You want to clear the router's log buffer.
Use the clear logging command to clear the router's internal log buffer:
Router#clear logging Clear logging buffer [confirm] Router#
There are times when it is useful to be able to clear your router's internal buffer log. For instance, while debugging a network problem, old debug messages can cause unnecessary confusion during stressful moments. This will clear the router log:
Router#clear logging Clear logging buffer [confirm] Router>show logging Syslog logging: enabled (0 messages dropped, 0 messages rate-limited, 0 flushes, 0 overruns) Console logging: level debugging, 64201 messages logged Monitor logging: level debugging, 64820 messages logged Buffer logging: level debugging, 9 messages logged Logging Exception size (4096 bytes) Trap logging: level debugging, 2253 message lines logged Logging to 172.25.1.1, 2253 message lines logged Log Buffer (4096 bytes): Router>
Note that this command has no effect on the other forms of logging.
Router Configuration and File Management
User Access and Privilege Levels
Handling Queuing and Congestion
Tunnels and VPNs
NTP and Time
Router Interfaces and Media
Simple Network Management Protocol
First Hop Redundancy Protocols
Appendix 1. External Software Packages
Appendix 2. IP Precedence, TOS, and DSCP Classifications