From Linux Man Pages
pivot_root - change the root file system
pivot_root new_root put_old
DESCRIPTION
pivot_root moves the root file system of the current process to the directory put_old and makes new_root the new
root file system. Since pivot_root(8) simply calls pivot_root(2), we refer to the man page of the latter for
further details.
Note that, depending on the implementation of pivot_root, root and cwd of the caller may or may not change. The
following is a sequence for invoking pivot_root that works in either case, assuming that pivot_root and chroot
are in the current PATH:
cd new_root
pivot_root . put_old
exec chroot . command
Note that chroot must be available under the old root and under the new root, because pivot_root may or may not
have implicitly changed the root directory of the shell.
Note that exec chroot changes the running executable, which is necessary if the old root directory should be
unmounted afterwards. Also note that standard input, output, and error may still point to a device on the old
root file system, keeping it busy. They can easily be changed when invoking chroot (see below; note the absence
of leading slashes to make it work whether pivot_root has changed the shell's root or not).
EXAMPLES
Change the root file system to /dev/hda1 from an interactive shell:
mount /dev/hda1 /new-root
cd /new-root
pivot_root . old-root
exec chroot . sh <dev/console >dev/console 2>&1
umount /old-root
Mount the new root file system over NFS from 10.0.0.1:/my_root and run init:
ifconfig lo 127.0.0.1 up # for portmap
# configure Ethernet or such
portmap # for lockd (implicitly started by mount)
mount -o ro 10.0.0.1:/my_root /mnt
killall portmap # portmap keeps old root busy
cd /mnt
pivot_root . old_root
exec chroot . sh -c 'umount /old_root; exec /sbin/init' \
<dev/console >dev/console 2>&1
RELATED
chroot(1), mount(8), pivot_root(2), umount(8)
CATEGORY