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NAME | SYNOPSIS | DESCRIPTION | INSTALLATION | FILES | PCP ENVIRONMENT | DEBUGGING OPTIONS | SEE ALSO | COLOPHON |
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PMDAMMV(1) General Commands Manual PMDAMMV(1)
pmdammv - memory mapped values performance metrics domain agent
(PMDA)
$PCP_PMDAS_DIR/mmv/pmdammv [-D debug] [-d domain] [-l logfile] [-U
username]
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.
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.
$PCP_PMCDCONF_PATH
command line options used to launch pmdammv
$PCP_TMP_DIR/mmv
directory housing memory mapped value files
$PCP_PMDAS_DIR/mmv/help
default help text file for the mmv metrics
$PCP_PMDAS_DIR/mmv/Install
installation script for the pmdammv agent
$PCP_PMDAS_DIR/mmv/Remove
undo installation script for the pmdammv agent
$PCP_LOG_DIR/pmcd/mmv.log
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).
The -D or --debug option enables the output of additional
diagnostics on stderr to help triage problems, although the
information is sometimes cryptic and primarily intended to provide
guidance for developers rather end-users. debug is a comma
separated list of debugging options; use pmdbg(1) with the -l
option to obtain a list of the available debugging options and
their meaning.
Debugging options specific to pmdammv are as follows:
┌────────┬─────────────────────┐
│ Option │ Description │
├────────┼─────────────────────┤
│ appl0 │ verbose diagnostics │
└────────┴─────────────────────┘
PCPIntro(1), pmcd(1), newgrp(1), setgid(2), mmv_stats_init(3),
mmv(5), pcp.conf(5) and pcp.env(5).
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at
⟨http://www.pcp.io/⟩. If you have a bug report for this manual
page, send it to pcp@groups.io. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-08-11.) 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
man-pages@man7.org
Performance Co-Pilot PCP PMDAMMV(1)
Pages that refer to this page: pmlogger(1), mmv(5)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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