I tried to boot the ACS install DVD in my ACS virtual machine and it gave me an "unable to find ADE-OS" message and would not attempt an admin password reset. Here is how I worked around the issue:
1. Boot a CentOS/RHEL 5 or 6 DVD into recovery mode on your ACS VM. This may work with other Linux distro's, but I only used RHEL6 myself.
*NOTE: This will NOT work for hardware ACS platforms because of their RAID controller's proprietary driver. You can boot the ACS installer DVD and act like you are going to install again and switch to another console (Alt-F2, F3, or F4... one of those) and get a root prompt and do the same thing I do in step 3.
2. Once you are in linux, mount the ACS system with the 'chroot /mnt/sysimage' command.
3. Now cd into the /storageconfig directory and you should see another directory in there called startup-<number>
4. Inside this folder you will find your ACS server's startup configuration. Use the vi editor to open the file and change the admin password line to something like:
user admin password plain MyNewPassword role admin
5. Save the file, exit and reboot the server. You should now be able to log into the admin account via SSH or console with the 'MyNewPassword'
Don't waste time trying to edit the /etc/shadow or /etc/passwd files, or using the passwd command, these files are all replaced every time you reboot.
