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).