2024-03-13 17:33:26 +08:00
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---
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title: VM Interface
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category: Interfaces
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layout: default
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SPDX-License-Identifier: LGPL-2.1-or-later
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---
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# The VM Interface
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Also consult [Writing Virtual Machine or Container
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Managers](https://systemd.io/WRITING_VM_AND_CONTAINER_MANAGERS).
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systemd has a number of interfaces for interacting with virtual machine
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managers, when systemd is used inside of a VM. If you work on a VM manager,
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please consider supporting the following interfaces.
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1. systemd supports passing immutable binary data blobs with limited size and
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restricted access to services via the `ImportCredential=`, `LoadCredential=`
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and `SetCredential=` settings. These credentials may be passed into a system
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via SMBIOS Type 11 vendor strings, see
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[systemd(1)](https://www.freedesktop.org/software/systemd/man/latest/systemd.html)
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2024-03-15 03:03:57 +08:00
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for details. This concept may be used to flexibly configure various facets
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2024-03-13 17:33:26 +08:00
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ot the guest system. See
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[systemd.system-credentials(7)](https://www.freedesktop.org/software/systemd/man/latest/systemd.system-credentials.html)
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for a list of system credentials implemented by various systemd components.
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2. Readiness, information about various system properties and functionality, as
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well as progress of boot may be reported by systemd to a machine manager via
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the `sd_notify()` protocol via `AF_VSOCK` sockets. The address of this
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socket may be configured via the `vmm.notify_socket` system credential. See
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[systemd(1)](https://www.freedesktop.org/software/systemd/man/latest/systemd.html).
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3. The
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[systemd-ssh-generator(8)](https://www.freedesktop.org/software/systemd/man/latest/systemd-ssh-generator.html)
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functionality will automatically bind SSH login functionality to `AF_VSOCK`
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port 22, if the system runs in a VM.
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4. If not initialized yet the system's
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[machine-id(5)](https://www.freedesktop.org/software/systemd/man/latest/machine-id.html)
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is automatically set to the SMBIOS product UUID if available and invocation
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in an VM environment is detected.
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5. The
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[`systemd-boot(7)`](https://www.freedesktop.org/software/systemd/man/latest/systemd-boot.html)
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and
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[`systemd-stub(7)`](https://www.freedesktop.org/software/systemd/man/latest/systemd-stub.html)
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components support two SMBIOS Type 11 vendor strings that may be used to
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extend the kernel command line of booted Linux environments:
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`io.systemd.stub.kernel-cmdline-extra=` and
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`io.systemd.boot.kernel-cmdline-extra=`.
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Also see
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[smbios-type-11(7)](https://www.freedesktop.org/software/systemd/man/latest/smbios-type-11.html)
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for a list of supported SMBIOS Type 11 vendor strings.
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