[Samba] mount.cifs -> Unisys MCP Mainframe -- Linux touch command "setting times of `testfile.txt': Permission denied"
jlayton at redhat.com
Wed Aug 31 13:41:25 MDT 2011
On Wed, 31 Aug 2011 14:55:26 -0400
Tim Lank <timlank at timlank.com> wrote:
> the mount.cifs is from (cifs-utils-4.8.1-2.el6.x86_64)
> On Tue, Aug 30, 2011 at 8:05 PM, Tim Lank <timlank at timlank.com> wrote:
> > I've got a share from a Unisys MCP Mainframe mounted with mount.cifs from
> > RHEL 6.1 (samba-common-3.5.6-86.el6.x86_64).
> > when I try to touch a file, it creates the file, but reports an error -
> > "setting times of `testfile.txt': Permission denied"
> > strace on the touch command shows that it is erroring out on the
> > utimensat() call
> > utimensat(0, NULL, NULL, 0) = -1 EACCES (Permission denied)
> > Documentation from the Unisys Mainframe can be found here....
> > http://public.support.unisys.com/aseries/docs/clearpath-mcp-12.0/pdf/70118328-103.pdf
> > Pages: C-2 and C3 show what POSIX functions are/not supported
> > utime() and utimensat() are not among the supported functions listed there.
> > Is there any combination of parameters to mount.cifs that can be used that
> > would prevent touch from reporting this error?
(cc'ing linux-cifs ml)
Most likely, this is a local (unix) permissions issue. CIFS has a rather
unintuitive permissions model. It attempts to enforce permissions
locally, but doesn't really have enough information to do so properly.
This leads to these sorts of problems.
When you create files as a particular user, then they end up being
owned by the "default" file owner on the mount rather than the user
that just created the file. Then when you go to set the time, the
kernel tries to enforce the permissions on the file and denies you
access to do so. This varies somewhat depending on whether CIFS posix
extensions are in force, but it's a common problem.
The best scheme is to switch the mount to being multiuser, but that
requires a kerberized setup at the moment.
Another workaround is to mount with '-o noperm' which disables local
permissions checking entirely. This will however allow any process on
the box to read and write to the server using the mount credentials.
Another idea is to get creative with the uid=,gid=,file_mode=, and
dir_mode= options. See the mount.cifs manpage. If you're careful, you
can craft a set of options that will allow the users you want to have
proper access without opening everything up.
My SambaXP talk from last year covers a lot of this in detail if you're
Jeff Layton <jlayton at redhat.com>
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