libvirt

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libvirt is a virtualization management toolkit..

The libvirt package comprises of a toolkit and a static object library. It primarily provides virtualization support for UNIX.

Overview

libvirt toolkit enable the creation of new domains, and configuration & adjustment of a domain’s resource allocation & virtual hardware, all from the command line interface (CLI).

Libvirt has the most features of any virtualizers given that it is the common library (but not limited) to QEMU, LXC, Docker, VMware, VirtualBox, Xen.

  • Firstly, libvirt is used by many Virtualization Software.
  • libvirt stores all its configuration in XML format for each virtual machine (VM) and containers under /etc/libvirt. For example, QEMU-specific goes under /etc/libvirt/qemu directory; LXC goes under /etc/libvirt/lxc
  • libvirt can create/delete/maintain an instance of many virtual machines (VM) and containers.
  • libvirt can start/stop a VM/container.
  • libvirt can save an snapshot instance of a VM.
  • libvirt can mount a CD-ROM ISO image
  • libvirt can create different networking connections for a guest OS in VM or a container to use
  • libvirt can create bridges, MACVLAN, static netdev, and NAT'd IP interface.
  • libvirt can create/delete/maintain storage pools using many different filesystems such as directory, direct hard drive, gluster, iSCSI, LVM, multi-path devices, netfs, SCSI, RADOS/Ceph, and Sheepdog.

libvirt can manage the following type of guest VM/container:

Installation

Kernel

The following kernel config is recommended by the libvirtd daemon.

Note
Check the logs to see if any additional kernel configs are requested by the build.
KERNEL libvirt (CONFIG_BRIDGE_EBT_MARK, CONFIG_NETFILTER_ADVANCED, CONFIG_NETFILTER_XT_CONNMARK, CONFIG_NETFILTER_XT_TARGET_CHECKSUM, CONFIG_IP6_NF_NAT)
[*] Networking support
    Networking Options  --->
        [*] Network packet filtering framework (Netfilter)  --->
            [*] Advanced netfilter configuration
            Core Netfilter Configuration  --->
                <*> "conntrack" connection tracking match support
                <*> CHECKSUM target support
            IPv6: Netfilter Configuration  --->
                <*> IP6 tables support (required for filtering)
                  <*> ip6tables NAT support
                
            <*> Ethernet Bridge tables (ebtables) support  --->
                <*> ebt: nat table support
                <*> ebt: mark filter support
        [*] QoS and/or fair queueing  --->
            <*> Hierarchical Token Bucket (HTB)
            <*> Stochastic Fairness Queueing (SFQ)
            <*> Ingress/classifier-action Qdisc
            <*> Netfilter mark (FW)
            <*> Universal 32bit comparisons w/ hashing (U32)
            [*] Actions
            <*>    Traffic Policing

The following kernel options are required to pass some checks by the virt-host-validate tool. That also means that are requirements for some functionality.

KERNEL Enabling blkio
General setup --->
[*] Control Group support --->
    --- Control Group support
        [*] IO controller
KERNEL Enabling memory
Device Drivers --->
    [*] Memory Controller drivers ---
        --- Memory Controller drivers
KERNEL Enabling tun (used in the default libvirt/virt-manager networking setup)
Device Drivers --->
    [*] Network device support  --->
        [*] Network core driver support
            <*> Universal TUN/TAP device driver support

USE flags

Some packages are aware of the libvirt USE flag.

Review the possible USE flags for libvirt:

