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Interrupt GRUB

Started by Calum Morrison , 11 October 2017 - 03:56 PM
5 replies to this topic

Best Answer Calum Morrison , Yesterday, 07:20 AM

Guys, thanks for your suggestions and help; luckily the correct password turned up and I am into the VM. Some useful info there though.

Calum Morrison Members

Calum Morrison
  • 3 posts

Posted 11 October 2017 - 03:56 PM

I've been asked to look at a CentOS guest running on Xen 6.5 but don't have the root password to get into it. 

All the usual attempts to break into it (press Esc, e or shift at boot) are failing as the screen is blank for the first few seconds of boot; the first thing I see displayed is:

 

PCI: Fatal: No config space access function found

Welcome to CentOS

Starting udev:

....

 

Is there any way in XenServer I can get into a guest to reset the root password?

 

thanks in advance



Tobias Kreidl CTP Member

Tobias Kreidl
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Posted 11 October 2017 - 07:58 PM

Did you try to set the VM to boot in "Single" instead of "graphical UTEF8" mode as a boot option?

 

Or, from the CLI, At "linux boot:" prompt (immediately after the BIOS messages and you only have two seconds to type this):

type/enter: menu.c32

 

Now you will enter a boot selection menu, select XE, then tab to edit entry.

 

For the XE entry add the key word "single" as shown below:

 

label xe  # XenServer
  kernel mboot.c32
  append /boot/xen.gz mem=1024G watchdog_timeout=300 cpuid_mask_xsave_eax=0 lowmem_emergency_pool=1M crashkernel=64M@32M console=vga vga=mode-0x0311 dom0_mem=3072M,max:4096M dom0_max_vcpus=1-8 --- /boot/vmlinuz-2.6-xen root=LABEL=root-yccsazim ro xencons=hvc console=hvc0 console=tty0 quiet vga=785 single --- /boot/initrd-2.6-xen.img

 

You will boot up in linux single user mode. However not much Xen functionality will be available, so maybe the next interactive boot mode procedure will be more useful.

 

-=Tobias


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Calum Morrison Members

Calum Morrison
  • 3 posts

Posted 12 October 2017 - 08:34 AM

Hi Tobias,

thanks for your help. I have now tried the "Single" boot option but it doesn't seem to help me; from a start up (in XenCenter), I don't see anything change on the console until the green progress bar at bottom right gets to 100% and the "PCI: Fatal: No config space access function found" prompt appears (i.e. no BIOS or equivalent) by which time it's too late.

I next went to the CLI (in XenCenter) for the host and tried booting it from there; that booted the machine, but there is nothing echoed to the screen that way so I was unable to Esc out of the boot. 

Is there anything else I can try?



Tobias Kreidl CTP Member

Tobias Kreidl
  • 18,831 posts

Posted 12 October 2017 - 04:22 PM

Oh, this is for a Linux guest OS. Here are some notes:

 

Rescue method #2 - detach vdi from vm and attach to second vm

Should a vm not be bootable or the root password is forgotten then use this procedure to mount disk onto a second running vm:

  1. from XenCenter vm-storage: detach VDI from original vm (note: make sure the vdi name/description is unique so that it can be identified)
  2. from XenCenter vm-storage: attach VDI on the second running vm
  3. in running vm: mount /dev/xvdb2 /mnt
  4. browse/edit as needed
  5. in running vm: umount /mnt
  6. typically before detach can work on second running vm
    1. from XenServer-acadvirtualX: xe vdi-disk-list vm=running-vm
    2. identify the associated VBD-UUID
    3. from XenServer-acadvirtualX: xe vbd-unplug uuid=VBD-UUID
  7. from XenCenter vm-storage: detach VDI on the second running vm
  8. from XenCenter vm-storage: attach VDI back on original vm
Rescue method #3 - Boot VMs from CDs

See http://forums.citrix.com/thread.jspa?messageID=1007675 for the source of this information.

Due to Linux machines being run in a para-virtualized environment, the "bios" that would normally boot the machine in a full-virtualization isn't used. So in order to boot from CD you will need to execute the following command on the acadvirtual machine.

 

HTH,

-=Tobias


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Marc O'Neill Citrix Employees

Marc O'Neill
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Posted 13 October 2017 - 11:06 AM

As this is 6.5 you should still be able to use the command line args. If you right click on the guest and choose properties you should have an option called "Boot Options" where you can specify the "single" option for the system to boot with.



Calum Morrison Members

Calum Morrison
  • 3 posts

Posted Yesterday, 07:20 AM

Guys, thanks for your suggestions and help; luckily the correct password turned up and I am into the VM. Some useful info there though.


Best Answer