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pivot_root

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Langue: en

Version: 364549 (ubuntu - 25/10/10)

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Section: 8 (Commandes administrateur)

NAME

pivot_root - change the root file system

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 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
 

SEE ALSO

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

AVAILABILITY

The pivot_root command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
Qu'il ne faut point tâcher de comprendre l'infini, mais seulement penser
que tout ce en quoi nous ne trouvons aucunes bornes est indéfini.
-+- René Descartes, Principes de la philosophie -+-