DOKK / manpages / debian 11 / libpcp3-dev / PCPIntro.3.en
PCPINTRO(3) Library Functions Manual PCPINTRO(3)

PCPIntro - introduction to the Performance Co-Pilot (PCP) libraries

Performance Co-Pilot (PCP) is a toolkit designed for monitoring and managing system-level performance.

The PCP libraries support the APIs required to create new performance monitoring tools and new agents (or PMDAs) to export performance data. The libpcp library is used in both cases. The libpcp_pmda library is used only for PMDAs.

Individual library routines are documented in their own manual page entries.

Most routines return an integer value; greater than equal to zero for success and less than zero for an error. The error codes have symbolic names defined in <pcp/pmapi.h>. Other negative values are used to encode errors that can be mapped to the traditional errno values defined in <errno.h>, with the value negated. To translate all PCP error codes into useful messages use either pmerr(1) or pmErrStr(3); the latter may also be used to decode the -errno cases.

These common errors may occur in various PCP interactions.

Timeout waiting for a response from PMCD
Many interactions between PCP applications involve synchronous message passing, and these are subject to timeout constraints. These errors are most frequently encountered when using network connections with slow data rates or long latencies.

For client-pmcd timeouts, refer to PCPIntro(1) for environment variables that may be used to modify the timeout thresholds. For pmcd-PMDA timeouts refer to the -t and -q options of pmcd(1) and the PCP metric pmcd.control.timeout that can be dynamically changed with pmstore(1).

Metric not supported by this version of monitored application
Some performance metrics are unavailable from specific versions of the associated PMDA, or may be unavailable because the underlying instrumentation has changed or is not installed or is not enabled. This error is used in results from pmFetch(3) to indicate these situations.
IPC protocol failure
Generic protocol failure on a pipe or socket connecting two PCP applications, eg. client-pmcd, or client-pmtime, or PMDA-pmcd or pmlc-pmlogger.
Oneline or help text is not available
Set by a PMDA, and passed back to a PCP client, to indicate that the PMDA is unable to supply the requested metric or instance domain help text.
Missing metric value(s)
This error is used for a number of conditions in which the value of a performance metric is inappropriate for the context in which it is being used, eg.
(a)
Bad value for the metric pmcd.timezone when trying to set the timezone via pmNewContextZone(3) for a remote or archive context.
(b)
Attempting to interpolate values for a metric with non-numeric data type from a set of PCP archives.
(c)
A bad result data structure passed to pmStore(3).
Unknown metric name
Just what the message says.
Unknown or illegal metric identifier
Just what the message says.
Unknown or illegal instance domain identifier
A request nominates an instance domain that is unknown or PM_INDOM_NULL. May occur as a consequence of the instance domain identifier passed by a PCP client to pmGetInDom(3), pmLookupInDom(3), pmNameInDom(3), pmGetInDomArchive(3), pmLookupInDomArchive(3), pmNameInDomArchive(3) or a request passed from pmcd(1) to a PMDA.
IPC channel closed
End of file on a pipe or socket connecting two PCP applications, eg. client-pmcd, or client-pmtime or PMDA-pmcd.
Attempt to use an illegal context
Typically caused by a PCP client that tries to make calls before calling pmNewContext(3) or after calling pmDestroyContext(3).
No permission to perform requested operation
PCP-specific access controls apply to pmcd(1) and pmlogger(1). Platform-specific permission errors are returned as -EPERM.
Impossible value or scale conversion
Some value conversion requests are illegal, eg. bad debug flag symbolic name for -D/--debug option, or asking pmExtractValue(3) to translate non-numeric data types to numbers and vice versa.
Truncation in value conversion
Some conversion requests to pmExtractValue(3) cannot be performed based on the metric types and values involved, in this case conversion would result in loss of precision.
Negative value in conversion to unsigned
Some conversion requests to pmExtractValue(3) cannot be performed based on the metric types and values involved, in this case converting a negative value to an unsigned value.
Unknown or illegal metric type
The metric type is held in the metric descriptor and sometimes encoded in the metric values returned from a call to pmFetch(3). Legal values for the metric type are defined by the PM_TYPE_* macros in <pcp/pmapi.h>.
Illegal pmUnits specification
Some conversion requests to pmConvScale(3) cannot be performed due to illegal or incompatible specifications of the source and destination units.
Explicit instance identifier(s) required
Some PMDAs, especially the proc PMDA, will not return ``all instances'' for a pmFetch(3) request due to the cost. The client must explicitly built an instance profile using pmAddProfile(3) and/or pmDelProfile(3) before calling pmFetch(3). See also the -F/--fetchall option to pminfo(1).
Unknown or illegal instance identifier
A request to a PMDA nominates an instance that is unknown. May occur as a consequence of the profile established prior to a pmFetch(3) call, or an explicit instance name or identifier to pmLookupInDom(3) or pmNameInDom(3).
Illegal mode specification
Illegal mode argument to pmSetMode(3).
NULL pmInDom with non-NULL instlist
Bad arguments passed from a PCP client to pmAddProfile(3).
Insufficient elements in list
Parameter passing error by caller specifying a list with less than one element to pmFetch(3), pmLookupName(3) or pmStore(3).
QA fault injected
For testing, there is a ``fault injection'' version of libpcp and this error indicates a misuse of the fault injection infrastructure.
Operation not supported for multi-threaded applications
As documented in PMAPI(3) and elsewhere, some libpcp routines are intended solely for use from single-threaded applications.
Container not found The user supplied container name does not match any known container.
Bad input to pmstore
The metric value provided for a pmStore(3) operation is in the wrong format, or of the wrong type or has the wrong number of values.
Result size exceeded
Indicates a fatal error in the message (or PDU) passing protocol between two PCP applications. This is an internal error, and other than an exotic networking failure, should not occur.
PMCD reset or configuration change
Not used.

