Cisco IOS: Logging only debug messages on command-line

I want to have a quiet command-line such as (config)# no logging console causes. Still, I want to make use of # debug commands. It appears to me that # debug depends on syslog level 7. So I cannot have a quiet CLI and read debug messages at the same time.

Is there a workaround?

Host(config)#logging ?
  Hostname or A.B.C.D  IP address of the logging host
  buffered             Set buffered logging parameters
  buginf               Enable buginf logging for debugging
  cns-events           Set CNS Event logging level
  console              Set console logging parameters
  count                Count every log message and timestamp last occurrence
  discriminator        Create or modify a message discriminator
  dmvpn                DMVPN Configuration
  esm                  Set ESM filter restrictions
  exception            Limit size of exception flush output
  facility             Facility parameter for syslog messages
  filter               Specify logging filter
  history              Configure syslog history table
  host                 Set syslog server IP address and parameters
  message-counter      Configure log message to include certain counter value 
  monitor              Set terminal line (monitor) logging parameters
  on                   Enable logging to all enabled destinations
  origin-id            Add origin ID to syslog messages
  persistent           Set persistent logging parameters
  queue-limit          Set logger message queue size
  rate-limit           Set messages per second limit
  reload               Set reload logging level
  server-arp           Enable sending ARP requests for syslog servers when first configured
  source-interface     Specify interface for source address in logging transactions
  trap                 Set syslog server logging level
  userinfo             Enable logging of user info on privileged mode enabling

Host(config)#logging console ?
  <0-7>          Logging severity level
  alerts         Immediate action needed           (severity=1)
  critical       Critical conditions               (severity=2)
  debugging      Debugging messages                (severity=7)
  discriminator  Establish MD-Console association
  emergencies    System is unusable                (severity=0)
  errors         Error conditions                  (severity=3)
  filtered       Enable filtered logging
  guaranteed     Guarantee console messages
  informational  Informational messages            (severity=6)
  notifications  Normal but significant conditions (severity=5)
  warnings       Warning conditions                (severity=4)
  xml            Enable logging in XML
  <cr>

An example using cpt_fink's solution:

After logging console critical and logging buffered 64000 debug and clear log on Host:

Host#show log
Syslog logging: enabled (12 messages dropped, 0 messages rate-limited,
                0 flushes, 0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.



No Inactive Message Discriminator.


    Console logging: level critical, 20 messages logged, xml disabled,
                     filtering disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging:  level debugging, 4 messages logged, xml disabled,
                     filtering disabled
    Logging Exception size (4096 bytes)
    Count and timestamp logging messages: disabled
    Persistent logging: disabled

No active filter modules.

ESM: 0 messages dropped

    Trap logging: level informational, 36 message lines logged

Log Buffer (64000 bytes):
Host#
Host#
Host#debug ip icmp
ICMP packet debugging is on
Host#
Host#
Host#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Host(config)#   
Host(config)#interface fastethernet0/1
Host(config-if)#
Host(config-if)#ip address 192.168.0.1 255.255.255.0
Host(config-if)#
Host(config-if)#no shut
Host(config-if)#end
Host#
Host#
Host#show log
Syslog logging: enabled (12 messages dropped, 0 messages rate-limited,
                0 flushes, 0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.



No Inactive Message Discriminator.


    Console logging: level critical, 20 messages logged, xml disabled,
                     filtering disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging:  level debugging, 5 messages logged, xml disabled,
                     filtering disabled
    Logging Exception size (4096 bytes)
    Count and timestamp logging messages: disabled
    Persistent logging: disabled

No active filter modules.

ESM: 0 messages dropped

    Trap logging: level informational, 37 message lines logged

Log Buffer (64000 bytes):

Nov  4 18:03:05.551: %SYS-5-CONFIG_I: Configured from console by console
Host#

Let's provoke one ICMP debug message.

Host_2#ping 192.168.0.1 repeat 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
.
Success rate is 0 percent (0/1)
Host_2#
Host_2#
Host_2#ping 192.168.0.1 repeat 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!
Success rate is 100 percent (1/1), round-trip min/avg/max = 12/12/12 ms
Host_2#

Let's look up syslog:

Host#show log
Syslog logging: enabled (12 messages dropped, 0 messages rate-limited,
                0 flushes, 0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.



No Inactive Message Discriminator.


