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Some hypervisors (e.g. hyperkit / xhyve) don't provide a good way to keep the VM's clock in sync with the Host's clock. NTP will usually keep the clocks together, but after a the host or VM is suspended and resumed the clocks can be suddenly too far apart for NTP to work properly. This simple daemon listens on an AF_VSOCK port and resynchronises the VM clock from the virtualised hardware clock. This is a Go conversion of original C code written by Magnus Skjegstad <magnus@skjegstad.com> Signed-off-by: David Scott <dave.scott@docker.com>
22 lines
909 B
Markdown
22 lines
909 B
Markdown
### host-timesync-daemon
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Some hypervisors (e.g. hyperkit / xhyve) don't provide a good way to keep
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the VM's clock in sync with the Host's clock. NTP will usually keep the
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clocks together, but after the host or VM is suspended and resumed the
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clocks can be suddenly too far apart for NTP to work properly.
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This simple daemon listens on an AF_VSOCK port. When a connection is
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received, the daemon
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- reads the (hypervisor's virtual) hardware clock via `RTC_RD_TIME` on
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`/dev/rtc0`
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- calls `settimeofday` to set the time in the VM
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- closes the connection
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Note the hardware clock has only second granularity so you will still need
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NTP (or some other process) to keep the clocks closely synchronised.
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To use this, simply connect to the AF_VSOCK port when you want the clock
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to be resynchronised. If you want to wait for completion then `read` from
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the socket -- `EOF` means the resychronisation is complete.
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