pmnewcontext(3) — Linux manual page


PMNEWCONTEXT(3)         Library Functions Manual         PMNEWCONTEXT(3)

NAME         top

       pmNewContext - establish a new PMAPI context

C SYNOPSIS         top

       #include <pcp/pmapi.h>

       int pmNewContext(int type, const char *name);

       cc ... -lpcp

DESCRIPTION         top

       An application using the Performance Metrics Application
       Programming Interface (PMAPI) may manipulate several concurrent
       contexts, each associated with a source of performance metrics,
       e.g. pmcd(1) on some host, or a set of archives of performance
       metrics as created by pmlogger(1), or a stand-alone connection on
       the local host that does not involve pmcd(1).

       pmNewContext may be used to establish a new context.  The source
       of the metrics is identified by name, and may be either a host
       name (type is PM_CONTEXT_HOST), or a comma-separated list of
       names referring to a set of archives (type is
       PM_CONTEXT_ARCHIVE).  Each element of the list may either be the
       base name common to all of the physical files of an archive or
       the name of a directory containing archives.

       For a type of PM_CONTEXT_HOST, in addition to identifying a host
       the name may also be used to encode additional optional
       information in the form of a pmcd(1) port number, a pmproxy(1)
       hostname and a proxy port number. For example the name
       "app23:14321," specifies a
       connection on port 14321 (or port 4321 if 14321 is unavailable)
       to pmcd(1) on the host app23 via port 11111 to pmproxy(1) on the

       For a type of PM_CONTEXT_ARCHIVE, each element of the list of
       names in name may also be the name of any of the physical files
       of an archive, e.g.  myarchive.meta (the metadata file) or
       myarchive.index (the temporal index) or myarchive.0 (the first
       data volume of the archive) or myarchive.0.bz2 or
       (the first data volume compressed with bzip2(1)) or
       myarchive.0.gz or myarchive.0.Z or myarchive.0.z (the first data
       volume compressed with gzip(1)), myarchive.1 or myarchive.3.bz2
       or myarchive.42.gz etc.

       If more than one archive is specified for a type of
       PM_CONTEXT_ARCHIVE, there are some restrictions on the archives
       within the set:
       •  The archives must all have been generated on the same host.
       •  The archives must not overlap in time.
       •  The archives must all have been created using the same time
       •  The PMID of each metric should be the same in all of the
          archives.  Multiple PMIDs are currently tolerated by using the
          first PMID defined for each metric and ignoring subsequent
       •  The type of each metric must be the same in all of the
       •  The semantics of each metric must be the same in all of the
       •  The units of each metric must be the same in all of the
       •  The instance domain of each metric must be the same in all of
          the archives.

       In the case where type is PM_CONTEXT_LOCAL, name is ignored, and
       the context uses a stand-alone connection to the PMDA methods
       used by pmcd(1).  The mechanism in the library uses the same
       ``plugin'' architecture that operates between pmcd(1) and DSO
       PMDAs, so operations involve function calls rather than IPC
       message passing - for PM_CONTEXT_LOCAL contexts this may mean
       lower latency for operations like pmFetch(3), but at the cost of
       longer initialization time and possible access control
       differences compared to pmcd(1).  When this type of context is
       used, the range of accessible performance metrics is constrained
       to those from the DSO PMDAs defined in the pmcd(1) configuration
       file /etc/pcp/pmcd/pmcd.conf, so those reported by the command
               $ awk '$3 == "dso" {print}' /etc/pcp/pmcd/pmcd.conf
       or alternatively reported by the command
               $ pminfo -f pmcd.agent.type | grep 'value 0'
       This usually means the PMDA exporting metrics from the operating
       system and the ``pmcd'', ``pmproxy'' and may includes some others
       like ``mmv''.  Alternate DSO PMDAs can be used, refer to

       In the case where type is PM_CONTEXT_HOST, additional flags can
       be added to the type to indicate if the connection to pmcd(1)
       should be encrypted (PM_CTXFLAG_SECURE), deferred
       (PM_CTXFLAG_SHALLOW) and if the file descriptor used to
       communicate with pmcd(1), should not be shared across contexts
       PM_CTXFLAG_EXCLUSIVE flags are now deprecated and ignored.

