Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.4T
Exclusive Configuration Change Access (Configuration Lock) and Access Session Locking
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Locking the Configuration

Table Of Contents

Locking the Configuration

Finding Feature Information

Contents

Information About Locking the Configuration

Exclusive Configuration Change Access and Access Session Locking

Access Session Locking

Parser Concurrency and Locking Improvements

How to Configure Configuration Lock

Enabling Exclusive Configuration Change Access and Access Session Locking

Obtaining Exclusive Configuration Change Access

Enabling Parser Concurrency and Locking Improvements

Restrictions

Monitoring and Troubleshooting Configuration Locking

Configuration Examples for Locking the Configuration

Configuring an Exclusive Lock in Auto Mode: Example

Configuring an Exclusive Lock in Manual Mode: Example

Configuring Parser Concurrency and Locking Improvements: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Locking the Configuration


Locking the Configuration


First Published: February 28, 2005
Last Updated: March 19, 2010

Cisco IOS software provides the user an option to lock the running configuration and prevent other users from concurrently accessing the Cisco IOS configuration. This module contains information and configuration tasks for locking the configuration.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Locking the Configuration" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

Information About Locking the Configuration

How to Configure Configuration Lock

Configuration Examples for Locking the Configuration

Additional References

Feature Information for Locking the Configuration

Information About Locking the Configuration

To lock the configuration, you should understand the following concepts:

Exclusive Configuration Change Access and Access Session Locking

Access Session Locking

Parser Concurrency and Locking Improvements

Exclusive Configuration Change Access and Access Session Locking

Devices running Cisco IOS software maintain a running configuration that determines the configuration state of the device. Changes to the running configuration alter the behavior of the device. Because Cisco IOS software allows multiple users to change the running configuration via the device CLI (including the device console and telnet Secure Shell (SSH)), in some operating environments it would be beneficial to prevent multiple users from making concurrent changes to the Cisco IOS running configuration. Temporarily limiting access to the Cisco IOS running configuration prevents inadvertent conflicts or cases where two users attempt to configure the same portion of the running configuration.

The Exclusive Configuration Change Access feature (also called the "Configuration Lock" feature) allows you to have exclusive change access to the Cisco IOS running configuration, preventing multiple users from making concurrent configuration changes.

This feature provides exclusive change access to the Cisco IOS running configuration from the time you enter global configuration mode by using the configure terminal command. This gives the effect of a "configuration lock," preventing other users from changing the Cisco IOS running configuration. The configuration lock is automatically released when the user exits Cisco IOS configuration mode.

The Exclusive Configuration Change Access feature is enabled using the configuration mode exclusive command in global configuration mode. Exclusive configuration change access can be set to auto, so that the Cisco IOS configuration mode is locked whenever anyone uses the configure terminal command, or it can be set to manual, so that the Cisco IOS configuration mode is locked only when the configure terminal lock command is issued.

The Exclusive Configuration Change Access feature is complementary with the locking mechanism for the Configuration Replace and Configuration Rollback feature introduced in Cisco IOS Release 12.2(25)S and 12.3(7)T.

Access Session Locking

The Access Session Locking feature extends the Exclusive Configuration Change Access feature such that show and debug commands entered by the user holding the configuration lock always have execution priority. This feature prevents concurrent configuration access and also provides an option to prevent simultaneous processes, such as a show command entered by another user, from executing while other configuration commands are being executed. When this feature is enabled, the commands entered by the user with the configuration lock (such as configuration commands) always have priority over commands entered by other users.

Parser Concurrency and Locking Improvements

In order to overcome the following limitations posed by the Exclusive Configuration Change Access feature, the Parser Concurrency and Locking Improvements feature was introduced in Cisco IOS Release 12.2(33)SRE:

The Exclusive Configuration Change Access feature locks the configuration to other users. The lock is automatically released when the lock holder exits from the configuration mode. Any other user in the configuration mode will be returned to the EXEC mode when the lock is acquired. Also, any user can execute the clear configuration lock command and forcibly remove the lock and allow normal access to all users.

The router can reload when multiple write processes belonging to the same client simultaneously access the Cisco IOS configurations in a shared mode.

The router can reload when EXEC commands concurrently access the data structure.

Effective from Cisco IOS Release 12.2(33)SRE, the Concurrency and Locking Improvements feature is the primary locking mechanism used to prevent concurrent configuration of Cisco IOS software by multiple users.

The Parser Concurrency and Locking Improvements feature provides a common interface that ensures that exclusive access is granted to the requested process and prevents others from concurrently accessing the Cisco IOS configuration. It allows access only to the user holding the lock and prevents other clients from accessing the configuration.

Effective from Cisco IOS Release 12.2(33)SRE, the configuration mode exclusive {auto | manual} command will not be available to enable single-user access functionality for the Cisco IOS CLI. Use the parser command serializer command to enable configuration access only to the users holding the lock and prevent other clients from accessing the configuration.

