DebugPrivileged EXEC

undebug all

Disables all active debug operations on the router, used to stop debugging output and reduce CPU load.

Syntax·Privileged EXEC

undebug all

When to Use This Command

After troubleshooting a routing protocol issue, disable all debugs to return the router to normal operation.
When debugging output is overwhelming the console or causing performance degradation, quickly stop all debugs.
Before performing a critical configuration change, ensure no debugs are running to avoid log interference.
When a junior engineer left debugs enabled, use undebug all to clean up the session.

Command Examples

Disabling all active debugs

Router# undebug all

All possible debugging has been turned off

The output confirms that all debug operations are now disabled. No further debug messages will be displayed.

Verifying debugs are off after undebug all

Router# show debug

Router#

After undebug all, show debug returns no output, indicating no debugs are active.

Understanding the Output

The output of 'undebug all' is a single confirmation line: 'All possible debugging has been turned off'. This indicates that all debug commands previously enabled (e.g., debug ip ospf events, debug ip rip) are now disabled. In a real network scenario, after issuing this command, you should verify with 'show debug' that no debugs remain. If the router continues to show debug messages, it may indicate that some debugs are persistent or that the command was not executed in privileged EXEC mode. Good practice is to always run 'undebug all' after troubleshooting to prevent CPU overload.

CCNA Exam Tips

CCNA exam tip: Remember that 'undebug all' is equivalent to 'u all' (short form).

CCNA exam tip: Debug commands are CPU-intensive; always disable them after use to avoid performance issues.

CCNA exam tip: You must be in privileged EXEC mode to use 'undebug all'; it will not work in user EXEC mode.

CCNA exam tip: The exam may test that 'undebug all' disables all debugs, including those enabled in other sessions.

Common Mistakes

Mistake 1: Typing 'no debug all' instead of 'undebug all' — 'no debug all' is not a valid command; use 'undebug all' or 'u all'.

Mistake 2: Forgetting to disable debugs after troubleshooting, leaving them running and degrading router performance.

Mistake 3: Assuming 'undebug all' only affects the current session; it actually disables debugs globally for all sessions.

Related Commands

debug ip ospf events

Enables real-time debugging of OSPF event messages to troubleshoot neighbor adjacency issues, route propagation problems, or OSPF state changes.

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