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NAME | SYNOPSIS | DESCRIPTION | INSTALLATION | FILES | PCP ENVIRONMENT | DEBUGGING OPTIONS | SEE ALSO | COLOPHON |
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PMDAJBD2(1) General Commands Manual PMDAJBD2(1)
pmdajbd2 - journal block device (JBD) performance metrics domain
agent (PMDA)
$PCP_PMDAS_DIR/jbd2/pmdajbd2 [-D debug] [-d domain] [-l logfile]
[-j path] [-U username]
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 default.
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 available.
If you do not use these metrics you can remove this PMDA, do the
following as root:
# cd $PCP_PMDAS_DIR/jbd2
# ./Remove
If you want to enable the installation again, do the following as
root:
# cd $PCP_PMDAS_DIR/jbd2
# ./Install
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.
$PCP_PMCDCONF_PATH
command line options used to launch pmdajbd2
$PCP_PMDAS_DIR/jbd2/help
default help text file for the jbd2 metrics
$PCP_PMDAS_DIR/jbd2/Install
installation script for the pmdajbd2 agent
$PCP_PMDAS_DIR/jbd2/Remove
undo installation script for the pmdajbd2 agent
$PCP_LOG_DIR/pmcd/jbd2.log
default log file for error messages and other information
from pmdajbd2
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.
PCPIntro(1), pmcd(1), 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 PMDAJBD2(1)
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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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