Tutorial: Enumeration via SMB/CIFS

Enumerate Users
nmap -sS --script=smb-enum-users ip_address

Enumerate Shared Folders
nmap -sS --script=smb-enum-shares ip_address

Enumeration with Metasploit Auxiliary module
cd /pentest/exploits/msf3
./msfconsole

msf > scanner/smb/smb_enumusers
msf > set RHOSTS ip_address
msf > run