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pmloadderivedconfig(3)

NAME

   pmLoadDerivedConfig - load derived metric definitions from files

C SYNOPSIS

   #include <pcp/pmapi.h>

   int pmLoadDerivedConfig(char *path);

   cc ... -lpcp

DESCRIPTION

   Derived  metrics  may  be used to extend the available metrics with new
   (derived) metrics using simple arithmetic expressions.  The definitions
   of these metrics can be persisted and loaded programatically by monitor
   tools using pmLoadDerivedConfig.

   The path parameter defines a  colon  separated  list  of  files  and/or
   directories  (the  syntax  is  the  same  as for the $PATH variable for
   sh(1)), from which derived metric specifications  are  to  be  sourced.
   The  path components are expanded into a list of files as follows: if a
   component is a file, then that file is added to the  list,  else  if  a
   component  is  a  directory then recursive descent is used to enumerate
   all files below that directory and these are added to the  list.   Each
   file  in  the  resulting  list is parsed in order, and according to the
   derived metrics syntax described below.

   Each line of the file(s) identified by path is either  a  comment  line
   (with  a ``#'' in the first position of the line) or the declaration of
   a derived performance metric, specified as:

   * the name of the derived  metric,  using  the  same  ``dot  notation''
     syntax  that is used for PCP performance metrics, see PCPIntro(1) and
     pmns(5).

   * an equals sign (``='')

   * a  valid  expression  for  a  derived   metric,   as   described   in
     pmRegisterDerived(3).

   White space is ignored in the lines.

   For    each    line    containing    a   derived   metric   definition,
   pmRegisterDerived(3) is called to register the new derived metric.

   Because pmLoadDerivedConfig may process many files, each of  which  may
   contain  many  derived  metric  specifications,  it  is not possible to
   provide very specific error status on return.  Hence  the  result  from
   pmLoadDerivedConfig  will be the number of derived metrics successfully
   loaded from files on the given path.  Catastrophic errors such  as  not
   being  able  to  open  one of the files on the given path will cause an
   immediate return with a negative return value that  can  be  passed  to
   pmErrStr(3) to obtain the associated error message.

   When  errors  are  encountered  in  the  derived  metric specifications
   diagnostic messages are generated by pmRegisterDerived(3) and displayed
   via pmprintf(3).

EXAMPLE

   # sample derived metric definitions
   bad_in_pkts = network.interface.in.errors + network.interface.in.drops
   # note the following would need to be on a single line ...
   disk.dev.read_pct = 100 * delta(disk.dev.read) /
               (delta(disk.dev.read) + delta(disk.dev.write))

SEE ALSO

   sh(1),  PCPIntro(1),  PMAPI(3),  pmRegisterDerived(3),  pmprintf(3) and
   pmns(5).



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