## Setup a virtual kernel environment 



A couple of steps are necessary in order to prepare the system to build and run a virtual kernel.

### Setting up the filesystem 

The vkernel architecture needs a number of files which reside in `/var/vkernel`.  Since these files tend to get rather big and the `/var` partition is usually of limited size, we recommend the directory to be created in the `/home` partition with a link to it in `/var`:

    

    mkdir /home/var.vkernel
    ln -s /home/var.vkernel /var/vkernel

Next, a filesystem image to be used by the virtual kernel has to be created and populated (assuming world has been built previously):    

    dd if=/dev/zero of=/var/vkernel/rootimg.01 bs=1m count=2048
    vnconfig -c -s labels vn0 /var/vkernel/rootimg.01
    disklabel -r -w vn0s0 auto
    disklabel -e vn0s0      # add 'a' partition with fstype `4.2BSD' size could be '*'
    newfs /dev/vn0s0a
    mount /dev/vn0s0a /mnt


Assuming that you build your world before, you can populate the image now.  If you didn't build your world see [chapter 21](../updating-makeworld.html).

    

    cd /usr/src
    make installworld DESTDIR=/mnt
    cd etc
    make distribution DESTDIR=/mnt


Create a fstab file to let the vkernel find your image file.

    

    echo '/dev/vkd0s0a      /       ufs     rw      1  1' >/mnt/etc/fstab
    echo 'proc              /proc   procfs  rw      0  0' >>/mnt/etc/fstab


Edit `/mnt/etc/ttys` and replace the console entry with the following line and turn off all other gettys.

    console "/usr/libexec/getty Pc"         cons25  on  secure


Then, unmount the disk.

    

    umount /mnt
    vnconfig -u vn0



### Compiling the virtual kernel 

In order to compile a virtual kernel use the VKERNEL kernel configuration file residing in `/usr/src/sys/config` (or a configuration file derived thereof):
    

    cd /usr/src
    make -DNO_MODULES buildkernel KERNCONF=VKERNEL
    make -DNO_MODULES installkernel KERNCONF=VKERNEL DESTDIR=/var/vkernel



### Enabling virtual kernel operation 

A special sysctl(8), `vm.vkernel_enable`, must be set to enable vkernel operation:

    sysctl vm.vkernel_enable=1


To make this change permanent, edit `/etc/sysctl.conf`