dbpmda(1) debugger for Performance Co-Pilot PMDAs


dbpmda [-efi] [-n pmnsfile] [-q timeout] [-U username]


dbpmda is an interactive interface to the interactions between a Performance Metric Domain Agent (PMDA(3)) and the Performance Metric Collector Daemon (pmcd(1)). This allows PMDAs to be attached, initialized and exercised to test for correctness.

dbpmda interactively prompts the user for commands, many of which emulate the Protocol Data Units (PDUs) that may be sent by a pmcd(1) process. After running dbpmda, enter the command help to get a list of the available commands. The example section below illustrates a session using dbpmda to test a PMDA.

To simplify repetitive testing of a PMDA, the file .dbpmdarc in the current working directory can contain a list of commands that will be executed by dbpmda on startup, before the user is prompted to enter further commands interactively. While processing the .dbpmdarc file, interactive mode and command echoing are enabled and then reset at the end of the .dbpmdarc file (see the -i and -e command line arguments below).

The -f command line option prevents startup processing of a .dbpmdarc file (if it exists).

If the system supports readline(3) then this will be used to read commands when input is from a tty device, so history and command line editing are available.

dbpmda accepts the following command line arguments:

Echo the input to stdout. This is useful when the input is redirected from a file.
Emulate interactive behavior and prompt for new commands, even if standard input is not a tty device.
-n pmnsfile
Normally dbpmda operates on the distributed Performance Metrics Name Space (PMNS), however if the -n option is specified an alternative local PMNS is loaded from the file pmnsfile.
-q timeout
The pmcd to agent version exchange protocol (new in PCP 2.0 - introduced to provide backward compatibility) uses this timeout to specify how long dbpmda should wait before assuming that no version response is coming from an agent. If this timeout is reached, the agent is assumed to be an agent which does not understand the PCP 2.0 protocol. The default timeout interval is five seconds, but the -q option allows an alternative timeout interval (which must be greater than zero) to be specified. The unit of time is seconds.
-U username
User account under which to run dbpmda.

As there are no timeout constraints on a PMDA while using dbpmda (as compared to pmcd(1)), another debugger like gdb(1) can be used on the PMDA process once it has been attached to dbpmda.


Below is a dbpmda session using the simple PMDA. A .dbpmdarc file is used to set the debugging flag, open the PMDA and display the current status of the debugger:

$ cat .dbpmdarc
debug libpmda
open dso pmda_simple.so simple_init 253

When dbpmda is run, the commands in the .dbpmdarc file are executed first:

$ dbpmda
.dbpmdarc> debug libpmda
.dbpmdarc> open dso pmda_simple.so simple_init 253
[Fri Sep 19 10:19:55] dbpmda(11651) Debug: pmdaInit: PMDA simple DSO: Metric 0.0.1(1) matched to indom 253.0(0)
[Fri Sep 19 10:19:55] dbpmda(11651) Debug: pmdaInit: PMDA simple DSO: help file $PCP_PMDAS_DIR/simple/help opened
[Fri Sep 19 10:19:55] dbpmda(11651) Info: name        = simple DSO
[Fri Sep 19 10:19:55] dbpmda(11651) Info: domain      = 253
[Fri Sep 19 10:19:55] dbpmda(11651) Info: num metrics = 4
[Fri Sep 19 10:19:55] dbpmda(11651) Info: num indom   = 1
[Fri Sep 19 10:19:55] dbpmda(11651) Info: direct map  = 1
.dbpmdarc> status
Namespace:              (default)
PMDA:                   ./pmda_simple.so
Connection:             dso
DSO Interface Version:  2
PMDA PMAPI Version:     2
pmDebug:                32768 ( libpmda )
Timer:                  off
Getdesc:                off
Dump Instance Profile state=INCLUDE, 0 profiles

To examine the metric and instance descriptors, the desc and instance commands can be used. Metrics may be identified either by name, or using the ``dotted'' notation to specify the domain, cluster and item fields of a PMID. Instance domains must be identified using a ``dotted'' notation to specify the domain and serial fields. The syntax for most commands will be displayed if the command is given without any arguments:

dbpmda> desc 253.0.0
PMID: 253.0.0
    Data Type: 32-bit unsigned int  InDom: PM_INDOM_NULL 0xffffffff
    Semantics: instant  Units: none
dbpmda> instance
instance indom# [ number | name | "name" ]
dbpmda> instance 253.0
pmInDom: 253.0
[  0] inst: 0 name: "red"
[  1] inst: 1 name: "green"
[  2] inst: 2 name: "blue"

To test the most important component of a PMDA, the fetch, it is often useful to determine the time it takes the PMDA to respond. The timer may be turned on before giving a fetch:

dbpmda> timer on
dbpmda> fetch simple.numfetch 253.0.1
PMID(s): 253.0.0 253.0.1
pmResult dump from 0x100078e0 timestamp: 0.000000 11:00:00.000 numpmid: 2
  253.0.0 (simple.numfetch): numval: 1 valfmt: 0 vlist[]:
   value 1 1.4012985e-45 0x1
  253.0.1 (simple.color): numval: 3 valfmt: 0 vlist[]:
    inst [0 or ???] value 1 1 1.4012985e-45 0x1
    inst [1 or ???] value 101 1.4153114e-43 0x65
    inst [2 or ???] value 201 2.8166099e-43 0xc9
Timer: 0.003921 seconds
dbpmda> timer off

The integer, floating point and hex translations of the values in the pmResult structure are dumped if getdesc is set to off (the default). Setting getdesc to on would result in only integer values being dumped in the above fetch as the descriptor describes the metrics of 32-bit unsigned integers.