Refer to pmFetch(3) for an alternative mechanism that may be used to notify a PCP client when pmcd(1) has experienced one or more configuration changes since the last request from the client. Usually these changes involve a change to the namespace exported via pmcd and/or changes to the PMDAs under pmcd's control.

QA fault injected
Used only for PCP Quality Assurance (QA) testing.
Functionality not yet implemented
Self explanatory and rarely used.
Generic error, already reported above
Rarely used, this error may be returned when the error condition is a consequent of some earlier returned error and a more precise characterization is not possible.
Derived metric definition failed
When registering a derived metric, the metric expression is either syntactically or semantically incorrect.
No support for metric label metadata
Operation requires metric labels, but none are available.

These errors may occur in the interactions between a PCP client and pmcd(1) providing real-time performance data.

No PMCD agent for domain of request
A request sent to pmcd(1) requires information from an agent or PMDA that does not exist. Usually this means the namespace being used by the client application contains metric names from a previously installed PMDA.
PMCD connection limit for this host exceeded
The client connection limit for pmcd(1) is controlled by the optional access controls in $PCP_PMCDCONF_PATH. By default there is no limit imposed by the PCP code, and this error would not be seen.
Try again. Information not currently available
Used to notify a PCP client that the PMDA responsible for delivering the information is temporarily unavailable. See also PM_ERR_PMDANOTREADY.
Missing profile - protocol botch
Internal error in the communication between a client application and pmcd(1) - should not occur.
PMCD requires a client certificate Authentication failure.
PMDA is currently fenced and unable to respond to requests
A privileged user has decided to isolate a PMDA from pmcd(1) using a pmStore(1) operation on the pmcd.agent.fenced metric, which means all fetch-level requests to that PMDA are being blocked.

These errors may occur in the interactions between a PCP client and the library routines that provide historical performance data from PCP archives created by pmlogger(1).

Missing archive file
Each PCP archive consists of multiple physical files as described in pmlogger(1). This error occurs when one of the physical files is missing or cannot be opened for reading.
End of PCP archive log
An attempt is made to read past the end file of the last volume of a set of PCP archives, or past the end of the time window (as specified with a -T/--finish option) for a set of PCP archives.
Operation requires context with host source of metrics
Calls to pmStore(3) require a host context and are not supported for PCP archives.

For archives created with versions of PCP prior to 4.0, the pmLookupText(3) and pmLookupInDomText(3) calls will return this code for archive PMAPI contexts (help and one-line text was not previously recorded in archive logs).

Corrupted record in a PCP archive log
PCP archives can become corrupted for a variety of reasons, but the most common is premature termination of pmlogger(1) without flushing its output buffers.
Illegal label record at start of a PCP archive log file
Each physical file in a PCP archive should begin with a common label record. This is a special case of PM_ERR_LOGREC errors.
Empty archive log file
An empty physical file can never be part of a valid PCP archive (at least the label record should be present). This is a special case of PM_ERR_LOGREC errors.
Operation requires context with archive source of metrics
A call to one of the archive variant routines, i.e. pmFetchArchive(3), pmGetInDomArchive(3), pmLookupInDomArchive(3) or pmNameInDomArchive(3), when the current context is not associated with a set of PCP archives.
Metric not defined in the PCP archive log
A PCP client has requested information about a metric, and there is no corresponding information in the set of PCP archives. This should not happen for well-behaved PCP clients.
Instance domain identifier not defined in the PCP archive log
A PCP client has requested information about an instance domain for one or more performance metrics, and there is no corresponding information in the set of PCP archives. If the client is using metric descriptors from the set of archives to identify the instance domain, this is less likely to happen.