USE flags for app-emulation/libvirt C toolkit to manipulate virtual machines

apparmor Enable support for the AppArmor application security system
audit Enable support for Linux audit subsystem using sys-process/audit
bash-completion Enable bash-completion support
caps Use Linux capabilities library to control privilege
dtrace Enable dtrace support via dev-util/systemtap
firewalld DBus interface to iptables/ebtables allowing for better runtime management of your firewall.
fuse Allow LXC to use sys-fs/fuse for mountpoints
glusterfs Enable GlusterFS support via sys-cluster/glusterfs
iscsi Allow using an iSCSI remote storage server as pool for disk image storage
iscsi-direct Allow using libiscsi for iSCSI storage pool backend
libssh Use net-libs/libssh to communicate with remote libvirtd hosts, for example: qemu+libssh://server/system
libssh2 Use net-libs/libssh2 to communicate with remote libvirtd hosts, for example: qemu+libssh2://server/system
libvirtd Builds the libvirtd daemon as well as the client utilities instead of just the client utilities
lvm Allow using the Logical Volume Manager (sys-fs/lvm2) as pool for disk image storage
lxc Support management of Linux Containers virtualisation (app-containers/lxc)
nfs Allow using Network File System mounts as pool for disk image storage
nls Add Native Language Support (using gettextGNU locale utilities)
numa Use NUMA for memory segmenting via sys-process/numactl and sys-process/numad
openvz Support management of OpenVZ virtualisation (openvz-sources)
parted Allow using real disk partitions as pool for disk image storage, using sys-block/parted to create, resize and delete them.
pcap Support auto learning IP addreses for routing
policykit Enable PolicyKit (polkit) authentication support
qemu Support management of QEMU virtualisation (app-emulation/qemu)
rbd Enable rados block device support via sys-cluster/ceph
sasl Add support for the Simple Authentication and Security Layer
selinux !!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
udev Enable virtual/udev integration (device discovery, power and storage device support, etc)
verify-sig Verify upstream signatures on distfiles
virt-network Enable virtual networking (NAT) support for guests. Includes all the dependencies for NATed network mode. Effectively any network setup that relies on libvirt to setup and configure network interfaces on your host. This can include bridged and routed networks ONLY if you are allowing libvirt to create and manage the underlying devices for you. In some cases this requires enabling the 'netcf' USE flag (currently unavailable).
virtualbox Support management of VirtualBox virtualisation (app-emulation/virtualbox)
wireshark-plugins Build the net-analyzer/wireshark plugin for the Libvirt RPC protocol
xen Support management of Xen virtualisation (app-emulation/xen)
zfs Enable ZFS backend storage sys-fs/zfs
Data provided by the Gentoo Package Database · Last update: 2023-03-21 19:18 More information about USE flags


Note
If libvirt is going to be used, you may need the usbredir USE flags to redirect USB devices to another machine over TCP.

libvirt comes with a number of USE flags. Please check those flags and set them according to your setup. These are recommended USE flags for libvirt:

FILE /etc/portage/package.use/qemu
app-emulation/libvirt pcap virt-network numa fuse macvtap vepa qemu
USE_EXPAND

Additional ebuild configuration frobs are provided as the USE_EXPAND variables QEMU_USER_TARGETS and QEMU_SOFTMMU_TARGETS. See app-emulation/qemu for a list of all the available targets (there are a heck of a lot of them; most of them are very obscure and may be ignored; leaving these variables at their default values will disable almost everything which is probably just fine for most users).

For each target specified, a qemu executable will be built. A softmmu target is the standard qemu use-case of emulating an entire system (like VirtualBox or VMWare, but with optional support for emulating CPU hardware along with peripherals). user targets execute user-mode code only; the (somewhat shockingly ambitious) purpose of these targets is to "magically" allow importing user-space linux ELF binaries from a different architecture into the native system (that is, they are like multilib, without the awkward need for a software stack or CPU capable of running it).

In order to enable QEMU_USER_TARGETS and QEMU_SOFTMMU_TARGETS we can edit the variables globally in /etc/portage/make.conf, i.e.:

FILE /etc/portage/make.conf
QEMU_SOFTMMU_TARGETS="arm x86_64 sparc"
QEMU_USER_TARGETS="x86_64"

Or, the /etc/portage/package.use file(s) can be modified. Two equivalent syntaxes are available: traditional USE flag syntax, i.e.:

FILE /etc/portage/package.use
app-emulation/qemu qemu_softmmu_targets_arm qemu_softmmu_targets_x86_64 qemu_softmmu_targets_sparc
app-emulation/qemu qemu_user_targets_x86_64

Another alternative is to use the newer sexy USE_EXPAND-specific syntax:

FILE /etc/portage/package.use
app-emulation/qemu QEMU_SOFTMMU_TARGETS: arm x86_64 sparc QEMU_USER_TARGETS: x86_64

Emerge

After reviewing and adding any desired USE flags, emerge app-emulation/qemu:

root #emerge --ask app-emulation/qemu


Additional software

Verify host as QEMU-capable

To verify that the host hardware has the needed virtualization support, issue the following command:

user $grep --color -E "vmx|svm" /proc/cpuinfo

The vmx or svm CPU flag should be red highlighted and available.

