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I am using Xen in CentOS 5.4. The guest vm is Centos 5.4 as well. How can I specify boot parameters before I can boot the VMs. I seem to have forgotten the root password for one of the VMs I created. I want to boot it into repair mode and change the password. Please suggest me the best way to achieve this.
Also, I tried to mount the vm disk image file but failed.
My question has everything to do with virtualization. I think you did not understand my problem well enough. I can't access the centos vm after booting it because I forgot the root password I set. So there is no way of modifying the grub config. I want to be able to pass a boot parameter, i.e., "single" so that the vm boots into single user mode which does not require a password. I could change the root password then.
I managed to mount the vm image file very painfully and have edited the config and set a new password. But I'd still like to know if and it is possible to pass boot parameter to guest linux guest vms beforehand. I tried using the "extra=whatever you want" line in vm config file but didn't work.
I'm afraid you do not understand what virtualization is, and how it works. You cannot pass OS level commands like that, unless the guest OS has a daemon listening for the command (usually over the hypercall device or simply over a network socket).
you can also pass keystrokes using qemuMonitor sendKey commands, but that's all.
Correct me if I'm wrong, but maybe you're just not bringing the console up fast enough, to be able to stop the grub prompt and enter the "single" option. In that case, it is possible to start qemu in paused mode, bring up the VNC console, and then unpause the VM, which gives you enough time for everything.