pmdajbd2 is a Performance Metrics Domain Agent (PMDA) which extracts
performance metrics from the Journal Block Device subsystem (version
2) in the Linux kernel. These metrics are exported by the kernel in
procfs files, one file per block device. The JBD2 subsystem is used
by several filesystems including ext3, ext4 and ocfs2.
The jbd2 PMDA exports metrics that measure detailed journal
transaction information, such as time spent waiting and locked,
request rates, blocks used and so on.
A brief description of the pmdajbd2 command line options follows
(these are only relevant when running the PMDA as a daemon, and not
as a shared library):
-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, when running as a daemon
a log file named jbd2.log is written in the current directory of
when pmdajbd2 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. When running in shared library
mode, and diagnostic information will be written into the pmcd
log file, namely $PCP_LOG_DIR/pmcd/pmcd.log.
-j Allows an alternate path to the jbd2 statistics files to be
specified. The default path is /proc/fs/jbd2.
-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
This PMDA is installed by default and in the shared library mode
(rather than as a separate daemon to pmcd(1)). Thus, the names, help
text and values for the jbd2 performance metrics should always be
If you do not use these metrics you can remove this PMDA, do the
following as root:
# cd $PCP_PMDAS_DIR/jbd2
If you want to enable the installation again, do the following as
# cd $PCP_PMDAS_DIR/jbd2
pmdajbd2 is launched by pmcd(1) and should never be executed
directly. The Install and Remove scripts notify pmcd(1) when the
agent is installed or removed.
command line options used to launch pmdajbd2$PCP_PMDAS_DIR/jbd2/help
default help text file for the jbd2 metrics
installation script for the pmdajbd2 agent
undo installation script for the pmdajbd2 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
email@example.com. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2020-07-14. (At that time, the date of the most recent commit that
was found in the repository was 2020-07-14.) 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 PMDAJBD2(1)