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 clixon_log_init:

clixon_log_init(h, 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: CLIXON_LOG_STDERR, _STDOUT, _SYSLOG, _FILE.

19.1.2 Error call

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

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


  • category is an error “category” including for example “yang”, “xml” See enum clixon_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 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. Levels can be combined and use either symbolic or numerical values. Example:

clixon_cli -D default -D detail

Levels are separated into subject-area and detail.

The subject-area levels are the following:

  • default Default logs

  • msg In/out messages and datastore reads

  • init Initialization

  • xml XML logs

  • xpath XPath processing logs

  • yang YANG processing logs

  • backend Backend-specific processing

  • cli CLI-frontend

  • netconf Netconf-frontend

  • restconf Restconf-frontend

  • snmp SNMP-frontend

  • nacm Netconf access control model

  • proc Process handling

  • datastore Datastore handling

  • event Event handling

  • rpc RPC handling

  • stream Notification streams

  • parse XML, YANG, XPath, etc parsing

  • app Application-specific handling, ie any application using clixon can use this

  • app2 Application-specific 2

  • app3 Application-specific 3

  • all All subject-area flags

The detail area levels are the following:

  • detail Detail logging

  • detail2 Extra details

  • detail3 Probably more detail than you want

You can combine flags, so that, for example -D 5 means default + detailed, but no packet debugs. Similarly, some messages require multiple flags, like XML + DETAIL would be -D 20.

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

19.3 Customization

Errors, logs and denugs can be customized by plugins via the ca_errmsg API.

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

The API provides a single function callback which can be used in a various ways. The example shows one simple way as described here.

First define an error message callback as part of the plugin initialization:

static clixon_plugin_api api = {

The errmsg callback has many parameters. Some are not always applicable:

  • h : Clixon handle

  • fn : name of source file (only err)

  • line: line of source file (only err)

  • type: log, err or debug (actual types called LOG_TYPE_LOG etc)

  • category: Error category (see Section Error categories) (only err)

  • suberr: Error number, eg errno (only err)

  • xerr: XML structure, either NETCONF (for err) or just generic XML (debug, log)

  • format: Format string similar to printf

  • ap: Variable argument list assciated with format. Similar to vprintf

  • cbmsg: Customized error message as output of the function. If NULL, use regular message.

A simple way to replace all error messages would be:

example_cli_errmsg(clixon_handle        h,
                   const char          *fn,
                   const int            line,
                   enum clixon_log_type type,
                   int                 *category,
                   int                 *suberr,
                   cxobj               *xerr,
                   const char          *format,
                   va_list              ap,
                   cbuf               **cbmsg)
    if (type != LOG_TYPE_ERR)
       return 0;
    if ((*cberr = cbuf_new()) == NULL){
       fprintf(stderr, "cbuf_new: %s\n", strerror(errno));
       return -1;
    cprintf(*cberr, "My error message");
    *category = 0;
    suerr = 0;
    retval = 0;
    return retval;

All error message are now:

My error message

Which may not be useful.

More logic needs to be added, for example a more advanced classification and translation/changing of error messages. Any field can be used to classify. The format string and the ap objects may be translated/converted which is out-of-scope of this document.

19.3.1 Indirection

The customized callback may also be changed dynamically. The example shows an extra indirection layer, where a new function is registered before a call, and deregistered after.

Please see the main example, where example_cli_errmsg just dispatches the call to a dynamic myerrmsg.