libvirt/libvirtd

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Warning
Since Libvirt 9.0, May 2022, libvirtd has been broken into multiple but modualized daemons

.

libvirtd is a daemon for Libvirt management of virtual machines.

The daemon is used to ensure consistent handling of virtual machines, containers, and domains.

Libvirt (and libvirtd) currently supports QEMU, LXC, Xen, KVM, OpenVZ, VirtualBox and VMware ESX.


Installation

See libvirt for installation of libvirtd.


Configuration

Environment variables

A list of optional environment variables that are read and checked by the virsh command:

Optional environment variable name Description Type
LIBVIRT_AUTH_FILE authentication, when libvirt clients (virsh, virt-manager) connecting to libvirtd daemon. contains authentication credentials for connecting to a libvirt daemon (like libvirtd or virtqemud) when using certain authentication mechanisms, particularly Polkit or SASL. Its file format is a simple INI containing a [credentials] section line followed by a username= and a password= keyvalue lines. If LIBVIRT_AUTH_FILE is explicitly set, libvirt uses that. If not set, libvirt checks $XDG_CONFIG_HOME/libvirt/auth.conf; If XDG_CONFIG_HOME is unset, then $HOME/.config/libvirt/auth.conf. SECURITY: The file should be readable only by the user. file path
LIBVIRT_DEFAULT_URI specify the default connection URI to a hypervisor or virtualization backend (like QEMU/KVM, Xen, LXC, etc.). It tells libvirt-based tools (like virsh, virt-manager, or libvirt API clients) which hypervisor and transport to connect to by default, when a URI is not explicitly given. Default for regular users is qemu:///session, for root is qemu:///system. See virt-admin(1) manpage. URI
LIBVIRT_LOG_FILTERS Filter list in which to select a category of debug outputs. A component:level colon-pair, each separated by commas. The levels are error, warning, info, debug, trace.; Some components are qemu, network, storage, cpu, driver, interface, xml, domain, migration, security, host, api, config, event, util.
QEMU_AUDIO_DRV type of audio driver to select pa, none, alsa, coreaudio, jack, oss, pipewire, sdl, spice or wav.
SDL_AUDIODRIVER SDL (Simple DirectMedia Layer) to control which audio backend it uses on your system. pipewire, pulseaudio, esd, alsa, jack, dsp, or arts.
VIRTD_PATH find the libvirtd executable. If not found or defined, fallback to LIBVIRTD_PATH. colon-separated directory path(s)
LIBVIRTD_PATH find the libvirtd executable; colon-separated directory spec(s). If VIRTD_PATH not found nor defined, this variable is tried. colon-separated directory path(s)


For debug-related envvar:

Debug environment variable names Description Type
LIBVIRT_DEBUG sets the verbosity level of libvirt logging. It works in conjunction with LIBVIRT_LOG_OUTPUTS to define how much detail is included in logs. It tells libvirt how detailed the log messages should be. verbosity level: 0 (fewer messages) to 4 (most verbose)
LIBVIRT_LOG_OUTPUTS control where log messages go (stdout, stderr, file, etc.) and what gets logged. File must be created manually. filepath
LIBVIRT_GNUTLS_DEBUG enable GNUTLS debug, if defined (none)
LIBVIRT_LIBSSH_DEBUG enable LIBSSH debug, if defined; use TRACE_LIBSSH=<level> to define debug level. (none)


For systemd support:

systemd environment variable name Description Type
LISTEN_FDS informs a service how many file descriptors have been passed to it by socket activation. For systemd only. file descriptor ID
LISTEN_PID the PID of the process the file descriptors are for (should match your PID). For systemd only. Process ID
NOTIFY_SOCKET inform systemd of its actual UNIX socket path for the client. for systemd-only. Unix domain socket path


