"S" mode for file permission?

[Tom H]

On Sat, Dec 12, 2020 at 6:46 PM Gary Aitken <ubuntu at dreamchaser.org> wrote:
>
> I'm having to fix some permissions in some ruby file hierarchies,
> and came across one with a 'S' for group (note, not 's'). man
> chmod doesn't mention 'S', although it does mention 'X'. Can
> someone tell me what 'S' represents, and why an attempt to chmod
> g+s results in a 'S'? Also, why it would be set that way for a
> particular directory when all others above it have 's'?

"rws" means that the sgid bit is set.

"rwS" means that the sgid bit is set and the file's not executable for
the group.