Problems with hwclock

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Revision as of 04:39, 23 May 2007 by Fo0bar (Talk | contribs) (Using the --directisa switch of hwclock(8))

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This page discusses the problem with /dev/rtc on certain models.

Problem description

On bootup,a message like this shows up:

select() to /dev/rtc to wait for clock tick timed out


The RTC kernel driver can't handle the system clock.

Possible solutions

Using the --directisa switch of hwclock(8)

The hwclock command knows the parameter --directisa to access the system clock "directly" instead of accessing it by using /dev/rtc. There are several ways of doing this automatically.

Generic instructions

Move /sbin/hwclock (or wherever it is located on your system) to /sbin/hwclock.dist and create the following shell script, which you place at /sbin/hwclock

#!/bin/sh
/sbin/hwclock.dist --directisa "$@"

Make the script executable (apply the same permissions you had for hwclock before) and keep your packaging system from overwriting it on updates.

Debian 4.0 (etch)

Add the following to /etc/default/rcS:

HWCLOCKPARS="--directisa"

Debian 3.1 (sarge) and previous

Edit /etc/init.d/hwclock.sh and change all instances of "/sbin/hwclock" to "/sbin/hwclock --directisa".

Compiling RTC-support into the kernel instead of as a module

Compiling RTC-support (CONFIG_RTC) into the kernel instead of compiling it as a module seems to work also. Tested on: 2.6.20.6 at Thinkpad Z61m 9450-3HG

Affected Models

Affected Operating Systems

  • Linux, all flavours. Tested with kernel 2.6.18, 2.6.19, 2.6.20.6