Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment
entirely from CD-ROM, or some other boot method, instead of the system's
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
By booting the system from other installation boot media, such
as USB flash devices.
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:
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 other media 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 connection,
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.
The following message is displayed:
The rescue environment will now attempt to find
your 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
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
combination to access VC 1 and
to access VC 2):
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:
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 to return to the prompt.
If you selected Skip, you can still try to mount
a partition or LVM2 logical volume manually inside rescue mode by
creating a directory such as
/foo, and typing the
mount -t ext3 /dev/mapper/VolGroup00-LogVol02 /foo
In the above command,
/foo is a directory that
you have created and
is the LVM2 logical volume you want to mount. If the partition is of
type ext2, replace ext3 with
If you do not know the names of all physical partitions, use the following
command to list them:
If you do not know the names of all LVM2 physical volumes, volume
groups, or logical volumes, use the following commands to list them:
From the prompt, you can run many useful commands, such as:
ssh, scp, and
ping if the network is started
dump and restore for users with
parted and fdisk for
rpm for installing or upgrading
joe for editing configuration files
If you try to start other popular editors such as
emacs, pico, or
vi, the joe editor is
In many cases, the GRUB boot loader can mistakenly be deleted,
corrupted, or replaced by other operating systems.
The following steps detail the process on how GRUB is reinstalled on
the master boot record:
Boot the system from an installation boot medium.
Type linux rescue at the installation boot
prompt to enter the rescue environment.
Type chroot /mnt/sysimage to mount the root
Type /sbin/grub-install /dev/hda to reinstall
the GRUB boot loader, where /dev/hda is the
Review the /boot/grub/grub.conf file, as
additional entries may be needed for GRUB to control additional
Reboot the system.