This document explains the use of the "logging exception" IOS Commmand. To limit the size of the exception flush output, use the "logging exception" command in global configuration mode.
Logging exception Size is used to limit size of exception flush output. The main purpose of it is to restrict or disable the amount of buffered log sent to the console on a system crash.
When crashing, the router displays the content of the logging buffer, whether no logging console is enabled or not. If you think this amount of messages is too high, you may configure the amount of the logging buffer to be displayed on the console with "logging exception" command.
Router(config)# logging ?
Hostname or A.B.C.D IP address of the logging host
buffered Set buffered logging parameters
console Set console logging level
exception Limit size of exception flush output
facility Facility parameter for syslog messages
history Configure syslog history table
host Set syslog server host name or IP address
monitor Set terminal line (monitor) logging level
on Enable logging to all supported destinations
rate-limit Set messages per second limit
source-interface Specify interface for source address in logging transactions
trap Set syslog server logging level
The following example shows how to set the size of the logging exception flush output to 4098 bytes:
Router# configure terminal
Router(config)# logging exception 4098
To display the state of system logging and the contents of the standard system logging buffer use "show logging" command.
Syslog logging: enabled (11 messages dropped, 6 messages rate-limited,
0 flushes, 0 overruns, xml disabled, filtering disabled)
No Active Message Discriminator.
No Inactive Message Discriminator.
Console logging: level debugging, 1029 messages logged, xml disabled,
Monitor logging: level debugging, 0 messages logged, xml disabled,
Buffer logging: disabled, xml disabled,
Logging Exception size (4098 bytes)
Count and timestamp logging messages: disabled
Persistent logging: disabled
No active filter modules.
ESM: 0 messages dropped
Trap logging: level informational, 1039 message lines logged
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)