Command:

logging on


Mode:

Router(config)#


Syntax:

logging on
no logging on

 

Syntax Description:

This command has no arguments or keywords.

 

Command Description:

To control logging of error messages, use the logging on global configuration command. This command sends debug or error messages to a logging process, which logs messages to designated locations asynchronously to the processes that generated the messages. To disable the logging process, use the no form of this command.

By default, the Cisco IOS software sends messages to the asynchronous logging process.

The logging process controls the distribution of logging messages to the various destinations, such as the logging buffer, terminal lines, or syslog server. You can turn logging on and off for these destinations individually using the logging buffered, logging monitor, and logging global configuration commands. However, if the logging on command is disabled, no messages will be sent to these destinations. Only the console will receive messages.

Additionally, the logging process logs messages to the console and the various destinations after the processes that generated them have completed. When the logging process is disabled, messages are displayed on the console as soon as they are produced, often appearing in the middle of command output.

The logging synchronous line configuration command also affects the displaying of messages to the console. When the logging synchronous command is enabled, messages will appear only after the user types a carriage return.


Example:

The following example shows command output and message output when logging is enabled. The ping process finishes before any of the logging information is printed to the console (or any other destination).

Router(config)# logging on
Router(config)# end
Router#
%SYS-5-CONFIG_I: Configured from console by console
Router# ping dirt
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.129, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
Router#
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1

In the following example, logging is disabled. The message output is displayed as messages are generated, causing the debug messages to be interspersed with the message "Type escape sequence to abort."

Router(config)# no logging on
Router(config)# end
%SYS-5-CONFIG_I: Configured from console by console
Router#
Router# ping dirt
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sendingTyp
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1e
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sending esc
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sendingape
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sendingse
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1
IP: s=172.21.96.41 (local), d=172.16.1.129 (Ethernet1/0), len 100, sendingquen
IP: s=171.69.1.129 (Ethernet1/0), d=172.21.96.41, len 114, rcvd 1ce to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.129, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 152/152/156 ms
Router#


Misconceptions:

Disabling the logging on command will substantially slow down the router. Any process generating debug or error messages will wait until the messages have been displayed on the console before continuing.


Related Commands:

logging buffered
logging monitor
logging synchronous

� Cisco Systems, Inc. 2001, 2002, 2003
World Wide Education

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