For libvirt_leasehelper during network setup:

libvirt_leasehelper environment variable name Description Type
DNSMASQ_CLIENT_ID a custom DHCP client ID set by the VM's DHCP client, or a MAC address, depending on how the VM was configured. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. 14-hex, 14-hex, colon-separated, or user-defined string
DNSMASQ_IAID the 32-bit IAID provided by the DHCP IPv6 client. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. 32-bit Decimal, or Hex (prefix, no-prefix, colon-separated).
DNSMASQ_INTERFACE The bridge network interface name on which the lease event occurred. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. network interface name
DNSMASQ_LEASE_EXPIRES Unix timestamp when the lease will expire (or 0 if expired). Used by libvirt_leaseshelper with dnsmasqd during bridge driver. UNIX timestamp (i.e., seconds since the epoch: Jan 1, 1970).
DNSMASQ_OLD_HOSTNAME Old hostname before the current lease change (as sent by client via DHCP option 12). Set by dnsmasq when a DHCP lease update causes a client's hostname to change. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. May be empty if previous not set. hostname/DNS label (RFC1036/RFC1123)
DNSMASQ_SERVER_DUID uniquely identifies a DHCPv6 server. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. hostname (RFC3315)
DNSMASQ_SUPPLIED_HOSTNAME Used by libvirt_leaseshelper with dnsmasqd during bridge driver. hostname/DNS label (RFC1036/RFC1123)
VIR_BRIDGE_NAME contains the hostname explicitly supplied by the client during its DHCP request --typically via DHCPv4 option 12 (Host Name) or DHCPv6 option 39 (FQDN or Client FQDN). It's different from DNSMASQ_HOSTNAME, which may include DNS-derived or static-host config values. Used by libvirt_leaseshelper with dnsmasqd during bridge driver. simple Linux bridge name


Part of the XDG Base Directory Specification, which standardizes where user-specific files for GUI support should be stored:

XDG environment variable name Description Type
XDG_RUNTIME_DIR Used to find the $XDG_RUNTIME_DIR/libvirt/ directory. directory path
XDG_CONFIG_HOME It specifies the base directory where user-specific configuration files should be stored. If XDG_CONFIG_HOME is not set, applications default to: $HOME/.config. file path
XDG_DATA_HOME store non-essential, user-specific data—things like icons, application state (like a game save), caches of downloaded data, plugin data, fonts installed only for the user. If XDG_DATA_HOME is not set, it defaults to $HOME/.local/share. directory path
XDG_CACHE_HOME location for user-specific non-essential cached data files. It's used by applications to store cached data that can be safely deleted without losing important information, it will be regenerated by the app if needed. If not explicitly set, it defaults to $HOME/.cache. file path

For VirtualBox support:

VirtualBox environment variable name Description Type
DISPLAY the display X server and screen to which graphical applications should be sent. For virtualbox-only X Display Offset
VBOX_APP_HOME for virtualbox-only directory path


Deprecated goes here:

Deprecated environment variable name Description Type
LIBVIRT_ADMIN_DEFAULT_URI administration, see virt-admin(1) manpage. (Deprecated; use LIBVIRT_DEFAULT_URI) URI
VIRSH_DEFAULT_CONNECT_URI administration, see virsh(1) manpage. (Deprecated; used LIBVIRT_DEFAULT_URI). URI

A list of optional environment variables that are read and checked by the libvirt.so library linked by libvirtd:

libvirt environment variable name Description Type
LC_ALL to force all locale settings (like language, number formatting, collation, etc.) for programs running in your environment.

It overrides all other locale-related variables such as: 

 LANG
 LC_CTYPE, LC_TIME, LC_NUMERIC, LC_MESSAGES, etc.
locale name
LD_PRELOAD Overrides library search paths; useful for debugging alternative GTK or QEMU builds. Useful for debugging by swapping out malloc() function. Colon-separated for 2 or more directories. Directory Path
LD_LIBRARY_PATH Overrides library search paths; useful for debugging alternative GTK or QEMU builds. colon-separated directory paths
DYLD_INSERT_LIBRARIES works similarly to LD_PRELOAD but for macOS platforms. SIP blocks this for macOS system binaries. Only works with DYLD_FORCE_FLAT_NAMESPACE=1 setting. colon-separated directory path(s)
DYLD_FORCE_FLAT_NAMESPACE macOS has 2-level deep namespace. Set to 1 to flatten. May cause symbol collisions. digit
USER login username of the current user. Often used by shell scripts. username
LOGNAME Use by system (e.g., login, at). username
TMPDIR temporary directory where programs should write temporary files. directory path