How to Configure Configuration Lock

This section contains the following procedures:

Enabling Exclusive Configuration Change Access and Access Session Locking (required)

Obtaining Exclusive Configuration Change Access (optional)

Enabling Parser Concurrency and Locking Improvements (required)

Monitoring and Troubleshooting Configuration Locking (optional)

Enabling Exclusive Configuration Change Access and Access Session Locking


Note Effective with Cisco IOS Release 12.2(33)SRE, the Exclusive Configuration Change Access and Access Session Locking feature is not available in Cisco IOS software. Use the Parser Concurrency and Locking Improvements feature instead of this feature. See the "Enabling Parser Concurrency and Locking Improvements" section for more information.


Perform this task to enable the Exclusive Configuration Change Access and Access Session Locking feature.

SUMMARY STEPS

1. enable

2. configure terminal

3. configuration mode exclusive {auto | manual}

4. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

configuration mode exclusive {auto | manual}

Example:

Router(config)# configuration mode exclusive auto

Enables exclusive configuration change access (configuration lock feature).

When the command is enabled, configuration sessions are performed in single-user (exclusive) mode.

The auto keyword automatically locks the configuration session whenever the configure terminal command is used. This is the default.

The manual keyword allows you to choose to lock the configuration session manually or leave it unlocked. If you use the manual keyword, you must perform the task described in the "Obtaining Exclusive Configuration Change Access" section.

Step 4 

end

Example:

Router(config)# end

Ends your configuration session and returns the CLI to privileged EXEC mode.

Obtaining Exclusive Configuration Change Access

Perform this task to obtain exclusive configuration change access for the duration of your configuration session. Use of the lock keyword with the configure terminal command is necessary only if the exclusive configuration mode has been set to manual (see the "Enabling Exclusive Configuration Change Access and Access Session Locking" section).

SUMMARY STEPS

1. enable

2. configure terminal

3. configure terminal lock

4. Configure the system by entering your changes to the running configuration.

5. end
or
exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

configure terminal lock

Example:

Router(config)# configure terminal lock

(Optional) Locks the Cisco IOS software in exclusive (single-user) mode.

This command can be used only if you have previously enabled configuration locking by using the configuration mode exclusive command.

This command is available in Cisco IOS Release 12.3(14)T or later releases.

Step 4 

Configure the system by entering your changes to the running configuration.

Step 5 

end

or

exit

Example:

Router(config)# end

or

Example:

Router(config)# exit

Ends your configuration session, automatically releases the session lock obtained in Step 1, and exits to privileged EXEC mode.

Note Either the end command, the exit command, or the Ctrl-Z key combination releases the configuration lock. Use of the end command is recommended.

Enabling Parser Concurrency and Locking Improvements

Perform this task to enable configuration access only to the users holding a configuration lock and to prevent other clients from accessing the running configuration.

Restrictions

The Parser Cconcurrency and Locking Improvements feature does not allow two or more processes to exist simultaneously within the critical section of Cisco IOS configurations.

This feature flags a command to prevent its serialization if an excessive amount of time is required to generate its output or if its use produces more than 10 kilobytes of output. Examples of commands that would not be serialized are the show terminal and show running-config commands.

SUMMARY STEPS

1. enable

2. configure terminal

3. parser command serializer

4. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

parser command serializer

Example:

Router(config)# parser command serializer

Introduces an exclusive lock to serialize access to Cisco IOS configurations.

Step 4 

exit

Example:

Router(config)# exit

(Optional) Exits global configuration mode.

Monitoring and Troubleshooting Configuration Locking

Perform either or both steps in this task to monitor or troubleshoot the Exclusive Configuration Change Access and Access Session Locking feature.

SUMMARY STEPS

1. show configuration lock

2. debug configuration lock

DETAILED STEPS

Step 1 show configuration lock

Use this command to display the status and details of any current configuration locks, including the owner, user, terminal, lock state, and lock class.

If you cannot enter global configuration mode, you can use this command to determine if the configuration session is locked by another user, and who that user is.

Router# show configuration lock
 
   
Parser Configure Lock
------------------------------------------------------
Owner PID                         : 3
User                              : unknown
TTY                               : 0
Type                              : EXCLUSIVE
State                             : LOCKED
Class                             : EXPOSED
Count                             : 1
Pending Requests                  : 0
User debug info                   : configure terminal 
Session idle state                : TRUE
No of exec cmds getting executed  : 0
No of exec cmds blocked           : 0
Config wait for show completion   : FALSE
Remote ip address                 : Unknown
Lock active time (in Sec)         : 6
Lock Expiration timer (in Sec)    : 593
Router(config)#
 
   

Step 2 debug configuration lock

Use this command to enable debugging of Cisco IOS configuration locks (exposed class locks or rollback class locks):

