Group permissions are broken?

[Michael Sierchio]

On Mon, Aug 15, 2011 at 1:06 PM, Yuri <yuri at rawbw.com> wrote:
> User john is a member of both webcamd and vboxusers:
> # grep john /etc/group
> webcamd:*:145:john
> vboxusers:*:920:john
>
> When the file /tmp/my-test is owned by webcamd, user john can touch it ok:
> $ ls -l /tmp/my-test ; touch  /tmp/my-test
> -rw-rw----  1 vboxusers  vboxusers  0 Aug 15 12:54 /tmp/my-test
>
> But when /tmp/my-test is owned by webcamd, user john gets an error:
> $ ls -l /tmp/my-test ; touch  /tmp/my-test
> -rw-rw----  1 webcamd  webcamd  0 Aug 15 13:02 /tmp/my-test
> touch: /tmp/my-test: Permission denied
>
> Why does this error occur? Two groups seem identical. Just different group
> ids.

/tmp has the sticky bit set.  man 8 sticky