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Set or get date from realtime clock (QNX Neutrino)

Note: You must be root to run this utility.


Update the current time based on the time from the specified clock:

rtc [-b [base][,[reg_shift][,[mem_map][,c_offset]]]]
    [-l] [-r rate] [-S seconds] clock_type

Set the time of the specified clock to the current time:

rtc [-b [base][,[reg_shift][,[mem_map][,c_offset]]]]
    -s [-l] clock_type

Runs on:



-b [base][,[reg_shift][,[mem_map][,c_offset]]]
The location of the RTC chip:
(“el”) Set hardware time to local time, not Coordinated Universal Time (UTC). UTC is the standard term for Greenwich Mean Time (GMT). The -l option has no effect if the clock_type is net.
-r rate
Rate at which to adjust the OS time if it's currently within 60 seconds (or value set by -S) of the time from the source specified by clock_type. The rate is turned into a percentage 1/rate. The default rate is 100 (1%).
-S seconds
Specify the maximum number of seconds difference between current time and new time before jam loading rather than slowly adjusting. (see -r for the convergence speed). Default: 60.
Set hardware to current date and time.
One of the following:
Clock type Description
hw Hardware clock (automatically selects one based on information provided by the startup)
at (deprecated) IBM PC/AT Compatible hardware clock
ds1386 Embedded Dallas Semiconductor DS1386
ps2 (deprecated) IBM PS/2 Compatible hardware clock
rtc72423 Embedded Fox RTC-72423
rtcsh4 Integrated into the Hitachi SH4 7750/7751 cpus
mc146818 IBM PC/AT Compatible hardware clock
m48t5x STMicroelectronics TIMEKEEPER Series clock
net [node] Hardware clock on a remote node


The rtc command gets or sets the date and time from a battery backed-up hardware clock.

If your machine has a builtin clock/calendar, you should include the following command in your startup script so QNX Neutrino automatically reads the time when the system starts:

rtc hw

If the RTC chip has been set to the UTC timezone, startup sets the correct time of day automatically on booting. If the RTC chip is set to local time, or for some reason startup doesn't know where the RTC chip is, you'll need to include the appropriate rtc command in the startup script specified in your mkifs buildfile.

You can use clock type net [node] to get the date from a specified node, or to set the date on a specified node. If node isn't specified, the default is the local machine. When clock type net [node] is used, the -l option has no effect.

Note: Be careful if you set the date during the period that a time zone is switching to daylight saving time (DST). When a time zone changes to DST, the local time goes back one hour (for example, 2:00 a.m. becomes 1:00 a.m.). The local time during this hour is ambiguous (e.g. 1:14 a.m. occurs twice in the morning that the time zone switches to DST). To avoid problems, use UTC time to set the date in this period.


Update the current date and time from the hardware clock:

rtc hw

Set hardware clock with current date and time:

rtc -s hw

Exit status:

An error occurred.

See also:

date, mkifs, phlocale