Each supported platform has a kernel Performance Metrics Domain
Agent (PMDA) which extracts performance metrics from the kernel
of that platfrom. A variety of platform-specific metrics are
available, with an equally varied set of access mechanisms -
typically this involves special system calls, or reading from
files in kernel virtual filesystems such as the Linux sysfs and
The platform kernel PMDA is one of the most critical components
of the PCP installation, and must be as efficient and reliable as
possible. In all installations the default kernel PMDA will be
installed as a shared library and thus executes directly within
the pmcd(1) process. This slightly reduces overheads associated
with querying the metadata and values associated with these
metrics (no message passing is required).
Unlike many other PMDAs, the kernel PMDA exports a number of
metric namespace subtrees, such as kernel, network, swap, mem,
ipc, filesys, nfs, disk and hinv (hardware inventory).
Despite usually running as shared libraries, most installations
also include a stand-alone executable for the kernel PMDA. This
is to aid profiling and debugging activities, with dbpmda(1) for
example. In this case (but not for shared libraries), the
following command line options are available:
-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
[platform].log is written in the current directory of
pmcd(1) when pmda[platform] 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
-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.
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
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
⟨https://github.com/performancecopilot/pcp.git⟩ on 2021-08-27.
(At that time, the date of the most recent commit that was found
in the repository was 2021-08-27.) 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 KERNEL_PMDAS(1)