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'' library).

       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 default.

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-writable $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-writable 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 root:

            # 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

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 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
       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)