This documentation is intended for internal Performance Co-Pilot
(PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed to
remain fixed across releases, and they may not work, or may provide
different semantics at some point in the future.
Given a PCP service name, as identified by service, and using the
type of discovery optionally specified in mechanism,
pmDiscoverServices returns, via urls, a list of URLs representing the
services discovered on the network.
The internal function __pmDiscoverServicesWithOptions performs the
same function and adds arguments for global options and a mechanism
for interrupting the discovery process.
The pmfind(1) utility provides command line access to both of these
pmDiscoverServices(service, mechanism, urls)
is equivalent to calling
__pmDiscoverServicesWithOptions(service, mechanism, NULL, NULL,
service specifies the PCP service to be discovered. Currently
supported services are PM_SERVER_SERVICE_SPEC and
PM_PROXY_SERVICE_SPEC which search for pmcd(1), and pmproxy(1)
mechanism specifies the style of discovery to be used.
The currently supported mechanisms are:
avahi This searches for services which are broadcasting using mDNS
via avahi-daemon(8). An optional suffix ",timeout=N" may be
added to specify the discovery timeout in floating-point
multiples of one second. The default timeout is 0.5 seconds,
which may be overridden by the AVAHI_DISCOVERY_TIMEOUT
environment variable, also specified in floating-point
multiples of one second. If both are specified, then the
value specified in the environment variable takes precedence.
Actively probes the given subnet for the requested PCP
service(s). <net-address> is an inet or ipv6 network address
and <mask-bits> is the number of bits used to define the
subnet. For example, 192.168.1.0/24 defines an 8 bit subnet
consisting of the addresses 192.168.1.0 through 192.168.1.255.
An optional suffix ",maxThreads=N" may be added to limit the
number of threads used while probing. The default is the
value of FD_SETSIZE (which is typically 1024) or the number of
addresses in the subnet, whichever is less. An optional
suffix ",timeout=N" may be added to specify the timeout for
each connection attempt in floating-point multiples of one
second. The default is 0.02 seconds (20 milliseconds).
shell Probes the list of addresses provided by scripts for requested
PCP service(s). Several optional, comma-separated parameters
can also be provided. Firstly, the "path=DIR" option
specifies the directory where commands like pcp-kube-pods(1)
are located (defaults to $PCP_BINADM_DIR/discover/). This
setting can be further restricted to an individual command
using the command=CMD option, but the default is to use all
available commands from the path. The "maxThreads=N" option
limits the number of threads used while probing. The default
is the value of FD_SETSIZE (which is typically 1024) or the
number of addresses returned by the scripts, whichever is
less. The "timeout=N" option may be added to limit the amount
of time spent waiting for each connection attempt. N is a
floating point number specifying the number of seconds to
wait. The default is 0.02 seconds (20 milliseconds).
mechanism may also be NULL, which means to use all available
For __pmDiscoverServicesWithOptions, optionsString specifies global
options to be applied to the discovery process. Options are comma-
separated and may be one or more of the following:
This requests that DNS name resolution be attempted for the
addresses of any discovered services.
This specifies a timeout period after which the discovery
process will be interrupted. N is a floating point number
representing the number of seconds before timing out.
optionsString may also be NULL, which means that no global options
For __pmDiscoverServicesWithOptions, flags specifies a pointer to an
object of type unsigned which is a bit mask of options/status flags
for the discovery process. The supported flags are:
Specifying this flag is equivalent to specifying resolve in
This flag must be unset when calling
__pmDiscoverServicesWithOptions but may be set asynchronously
(by an interrupt handler, for example) in order to interrupt
the service discovery process.
flags may also be NULL, which indicates that no flags are set.
pmDiscoverServices and __pmDiscoverServicesWithOptions will return
the number of services discovered, else a value less than zero for an
error. The value zero indicates that no services were discovered.
The resulting list of pointers, urls, and the values (the URLs) that
the pointers reference will have been allocated by pmDiscoverServices
or __pmDiscoverServicesWithOptions with a single call to malloc(3),
and it is the responsibility of the pmDiscoverServices or
__pmDiscoverServicesWithOptions caller to free(urls) to release the
space when it is no longer required.
When an error occurs, or no services are discovered, urls is
undefined (no space will have been allocated, and so calling free(3)
is a singularly bad idea).
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). Values for these
variables may be obtained programmatically using the pmGetConfig(3)
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at ⟨http://www.pcp.io/⟩.
If you have a bug report for this manual page, send it to
firstname.lastname@example.org. This page was obtained from the project's upstream
Git repository ⟨https://github.com/performancecopilot/pcp.git⟩ on
2020-08-13. (At that time, the date of the most recent commit that
was found in the repository was 2020-08-11.) If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
Performance Co-Pilot PCP PMDISCOVERSERVICES(3)