“When I try to join the domain I get the message, "The machine account for this computer either does not exist or is not accessible." What's wrong?”

This problem is caused by the PDC not having a suitable Machine Trust Account. If you are using the add machine script method to create accounts, then this would indicate that it has not worked. Ensure the domain admin user system is working.

Alternately, if you are creating account entries manually, then they have not been created correctly. Make sure that you have the entry correct for the Machine Trust Account in smbpasswd file on the Samba PDC. If you added the account using an editor rather than using the smbpasswd utility, make sure that the account name is the machine NetBIOS name with a “$” appended to it (i.e., computer_name$). There must be an entry in both the POSIX UNIX system account backend as well as in the SambaSAMAccount backend. The default backend for Samba-3 (i.e., the parameter passdb backend is not specified in the smb.conf file, or if specified is set to smbpasswd, are respectively the /etc/passwd and /etc/samba/smbpasswd (or /usr/local/samba/lib/private/smbpasswd if compiled using Samba Team default settings). The use of the /etc/passwd can be overridden by alternative settings in the NSS /etc/nsswitch.conf file.

Some people have also reported that inconsistent subnet masks between the Samba server and the NT client can cause this problem. Make sure that these are consistent for both client and server.