PMDAPIPE(1)

PMDAPIPE(1) — bestie edition 💖

okay so this is pmdapipe from section 1 of the General Commands Manual, aka the command output capture performance metrics domain agent (PMDA). yes it's a mouthful. we'll get through it together 🫶

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✨ NAME ✨

pmdapipe — command output capture performance metrics domain agent (PMDA). she watches your commands' output and turns it into metrics. iconic behavior honestly 👑

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🌸 SYNOPSIS 🌸

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

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🦋 DESCRIPTION 🦋

pmdapipe is a configurable command output monitoring Performance Metrics Domain Agent (PMDA). think of her as a restricted shell — you pass options to preset commands, and every single line of their output gets converted into a performance event. then client tools like pmval(1) can eat those events up. no cap 🍓

the pipe PMDA exports both:

• event-style metrics — timestamped event records for text-oriented command output
• the more orthodox sample-style metrics — event counts and throughput size values

the PMDA gets configured via a configfile, which has one line for each process you want to capture output from. all the deets are in the CONFIGURATION section below, don't skip it 💅

a brief description of the pmdapipe command line options follows:

• -c — 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.
• -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. like, do not play with this one bestie 😭
• -l — 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.
• -m — 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.

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🎀 CONFIGURATION 🎀

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, and honestly same, live a little 🌈) 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

where,

• instance — is a string identifying the pipe command, also exported as the metric instance identifier.
• username — is the name of the user account under which the command should run (e.g. "root")
• command — is the path to the binary which will be run to generate piped output
• options — 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 only — keep it clean, bestie ✨

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

[access]

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 💖

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💜 INSTALLATION 💜

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). it literally holds your hand, we love that 🫶

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. so like, hands off, she's got a manager 💅

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🌈 EXAMPLES 🌈

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

[access]
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]
bob>

ate. no crumbs. 🔥

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⭐ FILES ⭐

• $PCP_PMCDCONF_PATH — command line options used to launch pmdapipe
• $PCP_PMDAS_DIR/pipe/pipe.conf — default configuration file for the pipe metrics
• $PCP_PMDAS_DIR/pipe/help — default help text file for the pipe metrics
• $PCP_PMDAS_DIR/pipe/Install — installation script for the pmdapipe agent
• $PCP_PMDAS_DIR/pipe/Remove — undo installation script for the pmdapipe agent
• $PCP_LOG_DIR/pmcd/pipe.log — default log file for error messages and other information from pmdapipe
• $PCP_SYSCONF_DIR/pipe.conf.d — directory containing additional configuration files for the pipe metrics

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🧚 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). it's giving configurable 💅

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🔍 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 than for 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.

debugging options specific to pmdapipe are as follows:

• appl0 — event processing and generation, interactions with pmcd(1), client context handling, command execution
• appl1 — access controls, user and group diagnostics
• appl2 — configfile handling, bad command argument diagnostics, select(2) handling

ngl, if you're reading these logs as an end-user and you understand them, you're lowkey a wizard 🧙♀️✨

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👑 SEE ALSO 👑

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

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and that's the whole page, bestie!! this came to you from Performance Co-Pilot — that's the PCP crew — and the page itself is PMDAPIPE(1). go forth and pipe responsibly 💖✨🎀🦋🌸💅🫶