The netconfd-pro server reports protocol operation errors using the <rpc-error> structure defined in RFC 6241

This data structure is used to report 1 error and contains the following fields (NOTE: customizable fields are highlighted):

  • error-type: type of error (transport, rpc, protocol, application)
  • error-tag: standard error reason tag
  • error-severity: error or warning
  • error-app-tag: configurable application error tag
  • error-path: XPath expression identifying node that caused the error
  • error-message: configurable human-readable error message 
  • error-info: container of standard and configurable extra error information

Setting the error-message Language

The language used for the error-message field can be set on the server using the --errmsg-lang CLI parameter.

The error messages in languages other than English must be pre-configured using the CLI parameters and YANG extensions described below.

The default error-message language is English ("en"). 

      leaf errmsg-lang {
        type string {
          length "1 .. 7";
        default "en";
          "Specifies the language code for the error-message
           language. This is only relevant if there are errmsg
           parameters for multiple languages loaded in the program.
           This value should use the ISO-639-1 code.

The error-message field can be customized 3 different ways by the server:

  1. Standard YANG error-message statements
  2. Object-specific dynamic error messages
  3. Error number specific static error messages

1) Standard YANG Error Messages

The YANG error-message statement can be used inside the following statements, to create custom static error messages for a specific object.

  • must-stmt: generated if must-stmt test fails (returns false)
  • range-stmt: generated if a value is not in range
  • length-stmt: generated if a string is the wrong length
  • pattern-stmt: generated if a string does not match the pattern


     container interface {
       leaf ifType {
         type enumeration {
           enum ethernet;
           enum atm;
       leaf ifMTU {
         type uint32;
       must 'ifType != "ethernet" or ifMTU = 1500' {
         error-message "An Ethernet MTU must be 1500";
       must 'ifType != "atm" or'
          + ' (ifMTU <= 17966 and ifMTU >= 64)' {
         error-message "An ATM MTU must be 64 .. 17966";

2) Dynamic Object Specific Error Messages

Dynamic error messages can include parameters that are replaced at run-time with their current values, from the request message or the target configuration datastore.

The YumaWorks YANG extension "ywx:errmsg" is used to specify an error message for a YANG configuration data node object. This extension can be used either inline within the YANG module containing the object definition, or with an "annotation" file external to the source YANG module.

This extension has 4 sub-statements to specify parameters and filters for the errmsg statement.

  • errmsg:
    • errmsg-parm: Specify a dynamic error message parameter
    • errmsg-tag: Specify an error-tag filter
    • errmsg-apptag: Specify an error-app-tag filter
    • errmsg-lang: Specify an error-message language filter

The ywx:errmsg Extension

  extension errmsg {
      "Used within a data node statement to define
       a custom error-message filed within an 'rpc-error'
       or 'error' structure for some or all error conditions.

       The string format is restricted to plain text with
       the exception of the 2 character sequence '%s'.
       This special sequence will be replaced in the
       dynamic error message generation if an errmsg-parm
       statement is found to match the escape sequence.

       If this extension statement has no sub-statements,
       then it matches all errors for the object.
       If 'errmsg-tag' sub-statements are found, then
       this entry will match only those error-tag values.
       If 'errmsg-apptag' sub-statements are found, then
       this entry will match only those error-app-tag values.

       The 'basestr' argument must be formatted string.
       If any parameters are specified, then the corresponding
       'errmsg-parm' extension statements must be encoded within
       this errmsg statement.

       Multiple errmsg statements can be present in the same
       data node statement. They will be processed in order
       and the first matching statement will be used to
       generate the error-message value.


          leaf my-network-id {
            type int32;
            ywx:errmsg 'Not a valid network ID for interface %s' {
              ywx:errmsg-parm '../../if:name';
              ywx:errmsg-apptag 'network-error';

     argument basestr;

The ywx:errmsg-parm Extension

  extension errmsg-parm {
      "Used within an errmsg statement to define
       a parameter for expansion within the errmsg basestr.
       There should be the correct number of expected parameters
       for the corresponding 'basestr' format string.

       The 'parmstr' argument must be an XPath path expression.
       The context node will be the data node containing the
       errmsg statement.
     argument parmstr;

The ywx:errmsg-tag Extension

  extension errmsg-tag {
      "Used within an errmsg statement to define an
       error-tag value that will filter this errmsg.
       Multiple errmsg-tag and/or errmsg-apptag values
       form a conceptual OR expression.

