[clue] Change to credentials file in samba 4.

[David L. Anselmi]

So here's the problem:

sudo mount //server/dir /mnt --verbose -o credentials=.credentials

mount: no type was given - I'll assume cifs because of the // prefix
mount.cifs kernel mount options: ip=10.0.0.1,unc=\\server\dir,user=server\user,pass=********
mount error(13): Permission denied
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

And in kern.log:
Status code returned 0xc000006d NT_STATUS_LOGON_FAILURE
CIFS VFS: Send error in SessSetup = -13
CIFS VFS: cifs_mount failed w/return code = -13

It took a long time to figure out.  Finally, buried in a pile of sec=lanman (or ntlm, or ntlmv2, all 
of which did nothing useful):

sudo mount //server/dir /mnt --verbose -o domain=server,credentials=.credentials

Note the addition of domain= and change .credentials username:

was username=server\user
now username=user

Let's hope it's easier for the next poor sod to figure out.

Dave