11 minute mode not syncing hardware clock to system clock

Solution Verified - Updated -


  • 11 minute mode is not keeping the hardware clock in sync with the system clock
  • From the hwclock(8) man page:

    Automatic Hardware Clock Synchronization By the Kernel
           You should be aware of another way that the Hardware Clock is kept syn-
           chronized  in  some  systems.   The  Linux kernel has a mode wherein it
           copies the System Time to the Hardware Clock every 11 minutes.  This is
           a  good mode to use when you are using something sophisticated like ntp
           to keep your System Time synchronized. (ntp is a way to keep your  Sys-
           tem  Time synchronized either to a time server somewhere on the network
           or to a radio clock hooked up to your system.  See RFC 1305).
           This mode (we’ll call it "11 minute mode") is off until something turns
           it  on.   The  ntp daemon xntpd is one thing that turns it on.  You can
           turn it off by running anything, including hwclock --hctosys, that sets
           the System Time the old fashioned way.
           To see if it is on or off, use the command adjtimex --print and look at
           the value of "status".  If the "64" bit of this  number  (expressed  in
           binary) equal to 0, 11 minute mode is on.  Otherwise, it is off.
           If  your system runs with 11 minute mode on, don’t use hwclock --adjust
           or hwclock --hctosys.  You’ll just make a mess.  It  is  acceptable  to
           use a hwclock --hctosys at startup time to get a reasonable System Time
           until your system is able to set the  System  Time  from  the  external
           source and start 11 minute mode.
  • We experienced an issue with application software and saw this in the log.

    set_rtc_mmss: can't update from 56 to 8


  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • ntp

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