YANG and XML is the heart of Clixon. Yang modules are used as a specification for handling XML configuration data. The YANG spec is used to generate an interactive CLI, netconf and restconf clients. It also specifies the format of the XML datastore.

The YANG standards that Clixon follows include:

However, the following YANG syntax modules are not implemented (reference to RFC7950 in parenthesis):

  • deviation (7.20.3)
  • action (7.15)
  • augment in a uses sub-clause (7.17) (module-level augment is implemented)
  • require-instance
  • instance-identifier type (9.13)
  • status (7.21.2)
  • YIN (13)
  • Yang extended Xpath functions: re-match(), deref)(), derived-from(), derived-from-or-self(), enum-value(), bit-is-set() (10.2-10.6)
  • Default values on leaf-lists (7.7.2)
  • Lists without keys (non-config lists may lack keys)

Regular expressions

Clixon supports two regular expressions engines:

Posix is the default method, _translates_ XSD regexp:s to posix before matching with the standard Linux regex engine. This translation is not complete but can be considered “good-enough” for most yang use-cases. For reference, all standard Yang models have been tested.
Libxml2 uses the XSD regex engine. This is a complete XSD engine but you need to compile and link with libxml2 which may add overhead.

To use libxml2 in clixon you need enable libxml2 in both cligen and clixon:

./configure --with-libxml2 # both cligen and clixon

You then need to set the following configure option:



Clixon has its own implementation of XML and XPATH. See more in the detailed API reference.

The XML-related standards include:

The following XPATH axes are supported:

  • child,
  • descendant,
  • descendant_or_self,
  • self
  • parent

The following xpath axes are not supported: preceeding, preceeding_sibling, namespace, following_sibling, following, ancestor,ancestor_or_self, and attribute


Clixon implements the following NETCONF RFC:s:

The following RFC6241 capabilities/features are hardcoded in Clixon:

  • :candidate (RFC6241 8.3)
  • :validate (RFC6241 8.6)
  • :xpath (RFC6241 8.9)
  • :notification (RFC5277)

The following features are optional and can be enabled by setting CLICON_FEATURE:

  • :startup (RFC6241 8.7)

Clixon does not support the following NETCONF features:

  • :url capability
  • copy-config source config
  • edit-config testopts
  • edit-config erropts
  • edit-config config-text
  • edit-config operation


Clixon Restconf is a daemon based on FastCGI C-API. Instructions are available to run with NGINX. The implementatation is based on RFC 8040: RESTCONF Protocol.

The following features of RFC8040 are supported:

  • stream notifications (Sec 6)
  • query parameters: “insert”, “point”, “content”, “depth”, “start-time” and “stop-time”.
  • Monitoring (Sec 9)

The following features are not implemented:

  • ETag/Last-Modified
  • Query parameters: “fields”, “filter”, “with-defaults”