pmdaweblog (1) - Linux Manuals

pmdaweblog: performance metrics domain agent (PMDA) for Web server logs


pmdaweblog - performance metrics domain agent (PMDA) for Web server logs


$PCP_PMDAS_DIR/weblog/pmdaweblog [-Cp] [-d domain] [-h helpfile] [-i port] [-l logfile] [-n idlesec] [-S num] [-t delay] [-u socket] [-U username] configfile


pmdaweblog is a Performance Metrics Domain Agent (PMDA(3)) that scans Web server logs to extract metrics characterizing Web server activity. These performance metrics are then made available through the infrastructure of the Performance Co-Pilot (PCP).

The configfile specifies which Web servers are to be monitored, their associated access logs and error logs, and a regular-expression based scheme for extracting detailed information about each Web access. This file is maintained as part of the PMDA installation and/or de-installation by the scripts Install and Remove in the directory $PCP_PMDAS_DIR/weblog. For more details, refer to the section below covering installation.

Once started, pmdaweblog monitors a set of log files and in response to a request for information, will process any new information that has been appended to the log files, similar to a tail(1). There is also periodic "catch up" to process new information from all log files, and a scheme to detect the rotation of log files.

Like all other PMDAs, pmdaweblog is launched by pmcd(1) using command line options specified in $PCP_PMCDCONF_PATH - the Install script will prompt for appropriate values for the command line options, and update $PCP_PMCDCONF_PATH.

A brief description of the pmdaweblog command line options follows:

Check the configuration and exit.
-d domain
Specify the domain number. 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 pmdaweblog PMDA on all hosts.

For most installations, the default domain as encapsulated in the file $PCP_PMDAS_DIR/weblog/domain.h will suffice. For alternate values, check $PCP_PMCDCONF_PATH for the domain values already in use on this host, and the file $PCP_VAR_DIR/pmns/stdpmid contains a repository of ``well known'' domain assignments that probably should be avoided.

-h helpfile
Get the help text from the supplied helpfile rather than from the default location.
-i port
Communicate with pmcd(1) on the specified Internet port (which may be a number or a name).
-l logfile
Location of the log file. By default, a log file named weblog.log is written in the current directory of pmcd(1) when pmdaweblog 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.
-n idlesec
If a Web server log file has not been modified for idlesec seconds, then the file will be closed and re-opened. This is the only way pmdaweblog can detect any asynchronous rotation of the logs by Web server administrative scripts. The default period is 20 seconds. This value may be changed dynamically using pmstore(1) to modify the value of the performance metric web.config.check.
Communicate with pmcd(1) via a pipe.
-S num
Specify the maximum number of Web servers per sproc. It may be desirable (from a latency and load balancing perspective) or necessary (due to file descriptor limits) to delegate responsibility for scanning the Web server log files to several sprocs. pmdaweblog will ensure that each sproc handles the log files for at most num Web servers. The default value is 80 Web servers per sproc.
-t delay
To avoid the need to scan a lot of information from the Web server logs in response to a single request for performance metrics, all log files will be checked at least once every delay seconds. The default is 15 seconds. This value may by changed dynamically using pmstore(1) to modify the value of the performance metric web.config.catchup.
-u socket
Communicate with pmcd(1) via the given Unix domain socket.
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.


The PCP framework allows metrics to be collected on one host and monitored from another. These hosts are referred to as collector and monitor hosts, respectively. A host may be both a collector and a monitor.

Collector hosts require the installation of the agent, while monitoring hosts require no agent installation at all.

For collector hosts do the following as root:

# cd $PCP_PMDAS_DIR/weblog
# ./Install

The installation procedure prompts for a default or non-default installation. A default installation will search for known server configurations and automatically configure the PMDA for any server log files that are found. A non-default installation will step through each server, prompting the user for other server configurations and arguments to pmdaweblog. The end result of a collector installation is to build a configuration file that is passed to pmdaweblog via the configfile argument.

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

# cd $PCP_PMDAS_DIR/weblog
# ./Remove

pmdaweblog 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.


The configuration file for the weblog PMDA is an ASCII file that can be easily modified. Empty lines and lines beginning with '#' are ignored. All other lines must be either a regular expression or server specification.

Regular expressions, which are used on both the access and error log files, must be of the form:

regex regexName regexp or

regex_posix regexName ordering regexp_posix

The regexName is a word which uniquely identifies the regular expression. This is the reference used in the server specification. The regexp for access logs is in the format described for regcmp(3). The regexp_posix for access logs is in the format described for regcomp(3). The argument ordering is explained below. The Posix form should be available on all platforms.

The regular expression requires the specification of up to four arguments to be extracted from each line of a Web server access log, depending on the type of server. In the most common case there are two arguments representing the method and the size.

For the non- Posix version, argument $0 should contain the method: GET, HEAD , POST or PUT. The method PUT is treated as a synonym for POST, and anything else is categorized as OTHER.

The second argument, $1, should contain the size of the request. A size of ``-'' or `` '' is treated as unknown.

