31 lines
740 B
Bash
31 lines
740 B
Bash
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#!/bin/sh
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# This shell scripts writes the offset between 'hwclock' and 'swclock'
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# to a file.
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#
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# To keep the offset calculation simple, the epoch timestamp is used.
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#
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# The system time is read by command "date". The RTC is read from the
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# sysfs node.
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rtc_sys_node="/sys/class/rtc/rtc0/since_epoch"
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offset_directory="/var/cache/swclock-offset"
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# check presence of rtc sys node
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if [ ! -f $rtc_sys_node ]; then
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exit 1
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fi
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# check presence of offset directory
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if [ ! -d $offset_directory ]; then
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mkdir -p $offset_directory
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fi
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# calculate offset
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swclock_epoch=$(date --utc +%s)
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hwclock_epoch=$(cat $rtc_sys_node)
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offset_epoch=$((swclock_epoch - hwclock_epoch))
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# write offset file
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echo $offset_epoch > $offset_directory/offset-storage
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