10.6.2. How Does It Work?
Rescue mode uses the same Linux kernel, initrd ramdisk, and device probing that are used during the installation process to create a minimal work environment using only software loaded from the installation disc. The same code that is used to detect and mount existing Fedora partitions for an upgrade installation is used to mount the partitions during rescue mode.
The chroot command changes the definition of the root directory for one processin this case, a shelland any processes started by that shell. Changing the root directory effectively changes the PATH so that the software installed in the chroot environment (software on the hard disk) is used while the chroot is active. When you exit from the chroot shell, the root directory reverts to the root directory of the installation session, which is a ramdisk.
10.6.3. What About...
10.6.3.1. ...copying files to or from another machine while in rescue mode?
The scp command is available in rescue mode and can be used to copy files to or from another Fedora system (or other Linux host). You must enable the network interfaces in order for this to work.
To copy a file from an FTP or HTTP server, use wget :
sh-3.1# wget http://192.168.1.2/help.txt
10.6.3.2. ...using a GUI while in rescue mode?
Unfortunately, there's not enough of the supporting infrastructure in place in rescue mode to support the use of a GUI.
10.6.3.3. ...accessing software from the hard disk without using chroot?
Set your path to include directories on the mounted hard disk filesystems:
sh-3.1# PATH=$PATH:/mnt/sysimage/bin:/mnt/sysimage/usr/bin: /mnt/sysimage/sbin:/mnt/sysimage/usr/sbin:/mnt/sysimage/usr/local/bin
Type this command on one line.
10.6.4. Where Can I Learn More?
The Fedora Core Installation Manuaclass="underline" http://fedora.redhat.com/docs/fedora-install-guide-en/fc6/
The manpages for chroot , wget , scp , and lvm
10.7. Installing Xen Virtual Machines
Xen is a technology that permits one physical computer to act as two or more virtual machines (or domains ). Each domain is isolated from other domains, so administration privilege can be safely delegated; you can designate a system administrator for one domain and give him the root password for total control of that system, confident that he will not be able to touch the configuration of other domains.
Virtualization technology is also very helpful when testing multiple software versions or configurations, and since virtual machines can be migrated between physical systems, it provides a lot of flexibility for server deployment and management.
To use Xen, you must install a special kernel and utilities on your existing Fedora system, which then becomes your primary domain ( Domain-0 ). You can then install Fedora on as many additional domains as you want.
10.7.1. How Do I Do That?
To set up for Xen, install the kernel-xen and xen packages using Pirut or this command :
# yum -y install kernel-xen xen
Reboot your system. When the GRUB boot screen appears, press the spacebar to display the boot menu. Select the new xen kernel using the cursor keys, and then press Enter to boot.
To make your system boot the Xen kernel by default, edit /boot/grub/grub.conf (see Lab 10.5, "Configuring the GRUB Bootloader")
You can confirm that you are running the Xen kernel by using the uname command:
# uname -r
2.6.17-1.2564.fc6xen
The xend service should also be running, which you can confirm using the service command:
# service xend status
service xend is running
The Fedora installation that you are using is Domain-0 , the master domain. Additional virtual machines, called guest domains , must be installed from a network installation server. If you do not have one, you can quickly set up one within Domain-0 by inserting a Fedora Core DVD and typing:
# yum -y install httpd
...(Lines snipped)...
# setenforce 0
# ln -s /media/ disk /var/www/html/fedora
# service httpd start
Starting httpd: [ OK ]
The setenforce command just shown disables SELinux protection for your system, which presents a security risk. Re-enable SELinux as soon as you are finished using the network installation server:
# setenforce 1
To start the guest domain installation:
# xenguest-install
What is the name of your virtual machine? fedora
How much RAM should be allocated (in megabytes)? 256
What would you like to use as the disk (path)? /var/xen/fedora
How large would you like the disk to be (in gigabytes)? 2
Would you like to enable graphics support (yes or no) no
What is the install location? http://192.168.2.48/fedora
The name of the virtual machine can be any value that meets the requirements for a filename. The disk path and size requested are used to set up a file that will act as the hard disk for the guest domain. The install location is the URL of the network installation server; if you're using an HTTP server on Domain-0 , use the full IP address of that system instead of the loopback address 127.0.0.1 (since, inside a guest domain, the loopback destination is the guest domain itself, not Domain-0 ).
A regular Fedora installation will now start in text mode within the guest domain. After prompting you for the language and keyboard, the installer will give you the option of continuing with a text mode installation or using VNC for a graphical installation, as shown in Figure 10-29 .
Figure 10-29. Text mode and VNC installation options
This message indicates that the installer was unable to start X. This is normal, since the guest domain does not have a video card.