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This shows you the differences between two versions of the page.

--- linux:apps:kvm [2025/09/21 12:22] – [Libvirt default network] oscar
+++ linux:apps:kvm [2026/10/01 05:46] (current) – removed - external edit (Unknown date) 127.0.0.1
@@ Line 1: / Line 1: @@
-====== KVM ======
-S2YLNY0HA01587
-===== Installation =====
-Install all the required for the installation of Qemu, KVM hypervisor, and Libvirt
-  # apt install qemu-system libvirt-daemon-system qemu-utils virt-manager
-  * qemu-system: is an open source virtualizer that provides hardware emulation for the KVM hypervisor. It acts as a virtual machine monitor together with the KVM kernel modules, and emulates the hardware for a full system such as a PC and its associated peripherals.
-  * virt-manager: Virt-Manager is a graphical user interface (GUI) tool for managing virtual machines through libvirt-daemon.
-  * libvirt-daemon-system: provides API libraries that enables GUI apps such as virt-manager to communicate with libvirtd daemon, a system service libvirtd , and a virsh CLI tool
-  * qemu-utils: Various utilities e.g. for manipulating disk images
-  * virtinst: Allows to create Virtual Machines (VMs) from the command-line.
-Verify that the virtualization daemon, libvritd-daemon, is operating before moving on. Execute the command to achieve this.
-<code>
-#  systemctl status libvirtd
-Output:
-● libvirtd.service - Virtualization daemon
-     Loaded: loaded (/lib/systemd/system/libvirtd.service; enabled; preset: enabled)
-     Active: active (running) since Sun 2023-08-06 10:57:02 CEST; 1min 30s ago
-TriggeredBy: ● libvirtd-ro.socket
-             ● libvirtd-admin.socket
-             ● libvirtd.socket
-       Docs: man:libvirtd(8)
-             https://libvirt.org
-   Main PID: 7999 (libvirtd)
-      Tasks: 19 (limit: 32768)
-     Memory: 15.7M
-        CPU: 188ms
-     CGroup: /system.slice/libvirtd.service
-             └─7999 /usr/sbin/libvirtd --timeout 120
-Aug 06 10:57:02 pcwerkkamer systemd[1]: Starting libvirtd.service - Virtualization daemon...
-Aug 06 10:57:02 pcwerkkamer systemd[1]: Started libvirtd.service - Virtualization daemon.
-</code>
-Check if libvirtd service will start automatically at boot time.
-<code>
-# systemctl is-enabled libvirtd
-Output:
-enabled
-</code>
-If disabled run the following command to have it boot automatically:
-  # systemctl enable --now libvirtd
-Use the following command to determine whether the KVM modules are loaded:
-<code>
-$ lsmod | grep -i kvm
-kvm_intel             380928  0
-kvm                  1142784  1 kvm_intel
-irqbypass              16384  1 kvm
-</code>
-===== Configuration =====
-=== User priviliges ===
-In order to manage virtual machines as a regular user, that user needs to be added to the libvirt group:
-  # adduser <username> libvirt
-       or  (not sure if kvm group is needed)
-  # usermod -aG libvirt,kvm <username>
-=== User-specific and system-wide VMs ===
-By default, if virsh is run as a normal user it will connect to libvirt using: **qemu:%%///%%session** URI string. This URI allows virsh to manage only the set of VMs belonging to this particular user.
-To manage the system set of VMs (i.e., VMs belonging to root) virsh should be run as root or with: **qemu:%%///%%system** URI:
-  $ virsh --connect qemu:///system list --all
-To avoid having to use the --connect flag on every command, the URI string can be set in the LIBVIRT_DEFAULT_URI environment variable:
-  $ export LIBVIRT_DEFAULT_URI='qemu:///system'
-===== Libvirt default network =====
-If you use libvirt to manage your VMs, libvirt provides a NATed bridged network named "default/virbr0" that allows the host to communicate with the guests.
-<code>
-: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
-    link/ether 52:54:00:f5:c4:41 brd ff:ff:ff:ff:ff:ff
-    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
-       valid_lft forever preferred_lft forever
-</code>
-This network is available only for the system domains (that is VMs created by root or using the "qemu:system" connection URI). VMs using this network end up in 192.168.122.1/24 and DHCP is provided to them via dnsmasq. This network is not automatically started. To start it use:
-  virsh --connect=qemu:///system net-start default
-To make the default network start automatically use:
-  virsh --connect=qemu:///system net-autostart default
-===== Change XML configuration =====
-Extract the xml from an existing qcow2 image by:
-  virsh dumpxml Windows-11 > Windows-11.xml
-Edit and modify the tags in the XML file.
-Undefine the XML config from the old vm to prevent an error because of a duplicate UUID:
-  virsh undefine --nvram Windows-11
-  or
-  virsh undefine Windows-11
-Import / define the new XML file:
-  virsh define Windows-11.xml
-Of course you will have to stop and start the vm for the changes to take effect:
-  virsh destroy name_of_vm
-  virsh start name_of_vm
-===== Error Access ISO files, etc. =====
-Directory, that libvirt is using for storing/reading ISO and qcow2 files needs to be readable by libvirt-qemu user. In case of an error opening an ISO or image file, the "libvirt-qemu" user does not have access to the file or the directories holding the files. The "libvirt-qemu" user needs **"r+x"** permissions **all the way up the path**. You can check if unix permissions are correct by running a shell under user "libvirt-qemu" and see if you can ls along the path all the way up to the files:
-  $ sudo su -s /bin/bash libvirt-qemu
-If you can't ls with an account that does have access yields a result with a permission line that contains a dot such as drwxrwxr-x. meaning extended ACL permissions.
-=== Fix 1: ===
-Put the iso or image into one of the pool directories of libvirt manager. E.g. /var/lib/libvirt/images
-Or any other paths that have full r others rights.
-===== Convert VirtualBox to KVM =====
-  qemu-img convert -f vdi -O qcow2 virtualbox-name.vdi kvm-name.qcow2
-===== Shrink KVM  qcow2 image =====
-  qemu-img convert -O qcow2 source.qcow2 shrunk.qcow2
-===== Links =====
-  * [[https://wiki.debian.org/KVM#Installation]]