Print this page
8980 BIOS clock is sometimes one hour fast
Reviewed by: Toomas Soome <tsoome@me.com>
Reviewed by: C Fraire <cfraire@me.com>
@@ -1,74 +1,80 @@
RTC(1M) Maintenance Commands RTC(1M)
-
-
NAME
- rtc - provide all real-time clock and GMT-lag management
+ rtc - provide all real-time clock and UTC-lag management
SYNOPSIS
- /usr/sbin/rtc [-c] [-z zone-name]
+ rtc [-csuvw] [-z zone-name]
-
DESCRIPTION
- On x86 systems, the rtc command reconciles the difference in the way
- that time is established between UNIX and MS-DOS systems. UNIX systems
- utilize Greenwich Mean Time (GMT), while MS-DOS systems utilize local
- time.
+ The Real Time Clock (RTC) is the hardware device on x86 computers that
+ maintains the date and time. The RTC is battery-powered, so that it
+ keeps running when the computer is shut down. It can be set from the
+ BIOS and also from the operating system running on the computer. The RTC
+ has no setting for the time zone or for Daylight Saving Time (DST). It
+ relies on the operating system for these facilities and for automatic
+ changes between standard time and DST.
+ On x86 systems, the rtc command reconciles the difference in the way that
+ time is established between UNIX and Windows systems. The internal clock
+ on UNIX systems utilizes Universal Coordinated Time (UTC) while Windows
+ systems usually expect the RTC to run in local time, including DST
+ changes.
- Without arguments, rtc displays the currently configured time zone
- string. The currently configured time zone string is based on what was
- last recorded by rtc-z zone-name.
+ Without arguments, rtc displays the currently configured time zone string
+ for the RTC. The currently configured time zone string is based on what
+ was last recorded by rtc -z zone-name.
+ The rtc command is not normally run from a shell prompt; it is generally
+ invoked by the system. Commands such as date(1) and rdate(1M), which are
+ used to set the time on a system, invoke rtc -c to ensure that daylight
+ savings time (DST) is corrected for properly.
- The rtc command is not normally run from a shell prompt; it is
- generally invoked by the system. Commands such as date(1) and
- rdate(1M), which are used to set the time on a system, invoke
- /usr/sbin/rtc -c to ensure that daylight savings time (DST) is
- corrected for properly.
-
OPTIONS
- -c
- This option checks for DST and makes corrections if
- necessary. It is normally run once a day by a cron job.
+ -c This option checks for DST and makes corrections to the RTC if
+ necessary. It is normally run once a day by a cron(1M) job.
- If there is no RTC time zone or /etc/rtc_config file,
- this option will do nothing.
+ If there is no RTC time zone or /etc/rtc_config file, this option
+ will do nothing.
+ -s This option specifies that the RTC runs in local standard time
+ all year round. It is incompatible with Windows, but is
+ convenient if only one operating system is to be run on the
+ computer. The cron(1M) command is not necessary, and should not
+ be run.
- -z zone-name
- This option, which is normally run by the system at
- software installation time, is used to specify the time
- zone in which the RTC is to be maintained. It updates
- the configuration file /etc/rtc_config with the name of
- the specified zone and the current GMT lag for that
- zone. If there is an existing rtc_config file, this
- command will update it. If not, this command will
- create it.
+ -u This option specifies that the RTC runs in UTC time. As a side
+ effect, it sets the time zone in /etc/rtc_config to UTC. Windows
+ can operate in UTC time, but requires a registry change to do so.
+ The cron(1M) command is not necessary.
+ -v This option specifies that the RTC tracks local time, including
+ DST changes. This is the default. It accomodates Windows with
+ no changes. The cron(1M) command is necessary to change the RTC
+ when DST is in effect.
-FILES
- /etc/rtc_config
- The data file used to record the time zone and GMT
- lag. This file is completely managed by
- /usr/sbin/rtc, and it is read by the kernel.
+ -w This option does nothing. It is present for compatibility with
+ Solaris 11.
+ -z zone-name
+ This option, which is normally run by the system at software
+ installation time, is used to specify the time zone in which the
+ RTC is to be maintained. It updates the configuration file
+ /etc/rtc_config with the name of the specified zone and the
+ current UTC lag for that zone. If there is an existing
+ /etc/rtc_config file, this command will update it. If not, this
+ command will create it.
-ATTRIBUTES
- See attributes(5) for descriptions of the following attributes:
+FILES
+ /etc/rtc_config The data file used to record the time zone and UTC lag.
+ This file is completely managed by rtc. At boot time,
+ the kernel reads the UTC lag from this file, and uses it
+ to set the system time.
+ARCHITECTURE
+ x86
-
-
- +---------------+-----------------+
- |ATTRIBUTE TYPE | ATTRIBUTE VALUE |
- +---------------+-----------------+
- |Architecture | x86 |
- +---------------+-----------------+
-
SEE ALSO
- date(1), rdate(1M), attributes(5)
+ date(1), cron(1M), rdate(1M), attributes(5)
-
-
- October 3, 2003 RTC(1M)
+illumos January 31, 2018 illumos