pmdammv(1) — Linux manual page


PMDAMMV(1)                 General Commands Manual                PMDAMMV(1)

NAME         top

       pmdammv  -  memory  mapped  values  performance  metrics domain agent

SYNOPSIS         top

       $PCP_PMDAS_DIR/mmv/pmdammv [-d domain] [-l logfile] [-U username]

DESCRIPTION         top

       pmdammv is a Performance Metrics Domain Agent (PMDA) which exports
       application level performance metrics using memory mapped files.  It
       offers an extremely low overhead instrumentation facility that is
       well-suited to long running, mission critical applications where it
       is desirable to have performance metrics and availability information
       permanently enabled.

       The mmv PMDA exports instrumentation that has been added to an
       application using the MMV APIs (refer to mmv_stats_init(3) and mmv(5)
       for further details).  These APIs can be called from several
       languages, including C, C++, Perl, Python, Java (via the separate
       ``Parfait'' class library) and GoLang (via the separate ``Speed''

       A brief description of the pmdammv command line options follows:

       -d   It is absolutely crucial that the performance metrics domain
            number specified here is unique and consistent.  That is, domain
            should be different for every PMDA on the one host, and the same
            domain number should be used for the same PMDA on all hosts.

       -l   Location of the log file.  By default, a log file named mmv.log
            is written in the current directory of pmcd(1) when pmdammv is
            started, i.e.  $PCP_LOG_DIR/pmcd.  If the log file cannot be
            created or is not writable, output is written to the standard
            error instead.

       -U   User account under which to run the agent.  The default is the
            unprivileged "pcp" account in current versions of PCP, but in
            older versions the superuser account ("root") was used by

INSTALLATION         top

       Firstly, a security model for interprocess communication between
       instrumented applications and pmdammv (running as a shared library
       inside pmcd) must be chosen and established.

       This communication occurs through memory mapped files in a location
       known to both pmdammv and the instrumented applications.  That
       location is $PCP_TMP_DIR/mmv, although that is often hidden behind
       application APIs such as ``Parfait'' and mmv_stats_init(3).  The
       permissions set on this directory indicate the security model in use.

       The more secure method is to use an existing unprivileged group which
       is shared by instrumented applications, pmcd and pmdammv such as the
       "pcp" group.

            # . /etc/pcp.env
            # mkdir -m 775 $PCP_TMP_DIR/mmv
            # chgrp pcp $PCP_TMP_DIR/mmv

       Since this method requires instrumented applications to use this non-
       default group (see newgrp(1) and setgid(2)) a common alternative
       involves the use of a world-writeable $PCP_TMP_DIR/mmv directory with
       the sticky-bit set (similar to /tmp and /var/tmp, for example).

       This allows any application, running under any user account, to
       communicate with the PMDA (which runs under the "pcp" account by
       default).  This may not be desirable for all environments and one
       should consider the security implications of any directory setup like
       this (similar classes of issues exist as those that affect the system
       temporary file directories).

       pmdammv is enabled by default on all modern PCP installations, and
       thus the names, help text and values for the mmv performance metrics
       are available without the usual PMDA ./Install process.

       If the $PCP_TMP_DIR/mmv directory does not exist, then the ./Install
       script can be used to create a world-writeable sticky-bit-set
       directory for communication.  This is for backwards compatibility, as
       well as ease of use - to use this mechanism, do the following as

            # rmdir $PCP_TMP_DIR/mmv
            # cd $PCP_PMDAS_DIR/mmv
            # ./Install

       This installation process will not overwrite any existing
       $PCP_TMP_DIR/mmv directory.

       If you want to undo the installation, do the following as root:

            # cd $PCP_PMDAS_DIR/mmv
            # ./Remove

       pmdammv is launched by pmcd and should never be executed directly.
       The Install and Remove scripts notify pmcd when the agent is
       installed or removed.

FILES         top

                 command line options used to launch pmdammv
                 directory housing memory mapped value files
                 default help text file for the mmv metrics
                 installation script for the pmdammv agent
                 undo installation script for the pmdammv agent
                 default log file for error messages and other information
                 from pmdammv


       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).

SEE ALSO         top

       PCPIntro(1), pmcd(1), newgrp(1), setgid(2), mmv_stats_init(3),
       mmv(5), 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
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-08-11.)  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

Performance Co-Pilot                 PCP                          PMDAMMV(1)

Pages that refer to this page: pmlogger(1)mmv(5)