pmdammv - memory mapped values performance metrics domain agent (PMDA)
$PCP_PMDAS_DIR/mmv/pmdammv [
-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-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 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).
PCPIntro(1),
pmcd(1),
newgrp(1),
setgid(2),
mmv_stats_init(3),
mmv(5),
pcp.conf(5) and
pcp.env(5).