File /dev/kvm must exist.


System user/group

Group name libvirt is required. Defined by acct-group/libvirt; evoked by app-emulation/libvirt package.

Configuration

Environment variables

A list of all environment variables read by the libvirt library and its toolkit commands:


  • DISPLAY - for virtualbox-only
  • DNSMASQ_CLIENT_ID - Used with dnsmasqd
  • DNSMASQ_IAID - Used with dnsmasqd
  • DNSMASQ_INTERFACE - Used with dnsmasqd
  • DNSMASQ_LEASE_EXPIRES - Used with dnsmasqd
  • DNSMASQ_OLD_HOSTNAME - Used with dnsmasqd
  • DNSMASQ_SERVER_DUID - Used with dnsmasqd
  • DNSMASQ_SUPPLIED_HOSTNAME - Used with dnsmasqd
  • LIBVIRT_ADMIN_DEFAULT_URI - administration
  • LIBVIRT_AUTH_FILE - authentication
  • LIBVIRT_AUTOSTART
  • LIBVIRT_DEBUG
  • LIBVIRT_DEFAULT_URI
  • LIBVIRT_DIR_OVERRIDE
  • LIBVIRT_GNUTLS_DEBUG
  • LIBVIRT_LIBSSH_DEBUG
  • LIBVIRT_LOG_FILTERS
  • LIBVIRT_LOG_OUTPUTS
  • LISTEN_PID - For systemd only.
  • LISTEN_FDS - For systemd only.
  • NOTIFY_SOCKET - for systemd-only.
  • QEMU_AUDIO_DRV
  • SDL_AUDIODRIVER
  • VBOX_APP_HOME - for virtualbox-only
  • VIR_BRIDGE_NAME - Bridging
  • VIRSH_DEFAULT_CONNECT_URI
  • VIRTD_PATH


Files

Files that are read by the host-side OS; libvirt library, libvirtd daemon. and its sets of commands:

  • /etc/libvirt/hooks/
  • /etc/libvirt/libvirt-admin.conf
  • /etc/libvirt/libvirt.conf
  • /etc/libvirt/libvirtd.conf
  • /etc/libvirt/libxl.conf
  • /etc/libvirt/libxl-lockd.conf
  • /etc/libvirt/libxl-sanlock.conf
  • /etc/libvirt/lxc.conf
  • /etc/libvirt/nwfilter/
  • /etc/libvirt/secrets/
  • /etc/libvirt/storage/
  • /etc/libvirt/virtlockd.conf
  • /etc/libvirt/virtlogd.conf
  • /proc/cgroups
  • /proc/cpuinfo
  • /proc/modules
  • /proc/mounts
  • /proc/net/dev
  • /proc/stat
  • /proc/sys/ipv4/ip_forward
  • /proc/sys/ipv6/conf/all/forwarding
  • /proc/sys/ipv6/conf/%s/%s
  • /sys/class/fc_host/host0
  • /sys/class/fc_remote_ports
  • /sys/class/scsi_host
  • /sys/devices/system
  • /sys/devices/system/%s/cpu/online
  • /sys/devices/system/cpu/online
  • /sys/devices/system/node/node0/access1
  • /sys/devices/system/node/node0/meminfo
  • /sys/devices/system/node/node0/memory_side_cache
  • /sys/devices/system/node/online
  • /sys/fs/resctrl
  • /sys/fs/resctrl/info/%s/num_closids
  • /sys/kernel/mm/ksm
  • /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
  • /sys/fs/resctrl/%s/schemata
  • /sys/fs/resctrl/info/%s/min_cbm_bits
  • /sys/fs/resctrl/info/MB/bandwidth_gran
  • /sys/fs/resctrl/info/MB/min_bandwidth
  • /sys/fs/resctrl/info/MB/num_closids
  • /sys/fs/resctrl/info/L3_MON
  • /proc/vz/vestat - Only with openvz
  • /sys/fs/resctrl/info/L3_MON/num_rmids
  • /var/lib/libvirt/boot
  • /var/lib/libvirt/dnsmasq
  • /var/lib/libvirt/images
  • /var/lib/libvirt/sanlock

