GNU Linux Debian 10/11/Ubuntu – how to install kvm virtualization (qemu) – basic virsh commands – kvm cheat sheed – howto workaround virt-manager “emulator may not have search permissions for the path”

05.Dec.2020

Administration / Server, General / Allgemein, Virtualization / KVM / VirtualBox / xenserver


hostnamectl; # tested on 
   Static hostname: hpServerG6
  Operating System: Debian GNU/Linux 10 (buster)
            Kernel: Linux 4.19.0-12-amd64
      Architecture: x86-64

su - root;
apt update;
apt install qemu-kvm libvirt-clients libvirt-daemon-system bridge-utils virtinst libvirt-daemon virt-manager

# give non-root user kvm access (it might be required for that user to re-login or reboot pc)
# (still getting error: failed to get domain 'vmname')
usermod -aG kvm user
usermod -aG libvirt user


# auto starting the default nat network
virsh net-start default
Network default started
virsh net-autostart default
Network default marked as autostarted

now reboot the system to make changes effective

connect securely to remote server and start the vm management gui 🙂

remote server:

now comes the fancy part (that only GNU Linux can do with ease):

hostnamectl; # tested with client
  Operating System: Debian GNU/Linux 10 (buster)
            Kernel: Linux 4.19.0-17-amd64
      Architecture: x86-64

hostnamectl; # tested with server
   Static hostname: SuperStorageSrv1
  Operating System: Debian GNU/Linux 11 (bullseye)
            Kernel: Linux 5.10.0-8-amd64
      Architecture: x86-64

# if problems errors occur, they should be visible here
tail -f /var/log/syslog
# or here
tail -f /var/log/libvirt/qemu/*.log

# logout of the sever
Ctrl+D
# log back in with ssh -X (x11 forwarding)
ssh -X -v user@ip.of.ser.ver
# then start
virt-manager
# the output

ssh-logged in and when trying to start a x11 application, getting the error “Unable to init server: Could not connect: Connection refused”?
try ssh-re-login with:
```
ssh -v -X username@ip.of.server
```
it simply works (keep it that way X-D)
no need to setup a vpn to have encrypted tunneled remote desktop connection
no need to run a full-blown (Gnome or other) desktop software on the server
yes the output is not exactly fast X-D (no jpg-screen compression) but it works
- if more output speed is needed, checkout xpra

local server:

if the user-admin is on a local server, without a gui, there is no virt-manager

but kvm-qemu is nicely scriptable via bash-terminal 🙂

if there is a (as minimal as possible) gui on the server:

now under MATE hit Alt+F2 and type “virt”

to bring up the virt manager gui (root is required)

also: always go with the kvm native harddisk format (not vmware format, prone to trouble)

per default files of the vm are stored here

/etc/libvirt/qemu/vmname.xml; # config file
/var/log/libvirt/qemu/vmname.log; # log
/var/lib/libvirt/images/vmname.qcow2; # harddisk image

change where vms are stored

would prefer a path like

/home/user/vms/kvm

GNU Linux -> KVM -> How to change default location where libvirt VM images are saved – Connection Details greyed out

virt-manager as root “emulator may not have search permissions for the path”

this is because AppArmor or SELinux are blocking kvm qemu, to access files.

when running virt-manager as non-root, it will not be able to “correct this now”.

so try this trick:

vim /scripts/virt-manager.sh
# start virt-manager as root but with x11 gui output
# replace user with the user's default non-root user name
export DISPLAY=':0.0'
cp -v /home/user/.Xauthority /root/.Xauthority
virt-manager

# now run this as root
su - root
/scripts/virt-manager.sh

might not be optimal, but this way it is able to work around the problem

debian-11 guest vm running on debian-11 host

it might also help to modify this config file:

vim /etc/libvirt/qemu.conf

# The default security driver is SELinux. If SELinux is disabled
# on the host, then the security driver will automatically disable
# itself. If you wish to disable QEMU SELinux security driver while
# leaving SELinux enabled for the host in general, then set this
# to 'none' instead. It's also possible to use more than one security
# driver at the same time, for this use a list of names separated by
# comma and delimited by square brackets. For example:
#
#       security_driver = [ "selinux", "apparmor" ]
#
# Notes: The DAC security driver is always enabled; as a result, the
# value of security_driver cannot contain "dac".  The value "none" is
# a special value; security_driver can be set to that value in
# isolation, but it cannot appear in a list of drivers.
#
security_driver = "apparmor"


# then restart the service
systemctl restart libvirtd.service

basic virsh commands

virsh nodeinfo; # info about the system
CPU model:           x86_64
CPU(s):              4
CPU frequency:       1903 MHz
CPU socket(s):       1
Core(s) per socket:  2
Thread(s) per core:  2
NUMA cell(s):        1
Memory size:         7831316 KiB

virsh list --all; # list all (running and off vms)

