//po4a: entry man manual
= pivot_root(8)
:doctype: manpage
:man manual: System Administration
:man source: util-linux {release-version}
:page-layout: base
:command: pivot_root

== NAME

pivot_root - change the root filesystem

== SYNOPSIS

*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 current working directory 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).

== OPTIONS

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== EXAMPLE

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
....

== SEE ALSO

*chroot*(1),
*pivot_root*(2),
*mount*(8),
*switch_root*(8),
*umount*(8)

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