pmdajbd2(1) — Linux manual page


PMDAJBD2(1)              General Commands Manual             PMDAJBD2(1)

NAME         top

       pmdajbd2 - journal block device (JBD) performance metrics domain
       agent (PMDA)

SYNOPSIS         top

       $PCP_PMDAS_DIR/jbd2/pmdajbd2 [-d domain] [-l logfile] [-j path]
       [-U username]

DESCRIPTION         top

       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.

INSTALLATION         top

       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

            # 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.

FILES         top

              command line options used to launch pmdajbd2
              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
              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

SEE ALSO         top

       PCPIntro(1), pmcd(1), pcp.conf(5) and pcp.env(5).

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on 2023-12-22.
       (At that time, the date of the most recent commit that was found
       in the repository was 2023-12-16.)  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)