RTC(1M) Maintenance Commands RTC(1M)

rtc
provide all real-time clock and UTC-lag management

rtc [-csuvw] [-z zone-name]

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 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.

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.

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.
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.
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.
This option does nothing. It is present for compatibility with Solaris 11.
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.

/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.

x86

date(1), cron(1M), rdate(1M), attributes(5)
January 31, 2018 OmniOS