The simple PMDA also supports the store operation which can be tested with subsequent fetch commands:

dbpmda> store simple.numfetch "42"
PMID: 253.0.0
Getting description...
Getting Result Structure...
253.0.0: 2 -> 42
dbpmda> fetch simple.numfetch
PMID(s): 253.0.0
pmResult dump from 0x100078e0 timestamp: 0.000000 11:00:00.000 numpmid: 1
  253.0.0 (simple.numfetch): numval: 1 valfmt: 0 vlist[]:
   value 43

The value argument in the store command must be a string, which is enclosed in either single quotes (') or double quotes (").

A profile can be specified for each instance domain which includes all, some or no instances:

dbpmda> help profile
profile indom# [ all | none ]
profile indom# [ add | delete ] number
For the instance domain specified, the profile may be changed to
include 'all' instances, no instances, add an instance or delete 
an instance.
dbpmda> profile 253.0 none
dbpmda> getdesc on
dbpmda> fetch 253.0.1
PMID(s): 253.0.1
pmResult dump from 0x100078e0 timestamp: 0.000000 11:00:00.000 numpmid: 1
  253.0.1 (simple.color): No values returned!
dbpmda> profile 253.0 add 2
dbpmda> fetch 253.0.1
PMID(s): 253.0.1
pmResult dump from 0x100078e0 timestamp: 0.000000 11:00:00.000 numpmid: 1
  253.0.1 (simple.color): numval: 1 valfmt: 0 vlist[]:
   value 202
dbpmda> profile 253.0 add 0
dbpmda> fetch 253.0.1
PMID(s): 253.0.1
pmResult dump from 0x100078e0 timestamp: 0.000000 11:00:00.000 numpmid: 1
  253.0.1 (simple.color): numval: 2 valfmt: 0 vlist[]:
    inst [0 or ???] value 2
    inst [2 or ???] value 203
dbpmda> status
PMDA       = pmda_simple.so
Connection = dso
pmDebug    = 32768 ( libpmda )
Timer      = off
Dump Instance Profile state=INCLUDE, 1 profiles
        Profile [0] indom=1061158913 [253.0] state=EXCLUDE 2 instances
                Instances: [2] [0]
dbpmda> quit

The watch command (usage: watch filename ) opens an xterm window which tails the specified log file. This window must be closed by the user when no longer required.

The wait command is equivalent to sleep (1) and takes a single integer argument.

The introduction of dynamic subtrees in the PMNS and PMDA_INTERFACE_4 in libpcp_pmda has led to additional commands being supported in dbpmda to exercise the associated dynamic PMNS services. The examples below are based on the sample PMDA.

$ dbpmda
dbpmda> open pipe /var/lib/pcp/pmdas/sample/pmdasample -d 29
Start pmdasample PMDA: /var/lib/pcp/pmdas/sample/pmdasample -d 29
dbpmda> children sample.secret
Metric: sample.secret
   non-leaf foo
       leaf bar
dbpmda> traverse sample.secret.foo
Metric: sample.secret.foo
dbpmda> pmid sample.secret.foo.bar.four
Metric: sample.secret.foo.bar.four
dbpmda> name 29.0.1006
PMID: 29.0.1006

The children command returns the next name component for all the direct descendants of a node within a dynamic subtree of the PMNS. The related traverse command returns the full metric names for all leaf nodes in the PMNS below the specified non-leaf node in a dynamic subtree of the PMNS.

The name and pmid commands exercise the translation of metric names to PMIDs (and vice versa) for metrics within a dynamic subtree of the PMNS.

If the commands children, traverse, pmid or name are used with a PMDA that is not using PMDA_INTERFACE_4 or with performance metric names that are not part of a dynamic subtree of the PMNS, then the PMDA would be expected to return errors (PM_ERR_NAME or PM_ERR_PMID) to reflect the fact that the operation is in error (outside a dynamic subtree of the PMNS it is pmcd(1) and not the PMDA that is responsible for implementing these functions).

Client authentication mechanisms have been incorporated into the PMCS, providing per-user (and per-connection) information that is available to PMDAs. A PMDA using PMDA_INTERFACE_6 or later in libpcp_pmda is able to make use of the "attribute" method to gain visibility into these authenticated connections, with access to information including user and group identifiers, user name, and so on. The need to exercise and debug this interface has led to a new dbpmda command. The following example is based on the sample PMDA.

$ dbpmda
dbpmda> open pipe pmdasample -D AUTH -l logfile
Start pmdasample PMDA: pmdasample -D AUTH -l logfile
dbpmda> attr "username" "tanya"
Attribute: username=tanya
dbpmda> attr 11 "0"
Attribute: userid=0

The attr command passes connection attributes (PCP_ATTR keys) and their values into a PMDA in much the same way that PMCD would for a client connection. dbpmda always passes a client context identifier of zero, and while no validity checking on values is performed only recognised attributes can be set.

In the example above the AUTH debug flag is set for the PMDA, which uses this in its attribute callback and records each attribute and value pair sent to it in its logfile.

Note that authentication checks have already been performed by PMCD by the time a PMDA is presented with these attributes, so no further verification is necessary by the PMDA.


A value cannot be stored into metrics of type PM_TYPE_AGGREGATE or PM_TYPE_EVENT.

dbpmda uses fork(2) and exec(2) to attach to daemon PMDAs. dbpmda makes no attempt to detect the termination of the daemon PMDA process, so it is possible for a PMDA to exit unexpectedly without any notification. However, any further communication attempts with the PMDA will result in errors which will indicate that the PMDA is no longer responding.


List of commands to do on startup.


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).