Logging to the Internal Buffer
Every Catalyst switch has an internal memory buffer where syslog messages can be collected. The internal buffer is an efficient way to collect messages over time. As long as the switch is powered up, the logging buffer is available.
By default, the internal logging buffer is disabled. To enable it and begin sending system messages into the buffer, you can use the following command:
Switch(config)# logging buffered severity
The severity parameter can be either a severity level keyword, such as informational, or the corresponding numeric value (0 to 7).
The logging buffer has a finite size and operates in a circular fashion. If the buffer fills, the oldest messages roll off as new ones arrive. By default, the logging buffer is 4096 bytes or characters long, which is enough space to collect 50 lines of full-length text. If you depend on the logging buffer to keep a running history of logging messages, you might need to increase its size with the following command:
Switch(config)# logging buffered size
The buffer length is set to size (4096 to 2147483647) bytes. Be careful not to set the length too great, as the switch reserves the logging buffer space from the memory it might need for other operations.
To review the internal logging buffer at any time, you can use the show logging command.