       The 'tagstr' argument must be the error-tag value
       that will be matched.
     argument tagstr;

The ywx:errmsg-apptag Extension

  extension errmsg-apptag {
      "Used within an errmsg statement to define an
       error-app-tag value that will filter this errmsg.
       Multiple errmsg-tag and/or errmsg-apptag values
       form a conceptual OR expression.

       The 'apptagstr' argument must be the error-app-tag
       value that will be matched.
     argument apptagstr;

The ywx:errmsg-lang Extension

  extension errmsg-lang {
      "Used within an errmsg statement to define the
       language code value that will filter this errmsg.
       Only one errmsg-lang statement may appear within
       an errmsg statement. The 'langstr' value will
       be compared to the 'errmsg-lang' CLI variable setting.
       If the strings are the same, the entry is used.

       If this statement is not present, then the errmsg entry
       will be used regardless of the 'errmsg-lang' CLI variable

       The 'langstr' argument must be the language code
       value that will be matched.
     argument langstr;

Example using Inline YANG Module

        leaf test3 {
          type string;
          ywx:errmsg "This is %s the %s operation-failed %s msg" {
            ywx:errmsg-parm "../b";
            ywx:errmsg-parm "../test1";
            ywx:errmsg-parm ".";
            ywx:errmsg-lang "en";

          ywx:errmsg "C'est %s l'opération %s a échoué %s msg" {
            ywx:errmsg-parm "../b";
            ywx:errmsg-parm "../test1";
            ywx:errmsg-parm ".";
            ywx:errmsg-lang "fr";

Example using an Annotation File

module errmsg-if {

    namespace "";
    prefix "em";

    import yumaworks-extensions { prefix ywx; }
    import ietf-interfaces { prefix if; }

    revision 2018-04-12 {
        description "Initial revision.";

    deviation /if:interfaces/if:interface/if:type {
      deviate add {
          ywx:errmsg "This is the name %s and type %s of the interface" {
            ywx:errmsg-parm "../name";
            ywx:errmsg-parm ".";
            ywx:errmsg-lang "en";

3) Static Error Number Specific Error Messages

The server uses the internal data type status_t (found in status_enum.h) to define the error-number values used by the server.

There are built-in static error messages (found in status.c) for each error-number.

These error-numbers are defined in ranges:

  • Errors: 1 to 999
  • Warnings: 1000 to 1999
  • Info: 2000 to 2999

The --errmsg CLI Parameter

The CLI parameter --errmsg is used to define a static error-message string.

This parameter can be used multiple times. Each instance specifies an error message for 1 error-number and 1 error language.

      leaf-list errmsg {
        type string;
          "Specifies a replacement string for a specific error number.
           Can specify error message for 1 specific language.

           The 'num' component must match the <error-number>
           found in status_enum.h. New error enums are always added
           at the end of the list, so the numbers will not change.

           The 'lang' component should use the ISO-639-1 code
           Max length is 7 characters.

           The string has the format: '<num>:<lang>:error string'
               <num> = error number to use for error message
               <lang> = language code (en for English)
               error string = error string text


             Replace error 117 (ERR_WB_WRITE_FAILED) 'db write failed'

             errmsg='117:en:The database could not be written'


errmsg "14:en:internal read-write lock error"
errmsg "14:fr:erreur interne de verrouillage de lecture-écriture"
errmsg "14:de:interner Lese- / Schreibsperrfehler"
errmsg "14:ru:внутренняя ошибка блокировки чтения и записи"

Procedure to Generate errmsg Parameters with Google Translate

The directory /usr/share/yumapro/util/errmsg-lang contains some sample errmsg configuration files for specific languages.

The python program /usr/share/yumapro/util/ can be used to generate these files. The output can be edited (or generated by hand if desired)

The config files in this directory contain error-message values
for different languages. The Google Translate API is used
to generate the error message strings.

  > sudo pip install googletrans

Each configuration file contains the errmsg parameters for one
language.  The language codes are defined by ISO-639-1
The codes allowed by Google translate are listed here:

The file naming convention is errmsg-<lang>.conf

To create a new language-specific error-message file:

1) generate err.txt

  > yangdump-pro --lang-errors > err.txt

At this point the err.txt file contains all the default
English errmsg strings. This file can be edited to change
the default strings, if desired.

2) run (from netconf/util dir)

  > python err.txt <lang>

Example: Russian

  > python err.txt ru
  (Will create file errmsg-ru.conf)

Example: French

  > python err.txt fr
  (Will create file errmsg-fr.conf)