User permissions

After emerging, to run virt-manager as a normal user, ensure each user has been added to the libvirt group:

root #usermod -a -G libvirt <user>

Uncomment the following lines from the libvirtd configuration file:

FILE /etc/libvirt/libvirtd.conf
auth_unix_ro = "none"
auth_unix_rw = "none"
unix_sock_group = "libvirt"
unix_sock_ro_perms = "0777"
unix_sock_rw_perms = "0770"

Be sure to have the user log out then log in again for the new group settings to be applied.

Note
If policykit USE flag is not enabled for libvirt package, the libvirt group is not created, in which case another group, such as wheel must be used for unix_sock_group.

Service

The service needs to be started. It's also a good idea to enabled in order to be around once we restart the system.

To start libvirtd daemon using OpenRC:

root #rc-service libvirtd start && rc-update add libvirtd default

To enable and start libvirtd daemon using systemd:

root #systemctl enable --now libvirtd

virt-admin should now be launchable as a regular user.

Note
If permission denied issues are experienced when loading ISO images user directories (somewhere beneath /home/) then the /var/lib/libvirt/images/ directory can be used to store the images.

Firewall

The following firewall chain names have been reserved by the libvirt library and libvirtd daemon.

Reserved chain name Description
nat NAT
LIBVIRT_INP Firewall input
LIBVIRT_FWI Firewall input
LIBVIRT_FWO Firewall output
LIBVIRT_FWX Firewall forward
LIBVIRT_OUT Firewall output
LIBVIRT_PRT Firewall postrouting
Reserved Firewall Chain Names by libvirt (viriptable.c source)
Warning
To firewall administrators: nat chain name is often used by net-firewall/shorewall, net-firewall/firewalld, net-firewall/ufw, net-firewall/ipfw and possibly net-firewall/fwbuilder; it is far much easier to rename it at the firewall side than it is to rename nat within libvirt/libvirtd.

Networking

For configuration of networking under libvirt, continue reading at libvirt/QEMU networking.

Usage

A list of domains (configured VMs) can be obtained by running:

root #virsh list
 Id   Name     State
------------------------
 1    gentoo   running
 2    default  running
Important
If no VM is running at the moment, virsh list will output an empty list, use virsh list --all to see all VM's created, enabled, turned off or inactive.

Details of nodes (CPUs) can be checked by running:

user $virsh nodeinfo
CPU model:           x86_64
CPU(s):              4
CPU frequency:       1600 MHz
CPU socket(s):       1
Core(s) per socket:  4
Thread(s) per core:  1
NUMA cell(s):        1
Memory size:         16360964 KiB

The libvirtd daemon can be checked via Unix socket by running:

