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Generate a Persistent or Transient Configuration Change in Python Commit Scripts

Junos OS commit scripts enforce custom configuration rules and can automatically change the configuration when it does not comply with your custom configuration rules. To generate a persistent change or transient change using Python commit scripts:

  1. At the start of the script, include the Python boilerplate from Required Boilerplate for Commit Scripts, which is reproduced here for convenience:
  2. Include one or more programming instructions that test for your custom configuration rules.

    For example, the following code selects each SONET/SDH interface that does not have the MPLS protocol family enabled:

  3. Create an XML string that instructs Junos OS how to modify the configuration.

    This example enables the MPLS protocol family for the selected interfaces.

  4. To generate the persistent or transient change, call the jcs.emit_change method, and specify the type of change, either 'change' or 'transient-change', in the argument list.
  5. Include any additional required or optional code. This example generates a warning message that is displayed on the CLI when the commit script updates a SONET/SDH interface.
  6. Save the script with a meaningful name.
  7. Copy the script to either the /var/db/scripts/commit directory on the device hard disk or the /config/scripts/commit directory on the flash drive.
    Note:

    Unsigned Python scripts must be owned by either root or a user in the Junos OS super-user login class, and only the file owner can have write permission for the file.

  8. Enable the script by configuring the file filename statement at the [edit system scripts commit] hierarchy level.
  9. If the script generates transient changes, configure the allow-transients statement.

    Configure the statement at the [edit system scripts commit] hierarchy level to enable all commit scripts to make transient changes.

    Alternatively, on supported devices and releases, configure the statement at the [edit system scripts commit file filename] hierarchy level to enable only the individual script to make transient changes.

  10. Enable the execution of unsigned Python scripts on the device.
  11. Commit the configuration.

The resulting script searches for SONET/SDH interfaces that do not have the MPLS protocol family enabled, adds the family mpls statement at the [edit interfaces so-fpc/pic/port unit logical-unit-number] hierarchy level as a persistent change, and emits a warning message stating that the configuration has been changed.

If all enabled commit scripts run without errors, any persistent changes are loaded into the candidate configuration. Any transient changes are loaded into the checkout configuration, but not to the candidate configuration. The commit process then continues by validating the configuration and propagating changes to the affected processes on the device.

To display the configuration with both persistent and transient changes applied, issue the show | display commit-scripts configuration mode command.

To display the configuration with only persistent changes applied, issue the show | display commit-scripts no-transients configuration mode command.

Persistent and transient changes are loaded into the configuration in the same manner that the load replace configuration mode command loads an incoming configuration. When generating a persistent or transient change, adding the replace="replace" attribute to a configuration element produces the same behavior as a replace: tag in a load replace operation. Both persistent and transient changes are loaded into the configuration with the load replace behavior. However, persistent changes are loaded into the candidate configuration, and transient changes are loaded into the checkout configuration.

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