Thanks Michael,

That buffer, `debug tramp/su ...` is quite large, 1269 lines. I've
attached it as a txt file, if you'd prefer me to post it somewhere or
paste it inline, let me know. There is a second debug buffer `debug
tramp/nil nil`, which contains only:

;; GNU Emacs: 25.2.1 Tramp: 2.2.13.25.2 -*- mode: outline; -*-
;; Location: /usr/local/share/emacs/25.2/lisp/net/tramp.elc Git: nil
08:34:19.239257 tramp-call-process (6) # ‘locale -a’ nil  *temp*
08:34:19.241458 tramp-call-process (6) # 0
C
C.UTF-8
en_CA.utf8
POSIX


Best,

Tyler

-- 
plantarum.ca

On Sat, Mar 4, 2017, at 08:37 AM, Michael Albinus wrote:
> Tyler Smith <tyler@plantarum.ca> writes:
> 
> > Hello,
> 
> Hi Tyler,
> 
> > From emacs -Q, I issue
> > `(require 'tramp)`, customize tramp-verbose to 10, and try to open a
> > file as root: `C-x C-f /su::/etc/fstab`. I'm then prompted for my root
> > password. Entering the password, Emacs pauses for ca. 10 seconds, then
> > appears to open a new file called fstab, but it's not the fstab that
> > already exists in /etc/fstab. The message about calling make-directory
> > to create the parent directories shows up, so I've apparently opened a
> > new file somewhere. I can't see where, exactly, as `C-x C-f`, or even
> > `M-x shell-commmand pwd` both prompt me for the root password, and then
> > fail. 
> >
> > Despite having turned `tramp-verbose` to the maximum value, there's not
> > much in my *Messages* buffer after all this:
> >
> > Creating customization setup...done  
> > Tramp: Opening connection for root@<myhostname> using su...  
> > Tramp: Sending command ‘exec su - root’  
> > Tramp: Waiting for prompts from remote shell...  
> > Tramp: Sending Password  
> > Tramp: Waiting for prompts from remote shell...failed  
> > Tramp: Opening connection for root@<myhostname> using su...failed  
> 
> This tells us that the su command hasn't been successful. When you have
> turned `tramp-verbose' to 10, there is a Tramp debug buffer. Pls show
> this.
> 
> > Best,
> >
> > Tyler
> 
> Best regards, Michael.