root #virsh sysinfo
<sysinfo type='smbios'>
  <bios>
    <entry name='vendor'>Dell Inc.</entry>
    <entry name='version'>A22</entry>
    <entry name='date'>11/29/2018</entry>
    <entry name='release'>4.6</entry>
  </bios>
  <system>
    <entry name='manufacturer'>Dell Inc.</entry>
    <entry name='product'>OptiPlex 3010</entry>
    <entry name='version'>01</entry>
    <entry name='serial'>JRJ0SW1</entry>
    <entry name='uuid'>4c4c4544-0052-4a10-8030-cac04f535731</entry>
    <entry name='sku'>OptiPlex 3010</entry>
    <entry name='family'>Not Specified</entry>
  </system>
  <baseBoard>
    <entry name='manufacturer'>Dell Inc.</entry>
    <entry name='product'>042P49</entry>
    <entry name='version'>A00</entry>
    <entry name='serial'>/JRJ0SW1/CN701632BD05R5/</entry>
    <entry name='asset'>Not Specified</entry>
    <entry name='location'>Not Specified</entry>
  </baseBoard>
  <chassis>
    <entry name='manufacturer'>Dell Inc.</entry>
    <entry name='version'>Not Specified</entry>
    <entry name='serial'>JRJ0SW1</entry>
    <entry name='asset'>Not Specified</entry>
    <entry name='sku'>To be filled by O.E.M.</entry>
  </chassis>
  <processor>
    <entry name='socket_destination'>CPU 1</entry>
    <entry name='type'>Central Processor</entry>
    <entry name='family'>Core i5</entry>
    <entry name='manufacturer'>Intel(R) Corporation</entry>
    <entry name='signature'>Type 0, Family 6, Model 58, Stepping 9</entry>
    <entry name='version'>Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz</entry>
    <entry name='external_clock'>100 MHz</entry>
    <entry name='max_speed'>3200 MHz</entry>
    <entry name='status'>Populated, Enabled</entry>
    <entry name='serial_number'>Not Specified</entry>
    <entry name='part_number'>Fill By OEM</entry>
  </processor>
  <memory_device>
    <entry name='size'>8 GB</entry>
    <entry name='form_factor'>DIMM</entry>
    <entry name='locator'>DIMM1</entry>
    <entry name='bank_locator'>Not Specified</entry>
    <entry name='type'>DDR3</entry>
    <entry name='type_detail'>Synchronous</entry>
    <entry name='speed'>1600 MT/s</entry>
    <entry name='manufacturer'>8C26</entry>
    <entry name='serial_number'>00000000</entry>
    <entry name='part_number'>TIMETEC-UD3-1600</entry>
  </memory_device>
  <memory_device>
    <entry name='size'>8 GB</entry>
    <entry name='form_factor'>DIMM</entry>
    <entry name='locator'>DIMM2</entry>
    <entry name='bank_locator'>Not Specified</entry>
    <entry name='type'>DDR3</entry>
    <entry name='type_detail'>Synchronous</entry>
    <entry name='speed'>1600 MT/s</entry>
    <entry name='manufacturer'>8C26</entry>
    <entry name='serial_number'>00000000</entry>
    <entry name='part_number'>TIMETEC-UD3-1600</entry>
  </memory_device>
  <oemStrings>
    <entry>Dell System</entry>
    <entry>1[0585]</entry>
    <entry>3[1.0]
</entry>
    <entry>12[www.dell.com]
</entry>
    <entry>14[1]</entry>
    <entry>15[11]</entry>
  </oemStrings>
</sysinfo>

Host verification

To verify entire host setup of libvirtd, execute:

user $virt-host-validate
  QEMU: Checking for hardware virtualization                                 : PASS
  QEMU: Checking if device /dev/kvm exists                                   : PASS
  QEMU: Checking if device /dev/kvm is accessible                            : PASS
  QEMU: Checking if device /dev/vhost-net exists                             : PASS
  QEMU: Checking if device /dev/net/tun exists                               : PASS
  QEMU: Checking for cgroup 'cpu' controller support                         : PASS
  QEMU: Checking for cgroup 'cpuacct' controller support                     : PASS
  QEMU: Checking for cgroup 'cpuset' controller support                      : PASS
  QEMU: Checking for cgroup 'memory' controller support                      : PASS
  QEMU: Checking for cgroup 'devices' controller support                     : PASS
  QEMU: Checking for cgroup 'blkio' controller support                       : PASS
  QEMU: Checking for device assignment IOMMU support                         : PASS
  QEMU: Checking if IOMMU is enabled by kernel                               : PASS
  QEMU: Checking for secure guest support                                    : WARN (Unknown if this platform has Secure Guest support)
   LXC: Checking for Linux >= 2.6.26                                         : PASS
   LXC: Checking for namespace ipc                                           : PASS
   LXC: Checking for namespace mnt                                           : PASS
   LXC: Checking for namespace pid                                           : PASS
   LXC: Checking for namespace uts                                           : PASS
   LXC: Checking for namespace net                                           : PASS
   LXC: Checking for namespace user                                          : PASS
   LXC: Checking for cgroup 'cpu' controller support                         : PASS
   LXC: Checking for cgroup 'cpuacct' controller support                     : PASS
   LXC: Checking for cgroup 'cpuset' controller support                      : PASS
   LXC: Checking for cgroup 'memory' controller support                      : PASS
   LXC: Checking for cgroup 'devices' controller support                     : PASS
   LXC: Checking for cgroup 'freezer' controller support                     : FAIL (Enable 'freezer' in kernel Kconfig file or mount/enable cgroup controller in your system)
   LXC: Checking for cgroup 'blkio' controller support                       : PASS
   LXC: Checking if device /sys/fs/fuse/connections exists                   : PASS