Files

Files that are read by the host-side OS libvirtd daemon command:

  • /etc/libvirt/libvirtd.conf
  • /etc/libvirt/util.conf
  • /etc/machine-id
  • /etc/pki/CA/cacert.pem
  • /etc/pki/libvirt/servercert.pem
  • /etc/pki/libvirt/private/serverkey.pem
  • /proc/devices
  • /proc/filesystems
  • /proc/mounts
  • /proc/self/cgroup
  • /proc/%lld/cgroup
  • /proc/self/status
  • /proc/sys/kernel/cap_last_cap
  • [/var]/run/libvirt/libvirt-admin-sock
  • [/var]/run/libvirt/libvirt-sock
  • [/var]/run/libvirt/libvirt-sock-ro
  • [/var]/run/pid/libvirt.pid
  • /sys/devices/system/cpu/possible
  • /sys/devices/system/node/node0/meminfo
  • /sys/devices/system/node
  • /usr/lib/locale/locale-archive
  • /var/run/utmp
  • $HOME/.cache
  • $HOME/.local/share
  • $HOME/.pki/libvirt/cacert.pem
  • $HOME/.pki/libvirt/servercert.pem
  • $HOME/.pki/libvirt/serverkey.pem
  • $XDG_DATA_HOME
  • $XDG_CACHE_HOME


User permissions

libvirtd runs in either root (for system mode) or as a non-root user (for session mode).

See libvirt configuration for more setup on enabling a non-root user to use the libvirtd command.


Service

Typically, libvirtd daemon is run in system mode by the system startup script (like ATT SysV, rc.local, systemd). See libvirt service for more commands.

A quick test to see if the libvirtd daemon is up and running from the command line in one of three ways:


libvirtd service - status by CLI

host-root#virsh list --all
virsh list --all
 Id Name State
---------------------------
 16 gentoo running
 - gentoo2 shut off


libvirtd service - status by explicit channel

host-root#virsh -c qemu:///system list --all
virsh -c qemu:///system list --all
 Id Name State
---------------------------
 16 gentoo running
 - gentoo2 shut off


libvirtd service - status by environment variable

By environment variable, run:

CODE Use environment variable to define connect type
exportVIRSH_DEFAULT_CONNECT_URI=qemu:///system

then run:

host-root#virsh list --all
virsh list --all
 Id Name State
---------------------------
 16 gentoo running
 - gentoo2 shut off


libvirtd service - status by config file

The libvirt configuration file is in the following directory order:

1. /etc/libvirt/libvirt.conf

Note
There is no $HOME nor user-specific Libvirt configuration file.
CODE Libvirt configuration settings
#
# This can be used to setup URI aliases for frequently
# used connection URIs. Aliases may contain only the
# characters a-Z, 0-9, _, -.
#
# Following the '=' may be any valid libvirt connection
# URI, including arbitrary parameters
#uri_aliases = [
# "hail=qemu+ssh://root@hail.cloud.example.com/system",
# "sleet=qemu+ssh://root@sleet.cloud.example.com/system",
#]
#
# These can be used in cases when no URI is supplied by the application
# (@uri_default also prevents probing of the hypervisor driver).
#
#uri_default = "qemu:///system"

Use @uri_default if using this configuration file is copied as-is across multiple hosts; no probe for hypervisor driver done here, but if it does exist, use them.


Invocation

host$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


Removal

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

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

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/Front-ends — provide graphical, terminal, web-based, or command-line interfaces for configuring, managing, or accessing QEMU virtual machines.
  • Libvirt — a virtualization management toolkit
  • Virt-manager — lightweight GUI application designed for managing virtual machines and containers via the libvirt API.


External resources