superuser() -> constexpr uid_typeSuperuser ID. Always returns 0.
effective_user() -> uid_typeGet effective UID of the current process.
supergroup() -> constexpr gid_typeSuperuser group ID. Always returns 0.
group() -> gid_typeGet real GID of the current process.
effective_group() -> gid_typeGet effective GID of the current process.
user() -> uid_typeGet real UID of the current process.
Set both UID and GID of the current process.