mod_ruid2 is a suexec style module for apache 2.0, 2.2 and 2.4, based on
mod_ruid and mod_suid2 that allows the Apache webserver to run under the
UID and GID of the user account that controls a virtualhost. It also
includes functionality to chroot Apache into the virtualhost document
root prior to processing HTTP requests.
After processing each request, mod_ruid2 returns to its initial starting
state. For uid/gid changes this is done using linux capabilities. For
chroot, this is done by following a file descriptor that leads outside
of the chroot.
In versions of mod_ruid2 before 0.9.8, the filedescriptor used to break
out of the chroot is inherited by all Apache subprocesses. This allows
CGI scripts to also to break out of the chroot by performing a fchdir()
across the inherited file descriptor.
http://sourceforge.net/mailarchive/forum.php?thread_name=514C503E.4020109%40users.sourceforge.net&forum_name=mod-ruid-announce