docs/VM_INTERFACE.md

   1 ---
   2 title: VM Interface
   3 category: Interfaces
   4 layout: default
   5 SPDX-License-Identifier: LGPL-2.1-or-later
   6 ---
   7
   8 # The VM Interface
   9
  10 Also consult [Writing Virtual Machine or Container
  11 Managers](https://systemd.io/WRITING_VM_AND_CONTAINER_MANAGERS).
  12
  13 systemd has a number of interfaces for interacting with virtual machine
  14 managers, when systemd is used inside of a VM. If you work on a VM manager,
  15 please consider supporting the following interfaces.
  16
  17 1. systemd supports passing immutable binary data blobs with limited size and
  18    restricted access to services via the `ImportCredential=`, `LoadCredential=`
  19    and `SetCredential=` settings. These credentials may be passed into a system
  20    via SMBIOS Type 11 vendor strings, see
  21    [systemd(1)](https://www.freedesktop.org/software/systemd/man/latest/systemd.html)
  22    for details. This concept may be used to flexibly configure various facets
  23    ot the guest system. See
  24    [systemd.system-credentials(7)](https://www.freedesktop.org/software/systemd/man/latest/systemd.system-credentials.html)
  25    for a list of system credentials implemented by various systemd components.
  26
  27 2. Readiness, information about various system properties and functionality, as
  28    well as progress of boot may be reported by systemd to a machine manager via
  29    the `sd_notify()` protocol via `AF_VSOCK` sockets. The address of this
  30    socket may be configured via the `vmm.notify_socket` system credential. See
  31    [systemd(1)](https://www.freedesktop.org/software/systemd/man/latest/systemd.html).
  32
  33 3. The
  34    [systemd-ssh-generator(8)](https://www.freedesktop.org/software/systemd/man/latest/systemd-ssh-generator.html)
  35    functionality will automatically bind SSH login functionality to `AF_VSOCK`
  36    port 22, if the system runs in a VM.
  37
  38 4. If not initialized yet the system's
  39    [machine-id(5)](https://www.freedesktop.org/software/systemd/man/latest/machine-id.html)
  40    is automatically set to the SMBIOS product UUID if available and invocation
  41    in an VM environment is detected.
  42
  43 5. The
  44    [`systemd-boot(7)`](https://www.freedesktop.org/software/systemd/man/latest/systemd-boot.html)
  45    and
  46    [`systemd-stub(7)`](https://www.freedesktop.org/software/systemd/man/latest/systemd-stub.html)
  47    components support two SMBIOS Type 11 vendor strings that may be used to
  48    extend the kernel command line of booted Linux environments:
  49    `io.systemd.stub.kernel-cmdline-extra=` and
  50    `io.systemd.boot.kernel-cmdline-extra=`.
  51
  52 Also see
  53 [smbios-type-11(7)](https://www.freedesktop.org/software/systemd/man/latest/smbios-type-11.html)
  54 for a list of supported SMBIOS Type 11 vendor strings.