Because instance domains may vary over time, clients may need to use the variant routines pmGetInDomArchive(3) or pmLookupInDomArchive(3) or pmNameInDomArchive(3) to manipulate the union of the instances in an instance domain over the life of an archive.

Instance identifier not defined in the PCP archive log
A PCP client has requested information about a specific instance of a performance metric, and there is no corresponding information in the set of PCP archives. If the client is using instance names from the instance domain in the set of archives (rather than hard-coded instance names) and instance identifiers from the results returned by pmFetch(3) or pmFetchArchive(3) this is less likely to happen.

Because instance domains may vary over time, clients may need to use the variant routines pmLookupInDomArchive(3) or pmNameInDomArchive(3) to manipulate the union of the instances in an instance domain over the life of an archive.

Archives overlap in time
When using a context associated with a set of archives, the archives in the set may not overlap in time.
Archives differ by host
When using a context associated with a set of archives, the archives in the set must all have been generated on the same host.
The type of a metric differs among archives
When using a context associated with a set of archives, the type of each metric must be same in all of the archives.
The semantics of a metric differs among archives
When using a context associated with a set of archives, the semantics of each metric must be same in all of the archives.
The instance domain of a metric differs among archives
When using a context associated with a set of archives, the instance domain of each metric must be same in all of the archives.
The units of a metric differs among archives
When using a context associated with a set of archives, the units of each metric must be same in all of the archives.

These errors may occur in the interactions between a GUI PCP client and the time control services provided by pmtime(1).

Already Connected
A PCP client application called pmTimeConnect(3) when already connected to a pmtime(1) instance.
Not Connected
A PCP client application called one of the time control routines pmTime*(3) when not currently connected to any pmtime(1) instance.
A non-null port name is required
If a shared pmtime(1) instance is being created the port argument to pmTimeConnect(3) must not be invalid.

These errors may occur in the processing of PCP namespace operations. A PCP namespace, see PMNS(5), provides the external names and the internal identifiers for the available performance metrics.

Metric name is not a leaf in PMNS
The metric name passed to pmLookupName(3) names a non-terminal path in the namespace, i.e. a group of metrics rather than a single metric.
Attempt to reload the PMNS
When using an explicit local namespace, it is illegal to call either of pmLoadNameSpace(3) or pmLoadASCIINameSpace(3) more than once.
Problems parsing PMNS definitions
Only occurs when an ASCII namespace is explicitly loaded.
PMNS not accessible
Only occurs when an ASCII namespace is explicitly loaded.

These error codes are used in the interactions between pmcd(1) and the PMDAs that provide the performance data.

PMDA is not yet ready to respond to requests
Some PMDAs have long initialization or reset times, and will respond to pmcd(1) with this error if they are busy at the moment. This error translates to PM_ERR_AGAIN for the PCP client who made the request to pmcd which caused the initial request to the PMDA. At some later time the PMDA will inform pmcd (see PM_ERR_PMDAREADY) that it is now ready to process requests, and client requests will begin to succeed.
PMDA is now responsive to requests
Used by PMDAs to asynchronously inform pmcd(1) that they are now willing to resume processing requests. See also PM_ERR_PMDANOTREADY.

Environment variables with the prefix PCP_ are used to parameterize the file and directory names used by PCP. On each installation, the file /etc/pcp.conf contains the local values for these variables. The $PCP_CONF variable may be used to specify an alternative configuration file, as described in pcp.conf(5). Values for these variables may be obtained programmatically using the pmGetConfig(3) function.

PCPIntro(1), pmcd(1), pmerr(1), pminfo(1), pmtime(1), pmstore(1), pmlogger(1), PMAPI(3), pmAddProfile(3), pmDelProfile(3), pmConvScale(3), pmNewContext(3), pmDestroyContext(3), pmErrStr(3), pmExtractValue(3), pmFetch(3), pmFetchArchive(3), pmGetConfig(3), pmGetInDom(3), pmGetInDomArchive(3), pmLoadNameSpace(3), pmLookupInDom(3), pmLookupInDomText(3), pmLookupName(3), pmLookupText(3), pmNameInDom(3), pmNameInDomArchive(3), pmSetMode(3), pmStore(3), pmTimeConnect(3), pcp.conf(5), pcp.env(5) and PMNS(5).

PCP Performance Co-Pilot