Server boot issues

When you have installed Xen on your CentOS 7 server using this guide :

and on rebooting, the server hangs on a black screen with a blinking prompt then you will need to try to increase Dom-0 memory.

After the installation is completed, you can try to make an adjustment to the Domain0 memory parameters to. You’ll need to edit file /etc/default/grub

vi /etc/default/grub

The default for GRUB_CMDLINE_XEN_DEFAULT looks like this (For example):

GRUB_CMDLINE_XEN_DEFAULT=”dom0_mem=1024M,max:1024M cpuinfo com1=115200,8n1 console=com1,tty loglvl=all guest_loglvl=all”

You can make adjustments to the memory so it can look like this :

GRUB_CMDLINE_XEN_DEFAULT=”dom0_mem=2048M,max:4096M cpuinfo com1=115200,8n1 console=com1,tty loglvl=all guest_loglvl=all”

After you save your changes, run to update the grub2 configuration file.


After that command runs you can reboot your server. Once the server is back to a prompt, login and check running kernel :

uname -r

Next check Xen is running :

xl info

If it still fails to boot and shows a blank screen then you can disable I/OAT DMA Engine in BIOS. It was tested with the Dell server model R720 (gen. 12th) and server boots with Xen Kernel when I/OAT DMA Engine is off.

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