Red Hat Enterprise Linux 3: System Administration Guide
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# 11.2. Booting into Rescue Mode

Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment entirely from a diskette, CD-ROM, or some other boot method instead of the system's hard drive.

As the name implies, rescue mode is provided to rescue you from something. During normal operation, your Red Hat Enterprise Linux system uses files located on your system's hard drive to do everything — run programs, store your files, and more.

However, there may be times when you are unable to get Red Hat Enterprise Linux running completely enough to access files on your system's hard drive. Using rescue mode, you can access the files stored on your system's hard drive, even if you cannot actually run Red Hat Enterprise Linux from that hard drive.

To boot into rescue mode, you must be able to boot the system using one of the following methods:

- By booting the system from an installation boot diskette.[1]

- By booting the system from an installation boot CD-ROM.[1]

- By booting the system from the Red Hat Enterprise Linux CD-ROM #1.

Once you have booted using one of the described methods, add the keyword `rescue` as a kernel parameter. For example, for an x86 system, type the following command at the installation boot prompt:

    linux rescue

You are prompted to answer a few basic questions, including which language to use. It also prompts you to select where a valid rescue image is located. Select from Local CD-ROM, Hard Drive, NFS image, FTP, or HTTP. The location selected must contain a valid installation tree, and the installation tree must be for the same version of Red Hat Enterprise Linux as the Red Hat Enterprise Linux CD-ROM #1 from which you booted. If you used a boot CD-ROM or diskette to start rescue mode, the installation tree must be from the same tree from which the media was created. For more information about how to setup an installation tree on a hard drive, NFS server, FTP server, or HTTP server, refer to the Red Hat Enterprise Linux Installation Guide.

If you select a rescue image that does not require a network connect, you are asked whether or not you want to establish a network connection. A network connection is useful if you need to backup files to a different computer or install some RPM packages from a shared network location, for example.

You will also see the following message:

    The rescue environment will now attempt to find your Red Hat
    Linux installation and mount it under the directory
    /mnt/sysimage.  You can then make any changes required to your
    system.  If you want to proceed with this step choose
    'Continue'. You can also choose to mount your file systems
    read-only instead of read-write by choosing 'Read-only'.
    If for some reason this process fails you can choose 'Skip'
    and this step will be skipped and you will go directly to a
    command shell.

If you select Continue, it attempts to mount your file system under the directory `/mnt/sysimage/`. If it fails to mount a partition, it notifies you. If you select Read-Only, it attempts to mount your file system under the directory `/mnt/sysimage/`, but in read-only mode. If you select Skip, your file system is not mounted. Choose Skip if you think your file system is corrupted.

Once you have your system in rescue mode, a prompt appears on VC (virtual console) 1 and VC 2 (use the <KEYCAP >[Ctrl]</KEYCAP >-<KEYCAP >[Alt]</KEYCAP >-<KEYCAP >[F1]</KEYCAP > key combination to access VC 1 and <KEYCAP >[Ctrl]</KEYCAP >-<KEYCAP >[Alt]</KEYCAP >-<KEYCAP >[F2]</KEYCAP > to access VC 2):

    sh-2.05b#

If you selected Continue to mount your partitions automatically and they were mounted successfully, you are in single-user mode.

Even if your file system is mounted, the default root partition while in rescue mode is a temporary root partition, not the root partition of the file system used during normal user mode (runlevel 3 or 5). If you selected to mount your file system and it mounted successfully, you can change the root partition of the rescue mode environment to the root partition of your file system by executing the following command:

    chroot /mnt/sysimage

This is useful if you need to run commands such as `rpm` that require your root partition to be mounted as `/`. To exit the chroot environment, type `exit`, and you will return to the prompt.

If you selected Skip, you can still try to mount a partition manually inside rescue mode by creating a directory such as ``/foo``, and typing the following command:

    mount -t ext3 /dev/hda5 /foo

In the above command, ``/foo`` is a directory that you have created and ``/dev/hda5`` is the partition you want to mount. If the partition is of type `ext2`, replace `ext3` with `ext2`.

If you do not know the names of your partitions, use the following command to list them:

    fdisk -l

From the prompt, you can run many useful commands such as

- `list-harddrives` to list the hard drives in the system

- `ssh`, `scp`, and `ping` if the network is started

- `dump` and `restore` for users with tape drives

- `parted` and `fdisk` for managing partitions

- `rpm` for installing or upgrading software

- `joe` for editing configuration files (If you try to start other popular editors such as `emacs`, `pico`, or `vi`, the `joe` editor will be started.)

### Notes

[1] | Refer to the Red Hat Enterprise Linux Installation Guide for more details.

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