Router# debug configuration lock 
 
   
Session1 from console
==========================
 
   
Router# configure terminal lock 
 
   
Configuration mode locked exclusively. The lock will be cleared once you exit out of 
configuration mode using end/exit
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#
Parser : LOCK REQUEST in EXCLUSIVE mode
Parser: <configure terminal lock> - Config. Lock requested by process <3> client <PARSER 
Client>
Parser: <configure terminal lock> - Config. Lock acquired successfully !
Router(config)#

Configuration Examples for Locking the Configuration

This section provides the following configuration examples:

Configuring an Exclusive Lock in Auto Mode: Example

Configuring an Exclusive Lock in Manual Mode: Example

Configuring Parser Concurrency and Locking Improvements: Example

Configuring an Exclusive Lock in Auto Mode: Example

The following example shows how to enable the exclusive lock in auto mode for single-user auto configuration mode using the configuration mode exclusive auto command. Once the Cisco IOS configuration file is locked exclusively, you can verify this configuration by using the show configuration lock command.

Router# configure terminal 
Router(config)# configuration mode exclusive auto 
Router(config)# exit 
 
   
Router# configure terminal 
 
   
! Locks configuration mode exclusively.
 
   
Router# show configuration lock
 
   
Parser Configure Lock
 
   
Owner PID        :  10
User             :  User1
TTY              :  3
Type             :  EXCLUSIVE
State            :  LOCKED
Class            :  Exposed 
Count            :  0 
Pending Requests :  0 
User debug info  :  0 

Configuring an Exclusive Lock in Manual Mode: Example

The following example shows how to enable the exclusive locking feature in manual mode by using the configuration mode exclusive manual command. Once you have configured manual exclusive mode, you can lock the configuration mode by using the configure terminal lock command. In this mode, the configure terminal command will not automatically lock the parser configuration mode.

Router# configure terminal
Router(config)# configuration mode exclusive manual
Router(config)# exit
 
   
Router# configure terminal lock
 
   
Enter configuration commands, one per line.  End with CNTL/Z.
 
   
*Mar 25 17:02:45.928:  Configuration mode locked exclusively. The lock will be cleared 
once you exit out of configuration mode using end/exit

Configuring Parser Concurrency and Locking Improvements: Example

The following example shows how to enable the Parser Concurrency and Locking Improvements feature by using the parser command serializer command:

Router# configure terminal
Router(config)# parser command serializer
Router(config)# exit

Additional References

The following sections provide references related to locking the configuration.

Related Documents

Related Topic
Document Title

Commands for managing configuration files

Cisco IOS Configuration Management Command Reference

Information about managing configuration files

Managing Configuration Files


Standards

Standard
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


MIBs

MIB
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for Locking the Configuration

Table 1 lists the features in this module and provides links to specific configuration information.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.


Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.


.

Table 1 Feature Information for Locking the Configuration 

Feature Name
Releases
Feature Information

Exclusive Configuration Change Access and Access Session Locking

12.3(14)T
12.0(31)S
12.2(33)SRA
12.4(11)T
12.2(33)SXH
12.2(33)SB

The Exclusive Configuration Change Access feature (also called the "Configuration Lock" feature) allows you to have exclusive change access to the Cisco IOS running configuration, preventing multiple users from making concurrent configuration changes.

The Access Session Locking addition to this feature extends the Exclusive Configuration Change Access feature such that show and debug commands entered by the user holding the configuration lock always have execution priority; show and debug commands entered by other users are allowed to run only after the processes initiated by the configuration lock owner have finished.

The Exclusive Configuration Change Access feature is complementary with the locking mechanism for the Configuration Replace and Configuration Rollback feature ("rollback lock").

The Configuration Lock feature feature was integrated into Release 12.0S, and the Access Session Locking feature extension was implemented. The configuration mode exclusive command was extended to include the following keyword options: config_wait, expire, interleave, lock-show, retry_wait, and terminate. The output of the show configuration lock command was improved.

The extended feature was integrated into Releases 12.2(33)SRA, 12.4(11)T, 12.2(33)SXH, and 12.2(33)SB.

The following sections provide information about this feature:

Information About Locking the Configuration

How to Configure Configuration Lock

The following commands were introduced or modified: clear configuration lock, configuration mode exclusive, and configure terminal lock.

Parser Concurrency and Locking Improvements

12.2(33)SRE

15.1(1)T

The Parser Concurrency and Locking Improvements feature provides a common interface that ensures that exclusive access is granted to the requested process and prevents others from concurrently accessing the Cisco IOS configuration. It allows access only to the user holding the lock and prevents other clients from accessing the configuration.

The following sections provide information about this feature:

Parser Concurrency and Locking Improvements

Enabling Parser Concurrency and Locking Improvements

The following commands were introduced or modified: parser command serializer and test parser session-lock.