I was just reading about the effect of Set-user-Id and Set-group-Id bits on file creation, as they seem like they would be useful for me. Unfortunately, most of the documentation I have managed to find is related to GNU systems, and this could easily be different in OpenBSD. https://www.gnu.org/software/coreutils/manual/html_node/Directory-Setuid-and-Setgid.html
It appears that they have no effect on file creation. Rather, they a only "on execution", as specified in the manual. https://man.openbsd.org/chmod FreeBSD similarly seems to ignore these settings. https://www.freebsd.org/doc/handbook/permissions.html Perhaps this is why there is only GNU documentation on this feature; it seems that it does not exist in OpenBSD. Am I correct in my conclusion that files created in OpenBSD are always owned by the creator and group-owned by the directory's group? That is, a GNU system would mimic this behaviour when u-s,g+s (6000) is set on the directory? Suppose, for example, I run this as root. mkdir /test chown root:wheel /test chmod a+rwx,u-s,g-s /test And then this as tlevine touch /test/a This is the result. $ ls -lhd /test{,/a} drwxrwxrwx 2 root wheel 512B Jul 1 12:46 /test -rw-r--r-- 1 tlevine wheel 0B Jul 1 12:46 /test/a I repeat the process, except that I set the user and group id this time. As root, rm -R /test mkdir /test chown root:wheel /test chmod a+rwx,u-s,g-s /test As tlevine, touch /test/a The resulting /test/a has the same owner and group as before. $ ls -lhd /test{,/a} drwsrwsrwx 2 root wheel 512B Jul 1 12:48 /test -rw-r--r-- 1 tlevine wheel 0B Jul 1 12:48 /test/a Very conveniently for me, this behaviour (u-s,g+s in GNU) is the mode that I want. Perhaps this is by design.
