virt-install : ERROR the CPU is incompatible with host CPU: unknown host CPU

virt-install : ERROR the CPU is incompatible with host CPU: unknown host CPU

While installing operating system using the command virt-intsll or libvirt we might encounter the above error. The error might occur even if the cpu model is a popular one.

In some forums it is mentioned that this error could be because nx/xd feature of the CPU is not enabled, but some BIOS don't have this nx/xd feature at all making it very difficult to change or verify it.
The only work around that helped was using the cpu as "clear cpu configuration". That is while running the virt-install command pass the option "clear" for --cpu as shown below.

sudo virt-install --virt-type kvm --name guest --memory 2000 --cdrom debian.iso --disk pool=vmware,size=30 --cpu clear --video cirrus --os-variant debiansqueeze

If you are using libvirt then the option is available under hardware details->processor as shown in the figure below.

Setting this option might help get around the error.

use isoinfo to find if an iso image is bootable

Using iso images for installation is a common practice. But some isos might fail to boot when we try to use them. One of the reasons could be that the iso is not a bootable iso. One way to verify if the iso is bootable or now is to use the isoinfo command in linux.

isoinfo is a command that provides a lot of information regarding an iso file.

isoinfo: Usage: isoinfo [options] -i filename Options: -help,-h Print this help -version Print version info and exit -debug Print additional debug info -d Print information from the primary volume descriptor -f Generate output similar to 'find . -print' -J Print information from Joliet extensions -j charset Use charset to display Joliet file names -l Generate output similar to 'ls -lR' -p Print Path Table -R Print information from Rock Ridge extensions -s Print file size infos in multiples of sector size (2048 bytes). -N sector Sector number where ISO image should start on CD -T sector Sector number where actual session starts on CD -i filename Filename to read ISO-9660 image from dev=target SCSI target to use as CD/DVD-Recorder -x pathname Extract specified file to stdout

To view the information about whether the iso is bootable or not use the option -d.

isoinfo -d -i debian-8.7.1-i386-DVD-1.iso CD-ROM is in ISO 9660 format System id: Volume id: Debian 8.7.1 i386 1 Volume set id: Publisher id: Data preparer id: XORRISO-1.3.6 2014.04.08.180000, LIBISOBURN-1.3.6, LIBISOFS-1.3.6, LIBBURN-1.3.6 Application id: Copyright File id: Abstract File id: Bibliographic File id: Volume set size is: 1 Volume set sequence number is: 1 Logical block size is: 2048 Volume size is: 1949696 El Torito VD version 1 found, boot catalog is in sector 4808 Joliet with UCS level 3 found Rock Ridge signatures version 1 found Eltorito validation header: Hid 1 Arch 0 (x86) ID '' Key 55 AA Eltorito defaultboot header: Bootid 88 (bootable) Boot media 0 (No Emulation Boot) Load segment 0 Sys type 0 Nsect 4 Bootoff 12C9 4809

From the above output we can see that the iso has an Eltorito boot loader, thus it is a bootable iso. If the iso does not have a boot loader we would not see any boot loader information in the output of the above command.

We can also use the isoinfo command to list the contents of the iso usin the option -l

isoinfo -l -i debian-8.7.1-i386-DVD-1.iso