[Samba] Samba autofs autoumount problem with C$, D$, etc refusing to unmount

[Nico Kadel-Garcia]

This is primarily an autofs issue, but I wanted to get the problem and
the workaound into the Samba lists for reference. I use RHEL 5 and
RHEL 6 these days, and take advantage of CIFS automounting with the
built-in Samba pacakges. The problem still occurs with the more modern
cifs-utils that's been separated out in more recent Samba 3.6.x and
Samba 4 toolkits as well.

I use a very simple automounting setup. From /etc/auto.master:
   /mnt/cifs       /etc/auto.cifs  --timeout=600 --ghost

>From /etc/auto.cifs:
   # Default automounting for CIFS, all hosts
   # Restrictions go in auto.cifs.sub
   * -fstype=autofs,-Dhost=& file:/etc/auto.cifs.sub

>From /etc/auto.cifs.sub
  # Default "mount anything", not corrently enabled
  # 491 is a restricted loal user and gid, locked with no active shell.
  * -fstype=cifs,ro,credentials=/root/.cifs,uid=491,gid=491 ://${host}/&

That lets automounting work cleanly, with the credentials *out* of the
backups of the the /etc/ directory that I do for system maintenance.
(Never, never, never use your own credentials and leave them in the
backup system: that's begging to have your passwords stolen: and be
very careful about what uid and gid you use.)

The problem is that when I auto-mount drives such as \\windowsbox\C$
as /mnt/cifs/windowsbox/C$, the automounter can become confused by the
$. The result is that "mount" and "df" report things like
"/mnt/cifs/windowsbox/C$$$$" as being mounted, but they're not there,
and life gets very cofusing. This drives varous reporting of disk
usage insane. Rebooting clears it, but that sucks to do.

I have to assume it's a problem with how autofs parsing of the
"/mnt/cifs/windowsbox/C$" and logging it as
"/mnt/cifs/windowsbox/C$$$$$" and similar even longer names, and then
it can't be unmounted because it does not exist. But it causes
problems and complaints for CIFS and Samba users. The workaround is to
simply create the directories as needed: Duplicate the entry from the
error messages, and run these commands.

      mkdir -p 'mnt/cifs/windowsbox/C$$$$'
      umount 'mnt/cifs/windowsbox/C$$$$'

Note the single quotes!!!! Do not try to get cutesy and outsmart this
in shell scripting, the necessary backslash handling to get the $ into
the commands is awkward.

If folks want it, I'll publish a cleanup script. I just found this
workaround and wanted to get it into the search engines for the next
poor sucker.