pivot_root — change the root file system
pivot_root
new_root
put_old
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).
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