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NAME | C SYNOPSIS | DESCRIPTION | EXAMPLE | SEE ALSO | COLOPHON |
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PMLOADDERIVEDCONFIG(3) Library Functions Manual PMLOADDERIVEDCONFIG(3)
pmLoadDerivedConfig - load derived metric definitions from files
#include <pcp/pmapi.h>
int pmLoadDerivedConfig(char *path);
cc ... -lpcp
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 program‐
matically 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 be‐
low.
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 dec‐
laration 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).
For each line containing a derived metric definition,
pmRegisterDerived(3) is called to register the new derived metric.
Once a derived metric has been declared, it may be assigned addi‐
tional attributes with a line of the form:
* the name of the derived metric,
* a left parenthesis, an attribute type and a right parenthesis,
* an equals sign (``=''),
* an attribute value.
Currently, attribute type may be either oneline or helptext to
designate the ``one line'' or expanded help text to be associated
with the derived metric, see pmLookupText(3).
The attribute value may be either arbitrary text following the
``='' and ending at the end of the line, else a string enclosed in
either single quotes (') or double quotes ("). In the latter
case, the attribute value may span multiple lines, and a simple
escape mechanism is supported, namely for any character ``x'',
``\x'' is replaced by ``x'' (this allows quotes to be escaped
within a string, for example), and there is a special case when
the ``\'' comes at the end of the line in which case the following
newline is not included in the attribute value.
Outside of attribute values, white space is ignored in the lines,
and blank lines are ignored altogether.
Because pmLoadDerivedConfig may process many files, each of which
may contain many derived metric specifications, it is not possible
to provide a 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 giv‐
en path will cause an immediate return with a negative return val‐
ue that can be passed to pmErrStr(3) to obtain the associated er‐
ror message.
When errors are encountered in the derived metric specifications
diagnostic messages are generated by pmRegisterDerived(3) and dis‐
played via pmprintf(3).
# 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))
disk.dev.read_pct(oneline) = percentage of disk reads
disk.dev.read_pct(helptext) = '\
Percentage of disk reads compared to the total number of
disk reads and disk writes.'
sh(1), PCPIntro(1), PMAPI(3), pmLookupText(3),
pmRegisterDerived(3), pmprintf(3) and PMNS(5).
This page is part of the PCP (Performance Co-Pilot) project. In‐
formation about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
pcp@groups.io. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-11.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
Performance Co-Pilot PMLOADDERIVEDCONFIG(3)
Pages that refer to this page: pcp2elasticsearch(1), pcp2graphite(1), pcp2influxdb(1), pcp2json(1), pcp2openmetrics(1), pcp2spark(1), pcp2template(1), pcp2xlsx(1), pcp2xml(1), pcp2zabbix(1), pcpintro(1), pminfo(1), pmprobe(1), pmrep(1), pmaddderived(3), pmaddderivedtext(3), pmgetderivedcontrol(3), pmreconnectcontext(3), pmregisterderived(3), zbxpcp(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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