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Add documentation for virtio-rng

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Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
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Stefan Reiter 2020-03-10 18:01:22 +01:00 committed by Thomas Lamprecht
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commit adb2c91d58
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@ -791,6 +791,44 @@ device of the host use device passthrough (see
xref:qm_pci_passthrough[PCI Passthrough] and
xref:qm_usb_passthrough[USB Passthrough]).
[[qm_virtio_rng]]
VirtIO RNG
~~~~~~~~~~
A RNG (Random Number Generator) is a device providing entropy ('randomness') to
a system. A virtual hardware-RNG can be used to provide such entropy from the
host system to a guest VM. This helps to avoid entropy starvation problems in
the guest (a situation where not enough entropy is available and the system may
slow down or run into problems), especially during the guests boot process.
To add a VirtIO-based emulated RNG, run the following command:
----
qm set <vmid> -rng0 source=<source>[,max_bytes=X,period=Y]
----
`source` specifies where entropy is read from on the host and has to be one of
the following:
* `/dev/urandom`: Non-blocking kernel entropy pool (preferred)
* `/dev/random`: Blocking kernel pool (not recommended, can lead to entropy
starvation on the host system)
* `/dev/hwrng`: To pass through a hardware RNG attached to the host (if multiple
are available, the one selected in
`/sys/devices/virtual/misc/hw_random/rng_current` will be used)
A limit can be specified via the `max_bytes` and `period` parameters, they are
read as `max_bytes` per `period` in milliseconds. However, it does not represent
a linear relationship: 1024B/1000ms would mean that up to 1 KiB of data becomes
available on a 1 second timer, not that 1 KiB is streamed to the guest over the
course of one second. Reducing the `period` can thus be used to inject entropy
into the guest at a faster rate.
By default, the limit is set to 1024 bytes per 1000 ms (1 KiB/s). It is
recommended to always use a limiter to avoid guests using too many host
resources. If desired, a value of '0' for `max_bytes` can be used to disable
all limits.
[[qm_startup_and_shutdown]]
Automatic Start and Shutdown of Virtual Machines
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~