--- layout: doc title: Managing VM kernel permalink: /doc/managing-vm-kernel/ redirect_from: - /en/doc/managing-vm-kernel/ --- VM kernel managed by dom0 ------------------------- By default VMs kernels are provided by dom0. This means that: 1. You can select kernel version in VM settings; 2. You can modify kernel options in VM settings; 3. You can **not** modify any of above from inside of VM; 4. Installing additional kernel modules is cumbersome. To select which kernel a given VM will use, you can use either use Qubes Manager (VM settings, advanced tab), or `qvm-prefs` tool: ~~~ [user@dom0 ~]$ qvm-prefs my-appvm -s kernel Missing kernel version argument! Possible values: 1) default 2) none (kernels subdir in VM) 3) , one of: - 3.18.16-3 - 3.18.17-4 - 3.19.fc20 - 3.18.10-2 [user@dom0 ~]$ qvm-prefs my-appvm -s kernel 3.18.17-4 [user@dom0 ~]$ qvm-prefs my-appvm -s kernel default ~~~ To check/change the default kernel you can go either to "Global settings" in Qubes Manager, or use `qubes-prefs` tool: ~~~ [user@dom0 ~]$ qubes-prefs clockvm : sys-net default-fw-netvm : sys-net default-kernel : 3.18.17-4 default-netvm : sys-firewall default-template : fedora-21 updatevm : sys-firewall [user@dom0 ~]$ qubes-prefs -s default-kernel 3.19.fc20 ~~~ Installing different kernel using Qubes kernel package ================================== VM kernels are packages by Qubes team in `kernel-qubes-vm` packages. Generally system will keep the 3 newest available versions. You can list them with the `rpm` command: ~~~ [user@dom0 ~]$ rpm -qa 'kernel-qubes-vm*' kernel-qubes-vm-3.18.10-2.pvops.qubes.x86_64 kernel-qubes-vm-3.18.16-3.pvops.qubes.x86_64 kernel-qubes-vm-3.18.17-4.pvops.qubes.x86_64 ~~~ If you want more recent version, you can check `qubes-dom0-unstable` repository. As the name suggest, keep in mind that those packages may be less stable than the default ones. Checking available versions in `qubes-dom0-unstable` repository: ~~~ [user@dom0 ~]$ sudo qubes-dom0-update --enablerepo=qubes-dom0-unstable --action=list kernel-qubes-vm Using sys-firewall as UpdateVM to download updates for Dom0; this may take some time... Running command on VM: 'sys-firewall'... Loaded plugins: langpacks, post-transaction-actions, yum-qubes-hooks Installed Packages kernel-qubes-vm.x86_64 1000:3.18.10-2.pvops.qubes installed kernel-qubes-vm.x86_64 1000:3.18.16-3.pvops.qubes installed kernel-qubes-vm.x86_64 1000:3.18.17-4.pvops.qubes installed Available Packages kernel-qubes-vm.x86_64 1000:4.1.12-6.pvops.qubes qubes-dom0-unstable No packages downloaded Installed Packages kernel-qubes-vm.x86_64 1000:3.18.10-2.pvops.qubes @anaconda/R3.0 kernel-qubes-vm.x86_64 1000:3.18.16-3.pvops.qubes @/kernel-qubes-vm-3.18.16-3.pvops.qubes.x86_64 kernel-qubes-vm.x86_64 1000:3.18.17-4.pvops.qubes @qubes-dom0-cached ~~~ Installing new version from `qubes-dom0-unstable` repository: ~~~ [user@dom0 ~]$ sudo qubes-dom0-update --enablerepo=qubes-dom0-unstable kernel-qubes-vm Using sys-firewall as UpdateVM to download updates for Dom0; this may take some time... Running command on VM: 'sys-firewall'... Loaded plugins: langpacks, post-transaction-actions, yum-qubes-hooks Resolving Dependencies (...) =========================================================================================== Package Arch Version Repository Size =========================================================================================== Installing: kernel-qubes-vm x86_64 1000:4.1.12-6.pvops.qubes qubes-dom0-cached 40 M Removing: kernel-qubes-vm x86_64 1000:3.18.10-2.pvops.qubes @anaconda/R3.0 134 M Transaction Summary =========================================================================================== Install 1 Package Remove 1 Package Total download size: 40 M Is this ok [y/d/N]: y Downloading