mount.cifs for mounting NAS unit not working on 17.10

This worked fine on 17.04:

sudo mount -v -t cifs -o username=myname,password=mypassword //nas/share /mnt/nas

Now on 17.10 it gives me:

mount.cifs kernel mount options: ip=192.168.1.150,unc=\\nas\share,user=myname,pass=********
mount error(95): Operation not supported
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

A singularly unhelpful error message, given that the manpage hasn't changed. I can't figure out how to increase the verbosity of the error message beyond the above. How do I persuade mount.cifs to tell me what it doesn't like?

2 Answers

Never mind. Solved.

"cifs troubleshooting" turned out to be the magic words for Google, rather than "mount verbosity" etc.

# modprobe cifs
# echo 7 > /proc/fs/cifs/cifsFYI
# mount... etc.
# dmesg

Gave me:

CIFS VFS: Dialect not supported by server. Consider specifying
vers=1.0 or vers=2.1 on mount for accessing older servers

And adding "vers=2.1" to the options fixed it.

After doing a modprobe / dmesg, I got this message:

No dialect specified on mount. Default has changed to a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS (SMB1). To use the less secure SMB1 dialect to access old servers which do not support SMB3 (or SMB2.1) specify vers=1.0 on mount.

Thus it worked adding the "vers=1.0" to the options.