for it, which might be breaking the EULA although there's at least one article that argues against it.
Join Ubuntu machine to AD Edit
You can join your Ubuntu machine to the AD domain with the following steps: Edit /etc/nsswitch.conf and change the line:
hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
hosts: files dns mdns4_minimal mdns4 winbind
Then do the following (the domainjoin-cli command will require AD rights to join computers to the domain):
sudo apt-get update sudo apt-get install likewise-open sudo domainjoin-cli join DOMAIN.LOCAL Administrator sudo update-rc.d likewise-open defaults sudo /etc/init.d/likewise-open start
Default domain Edit
You can set the default domain in
/etc/samba/lwiauthd.conf, so you don't have to use DOMAIN\username as username everytime, with the following line:
winbind use default domain = yes