My inability to see the issue came from the fact that all other
similar programs (I'm aware of) do in fact add the supplementary groups.
Then you are not aware of Bernstein daemontools, where setuidgid does
not. (-:
# /package/admin/djbwares/command/setuidgid operator id
uid=2(operator) gid=5(operator) groups=5(operator)
#
* http://jdebp.uk./Softwares/djbwares/guide/commands/setuidgid.xml
Setting only one group was the behaviour of the original tool. Setting
the supplementary groups as well is behaviour that others added to their
toolsets later. Bruce Guenter (in daemontools-encore) and I added it as
an optional behaviour for setuidgid.
# /package/admin/nosh/command/setuidgid operator id
uid=2(operator) gid=5(operator) groups=5(operator)
# /package/admin/nosh/command/setuidgid --supplementary operator id
uid=2(operator) gid=5(operator) groups=5(operator),1298(log)
#
* http://jdebp.uk./Softwares/nosh/guide/commands/setuidgid.xml
* http://untroubled.org/daemontools-encore/setuidgid.8.html
