Explanation of the "logging exception" IOS command

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Feb 5, 2010 1:04 PM
Feb 5th, 2010

Introduction

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.

Description:

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.

Configuration Example:

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> enable

Router# configure terminal

Router(config)# logging exception 4098

Router(config)#end

To display the state of system logging and the contents of the standard system logging buffer use "show logging" command.

Router#sh logging

 

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,

 

                     filtering disabled

 

    Monitor logging: level debugging, 0 messages logged, xml disabled,

 

                     filtering disabled

 

    Buffer logging:  disabled, xml disabled,

 

                     filtering 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)

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