Argument $3 should contain the status code returned to the client browser and argument $4 should contain the status code returned to the server from a remote host. These latter two arguments are used for caching servers and must be specified as a pair (or $3 will be ignored). For further information on status codes, refer to the web site

Some legal non- Posix regex expression specifications for monitoring an access log are:

# pattern for CERN, NCSA, Netscape etc Access Logs
regex CERN ] "([A-Za-z][-A-Za-z]+)$0 .*" [-0-9]+ ([-0-9]+)$1

# pattern for FTP Server access logs (normally in SYSLOG)
regex SYSLOG_FTP ftpd[.*]: ([gp][-A-Za-z]+)$0( )$1

There is 1 special types of access logs with the RegexName SQUID. This formats extract 4 parameters but since the Squid log file uses text-based status codes, it is handled as a special case.

In the examples below, NS_PROXY parses the Netscape/W3C Common Extended Log Format and SQUID parses the default Squid Object Cache format log file.

# pattern for Netscape Proxy Server Extended Logs
regex NS_PROXY ] "([A-Za-z][-A-Za-z]+)$0 .*" ([-0-9]+)$2 \
([-0-9]+)$1 ([-0-9]+)$3

# pattern for Squid Cache logs
regex SQUID [0-9]+.[0-9]+[ ]+[0-9]+ [a-zA-Z0-9.]+ \
([_A-Z]+)$3/([0-9]+)$2 ([0-9]+)$1 ([A-Z]+)$0

The regexp for the error logs does not require any arguments, only a match. Some legal expressions are:

# pattern for CERN, NCSA, Netscape etc Error Logs
regex CERN_err .

# pattern for FTP Server error logs (normally in SYSLOG)

If POSIX compliant regular expressions are used, additional information is required since the order of parameters cannot be specified in the regular expression. For backwards compatibility, the common case of two parameters the order may be specified as method,size or size,method In the general case, the ordering is specified by one of the following methods:

where nX is a digit between 1 and 4. Each comma-seperated field represents (in order) the argument number for method,size,client_status,server_status
Used for cases like the error logs where the content is ignored.

As for the non- Posix format, the SQUID RegexName is treated as a special case to match the non-numerical status codes.

Some legal Posix regex expression specifications for monitoring an access log are:

# pattern for CERN, NCSA, Netscape, Apache etc Access Logs
regex_posix CERN method,size ][ \]+"([A-Za-z][-A-Za-z]+) \
[^"]*" [-0-9]+ ([-0-9]+)

# pattern for CERN, NCSA, Netscape, Apache etc Access Logs
regex_posix CERN 1,2 ][ \]+"([A-Za-z][-A-Za-z]+) \
[^"]*" [-0-9]+ ([-0-9]+)

# pattern for FTP Server access logs (normally in SYSLOG)
regex_posix SYSLOG_FTP method,size ftpd[.*]: \
([gp][-A-Za-z]+)( )

# pattern for Netscape Proxy Server Extended Logs
regex_posix NS_PROXY 1,3,2,4 ][ ]+"([A-Za-z][-A-Za-z]+) \
[^"]*" ([-0-9]+) ([-0-9]+) ([-0-9]+)

# pattern for Squid Cache logs
regex_posix SQUID 4,3,2,1 [0-9]+.[0-9]+[ ]+[0-9]+ \
[a-zA-Z0-9.]+ ([_A-Z]+)/([0-9]+) ([0-9]+) ([A-Z]+)

# pattern for CERN, NCSA, Netscape etc Error Logs
regex_posix CERN_err - .

# pattern for FTP Server error logs (normally in SYSLOG)

A Web server can be specified using this syntax:

server serverName on|off accessRegex accessFile errorRegex errorFile

The serverName must be unique for each server, and is the name given to the instance for the associated performance metrics. See PMAPI(3) for a discussion of PCP instance domains. The on or off flag indicates whether the server is to be monitored when the PMDA is installed. This can altered dynamically using pmstore(1) for the metric web.perserver.watched, which has one instance for each Web server named in configfile.

Two files are monitored for each Web server, the access and the error log. Each file requires the name of a previously declared regular expression, and a file name. The log files specified for each server do not have to exist when the weblog PMDA is installed. The PMDA will continue to check for non-existent log files and open them when possible. Some legal server specifications are:

# Netscape Server on Port 80 at IP address 127.55.555.555
server 127.55.555.555:80 on CERN /logs/access CERN_err /logs/errors

# FTP Server.
server ftpd on SYSLOG_FTP /var/log/messages SYSLOG_FTP_err /var/log/messages


Specifying regular expressions with an incorrect number of arguments, anything other than 2 for access logs, and none for error logs, may cause the PMDA to behave incorrectly and even crash. This is due to limitations in the interface of regex(3).


installation directory for the weblog PMDA
installation script for the weblog PMDA
de-installation script for the weblog PMDA
default log file for error reporting
pmcd configuration file that specifies the command line options to be used when pmdaweblog is launched
log of PMDA installations and removals
likely location of the weblog PMDA configuration file
the online HTML documentation for PCPWEB


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).


pmcd(1), pmchart(1), pmdawebping(1), pminfo(1), pmstore(1), pmview(1), tail(1), weblogvis(1), webvis(1), PMAPI(3), PMDA(3) and regcmp(3).