pmdajbd2 - journal block device (JBD) performance metrics domain agent (PMDA)
$PCP_PMDAS_DIR/jbd2/pmdajbd2 [-d domain] [-l logfile] [-j path] [-U username]
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
-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.
This PMDA is installed by default and in the shared library mode (rather than as a sepa-
rate 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
If you want to enable the installation again, do the following as root:
# cd $PCP_PMDAS_DIR/jbd2
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.
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 config-
uration file, as described in pcp.conf(5).
PCPIntro(1), pmcd(1), pcp.conf(5) and pcp.env(5).
Performance Co-Pilot PCP PMDAJBD2(1)