I identified the problem source: this version of Samba does not accept "security = share" any more and the /etc/init.d/nmbd script fails. The reason is that:
# samba-tool testparm --parameter-name="server role" WARNING: Ignoring invalid value 'share' for parameter 'security' ERROR: Unable to load default file however, this specific output is not checked for in /etc/init.d/nmbd, which fails without giving any meaningful error, and nothing meaningful is logged either. In short, before upgrading Samba, a check of configuration validity should be done and upgrading should be stopped if "security = share" is found in /etc/smb.conf. By the way, the configuration check could also warn about deprecated verbs in the configuration file. -- Francesco Potortì (ricercatore) Voice: +39.050.621.3058 ISTI - Area della ricerca CNR Mobile: +39.348.8283.107 via G. Moruzzi 1, I-56124 Pisa Skype: wnlabisti (entrance 20, 1st floor, room C71) Web: http://fly.isti.cnr.it