# pmdajbd2

## NAME



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


## SYNOPSIS



           **$PCP_PMDAS_DIR/jbd2/pmdajbd2**[**-D** _debug_] [**-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).
    


## DEBUGGING OPTIONS



           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.
    


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