Blame SOURCES/rhel-rt.rules

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# udev rules specific to RHEL-RT Realtime kernel
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# insure /dev/rtc points to /dev/rtc0
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# we use PROGRAM rather than SYMLINK because there is
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# a (good) possiblity that a /dev/rtc device file
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# already exists and we want to replace it (hence the
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# ln -sf)
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KERNEL=="rtc0", PROGRAM+="/bin/ln -sf rtc0 /dev/rtc"
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# Give permission to the realtime group to write a zero to /dev/cpu_dma_latency
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# This will tell the power management system not to tranistion to a high cstate
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KERNEL=="cpu_dma_latency", GROUP="realtime"