Changing the password on the RHEL 7 kvm qcow2 download (links updated 3/15/2016)

(Links updated / last reviewed March 15, 2016)

Environment

• Freshly downloaded RHEL7 qcow2 KVM image to be a guest virtual system under KVM virtualization.
• Red Hat Enterprise Linux 6 as the host system running KVM virtualization.
• This is in review for Fedora Linux as a host system running KVM virtualization (this review is not completed)

Introduction

You will find you need to change the password if you download a RHEL 7 kvm qcow2 image. This discussion goes into two different methods to do this. Make a note in the discussion area if you happen to have any suggestions etc...

Red Hat Enterprise Linux 7.x is now Generally Available (GA) (getting started guide) and available including in a qcow2 KVM image at the Red Hat Enterprise Linux product page (NOTE: a subscription is required, and this link is subject to change). The image is approximately 5 GB). You have to "root the system" after attaching it to a KVM session.

Download 7.2 KVM image at:

• Use this link to download 7.2 RHEL qcow2 image (link last checked 3/15/2016)

Method 1, Red Hat Documentation, Recovering Root Password (with grub 2)

See Red Hat Enterprise Linux 7 System Administrator's Guide: Changing and Resetting the Root Password.

Method 2 - Using "guestfish" to change the Password for the root account

You can use guestfish to edit a running system under KVM virtualization:
- You can use "guestfish" to edit the /etc/shadow file and change the root password.
- Guestfish is an interactive shell that you can use from the command line or from shell scripts to access guest virtual machine file systems. (See example below):

• If needed, first install the guestfish rpm.
• Red Hat Enterprise Linux 7.x (This command will not work on Fedora, If you are using Fedora Linux, see next block)

        

yum -y install guestfish

Thanks Ben Woodard from Red Hat FEDORA LINUX 20

# yum -y install libguestfs-tools

• Import the qcow2 image into KVM. The image will be named something along the lines of: "rhel-guest-image-7.1-20150224.0.x86_64.qcow2", (as of July 2nd, 2015, the version will of course change over time)
  • Change the password on the newly imported KVM to get on the pre-built system.

Example steps to change the root password using guestfish:
- This set of instructions is for use on the host system that has the kvm RHEL 7 guest. The following is from Red Hat solution ID 641193
- The syntax is: guestfish --rw -a <image-name>
- (Note, your system may be /dev/vda1, mine was /dev/sda1. Use the 'list-filesystems' command)

root@box1 # guestfish --rw -a ./rhel-guest-image-7.1-20150224.0.x86_64.qcow2
><fs> run
><fs> list-filesystems
><fs> mount /dev/sda1 /
><fs> vi /etc/shadow

NOTE: after you perform the following steps you use "quit" to exit. 
DO NOT EXIT NOW, proceed with the following steps

• Replace the encrypted password (add it while you are still in vi).
  This will set the password for the image permanently.
• An encrypted password can be created using the openssl command (see an example below).

NOTE: Open a separate terminal window to create an encrypted password with the openssl command (see example just below)

Separate window, different terminal window

[root@someothersystem ~]# openssl passwd -1 changeme
$1$QiSwNHrs$uID6S6qOifSNZKzfXsmQG1

• There is a vi session open from the guestfish session mentioned above.
• Copy the output of the openssl command above and appropriately place it into the /etc/shadow file you have opened with vi.

When done type "quit"

><fs> quit

原文参见：https://access.redhat.com/discussions/664843