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   pmcd    ( 1 )

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Описание (Description)

pmcd is the collector used by the Performance Co-Pilot (see
       PCPIntro(1)) to gather performance metrics on a system.  As a
       rule, there must be an instance of pmcd running on a system for
       any performance metrics to be available to the PCP.

       pmcd accepts connections from client applications running either
       on the same machine or remotely and provides them with metrics
       and other related information from the machine that pmcd is
       executing on.  pmcd delegates most of this request servicing to a
       collection of Performance Metrics Domain Agents (or just agents),
       where each agent is responsible for a particular group of
       metrics, known as the domain of the agent.  For instance, the
       postgresql agent is responsible for reporting information
       relating to the PostgreSQL database, such as the transaction and
       query counts, indexing and replication statistics, and so on.

       The agents may be processes started by pmcd, independent
       processes or Dynamic Shared Objects (DSOs, see dlopen(3))
       attached to pmcd's address space.  The configuration section
       below describes how connections to agents are specified.

       Note that if a PDU exchange with an agent times out, the agent
       has violated the requirement that it delivers metrics with little
       or no delay.  This is deemed a protocol failure and the agent is
       disconnected from pmcd.  Any subsequent requests for information
       from the agent will fail with a status indicating that there is
       no agent to provide it.

       It is possible to specify access control to pmcd based on users,
       groups and hosts.  This allows one to prevent users, groups of
       users, and certain hosts from accessing the metrics provided by
       pmcd and is described in more detail in the access control
       section below.