    Console logging: level critical, 20 messages logged, xml disabled,
                     filtering disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging:  level debugging, 6 messages logged, xml disabled,
                     filtering disabled
    Logging Exception size (4096 bytes)
    Count and timestamp logging messages: disabled
    Persistent logging: disabled

No active filter modules.

ESM: 0 messages dropped

    Trap logging: level informational, 37 message lines logged

Log Buffer (64000 bytes):

Nov  4 18:03:05.551: %SYS-5-CONFIG_I: Configured from console by console
Nov  4 18:04:47.527: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Host#

Let's issue commands which usually cause annoying messages:

Host#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Host(config)#
Host(config)#interface fastethernet0/0
Host(config-if)#
Host(config-if)#shut
Host(config-if)#
Host(config-if)#exit
Host(config)#
Host(config)#
Host(config)#interface fastethernet0/1
Host(config-if)#
Host(config-if)#shut
Host(config-if)#    
Host(config-if)#exit
Host(config)#
Host(config)#end
Host#

Let's look up syslog:

Host#show log
Syslog logging: enabled (12 messages dropped, 0 messages rate-limited,
                0 flushes, 0 overruns, xml disabled, filtering disabled)

No Active Message Discriminator.



No Inactive Message Discriminator.


    Console logging: level critical, 20 messages logged, xml disabled,
                     filtering disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging:  level debugging, 11 messages logged, xml disabled,
                     filtering disabled
    Logging Exception size (4096 bytes)
    Count and timestamp logging messages: disabled
    Persistent logging: disabled

No active filter modules.

ESM: 0 messages dropped

Trap logging: level informational, 42 message lines logged

Log Buffer (64000 bytes):

Nov  4 18:03:05.551: %SYS-5-CONFIG_I: Configured from console by console
Nov  4 18:04:47.527: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  4 18:11:57.371: %LINK-5-CHANGED: Interface FastEthernet0/0, changed state to administratively down
Nov  4 18:11:58.371: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to down
Nov  4 18:12:07.619: %LINK-5-CHANGED: Interface FastEthernet0/1, changed state to administratively down
Nov  4 18:12:08.619: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1,     changed state to down
Nov  4 18:12:36.111: %SYS-5-CONFIG_I: Configured from console by console
Host#

What I like: I can work on the CLI without interruptions.
What I do not like: I still get messages not logged by debug ip icmp.

An example using cpt_fink's solution marked as correct answer:

Configuration:

Router_1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router_1(config)#
Router_1(config)#logging console
Router_1(config)#
Router_1(config)#logging console critical
Router_1(config)#
Router_1(config)#logging buffered 64000 debug
Router_1(config)#
Router_1(config)#do clock set 07:29:30 5 november 2014
Router_1(config)#
Router_1(config)#end
Router_1#
Router_1#debug ip icmp
ICMP packet debugging is on
Router_1#

Let's create at least one message:

Router_2#ping 192.168.0.1 repeat 2

Type escape sequence to abort.
Sending 2, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!!
Success rate is 100 percent (2/2), round-trip min/avg/max = 4/4/4 ms
Router_2#

Let's look up syslog:

Router_1#show logging | include ICMP
Nov  5 07:30:05.463: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:30:05.467: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Router_1#

Let's provoke more messages:

Router_2#ping 192.168.0.1 repeat 11

Type escape sequence to abort.
Sending 11, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!!!!!!!!!!!
Success rate is 100 percent (11/11), round-trip min/avg/max = 4/4/4 ms
Router_2#

Let's look up syslog:

Router_1#show logging | include ICMP
Nov  5 07:30:05.463: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:30:05.467: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.807: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.811: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.815: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.819: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.823: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.827: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.831: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.835: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.839: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.843: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Nov  5 07:32:24.847: ICMP: echo reply sent, src 192.168.0.1, dst 192.168.0.2
Router_1#

Best Answer

I would suggest logging console critical and logging buffered 64000 debug which lets you use the sho log command to see historical output without clogging the low-speed physical console with messages, while still receiving critical or higher messages on the console.

Also useful when using the log buffer are correctly setting your system time (with NTP or clock set ... from exec) and timezone/DST clock timezone XXX -# and clock summer-time XXX recurring and using the service timestamps log datetime local ms and service timestamps debug date local ms commands to mark your messages as they are output.

As a side note terminal monitor (and terminal no monitor to disable it) are a way to get immediate output when remotely connected. You can set the logging monitor [level] to include debug, or only higher importance messages.

Best Answer

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