pmdabash (1) - Linux Manuals

pmdabash: Bourne-Again SHell trace performance metrics domain agent

Command to display pmdabash manual in Linux: $ man 1 pmdabash

NAME

pmdabash - Bourne-Again SHell trace performance metrics domain agent

SYNOPSIS

$PCP_PMDAS_DIR/bash/pmdabash [-C] [-d domain] [-l logfile] [-I interval] [-t timeout] [-U username] configfile

DESCRIPTION

pmdabash is an experimental Performance Metrics Domain Agent (PMDA) which exports "xtrace" events from a traced bash(1) process. This includes the command execution information that would usually be sent to standard error with the set -x option to the shell.

Event metrics are exported showing each command executed, the function name and line number in the script, and a timestamp. Additionally, the process identifier for the shell and its parent process are exported.

This requires bash version 4 or later.

A brief description of the pmdabash command line options follows:

-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, a log file named bash.log is written in the current directory of pmcd(1) when pmdabash 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.
-s: Amount of time (in seconds) between subsequent evaluations of the shell trace file descriptor(s). The default is 2 seconds.

-m: Maximum amount of memory to be allowed for each event queue (one per traced process). The default is 2 megabytes.
-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

In order for a host to export the names, help text and values for the bash performance metrics, do the following as root:

# cd $PCP_PMDAS_DIR/bash
# ./Install

As soon as an instrumented shell script (see INSTRUMENTATION selection below) is run, with tracing enabled, new metric values will appear - no further setup of the agent is required.

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

# cd $PCP_PMDAS_DIR/bash
# ./Remove

pmdabash 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.

INSTRUMENTATION

In order to allow the flow of event data between a bash(1) script and pmdabash, the script should take the following actions:

#!/bin/sh
source $PCP_DIR/etc/pcp.sh

pcp_trace on $@       # enable tracing
echo "awoke, $count"

pcp_trace off         # disable tracing

The tracing can be enabled and disabled any number of times by the script. On successful installation of the agent, several metrics will be available:

$ pminfo bash
bash.xtrace.numclients
bash.xtrace.maxmem
bash.xtrace.queuemem
bash.xtrace.count
bash.xtrace.records
bash.xtrace.parameters.pid
bash.xtrace.parameters.parent
bash.xtrace.parameters.lineno
bash.xtrace.parameters.function
bash.xtrace.parameters.command

When an instrumented script is running, the generation of event records can be verified using the pmevent(1) command, as follows:

$ pmevent -t 1 -x '' bash.xtrace.records
host:      localhost
samples:   all
bash.xtrace.records["4538 ./test-trace.sh 1 2 3"]: 5 event records
  10:00:05.000 --- event record [0] flags 0x19 (point,id,parent) ---
    bash.xtrace.parameters.pid 4538
    bash.xtrace.parameters.parent 4432
    bash.xtrace.parameters.lineno 43
    bash.xtrace.parameters.command "true"
  10:00:05.000 --- event record [1] flags 0x19 (point,id,parent) ---
    bash.xtrace.parameters.pid 4538
    bash.xtrace.parameters.parent 4432
    bash.xtrace.parameters.lineno 45
    bash.xtrace.parameters.command "((  count++  ))"
  10:00:05.000 --- event record [2] flags 0x19 (point,id,parent) ---
    bash.xtrace.parameters.pid 4538
    bash.xtrace.parameters.parent 4432
    bash.xtrace.parameters.lineno 46
    bash.xtrace.parameters.command "echo 'awoke, 3'"
  10:00:05.000 --- event record [3] flags 0x19 (point,id,parent) ---
    bash.xtrace.parameters.pid 4538
    bash.xtrace.parameters.parent 4432
    bash.xtrace.parameters.lineno 47
    bash.xtrace.parameters.command "tired 2"
  10:00:05.000 --- event record [4] flags 0x19 (point,id,parent) ---
    bash.xtrace.parameters.pid 4538
    bash.xtrace.parameters.parent 4432
    bash.xtrace.parameters.lineno 38
    bash.xtrace.parameters.function "tired"
    bash.xtrace.parameters.command "sleep 2"

FILES

$PCP_PMCDCONF_PATH: command line options used to launch pmdabash
$PCP_PMDAS_DIR/bash/help: default help text file for the bash metrics
$PCP_PMDAS_DIR/bash/Install: installation script for the pmdabash agent
$PCP_PMDAS_DIR/bash/Remove: undo installation script for pmdabash
$PCP_LOG_DIR/pmcd/bash.log: default log file for error messages and other information from pmdabash

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).