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It takes a long time to set up the operating
system for a RAC install only to discover on reboot that a
typographical error in a configuration is preventing the node from
booting. If a problem such as this occurs, it is necessary to boot to
a different Linux kernel, mount the disk with the offending
configuration file and edit the file.
Chapter 2 covers downloading and burning to CD the
software SystemRescueCd freely available at http://www.sysresccd.org/.
This software is a bootable Linux kernel which includes a complete set
of Linux commands that can be used to rescue a node that will not
boot. The CD includes many other programs, most notably Partimage.
This program can be used to quickly make a compressed image of a
partition and will back up all the work done to configure a node up to
that point.
The tricky part of using SystemRescueCd is
mounting the right file system. Figure D.1 shows a screenshot of using
the command fdisk ‑l to determine the available hard disk partitions.
Take note, the names of partitions such as /dev/hda1 and /dev/hda2
that are used in Fedora are quite different when using SystemRescueCd.
As Figure D.1 shows, the first hard drive is called /dev/ide/host0/bus0/target0/lun0/disc
and the first partition is called /dev/ide/host0/bus0/target0/lum0/part1.
There are a few mount-points available in the
directory /mnt. As an alternative, a new mount-point can be created
with the command mkdir /mnt/mount‑point‑name, using whatever name for
the mount-point that is preferred such as /mnt/hd.
Mounting a partition requires a rather lengthy
command. The file system type switch is optional:
mount /dev/ide/host0/bus0/target1/lun0/part1 /mnt/hd -t ext3.
Once a file system is mounted, it is a simple
matter to use the vieditor to edit
and save a configuration file. A wide range of Linux commands can be
used to create, delete, move, compile, change file attributes or do
most anything that needs done to fix a problem.
Partimage
The SystemRescueCd includes Partimage, an
easy-to-use software for taking an image of a partition. That image
can later be used to revert to that point in the configuration.
Partimage was used repeatedly in writing this book and is worthy of
mention.
The nodes used for writing this book had two
internal hard disks installed. On a given node, the hard disk used for
installing Fedora and Oracle was the one with the most space, between
10 to 20 gigabytes. The smaller disk was used to store images of the
install.
To take an image of a partition, boot to the
SystemRescueCd and mount the partition used for storing images as
shown in Figure D.1. Do not mount the other partitions. Launch the
software with the command partimage.
Follow the steps on the partimage screen. It is a
simple matter to determine the partitions to save. The boot partition
will be small and its file system will be ext3. The Fedora partition
will be large and its file system will be ext3. Take images of both.
Saving an image takes about one minute per 500
megabytes when saving to a partition on a separate physical disk;
whereas, saving a partition to a file on the same physical disk will
take much longer. The image file of a partition will likely require 10
to 20 percent of the disk space required for the entire partition.
Reverting to a partition is also very simple and
much faster than saving. It takes from 5 to 7 minutes to revert to a
saved image for a partition of 15 gigabytes when using separate
physical disks.
The most desirable points in which to take an
image of the system are just before the Oracle 9i software install and
just before the install of each Oracle 10g release.
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