# [OmniOS-discuss] /usr/bin/chmod and the set-gid-bit

Hugh McIntyre lists at mcintyreweb.com
Wed Aug 7 23:30:09 UTC 2013

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    On 8/7/13 10:14 AM, Tim Rice wrote:
    > On Wed, 7 Aug 2013, Tobias Oetiker wrote:
    >
    >> Hi,
    >>
    >> /usr/bin/chmod seems to ignore the set-group-id bit when called
    >> with an octal permission string. try this on a zfs filesystem
    >
    > That behavior seems to be intentional for directories and is documented
    > in the man page.
    > It has been that way a long time. Probably since the SVR4.0 days.

    I always this assumed this was because of the typical usage on
    directories of setting the SGID bit at the top level of a directory and
    expecting the bit to then be set (and stay set) on all subsequently
    created directories all the way down.  Including in the presence of
    older software that just said "chmod 755".

    FWIW, Linux (e.g. Ubuntu 12.04) also does not allow you to clear the bit
    with octal mode, although they do allow you to set the SGID bit this
    way.  Arguably this is a better solution, but whether people will want
    to change the Illumos chmod at this point is debatable.  From Linux:

            chmod preserves a directory's set-user-ID and set-group-ID bits
            unless you explicitly specify otherwise.  You can set or clear
            the bits with symbolic modes like u+s and g-s, and you can set
            (but not clear) the bits with a numeric mode.

    Hugh.

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