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Catalyst 6500 series switches with Supervisor III that runs Cisco IOS resets due to watchdog timeout or incorrect bootup cause with error message System returned to ROM by unknown reload cause - suspect boot_data[BOOT_COUNT] 0x0, BOOT_COUNT 0, BOOTDATA 19
The Cisco processors have timers that guard against certain types of system hangs. The CPU periodically resets a watchdog timer. The watchdog timer basically controls the time of each process. If the timer is not reset, a trap occurs. If a process is longer than it should be, the watchdog timer is used to escape from this process.
The watchdog timer fires incorrectly during the reload process. While ROMMON records the reload reason, the watchdog prematurely resets the CPU and you lose part of the string, which prints out the reason for the reload in theshow version command.
When Cisco IOS reboots, it tries to get this string from rommon through another EMT exception, which just returns the incomplete/garbled string and Cisco IOS interprets the last reload reason in the show version output as - System returned to ROM by unknown reload cause - suspect boot_data[BOOT_COUNT] 0x0, BOOT_COUNT 0, BOOTDATA 19).
This symptom is observed on a Catalyst 6000 series switch that runs Cisco IOS Software Release 12.2S.
This problem is documented in Cisco bug ID CSCef80423.
There is no workaround hence, in order to resolve this issue, upgrade the Cisco IOS software to Cisco IOS Software Release12.2(18)SXE or Cisco IOS Software Release 12.2(17d)SXB8. These software releases can be downloaded from Cisco Downloads.