sys-utils/pivot_root.8

   1 .TH PIVOT_ROOT 8 "August 2011" "util-linux" "System Administration"
   2 .SH NAME
   3 pivot_root \- change the root filesystem
   4 .SH SYNOPSIS
   5 .B pivot_root
   6 .I new_root put_old
   7 .SH DESCRIPTION
   8 \fBpivot_root\fP moves the root file system of the current process to the
   9 directory \fIput_old\fP and makes \fInew_root\fP the new root file system.
  10 Since \fBpivot_root\fP(8) simply calls \fBpivot_root\fP(2), we refer to
  11 the man page of the latter for further details.
  12
  13 Note that, depending on the implementation of \fBpivot_root\fP, root and
  14 cwd of the caller may or may not change. The following is a sequence for
  15 invoking \fBpivot_root\fP that works in either case, assuming that
  16 \fBpivot_root\fP and \fBchroot\fP are in the current \fBPATH\fP:
  17 .sp
  18 cd \fInew_root\fP
  19 .br
  20 pivot_root . \fIput_old\fP
  21 .br
  22 exec chroot . \fIcommand\fP
  23 .sp
  24 Note that \fBchroot\fP must be available under the old root and under the new
  25 root, because \fBpivot_root\fP may or may not have implicitly changed the
  26 root directory of the shell.
  27
  28 Note that \fBexec chroot\fP changes the running executable, which is
  29 necessary if the old root directory should be unmounted afterwards.
  30 Also note that standard input, output, and error may still point to a
  31 device on the old root file system, keeping it busy. They can easily be
  32 changed when invoking \fBchroot\fP (see below; note the absence of
  33 leading slashes to make it work whether \fBpivot_root\fP has changed the
  34 shell's root or not).
  35 .SH OPTIONS
  36 .TP
  37 \fB\-V\fR, \fB\-\-version\fR
  38 Display version information and exit.
  39 .TP
  40 \fB\-h\fR, \fB\-\-help\fR
  41 Display help text and exit.
  42 .SH EXAMPLES
  43 Change the root file system to /dev/hda1 from an interactive shell:
  44 .sp
  45 .nf
  46 mount /dev/hda1 /new-root
  47 cd /new-root
  48 pivot_root . old-root
  49 exec chroot . sh <dev/console >dev/console 2>&1
  50 umount /old-root
  51 .fi
  52 .sp
  53 Mount the new root file system over NFS from 10.0.0.1:/my_root and run
  54 \fBinit\fP:
  55 .sp
  56 .nf
  57 ifconfig lo 127.0.0.1 up   # for portmap
  58 # configure Ethernet or such
  59 portmap   # for lockd (implicitly started by mount)
  60 mount -o ro 10.0.0.1:/my_root /mnt
  61 killall portmap   # portmap keeps old root busy
  62 cd /mnt
  63 pivot_root . old_root
  64 exec chroot . sh -c 'umount /old_root; exec /sbin/init' \\
  65   <dev/console >dev/console 2>&1
  66 .fi
  67 .SH "SEE ALSO"
  68 .BR chroot (1),
  69 .BR pivot_root (2),
  70 .BR mount (8),
  71 .BR switch_root (8),
  72 .BR umount (8)
  73 .SH AVAILABILITY
  74 The pivot_root command is part of the util-linux package and is available from
  75 https://www.kernel.org/pub/linux/utils/util-linux/.