Книга: Fedora™ Unleashed, 2008 edition

Using the Recovery Facility from the Installation Disc

Using the Recovery Facility from the Installation Disc

Rescue mode runs a version of Fedora from the DVD that is independent of your system and permits you to mount your root partition for maintenance. This alternative is useful when your root partition is no longer bootable because something has gone wrong. Fedora is constantly improving the features of the Recovery Facility.

On beginning the rescue mode, you get your choice of language and keyboard layouts. You are given an opportunity to configure networking in rescue mode and are presented with a nice ncurses-based form to fill in the information. The application attempts to find your existing partitions and offers you a choice of mounting them read-write, read only (always a wise choice the first time), or skip any mounting and drop to a command prompt. With multiple partitions, you must then indicate which is the root partition. That partition is then mounted at /mnt/sysimage. When you are finally presented with a command prompt, it is then possible to make your system the root file system with the following:

# chroot /mnt/sysimage

To get back to the rescue file system, type exit at the prompt. To reboot, type exit at the rescue system's prompt.

The rescue function does offer support for software RAID arrays (RAID 0, 1, and 5), as well as IDE or SCSI partitions formatted as ext2/3. After the recovery facility asks for input if it is unsure how to proceed, you eventually arrive at a command shell as root; there is no login or password. Depending on your configuration, you might or might not see prompts for additional information. If you get lost or confused, you can always reboot. (It helps to practice the use of the rescue mode.)

In rescue mode, a number of command-line tools are available for you, but no GUI tools are provided. For networking, you have the ifconfig, route, rcp, rlogin, rsh, and ftp commands. For archiving (and restoring archives), gzip, gunzip, dd, zcat, and md5sum commands are there. As for editors, vi is emulated by BusyBox, and pico, jmacs, and joe are provided by the joe editor. There are other useful system commands. A closer look at these commands reveals that they are all links to a program called BusyBox (home page at http://www.busybox.net/).

BusyBox provides a reasonably complete POSIX environment for any small or embedded system. The utilities in BusyBox generally have fewer options than their full-featured GNU cousins; however, the included options "provide the expected functionality and behave very much like their GNU counterparts." This means that you should test the rescue mode first to see whether it can restore your data and check which options are available to you because the BusyBox version will behave slightly differently than the full GNU version. (Some options are missing; some options do not work quite the same — you need to know whether this will affect you before you are in an emergency situation.)

There are a few useful tricks to know when using rescue mode. If your system is functional, you can use the chroot command to change the root file system from the CD to your system in this manner:

# chroot /mnt/sysimage

You will find yourself at a new command prompt with all your old files in — you hope — the right place. Your familiar tools — if intact — should be available to you. To exit the chrooted environment, use the exit command to return to the rescue system prompt. If you use the exit command again, the system reboots.

The rescue environment provides a nice set of networking commands and network-enabled tools such as scp, sftp, and some of the rtools. It also provides rpm, which can fetch packages over a network connection. Installing them is tricky because you want them installed in the file system mounted at /mnt/sysimage, not at /. To accomplish that, use the --root argument to set an alternative path to root:

# rpm -ivh --root /mnt/sysimage ftp://location/package.rpm

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