disk-utils/README.bootutils-0.1

   1 bootutils-0.1
   2
   3 * ALPHA RELEASE: Use at your own risk! *
   4
   5 * You MUST have 0.99pl10 or later kernel to make use of all of the
   6   facilities of this package.  If you can live without the unmount-root
   7   feature, then 0.99pl9 will work. *
   8
   9 This is the first release of a set of utilities designed to automate
  10 the management and checking of filesystems at boot time and shutdown.
  11 It supports automatic and safe 'fsck' of all filesystems (including
  12 root) at boot time by booting with root readonly; if the fsck succeeds
  13 then root is remounted read-write and booting can continue.
  14
  15 Why bother?
  16
  17 Well, many people like to have a safe and reliable check of all their
  18 filesystems during boot.  This is especially true for ext2fs, because
  19 all ext2fs filesystems have a special 'clean' flag which gets set when
  20 the filesystem is cleaned (by e2fsck) or is unmounted cleanly, and
  21 which gets unset when the filesystem is active.  e2fsck can sense this
  22 flag, and will skip over filesystems which are clean.
  23
  24 This means that e2fsck won't bother you with a laborious filesystem
  25 check at each startup, as long as you always shut down cleanly; but it
  26 will check your filesystems automatically if you ever have a crash,
  27 because afterwards the filesystem 'clean' flags will not be set.  You
  28 *can* still mount an unclean filesystem, but ext2fs will give you a
  29 warning and will not mark it clean when it gets unmounted.
  30
  31 One of the problems with automatic fsck'ing is that it is unsafe to
  32 check mounted, active filesystems.  The solution is to initially mount
  33 only the root filesystem, and to mount it in readonly mode.  In this
  34 situation, fsck can run safely on all filesystems, without the danger
  35 that the kernel might start conflicting with the repairs being done to
  36 the filesystem.
  37
  38 If any repairs were done, it is unsafe to proceed any further because
  39 the kernel might have cached old information about the filesystems
  40 which has been updated by fsck.  However, if the fsck succeeded, then
  41 we can remount the root filesystem in read-write mode and proceed to
  42 mount all of the other filesystems.
  43
  44 Finally, in order to ensure that filesystems are correctly tidied up
  45 on shutdown, we need to unmount the root at shutdown.  This is usually
  46 done automatically; the standard Linux shutdown programs do a 'umount
  47 - -a' command to unmount all mounted filesystems.  You MUST have a
  48 0.99pl10 or later kernel for this to work.  Many versions of umount
  49 explicitly do not try to unmount the root, since pre-99pl10 kernels
  50 forbade this.  The umount included here will unmount even the root
  51 filesystem.  (A special kernel trick in pl10 allows this to work by
  52 keeping the filesystem alive in readonly mode after it has been tidied
  53 up.)
  54
  55 The bootup operation of this package is invoked by the /etc/rc shell
  56 script, an example of which is in mount/etc/rc.  It contains the
  57 following important lines:
  58
  59     # Check the integrity of all filesystems
  60     /bin/fsck -A -a
  61     # If there was a failure, drop into single-user mode.
  62     if [ $? -gt 1 ] ; then
  63             echo fsck failed.  Please reboot.
  64             sh
  65     fi
  66
  67     # Remount the root filesystem in read-write mode
  68     /etc/mount -n -o remount /dev/hda3 /
  69
  70     # remove /etc/mtab* so that mount will create it with a root entry
  71     /bin/rm -f /etc/mtab* /etc/nologin /etc/utmp
  72
  73     # mount file systems in fstab (and create an entry for /)
  74     # but not NFS because TCP/IP is not yet configured
  75     /etc/mount -avt nonfs
  76
  77
  78 This is the first attempt at a complete package for automated clean
  79 fsck support, so you may well find that you would like a slightly
  80 different behaviour.  Please feel free to send me comments, bug
  81 reports and improvements!
  82
  83
  84 This package includes three separate items, shamelessly adapted from
  85 other, more or less standard Linux programs.
  86
  87 * rdev.c: a modified rdev which is extended to allow the
  88   readonly/readwrite status of the kernel image to be altered.  Use
  89         rdev -R <kernel> 1
  90   to make the kernel mount in readonly mode.  This can be overridden
  91   by the use of the 'read-only' or 'read-write' keywords of the most
  92   recent version of LILO.
  93
  94 * Mount/umount package: This was recently posted to the net, and
  95   implements the '-o remount' mount option which allows filesystems to
  96   be remounted.  Unlike the previous post, the version included here
  97   also attempts to unmount the root filesystem on 'umount -a'.  I have
  98   also tried to clean up the man-pages.
  99
 100 * fsck package: David Engel's fsck front-end.  Read the README for it.
 101   This package implements the 'fsck -A' command which will check all
 102   filesystems in /etc/fstab automatically.
 103
 104 Stephen Tweedie <sct@dcs.ed.ac.uk>