NAME

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

SYNOPSIS

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

DESCRIPTION

       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

       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.

FILES

       $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

PCP ENVIRONMENT

       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

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