The following steps describes the steps to change the root password on the Unix system:
Prerequisites:
You must be able to boot the system using one of the following methods:
- By booting the system from an installation boot diskette
- By booting the system from an installation boot CD-ROM
- 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 [Ctrl]-[Alt]-[F1] key combination to access VC 1 and
[Ctrl]-[Alt]-[F2] 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
Change the root password using the following commands
sh-2.05b# passwd
Enter New root Password:
Source: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/3/html/System_Administration_Guide/s1-rescuemode-boot.html
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