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  1. David Lee

    497 days and counting........

    You might have received an alert saying your linux based device has just rebooted, but you know that it has been up a long time. A switch might have just sent an alert for every interface flapping when they have all been up solidly. The important question to ask here is how long has the device been up? If its been up for 497 days,994 days,1491 days or any multiple of 497 then you are seeing the 497 day bug, that hits almost every linux based device that is up for a good length of time. Anything using a kernel less than 2.6 computes the system uptime based on the internal jiffies counter, which counts the time since boot in units of 10 milliseconds, or jiffies. This counter is a 32-bit counter, which has a maximum value of 2^32, or 4,294,967,296. When the counter reaches this value (after 497 days, 2 hours, 27 minutes, and 53 seconds, or approximately 16 months), it wraps back around to zero and continues to increment. This can result in alerts about reboots that didn’t happen and cause switches to report a flap on all interfaces. Systems that use 2.6 Kernel and properly supply a 64 bit counter will still alert incorrectly when the 64 bit counter wraps. A 32 bit counter can hold 4,294,967,295( /4,294,967,295864000/8640000 = 497.1 days) A 64 bit counter can hold 18,446,744,073,709,551,615 . (18,446,744,073,709,551,615/8640000 = 2135039823346 days or 5849424173 years) Though I expect in 6,000 million years we will all have other things to worry over.