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
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
-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
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
# . /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 no explicit security model has been selected (as described above),
the ./Install script will create a world-writeable sticky-bit-set mmv
directory for communication. This is for backwards compatibility, as
well as ease of use - to use this, do the following as root:
# cd $PCP_PMDAS_DIR/mmv
This installation process will not overwrite any existing
If you want to undo the installation, do the following as root:
# cd $PCP_PMDAS_DIR/mmv
pmdammv is launched by pmcd and should never be executed directly.
The Install and Remove scripts notify pmcd when the agent is
installed or removed.
command line options used to launch pmdammv$PCP_TMP_DIR/mmv
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
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).
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
firstname.lastname@example.org. This page was obtained from the project's upstream
Git repository ⟨git://git.pcp.io/pcp⟩ on 2017-03-13. 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
Performance Co-Pilot PCP PMDAMMV(1)