# list all vms and their status, refresh every 1sec
# run this as non-root but also as root, the output might be different
# e.g. vms that are off might only show up when run as root
while true; do virsh list --all; sleep 1; clear; done

# now let's create a virtual harddisk
cd /home/user/vms/kvm

# create a new thin(!)provisioned harddisk, a bit slower, but way less harddisk space used
qemu-img create -f qcow2 name-of-harddisk-image.qcow2 64G

# do not forget to manually select it during setup



virsh start vmname; # start vm
virsh reboot vmname; # reboot vm
virsh suspend vmname; # pause vm
virsh resume vmname; # resume paused
virsh shutdown vmname; # shutdown vm like power button apci
virsh destroy vmname; # forcefull poweroff vm

virsh autostart vmname; # set vmname to autostart when host system starts
virsh autostart --disable vmname; # disable autostart for vmname

# shutdown all vms
for i in `sudo virsh list | grep running | awk '{print $2}'` do
    sudo virsh shutdown $i
done

# delete remove vmname (cleanly)
# including its storage columes
virsh destroy vmname 2> /dev/null
virsh undefine vmname
virsh pool-refresh default
virsh vol-delete --pool default vmname.qcow2

# take snapshot
virsh snapshot-create-as --domain vmname --name "snapshot-name" --description "description"
# use the current date-and-time for as snapshot-name
virsh snapshot-create-as --domain vmname --name "$(date '+%Y-%m-%d-%H-%M')" --description "description"
# same +seconds
virsh snapshot-create-as --domain vmname --name "$(date '+%Y-%m-%d-%H-%M-%S')" --description "description"
# list all snapshots of vmname
virsh snapshot-list --domain vmname
# revert to snapshot
virsh snapshot-revert vmname snapshot-name
# rename a vm
virsh domrename vmname newvmname
# resize an kvm harddisk file by 1024GBytes (1TB)
qemu-img resize /path/to/kvm-harddisk-file.qcow2 +1024G

# neat script to start any arbitrary vm
# and immediately connect to it's desktop
# modify the user (is the default user that is running the desktop/x11/lightdm)

vim /home/user/scripts/kvm/start.sh
#!/bin/bash
VMNAME=$1
echo "=== starting $VMNAME ==="
# the below is optional, but might be usefull
# in some scenarios where the user want's
# a guranteed-to-work state
# echo "=== revert to working snapshot ==="
# cvirsh destroy $VMNAME
# cvirsh snapshot-revert $VMNAME works

virsh start $VMNAME
export DISPLAY=':0.0'
/usr/bin/cp -fv /home/user/.Xauthority /root/.Xauthority
virt-viewer $VMNAME
# as soon as the viewer window is closed either:
# destroy (forecfull power off)
# virsh destroy $VMNAME
# or graceful shutdown
# virsh shutdown $VMNAME

# usage example
# (under Debian11 have to run the script as root
# the viewer run's as root then, but not the vm (user: libvirt-q)
/home/user/scripts/kvm/start.sh vmname

gpu pass through

kvm is used by many companies such as https://www.hetzner.com/

or proxmox:

How To: Proxmox VE Lenovo Nano Cluster

not many virtualization technologies can do that: https://dwaves.de/2017/12/23/kvm-gpu-graphic-card-pass-through-windows-games-on-linux/

GNU Linux How To – kvm qemu shutdown all vms – start all vms with keyword in name – snapshot all vms

for better GNU Linux and Windows guest vm integration check out

(shared clipboard, GNU Linux auto resize screen)

GNU Linux Debian 10/11/Ubuntu – kvm-qemu virtualization host – disk bench Windows 7 64Bit vm guest (only 32Bit works) – “Unable to init server: Could not connect: Connection refused”

how to make kvm-vms take less disk space:

how to gnu linux – thin provisioning kvm virtual machines with virt-manager (bigger than physical virtual harddisks)

have a server with multiple GPUs? asign them dedicated to a vm! X-D

KVM QEMU GPU Graphic Card Pass Through – Windows Games on GNU Linux

esxi inside kvm-qemu? holy crap! yes! kvm can do that 🙂

KVM QEmu virt-manager for a test drive on HP ProLiant DL360 G6 – Windows 7 64Bit Guest Harddisk Benchmark – nested virtualization vmware esxi 6.5 inside kvm

networking: VMs in NAT mode should work by now 🙂 (thanks all involved!)

GNU Linux – how to – kvm-qemu port forwarding – how to forward host-port to guest-vm in NAT networking mode

Links & Credits:

https://github.com/andreabolognani https://kiyuko.org/home

https://www.linuxtechi.com/install-configure-kvm-debian-10-buster/ (thanks despite insane amount of ads) X-D (block this waste in Firefox with uBlock)

https://computingforgeeks.com/virsh-commands-cheatsheet/

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