19 Errors and debug

19.1 Error reporting

19.1.1 Initialization

Clixon core applications typically have a command-line option controlling the logs as follows:

-l <option>

Log on (s)yslog, std(e)rr, std(o)ut or (f)ile. Syslog is default. If foreground, then syslog and stderr is default. Filename is given after -f as follows: -lf<file>.

An example of a clixon error as it may appear in a syslog:

Mar 24 10:30:48 Alarik clixon_restconf[3993]: clixon_restconf openssl: 3993 Started

In C-code, clixon error and logging is initialized by clicon_log_init:

clicon_log_init(prefix, upto, flags);


  • prefix: appears first in the error string

  • upto: log priority as defined by syslog(3), eg: LOG_DEBUG, LOG_INFO,..

  • flags: a bitmask of where logs appear, values are: CLICON_LOG_STDERR, _STDOUT, _SYSLOG, _FILE.

19.1.2 Error call

An error is typically called by clicon_err() and a return value of -1 as follows:

clicon_err(category, errno, format, ...)
return -1;


  • category is an error “category” including for example “yang”, “xml” See enum clicon_err for more examples.

  • errno if given, usually errors as given by errno.h

  • format A variable arg string describing the error.

19.1.3 CLI Errors

There are several types of error messages in the CLI. The first class is “syntax” errors with things like:

cli> command
CLI syntax error: "foo": Unknown command

These are errors immediately detected by the CLIgen parser and are internally generated in CLIgen. Errors include command, syntax and type checking. They are shown on stderr, the CLI continues, without logging.

A second type of errors are “semantic” errors detected when processing CLI callbacks. These errors are more heavyweight than syntax errors and are declared in code using standard clixon Error call. They are logged and can be directed to syslog, and are by default printed on stderr. The CLI continues after the error message is printed. Typical places are user callbacks, backend rpc errors, validation, etc, either system-defined or user-defined callbacks. They are on the form:

cli> command
Nov 15 15:42:56: acl_get_list: 334: Yang error: no ACLs defined
CLI command error

A third class of CLI errors are similar to the previous class but quits the CLI:

cli> command
Nov 15 15:42:56: acl_get_list: 334: Yang error: no ACLs defined

These errors are typically due to system functions failing in a fatal way.

19.1.4 Customized errors

Netconf errors, such as returned by the backend on error, may be shown as a log message or CLI output. A default Netconf to text translation is provided by the system, but it is possible to customize the message by defining the ca_errmsg callback.

Customized errors applies to all clixon applications. In particular, logs for the backend and return output in the CLI.

For example, a Netconf message could be:

<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
      <error-message>List key m1 length mismatch</error-message>

The default error message is constructed from the Netconf message as follows:

rpc malformed-message List key m1 length mismatch

To replace this message with a customized variant, a callback is written as follows in plugin code:

example_cli_errmsg(clicon_handle h,
                   cxobj        *xerr,
                   cbuf         *cberr)
    int    retval = -1;
    cxobj *x;

    cprintf(cberr, "My error message: ");
    if ((x=xpath_first(xerr, NULL, "//error-message"))!=NULL)
       cprintf(cberr, "%s ", xml_body(x));
    retval = 0;
    return retval;

static clixon_plugin_api api = {

The error message is now:

My error message: List key m1 length mismatch

The example above is taken from the main example for CLI. Customizing error messages for backend or other applications is similar.

Note that the Netconf errors are only a part of all errors. The CLI in particular have error messages (or part of messages) that are not related to NETCONF and are therefore not affected by this translation.

19.1.5 Error categories

An application can specialize error handling for a specific category by using clixon_err_cat_reg() and a log callback. Example:

/* Clixon error category log callback
 * @param[in]    handle  Application-specific handle
 * @param[out]   cb      Read log/error string into this buffer
static int
my_log_cb(void  *handle,
          cbuf  *cb)
    cprintf(cb, "Myerror");
    return 0;

  /* Register error callback for category */
  clixon_err_cat_reg(OE_SSL, h, openssl_cat_log_cb);

In this example, “Myerror” will appear in the log string.

19.2 Debugging

19.2.1 Debug flags

Each clixon application has a -D <level> command-line option to enable debug flags when starting a program. The following flags are defined:

  • CLIXON_DBG_DEFAULT (= 1) Default logs

  • CLIXON_DBG_MSG (= 2) In/out messages and datastore reads

  • CLIXON_DBG_DETAIL (= 4) Detailed logs

  • CLIXON_DBG_EXTRA (= 8) Extra Detailed logs

You can combine flags, so that, for example -D 5 means default + detailed, but no packet debugs.

You can direct the debug logs using the -l <option> as follows:

  • s : syslog

  • e : stderr

  • o : stdout

  • n : none

  • f : file, followed by a filename, eg -f/tmp/foo


clixon_backend -D 5 -f/tmp/log.txt

19.2.2 Change debug

You can also change debug level in run-time in different ways. For example, using netconf to change debug level in backend:

echo "<rpc username=\"root\" xmlns=\"urn:ietf:params:xml:ns:netconf:base:1.0\"><debug xmlns=\"http://clicon.org/lib\"><level>1</level></debug></rpc>]]>]]>" | clixon_netconf -q0

In this example, netconf is run using EOM encoding and does not require hello:s.

Using curl to change debug in backend via the restconf daemon:

curl -Ssik -X POST -H "Content-Type: application/yang-data+json" http://localhost/restconf/operations/clixon-lib:debug -d '{"clixon-lib:input":{"level":1}}'

19.2.3 Debugger

Enable debugging when configuring (compile-time):

./configure --enable-debug

which includes symbol table info so that you can make breakpoints on functions(output is omitted):

> sudo gdb clixon_backend
(gdb) run -FD 1 -l e
Starting program: /usr/local/sbin/clixon_backend -FD 1 -l e
(gdb) b main
Breakpoint 1 at 0x55555555bcea: file backend_main.c, line 492.
(gdb) where
#0  main (argc=5, argv=0x7fffffffe4e8) at backend_main.c:492

In the example, the backend runs in the foreground(-F), runs with debug level 1 and directs the debug messages to stderr.

19.2.4 Valgrind and callgrind

Examples of using valgrind for memeory checks:

valgrind --leak-check=full --show-leak-kinds=all clixon_netconf -qf /tmp/myconf.xml -y /tmp/my.yang

Example of using callgrind for profiling:

LD_BIND_NOW=y valgrind --tool=callgrind clixon_netconf -qf /tmp/myconf.xml -y /tmp/my.yang
sudo kcachegrind

Or massif for memory usage:

valgrind --tool=massif clixon_netconf -qf /tmp/myconf.xml -y /tmp/my.yang