The following example shows how to set the size of the logging exception flush output to 4098 bytes:
To display the state of system logging and the contents of the standard system logging buffer use "show logging" command.
Debugging and Logging
Cisco IOS software allows for detailed debugging for all protocols and processes running in the system for troubleshooting purposes. More information on debugging can be obtained in the Cisco IOS Debug Command Reference
Enabling a higher level of messages shows all lower-level messages as well. The debugging level, or level 7, shows all messages. System messages may also be buffered and seen using the show logging command in privileged mode. A user may also send logging messages to a syslog server using the logging host command in configuration mode. A syslog server can be configured on a UNIX device or PC to accept these messages from a router and place them in a file. This allows for large files containing system messages to be maintained, because you are not restricted by the amount of memory on the router.
Only Cisco IOS experts should enable and disable debug commands, because they can have a severe performance impact and should be used with care. Improper use might leave the system inaccessible and in a frozen state in which no packet forwarding takes place.
System messages are shown on the console and can be enabled for any session into the router. Different levels of severity can be configured for different access methods into the router. The eight message severity levels are as follows:
Emergency (severity 0)—The system is unusable
Alert (severity 1)—Immediate action is needed
Critical (severity 2)—Critical condition
Error (severity 3)—Error condition
Warning (severity 4)—Warning condition
Notification (severity 5)—Normal but significant condition
Informational (severity 6)—Informational message
Debugging (severity 7)—Debugging message
IOS(config)# logging console ?
<0-7> Logging severity level
alerts Immediate action needed (severity=1)
critical Critical conditions (severity=2)
debugging Debugging messages (severity=7)
emergencies System is unusable (severity=0)
errors Error conditions (severity=3)
guaranteed Guarantee console messages
informational Informational messages (severity=6)
notifications Normal but significant conditions (severity=5)
warnings Warning conditions (severity=4)