HWCLOCK(8) HWCLOCK(8) hwclock - hwclock [] [...] hwclock . : (NTP) ( Alpha ) . v2.26 --hctosys --directisa --update-drift. . . --show. -a, --adjust . The Adjust Function. --getepoch; --setepoch Alpha RTC . . . BIOS 1952 1952. --setepoch --epoch . : hwclock --setepoch --epoch=1952 RTC . hwclock Alpha. ISA 1900. --param-get=; --param-set== RTC. RTC RTC. RTC ( include/uapi/linux/rtc.h ) . --help . 0x . --param-index RTC number. number 0. --predict --date /etc/adjtime. () . rtcwake(8). hwclock ' 11 ' . -r --show; --get ISO 8601. UTC. --localtime. . --get /etc/adjtime. hwclock ' 11 ' . -s --hctosys . . The Adjust Function. UTC . UTC . --hctosys /etc/adjtime --localtime --utc. : . LOCAL vs UTC. --hctosys . TZ /etc/localtime tzset(3). tz_dsttime . ( settimeofday(2).) --hctosys settimeofday(2) NTP ' 11 ' persistent_clock_is_local. . Automatic Hardware Clock Synchronization by the Kernel. /. . . ' 11 ' NTP --hctosys . /etc/adjtime . --update-drift --systohc ( ). --noadjfile --hctosys. /etc/adjtime. Hwclock UTC . . hwclock --localtime --adjust . hwclock . . hwclock . --set --date /etc/adjtime. --update-drift . --set. --update-drift . --systz --hctosys . 2.6 . --hctosys: o UTC . hwclock . o ' 11 ' NTP . o . settimeofday(2) . . . -w --systohc /etc/adjtime. --update-drift . --systohc. --update-drift . --vl-read --vl-clear RTC . --vl-read . --vl-clear RTC . include/uapi/linux/rtc.h . RTC . -h --help . -V --version . --adjfile=_ /etc/adjtime . --date=_ --set --predict . hwclock --set --date='16:45' hwclock --predict --date='2525-08-14 07:11:05' UTC. --localtime. . "+5 " hwclock . . . --delay= . 0.5 (500 ) rtc_cmos RTC 0. RTC ( sysfs) 0.5 . 500 (x86) MC146818A . . . 500 . . -D --debug --verbose. --debug . --directisa ISA x86 x86_64. . hwclock / . hwclock rtc RTC. v2.26 directisa rtc . . --rtc. --epoch= --setepoch. 1900. (ULONG_MAX - 1). -f --rtc=_ rtc hwclock. : /dev/rtc /dev/rtc0 /dev/misc/rtc. IA-64: /dev/efirtc /dev/misc/efirtc -l --localtime; -u --utc . (UTC) . --localtime --utc hwclock. ( ) . --utc --localtime (--set --systohc --adjust) /etc/adjtime. adjtime UTC. : . LOCAL vs UTC. --noadjfile /etc/adjtime. hwclock . --utc --localtime . --test /etc/adjtime (--verbose ). --update-drift /etc/adjtime. --set --systohc. . . . v2.26 hwclock --systohc : o NTP '11 ' . o ''. '' . . o () . . o ( v2.31 --update-drift RTC). hwclock /etc/adjtime. . . The Adjust Function. . . . . . -v --verbose hwclock . : : ( ) . ISA ISA. 1 . (RTC) BIOS CMOS. Hardware Clock hwclock. . ISA . I2C SPI . : . ( ISA ISA). . 00:00:00 1 1970 UTC ( 1969 UTC). . . . DOS ISA . date(1) . . : hwclock --systohc . hwclock. - . ( ) : TZ /etc/localtime tzset(3). . vfat. vfat . '11 ' NTP . / persistent_clock_is_local ' 11 '. . hwclock TZ /etc/localtime --hctosys --systz. : 1) tz_minuteswest ( ) UTC 2) tz_dsttime (DST) . . settimeofday(2). hwclock . / (I/O) rtc rtc. rtc udev . rtc --rtc. rtc. . ISA hwclock " CMOS" / 0x70 0x71. / . --directisa. / . hwclock ISA rtc . . - . . --adjust hwclock . : hwclock /etc/adjtime . adjtime. adjtime. hwclock --set . hwclock adjtime . 10 hwclock --set --update-drift 10 . hwclock adjtime . 24 hwclock --adjust. hwclock adjtime . . . 24 hwclock --adjust . hwclock : adjtime . --update-drift --set --systohc 24 adjtime. /etc/adjtime. --adjust . --adjust . hwclock --hctosys adjtime . --adjust . adjtime. --adjust . Adjtime hwclock . adjtime ASCII: 1: : 1) 2) 1969 UTC 3) ( clock(8)) . 2: : 1969 UTC . ( ). . 3: "UTC" "LOCAL". . hwclock. adjtime clock(8) hwclock. . 11 . . NTP . (NTP . RFC 1305.) ' 11 ' . 6 ( 0x0040) time_status . 'status' adjtimex --print ntptime. NTP ' 11 '. hwclock --hctosys. NTP ' 11 ' . ' 11 ' --hctosys --systz . . UTC . . persistent_clock_is_local. --hctosys --systz adjtime . . hwclock --adjust ' 11 ' NTP. ISA 50 CMOS ISA . hwclock . CMOS hwclock . "ISA " . ACPI . : o NTP cron." o . POSIX vs 'RIGHT'. o : adjtimex --tick --frequency hwclock --hctosys o : hwclock --systohc o adjtimex ntptime. NTP . . '' . . . . . . hwclock ( ) . --tick --frequency adjtimex(8). : tick frequency . ( adjtimex ntptime -f ppm .) adjtimex. . . --log adjtimex. sntp date -Ins . (tick) . adjtimex(2) . . (cold drift) . . . . : 1 NTP . 2 ! 3 . 4 . 5 . 6 hwclock --update-drift. : --systohc 6 ( 6) . hwclock /etc/adjtime . . sntp date -Ins . (UTC) : o . o . ISA . hwclock "" . UTC. hwclock --date. POSIX UTC. UTC . . MS Windows . Windows 7 RealTimeIsUniversal UTC. POSIX 'RIGHT' tzset(3). 'right' tz zoneinfo. zoneinfo posix 'right'. 'right' ( zoneinfo-leaps) posix. 'right' (UTC + ) (TAI - 10). . UTC 'right' . : . /usr/share/zoneinfo. posix 'right' TZ='right/Europe/Dublin'. zoneinfo posix 'right' zoneinfo : /usr/share/zoneinfo /usr/share/zoneinfo-posix /usr/share/zoneinfo-leaps . 'right' . zoneinfo . World Clock South_Pole MTA hwclock UTC /usr/share/zoneinfo . . . zoneinfo posix 'right' TZDIR. : EXIT_SUCCESS ('0' POSIX) . EXIT_FAILURE ('1' POSIX) . TZ . TZDIR . /etc/adjtime hwclock. adjtime_config(5). /etc/localtime . /usr/share/zoneinfo/ . hwclock : /dev/rtc /dev/rtc0 /dev/misc/rtc /dev/efirtc /dev/misc/efirtc date(1) adjtime_config(5) adjtimex(8) gettimeofday(2) settimeofday(2) crontab(1p) tzset(3) Bryan Henderson 1996 clock(8) Charles Hedrick Rob Hooft Harald Koenig. . . hwclock util-linux . util-linux 2.42.1 2026-05-18 HWCLOCK(8)