Editing Setuid (section)

===When set on a directory===
Setting the <code>setgid</code> permission on a directory causes files and subdirectories created within to inherit its group ownership, rather than the primary group of the file-creating process. Created subdirectories also inherit the <code>setgid</code> bit. The policy is only applied during creation and, thus, only prospectively. Directories and files existing when the <code>setgid</code> bit is applied are unaffected, as are directories and files moved into the directory on which the bit is set.

Thus is granted a capacity to work with files amongst a group of users without explicitly setting permissions, but limited by the security model expectation that existing files permissions do not implicitly change.

The <code>setuid</code> permission set on a directory is ignored on most [[UNIX]] and [[Linux]] systems.<ref>{{cite web |title=27.5 Directories and the Set-User-ID and Set-Group-ID Bits |url=https://www.gnu.org/software/coreutils/manual/html_node/Directory-Setuid-and-Setgid.html#Directories-and-the-Set_002dUser_002dID-and-Set_002dGroup_002dID-Bits |website=GNU Coreutils 9.1 |publisher=Free Software Foundation |access-date=13 December 2022}}</ref>{{Citation needed|date=November 2017}} However [[FreeBSD]] can be configured to interpret <code>setuid</code> in a manner similar to <code>setgid</code>, in which case it forces all files and sub-directories created in a directory to be owned by that directory's owner - a simple form of inheritance.<ref>{{cite web |url=http://www.freebsd.org/cgi/man.cgi?query=chmod&apropos=0&sektion=0&manpath=FreeBSD+6.1-RELEASE&format=html |title=chmod -- change file modes|website=freebsd.org}}</ref> This is generally not needed on most systems derived from [[BSD]], since by default directories are treated as if their <code>setgid</code> bit is always set, regardless of the actual value. As is stated in <code>open(2)</code>, "When a new file is created it is given the group of the directory which contains it."<ref>{{cite web |title=open, openat -- open or create a file for reading, writing or executing|url=https://www.freebsd.org/cgi/man.cgi?query=open&sektion=2 |website=freebsd.org}}</ref>