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

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

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

       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 pcp.conf(5).

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
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-08-11.)  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

Performance Co-Pilot                 PCP                         PMDAJBD2(1)