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:
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 neces-
sary 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
Display version information and exit.
Display help text and exit.
Change the root file system to /dev/hda1 from an interactive shell:
mount /dev/hda1 /new-root
pivot_root . old-root
exec chroot . sh <dev/console >dev/console 2>&1
Mount the new root file system over NFS from 10.0.0.1:/my_root and run
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
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