pivot_root
change the root filesystem
see also :
chroot - mount - umount
Synopsis
pivot_root
new_root put_old
add an example, a script, a trick and tips
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
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).
availability
The pivot_root command is part of the util-linux package and is
available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
see also
chroot ,
mount , pivot_root, umount