pmdapipe — command output capture performance metrics domain agent (PMDA)


$PCP_PMDAS_DIR/pipe/pmdapipe [-c configfile] [-d domain] [-l logfile] [-m memory]


pmdapipe is a configurable command output monitoring Performance Metrics Domain Agent (PMDA). It can be seen as analogous to a restricted shell, where options can be passed to preset commands, and each line of their output is converted into a performance event. These events can be consumed by client tools like pmval(1).

The pipe PMDA exports both event-style metrics reflecting timestamped event records for text-oriented command output, as well as the more orthodox sample-style metrics such as event counts and throughput size values.

The PMDA is configured via a configfile which contains one line for each process from which output can be captured, as described in the “Configuration” section below.

A brief description of the pmdapipe command line options follows:


specifies an alternate configuration file for the PMDA. By default, a file named $PCP_PMDAS_DIR/pipe/pipe.conf and any files below the $PCP_SYSCONF_DIR/pipe.conf.d/ directory are used.


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.


Location of the log file.  By default, a log file named pipe.log is written in the current directory of pmcd(1) when pmdapipe 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.


Limit the physical memory used by the PMDA to buffer event records to maxsize bytes. As log events arrive at the PMDA, they must be buffered until individual client tools request the next batch since their previous batch of events. The default maximum is 2 megabytes.


The set of allowed pipe commands is configured by simple text file(s). The format is a single line for each command followed by an optional access control section.

Blank lines and comments are permitted (even encouraged) in the configuration file. A comment begins with a “#” character and finishes at the end of the line.

Each command configuration line is of the form:

instance username command options



is a string identifying the pipe command, also exported as the metric instance identifier.


is the name of the user account under which the command should run (e.g. "root")


is the path to the binary which will be run to generate piped output


is an optional space-separated list of parameters to pass to the command

This options list may contain numeric parameters prefixed by the dollar-sign, and these will be substituted with user-supplied values at the time the command is run (similar to shell parameter substitution).

Parameters are passed as a single space-separated or comma-separated string to the pipe.firehose metric, using the pmStore (3) interface. The pmval command provides store access via its -x option. User-supplied parameters are restricted to containing alphanumeric characters.

The access control section of the file must start with a line of the form:


Leading and trailing whitespace may appear around and within the brackets and the case of the access keyword is ignored. No other text may appear on the line except a trailing comment.

Following this line, the remainder of the configuration file should contain lines that allow or disallow use of commands from particular users or groups.

User names and group names will be verified using the local /etc/passwd and /etc/groups files (or an alternative directory service), using the getpwent(3) and getgrent(3) routines.

Access for users or groups are allowed or disallowed by specifying statements of the form:

allow user username : instance
disallow user username : instance
allow group groupname : instance
disallow group groupname : instance

The username and groupname names will be verified using the local /etc/passwd and /etc/groups files (or an alternative directory service), using the getpwent(3) and getgrent(3) routines.

The wildcard “*” can be used to refer to all instance names.


If you want access to the names, help text and values for the pipe performance metrics, do the following as root:

# cd $PCP_PMDAS_DIR/pipe
# ./Install

This is an interactive installation process which prompts for each log file path to be monitored (or command to be run), a metric instance name to identify it, and whether access should be restricted (refer to the -x option to pmval(1) for further details).

If you want to undo the installation, do the following as root:

# cd $PCP_PMDAS_DIR/pipe
# ./Remove

pmdapipe is launched by pmcd and should never be executed directly. The Install and Remove scripts notify pmcd when the agent is installed or removed.


Following is a simple example of pmdapipe configuration and use of the pipe metrics to run the btrace command, by user bob:

bob> cat $PCP_PMDAS_DIR/pipe/pipe.conf
# instance      user      command
rw_syscalls     root      perf script rw-by-file $1
bdev_trace      root      btrace -w $1 /dev/$2

allow user bob : *;
allow user jane : bdev_trace;
allow group perf : rw_syscalls;

bob> pmval -i bdev_trace -x '5 sda' pipe.firehose
 8,2  5  1  0.000000000 25227  A  WS 734332384 + 24 <- (253,2) 734330336
 8,0  5  2  0.000000414 25227  A  WS 735358432 + 24 <- (8,2) 734332384
 8,0  5  3  0.000000756 25227  Q  WS 735358432 + 24 [qemu-kvm]
 [...5 seconds worth]



command line options used to launch pmdapipe


default configuration file for the pipe metrics


default help text file for the pipe metrics


installation script for the pmdapipe agent


undo installation script for the pmdapipe agent


default log file for error messages and other information from pmdapipe


directory containing additional configuration files for the pipe metrics

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), pmval(1), pmcd(1), getpwent(3), getgrent(3), pmStore(3), pcp.conf(5) and pcp.env(5).


PCP Performance Co-Pilot