The `pivotchroot` program

pivotchroot performs a pivot_root system call, then changes root to the new root filesystem and executes a program.

Interface

     pivotchroot newroot putold prog...

pivotchroot sets the root filesystem to newroot, which must be a mounted filesystem entry point. The old root filesystem will be available under putold (relative to the old root).
pivotchroot changes directory to the new root, performs a chroot system call to the new root, and executes prog with its arguments. prog is searched under the new root.
pivotchroot exits 111 on a temporary error.