pmdabash - Online in the Cloud

PROGRAM:

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"

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