Invocation

For invocation of the command line interface (CLI) of libvirt, see virsh invocation.

For invocation of the libvirtd daemon:

user $libvirtd --help
Usage:
  libvirtd [options]

Options:
  -h | --help            Display program help
  -v | --verbose         Verbose messages
  -d | --daemon          Run as a daemon & write PID file
  -l | --listen          Listen for TCP/IP connections
  -t | --timeout <secs>  Exit after timeout period
  -f | --config <file>   Configuration file
  -V | --version         Display version information
  -p | --pid-file <file> Change name of PID file

libvirt management daemon:

  Default paths:

    Configuration file (unless overridden by -f):
      /etc/libvirt/libvirtd.conf

    Sockets:
      /run/libvirt/libvirt-sock
      /run/libvirt/libvirt-sock-ro

    TLS:
      CA certificate: /etc/pki/CA/cacert.pem
      Server certificate: /etc/pki/libvirt/servercert.pem
      Server private key: /etc/pki/libvirt/private/serverkey.pem

    PID file (unless overridden by -p):
      /run/libvirtd.pid
Note
virsh cannot assist with the creation of XML files needed by libvirt. This is what some virt-* tools and QEMU front-ends are for.

Removal

Removal of libvirt package (toolkit, library, and utilities) can be done by executing:

root #emerge --ask --depclean --verbose app-emulation/libvirt

Troubleshooting

Messages mentioning ...or mount/enable cgroup controller in your system

Some of those messages are addressed on the previous section about the kernel configuration.

If the above doesn't fix the problem, follow the section Control groups on the LXC page to activate the correct kernel options.

WARN (Unknown if this platform has Secure Guest support)

This message appears on non IBM s390 or AMD systems and seems to be of little relevance [1] [2] [3] [4].

See also

  • Virtualization — the concept and technique that permits running software in an environment separate from a computer operating system.
  • QEMU — a generic, open source hardware emulator and virtualization suite.
  • QEMU/QEMU front-ends — user interface application to the QEMU/libvirt API/library.
  • Libvirt/QEMU_networking — details the setup of Gentoo networking by Libvirt for use by guest containers and QEMU-based virtual machines.
  • Libvirt/QEMU_guest — covers libvirt and its creation of a virtual machine (VM) for use under the soft-emulation mode QEMU hypervisor Type-2, notably using virsh command.
  • Virt-manager — desktop user interface for management of virtual machines and containers through the libvirt library
  • Virt-manager/QEMU_guest — QEMU creation of a guest (VM or container)
  • QEMU/Linux guest — describes the setup of a Gentoo Linux guest in QEMU using Gentoo bootable media.

External resources

References

  1. ↑ Libvirt Protected Virtualization on s390
  2. ↑ libvir-list mailing list PATCH 3/6 qemu: check if AMD secure guest support is enabled
  3. ↑ libvir-list mailing list PATCH 4/6 tools: secure guest check on s390 in virt-host-validate
  4. ↑ libvir-list mailing list PATCH 5/6 tools: secure guest check for AMD in virt-host-validate
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