Re: 2.4.x kernel uptime counter problem

[Nick <nick@linicks.net>]

On 1/19/06, Rumi Szabolcs <rumi_ml@rtfm.hu> wrote:
> Hello!
>
> I've got a Linux system running the 2.4.26 kernel which was about
> to pass the 500 day mark these days and now suddenly what I see is
> that the uptime counter has reset:
>
> $ uname -a && w && cat /proc/uptime && last -1 reboot
> Linux quasar 2.4.26 #3 SMP Tue Sep 7 09:22:08 CEST 2004 i686 Intel(R) Pentium(R) 4 CPU 2.60GHz GenuineIntel GNU/Linux
>  09:38:08 up 1 day, 12:49,  5 users,  load average: 0.00, 0.00, 0.00
> USER     TTY        LOGIN@   IDLE   JCPU   PCPU WHAT
> rumi     pty/s0    08:53    0.00s  0.04s  0.02s screen -r
> rumi     ttyp1     10Sep04 31:58   9:12   9:12  epic
> rumi     ttyp3     Tue12   44:33m  0.01s  0.01s -/bin/bash
> rumi     ttyp2     13Feb05  8days  0.11s  0.11s -/bin/bash
> rumi     ttypc     11Dec05  0.00s  0.12s  0.11s -/bin/bash
> 132596.51 39801752.60
> reboot   system boot  2.4.26           Tue Sep  7 18:47         (498+15:50)
>
> From the above it can be seen that the system is running continuously
> and wasn't rebooted 36 hours ago as the uptime counter would suggest.
>
> Is this a known bug?


It's not a bug - it is a feature.  uptime rolls over after 497 days.

[sic]
It computes the result of the "uptime" based on the internal "jiffies"
counter, which counts the time since boot, in units of 10
milliseconds.
This is typecast as an "unsigned long" - on the Intel boxes, that's an
unsigned 32-bit number.
Well, it turns out that in a 32-bit number, you can store 497.1 days
before the number wraps.


You can use:
last -xf /var/run/utmp runlevel

to get true uptime in this instance.

Nick

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