       When type is PM_CONTEXT_ARCHIVE, additional flags can be added to
       the type for restricted handling of the archive suited to
       applications that are aware of the structure of PCP archives,
       namely PM_CTXFLAG_NO_FEATURE_CHECK (do not check feature
       compatibility for archive label records) and
       PM_CTXFLAG_METADATA_ONLY (open only the metadata, not the data
       volume(s) nor the index).  Currently these additional flags are
       only used by pmlogrewrite(1) and pmlogdump(1).

       The initial instance profile is set up to select all instances in
       all instance domains.  In the case of a set of archives, the
       initial collection time is also set to zero, so that an initial
       pmFetch(3) will result in the earliest set of metrics being
       returned from the set of archives.

       Once established, the association between a context and a source
       of metrics is fixed for the life of the context, however routines
       are provided to independently manipulate both the instance
       profile (see pmAddProfile(3) and pmDelProfile(3)) and the
       collection time for archives (see pmSetMode(3)).

       pmNewContext returns a handle that may be used with subsequent
       calls to pmUseContext(3).

       The new context remains the current PMAPI context for all
       subsequent calls across the PMAPI, until another call to
       pmNewContext(3) is made, or the context is explicitly changed
       with a call to pmDupContext(3) or pmUseContext(3), or destroyed
       using pmDestroyContext(3).

       When attempting to connect to a remote pmcd(1) on a machine that
       is booting, pmNewContext could potentially block for a long time
       until the remote machine finishes its initialization.
       pmNewContext will abort and return an error if the connection has
       not been established after some specified interval has elapsed.
       The default interval is 5 seconds.  This may be modified by
       setting PMCD_CONNECT_TIMEOUT in the environment to a real number
       of seconds for the desired timeout.  This is most useful in cases
       where the remote host is at the end of a slow network, requiring
       longer latencies to establish the connection correctly.

CAVEATS         top

       When using a type of PM_CONTEXT_LOCAL, the operating system PMDA
       may export data structures directly from the kernel, which means
       that the pmNewContext caller should be an executable program
       compiled for the same object code format as the booted kernel.

       In addition, applications using a PM_CONTEXT_LOCAL context must
       be single-threaded because the various DSO PMDAs may not be
       thread-safe.  This restriction is enforced at the PMAPI(3), where
       routines may return the error code PM_ERR_THREAD if the library
       detects calls from more than one thread.

       Applications that use gethostbyname(3) should exercise caution
       because the static fields in struct hostent may not be preserved
       across some PMAPI(3) calls.  In particular, pmNewContext(3) and
       pmReconnectContext(3) both may call gethostbyname(3) internally.

DIAGNOSTICS         top


              No permission to perform requested operation


              PMCD connection limit for this host exceeded


              Requested context type was not PM_CONTEXT_LOCAL,


              Archives overlap in time


              Archives differ by host


              The type of a metric differs among archives


              The semantics of a metric differs among archives


              The instance domain of a metric differs among archives


              The units of a metric differs among archives

ENVIRONMENT         top

              Timeout period (in seconds) for pmcd(1) connection

              TCP/IP port(s) for connecting to pmcd(1), historically was
              4321 and more recently the officially registered port
              44321; in the current release, pmcd listens on both these
              ports as a transitional arrangement.  If used, should be
              set to a comma-separated list of numerical port numbers.

SEE ALSO         top

       pmcd(1), pminfo(1), pmproxy(1), PMAPI(3), pmAddProfile(3),
       pmDelProfile(3), pmDestroyContext(3), pmDupContext(3),
       pmFetch(3), pmGetConfig(3), pmReconnectContext(3), pmSetMode(3),
       pmSpecLocalPMDA(3), pmUseContext(3), pmWhichContext(3),
       pcp.conf(5) and pcp.env(5).

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on 2024-06-14.
       (At that time, the date of the most recent commit that was found
       in the repository was 2024-06-14.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

Performance Co-Pilot               PCP                   PMNEWCONTEXT(3)

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