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NAME | C SYNOPSIS | DESCRIPTION | RETURN VALUES | OTHER OPTIONS | SEE ALSO | COLOPHON |
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PMDERIVEDCONTROL(3) Library Functions Manual PMDERIVEDCONTROL(3)
pmGetDerivedControl, pmSetDerivedControl - get and set controls
for derived metrics
#include <pcp/pmapi.h>
int pmGetDerivedControl(int what, int *valuep);
int pmSetDerivedControl(int what, int value);
cc ... -lpcp
These routines may be used to influence the behaviour of the de‐
rived metric services that are activated for global derived met‐
rics using pmRegisterDerived(3), pmRegisterDerivedMetric(3) and
pmLoadDerivedConfig(3), or per-context derived metrics using
pmAddDerived(3) and pmAddDerivedMetric(3).
The what argument selects a control or option, the value argument
provides a value for pmSetDerivedControl and the valuep argument
is used to return the value for pmGetDerivedControl.
The what argument has one of the following values:
PCP_DERIVED_GLOBAL_LIMIT
The maximum number of global derived metrics that may be
defined. The value should be greater than zero, or -1 (for
no limit). The initial value is -1.
PCP_DERIVED_CONTEXT_LIMIT
The maximum number of per-context derived metrics that may
be defined. The value should be greater than zero, or -1
(for no limit). The initial value is -1.
PCP_DERIVED_DEBUG_SYNTAX
Debug diagnostics during parsing of derived metric expres‐
sion. The value 1 enables the diagnostics, 0 disables
them. The initial value is 0.
PCP_DERIVED_DEBUG_SEMANTICS
Debug diagnostics for semantic checks during the binding of
metrics in the derived metric expression to the available
metrics in a new PMAPI context. The value 1 enables the
diagnostics, 0 disables them. The initial value is 0.
PCP_DERIVED_DEBUG_EVAL
Debug diagnostics when derived metrics are used in PMAPI
operations like pmFetch(3), pmGetChildren(3),
pmGetChildrenStatus(3), pmLookupDesc(3), pmLookupName(3),
pmNameAll(3), pmNameID(3) and pmTraversePMNS(3). The value
1 enables the diagnostics, 0 disables them. The initial
value is 0.
PCP_DERIVED_OPTION_NOVALUE
When a performance metric (used as an operand in a derived
metric expression) is no available (e.g. missing from a PCP
archive context or not provided by any PMDA for a host con‐
text), then the default behaviour is to mark the derived
metric as undefined. If this option is set to 1 (the de‐
fault is 0), then any metric that is not available is
mapped to the novalue() constructor (refer to
pmRegisterDerived(3) for details), which in essence means
the metric is defined, but attempts to retrieve values via
pmFetch(3) will return PM_ERR_VALUE (Missing metric val‐
ue(s)).
Both routines return 0 on success, else a value less than 0 that
can be decoded using pmErrStr(3).
Some overloading of error codes is needed to accommodate the un‐
usual semantics of these routines, as described below.
┌──────────────────┬─────────────────────────────────────────────┐
│ Error │ Meaning │
├──────────────────┼─────────────────────────────────────────────┤
│ PM_ERR_NAME │ what is not one of the expected values │
├──────────────────┼─────────────────────────────────────────────┤
│ PM_ERR_ARG │ the value provided to pmSetDerivedControl │
│ │ is not within the acceptable range │
├──────────────────┼─────────────────────────────────────────────┤
│ PM_ERR_NOCONTEXT │ getting or setting PCP_DERIVED_CONTEXT_LIM‐ │
│ │ IT only makes sense when there is a current │
│ │ PMAPI context │
├──────────────────┼─────────────────────────────────────────────┤
│ PM_ERR_AGAIN │ pmSetDerivedControl request would violate │
│ │ precedence rules (see below) │
└──────────────────┴─────────────────────────────────────────────┘
All of the controls and options that are exposed by pmSetDerived‐
Control can also be set in two other ways.
1. Setting the PCP_DERIVED_CONTROL environment variable to a val‐
ue of the form name=integer where name is one of the what
macros described above, stripped of the PCP_DERIVED_ prefix,
e.g. novalue=1. name is case insensitive and multiple speci‐
fications are allowed, separated by commas. No whitespace is
allowed.
2. Use of a #control line in a derived metric configuration file,
where the text following the #control follows exactly the same
rules as for the PCP_DERIVED_CONTROL environment variable de‐
scribed above.
Given these options can be specified in multiple ways, possibly
with different values, the precedence rules are if PCP_DE‐
RIVED_CONTROL is set, then that value is honoured, else the most
recently set value from #control or pmSetDerivedControl is used.
PCPIntro(1), pmAddDerived(3), pmAddDerivedMetric(3), PMAPI(3),
pmErrStr(3), pmLoadDerivedConfig(3), pmRegisterDerived(3),
pmRegisterDerivedMetric(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
2026-05-24. (At that time, the date of the most recent commit
that was found in the repository was 2026-05-24.) 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 PMDERIVEDCONTROL(3)
Pages that refer to this page: pcpintro(1), pmloadderivedconfig(3), pmregisterderived(3)
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HTML rendering created 2026-05-24 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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