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Don Burleson Blog 







System Rescue and Reverting to an Image

Oracle Database Tips by Donald Burleson

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 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.


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.

Learn More about PC RAC:

If you want to learn RAC at home, get the bestselling book "Personal Oracle Real Application Clusters" by Edward Stoever.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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