CHROOT parameter == CHROOT=dirPath
-- default: none
-- restriction: super-user only on most of Unix
Change the root of file system to dirPath at the start
using chroot(2) system call,
restricting accessible (visible) files to ones under dirPath.
This is effective to isolate the DeleGate from the whole file system
of the host machine preventing DeleGate from possible destruction of them
by its bug or by intrusion.
DGROOT is interpreted after the root is changed.
A special case CHROOT="/" means using the value of
(default or specified) DGROOT as CHROOT and set DGROOT="/".
That is, DGROOT="/path" with CHROOT="/" are equal to
DGROOT="/" with CHROOT="/path".