packages: Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : 1000:kernel-qubes-vm-4.1.12-6.pvops.qubes.x86_64 1/2 mke2fs 1.42.12 (29-Aug-2014) This kernel version is used by at least one VM, cannot remove error: %preun(kernel-qubes-vm-1000:3.18.10-2.pvops.qubes.x86_64) scriptlet failed, exit status 1 Error in PREUN scriptlet in rpm package 1000:kernel-qubes-vm-3.18.10-2.pvops.qubes.x86_64 Verifying : 1000:kernel-qubes-vm-4.1.12-6.pvops.qubes.x86_64 1/2 Verifying : 1000:kernel-qubes-vm-3.18.10-2.pvops.qubes.x86_64 2/2 Installed: kernel-qubes-vm.x86_64 1000:4.1.12-6.pvops.qubes Failed: kernel-qubes-vm.x86_64 1000:3.18.10-2.pvops.qubes Complete! [marmarek@dom0 ~]$ ~~~ In the above example, it tries to remove 3.18.10-2.pvops.qubes kernel (to keep only 3 installed), but since some VM uses it, it fails. Installation of new package is unaffected by this event. The newly installed package is set as default VM kernel. Installing different VM kernel based on dom0 kernel =================================================== It is possible to package kernel installed in dom0 as VM kernel. This makes it possible to use VM kernel, which is not packaged by Qubes team. This includes: * using Fedora kernel package * using manually compiled kernel To prepare such VM kernel, you need to install `qubes-kernel-vm-support` package in dom0 and also have matching kernel headers installed (`kernel-devel` package in case of Fedora kernel package). You can install required stuff using `qubes-dom0-update`: ~~~ [user@dom0 ~]$ sudo qubes-dom0-update qubes-kernel-vm-support kernel-devel Using sys-firewall as UpdateVM to download updates for Dom0; this may take some time... Running command on VM: 'sys-firewall'... Loaded plugins: langpacks, post-transaction-actions, yum-qubes-hooks Package 1000:kernel-devel-4.1.9-6.pvops.qubes.x86_64 already installed and latest version Resolving Dependencies (...) ================================================================================ Package Arch Version Repository Size ================================================================================ Installing: qubes-kernel-vm-support x86_64 3.1.2-1.fc20 qubes-dom0-cached 9.2 k Transaction Summary ================================================================================ Install 1 Package Total download size: 9.2 k Installed size: 13 k Is this ok [y/d/N]: y Downloading packages: Running transaction check Running transaction test Transaction test succeeded Running transaction (shutdown inhibited) Installing : qubes-kernel-vm-support-3.1.2-1.fc20.x86_64 1/1 Creating symlink /var/lib/dkms/u2mfn/3.1.2/source -> /usr/src/u2mfn-3.1.2 DKMS: add completed. Verifying : qubes-kernel-vm-support-3.1.2-1.fc20.x86_64 1/1 Installed: qubes-kernel-vm-support.x86_64 0:3.1.2-1.fc20 Complete! ~~~ Then you can call `qubes-prepare-vm-kernel` tool to actually package the kernel. The first parameter is kernel version (exactly as seen by the kernel), the second one (optional) is short name being visible in Qubes Manager and `qvm-prefs` tool. ~~~ [user@dom0 ~]$ sudo qubes-prepare-vm-kernel 4.1.9-6.pvops.qubes.x86_64 4.1.qubes --> Building files for 4.1.9-6.pvops.qubes.x86_64 in /var/lib/qubes/vm-kernels/4.1.qubes ---> Recompiling kernel module (u2mfn) ---> Generating modules.img mke2fs 1.42.12 (29-Aug-2014) ---> Generating initramfs --> Done. ~~~ Using kernel installed in the VM ================================ **This option is available only in Qubes R3.1 or newer** It is possible to use kernel installed in the VM (in most cases - TemplateVM). This is possible thanks to PV GRUB2 - GRUB2 running in the VM. To make it happen, you need to: 1. Install PV GRUB2 in dom0 - package is named `grub2-xen`. 2. Install kernel in the VM. As with all VM software installation - this needs to be done in TemplateVM (of StandaloneVM if you are using one). 