NAME¶

pmwebd - bridge client PMAPI to HTTP

SYNOPSIS¶

pmwebd [ -p port] [ -4] [ -6] [ -t timeout] [ -R resdir] [ -c number] [ -h hostname] [ -a archive] [ -L] [ -N] [ -K spec] [ -A archdir] [ -f] [ -l logfile] [ -U username] [ -x file] [ -v] [ -?]

DESCRIPTION¶

pmwebd is a long-running network daemon. It binds a subset of the Performance Co-Pilot (PCP) client API (PMAPI) to RESTful web applications using the HTTP (PMWEBAPI) protocol. Web clients request a URI with the prefix /pmapi to access the bindings. pmwebd creates dynamic PCP contexts as requested by a dynamic pool of remote clients, and maintains them as long as the clients regularly reconnect to request PMAPI operations. Otherwise, PCP contexts are closed after a timeout. Permanent contexts may be requested on the command line. In addition to the API binding, pmwebd may be optionally configured as a simple HTTP file server, in order to feed the web application itself to a web browser. URIs not matching the /pmapi prefix are mapped to files under the configured resource directory, if the -R option was given. The options to pmwebd are as follows.

-p port

Set the TCP port number on which pmwebd will listen for HTTP requests. The default is 44323.

-4 or -6

Listen only on IPv4 or IPv6. By default, pmwebd will listen on both protocols, if possible.

-R resdir

Activate file serving beneath the given resource directory. All regular files there may be read & transcribed to remote clients. By default, file serving is disabled.

-t timeout

Set the maximum timeout (in seconds) after the last operation on a web context, before it is closed by pwmebd. A smaller timeout may be requested by the web client.

-c number

Reset the next PMWEBAPI permanent context identifier as given. The default is 1.

-h hostname or -a archive or -L

Assign the next permanent PMWEBAPI context identifier to a PMAPI connection to the given host (with an extended syntax as given in PCPIntro(1)), or archive file, or the PM_CONTEXT_LOCAL.

-A archdir

Limit remote new-context requests for archives to beneath the given directory. By default, only files beneath the initial working directory may be accessed.

-N

Disable creation of new PMWEBAPI contexts via HTTP requests, leaving only permanent ones accessible.

-K spec

When fetching metrics from a local context, the -K option may be used to control the DSO PMDAs that should be made accessible. The spec argument conforms to the syntax described in __pmSpecLocalPMDA(3). More than one -K option may be used.

-f

By default pmwebd is started as a daemon. The -f option indicates that it should run in the foreground. This is most useful when trying to diagnose problems with establishing connections.

-l logfile

By default a log file named pmwebd.log is written in the current directory. The -l option causes the log file to be written to logfile instead of the default. If the log file cannot be created or is not writable, output is written to the standard error instead.

-U username

Assume the identity of username before starting to accept incoming requests from web clients.

-x file

Before the pmwebd logfile can be opened, pmwebd may encounter a fatal error which prevents it from starting. By default, the output describing this error is sent to /dev/tty but it may redirected to file.

-v

Increase the verbosity of the pmwebd program as it logs to its standard error.

-?

Show pmwebd invocation help and exit.

SECURITY¶

The current release of pmwebd is suitable for direct exposure to trusted networks only, due to several security limitations. Most or all of these limitations may be worked around by use of a web application firewall (for example, an Apache HTTPD proxy), which would add the constraints and capabilities absent within pmwebd. Such configuration is beyond the scope of this document.

encryption/confidentiality

The pmwebd program is does not currently support HTTPS (SSL/TLS), so the HTTP traffic is not protected against network-level attacks.

authentication

The PMAPI layer does not possess a mandatory authentication mechanism, so any remote connection can access any metric exposed by suchly connected PMAPI contexts. However, a new host-context string may use authentication clauses of the longer host URLs, for example pcps://hostname?method=plain&user=userid&pass=password.

inbound admission control

The pmwebd program does not impose ACLs on the origin or rate of its incoming requests. It may be possible for some clients to starve others.

outbound admission control

The pmwebd program does not impose ACLs on outbound connections when a new PMAPI context is created for a remote third-party PMCD. For an archive type context, the files must be located under the pmwebd current directory, or another directory specified by -A. One may entirely disable remotely specified PMAPI context creation using the -N option; in this case, specify a static set of contexts using the -h , -a , and/or -L options. You may assign them arbitrary context numbers with the -c option.

context ownership

Authenticated PCP contexts are protected by requiring the same HTTP PLAIN/simple userid/password credentials for related /pmapi requests. However, unauthenticated contexts for different web clients are kept distinct only by the assignment of large pseudorandom identifiers. It may be possible to find these by brute-force search or other techniques, thereby letting a web client impersonate another. For more privacy of the permanent contexts, use the -c option to reset their starting web context identifiers to a number much different from 1. On the other hand, context ownership is not that precious, since there exist no state-destructive operations for them, except perhaps instance profile settings.

STARTING AND STOPPING PMWEBD¶

Normally, pmwebd is started automatically at boot time and stopped when the system is being brought down. Under certain circumstances it is necessary to start or stop pmwebd manually. To do this one must become superuser and type # $PCP_RC_DIR/pmwebd start to start pmwebd, or # $PCP_RC_DIR/pmwebd stop to stop pmwebd. Starting pmwebd when it is already running is the same as stopping it and then starting it again.

FILES¶

PCP_PMWEBDOPTIONS_PATH

command line options and environment variable settings for pmwebd when launched from $PCP_RC_DIR/pmwebd All the command line option lines should start with a hyphen as the first character. This file can also contain environment variable settings of the form "VARIABLE=value".

./pmwebd.log

(or $PCP_LOG_DIR/pmwebd/pmwebd.log when started automatically)

 

All messages and diagnostics are directed here

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).

SEE ALSO¶

PCPIntro(1), PMAPI(3), PMWEBAPI(3), pcp.conf(5), pcp.env(5) and pmns(5).