rtc(4) Device Drivers Manual rtc(4) rtc - #include int ioctl(fd, RTC_request, param); (RTCs). " " . " " (RTCs). . . i386 ACPI Motorola MC146818 PC/AT . ( ) . (system-on-chip) . PC/AT. gettimeofday(2) time(2) . (POSIX Epoch): 1970-01-01 00:00:00 +0000 (UTC). ( "" (jiffy) 100 250 1000 ). . ( "") . . . . hwclock(8) ioctl(2) . o ( ) o 2 2 8192 o . . (STR S3 ACPI) ( S4 ACPI) "" ( S5 ACPI). . /dev/rtc ( /dev/rtc0 /dev/rtc1 ) ( ) . read(2) select(2) . (long integer) read(2). ioctl(2) ioctl(2) : RTC_RD_TIME : struct rtc_time { int tm_sec; int tm_min; int tm_hour; int tm_mday; int tm_mon; int tm_year; int tm_wday; /* */ int tm_yday; /* */ int tm_isdst; /* */ }; tm gmtime(3). ioctl(2). RTC_SET_TIME rtc_time ioctl(2). ( CAP_SYS_TIME). RTC_ALM_READ RTC_ALM_SET . RTC_AIE_ON RTC_AIE_OFF. ioctl(2) rtc_time. tm_sec tm_min tm_hour . RTC_IRQP_READ RTC_IRQP_SET . RTC_PIE_ON RTC_PIE_OFF. ioctl(2) unsigned long * unsigned long . . 2 8192. ( CAP_SYS_RESOURCE) /proc/sys/dev/rtc/max-user-freq. ( 64 ). RTC_AIE_ON RTC_AIE_OFF . ioctl(2). RTC_UIE_ON RTC_UIE_OFF . ioctl(2). RTC_PIE_ON RTC_PIE_OFF . ioctl(2). ( CAP_SYS_RESOURCE) /proc/sys/dev/rtc/max-user-freq. RTC_EPOCH_READ RTC_EPOCH_SET 8 8 BCD. . 1900 Alpha MIPS 1952 1980 2000 . . ioctl(2) unsigned long * unsigned long ( ) . ( CAP_SYS_TIME). RTC_WKALM_RD RTC_WKALM_SET ioctls ( ) : struct rtc_wkalrm { unsigned char enabled; unsigned char pending; struct rtc_time time; }; enabled RTC_AIE_ON RTC_AIE_OFF. pending RTC_WKALM_RD ( EFI ). time RTC_ALM_READ RTC_ALM_SET tm_mday tm_mon tm_year . ioctl(2). /dev/rtc /dev/rtc0 /dev/rtc1 ... . /proc/driver/rtc (). adjtimex(2) 11 . . . 1970 100 2000 2069. "" . . . date(1), adjtimex(2), gettimeofday(2), settimeofday(2), stime(2), time(2), gmtime(3), time(7), hwclock(8) Documentation/rtc.rst 3 . . : . 6.18 8 2026 rtc(4)