3. Set VM kernel to `pvgrub2` value. You can use `pvgrub2` in selected VMs, not necessary all of them, even when it's template has kernel installed. You can still use dom0-provided kernel for selected VMs. **WARNING: When using kernel from within VM, `kernelopts` parameter is ignored.** ### Installing PV GRUB2 Simply execute: ~~~ sudo qubes-dom0-update grub2-xen ~~~ ### Installing kernel in Fedora VM In Fedora based VM, you need to install `qubes-kernel-vm-support` package. This package include required additional kernel module and initramfs addition required to start Qubes VM (for details see [template implementation](/doc/template-implementation/)). Additionally you need some GRUB tools to create it's configuration. Note: you don't need actual grub bootloader as it is provided by dom0. But having one also shouldn't harm. ~~~ sudo yum install qubes-kernel-vm-support grub2-tools ~~~ Then install whatever kernel you want. If you are using distribution kernel package (`kernel` package), initramfs and kernel module should be handled automatically. If you are using manually build kernel, you need to handle this on your own. Take a look at `dkms` and `dracut` documentation. When kernel is installed, you need to create GRUB configuration. You may want to adjust some settings in `/etc/default/grub`, for example lower `GRUB_TIMEOUT` to speed up VM startup. Then you need to generate actual configuration: In Fedora it can be done using `grub2-mkconfig` tool: ~~~ sudo grub2-mkconfig -o /boot/grub2/grub.cfg ~~~ You can safely ignore this error message: ~~~ grub2-probe: error: cannot find a GRUB drive for /dev/mapper/dmroot. Check your device.map ~~~ Then shutdown the VM. From now you can set `pvgrub2` as VM kernel and it will start kernel configured within VM. ### Installing kernel in Debian VM In Debian based VM, you need to install `qubes-kernel-vm-support` package. This package include required additional kernel module and initramfs addition required to start Qubes VM (for details see [template implementation](/doc/template-implementation/)). Additionally you need some GRUB tools to create it's configuration. Note: you don't need actual grub bootloader as it is provided by dom0. But having one also shouldn't harm. ~~~ sudo apt-get update sudo apt-get install qubes-kernel-vm-support grub2-common ~~~ Ignore warnings about `version '...' has bad syntax`. Then install whatever kernel you want. If you are using distribution kernel package (`linux-image-amd64` package), initramfs and kernel module should be handled automatically. If you are using manually build kernel, you need to handle this on your own. Take a look at `dkms` and `initramfs-tools` documentation. When kernel is installed, you need to create GRUB configuration. You may want to adjust some settings in `/etc/default/grub`, for example lower `GRUB_TIMEOUT` to speed up VM startup. Then you need to generate actual configuration: In Fedora it can be done using `update-grub2` tool: ~~~ sudo mkdir /boot/grub sudo update-grub2 ~~~ You can safely ignore this error message: ~~~ grub2-probe: error: cannot find a GRUB drive for /dev/mapper/dmroot. Check your device.map ~~~ Then shutdown the VM. From now you can set `pvgrub2` as VM kernel and it will start kernel configured within VM. ### Troubleshooting In case of problems, you can access VM console (using `sudo xl console VMNAME` in dom0) to access GRUB menu. You need to call it just after starting VM (until `GRUB_TIMEOUT` expires) - for example in separate dom0 terminal window. In any case you can later access VM logs (especially VM console log (`guest-VMNAME.log`). You can always set kernel back to some dom0-provided value to fix VM kernel installation.