2440: 141 Web Site Administration Web Server Monitoring and Analysis Instructor: Enoch E. Damson

Monitoring and Analyzing Systems Monitoring operating systems, Web servers, applications, etc typically involves analyzing log files Log files – contain information recorded by the operating system in response to certain events Monitoring and Analyzing the Web Server Environment2

Monitoring Operating Systems Logs are used to detect problems OS, application, or security problems Various tools can monitor performance Monitoring and Analyzing the Web Server Environment3

Monitoring Windows Performance monitoring allows you to compare system performance over time Windows Task Manager highlights CPU and memory usage You can modify services to notify you if a service fails Monitoring and Analyzing the Web Server Environment4

Windows Event Viewer The event viewer contains six event types shown in the left pane Monitoring and Analyzing the Web Server Environment5

Windows Event Logs System and application events display three levels of messages Information Warning Error Because many messages can be generated, a filter focuses on what you want to see Over time, the logs fill up so you should clear them or save them Monitoring and Analyzing the Web Server Environment6

Monitoring Linux Logging is controlled by the syslogd daemon Below are some facilities which represent daemons using syslogd Monitoring and Analyzing the Web Server Environment7

Eight Levels of Message Priorities in syslogd Monitoring and Analyzing the Web Server Environment8

Web Server Log Files Files that keep track of Web server transactions Most Web servers write two log files to disk: Access log – contains a line for each Web server request Error log – contains a line for each generated error response When log files grow: A common practice is to put the log files on a separate drive or partition A better solution is to rotate the log files Rename or remove the log files at regular intervals (weekly, monthly, etc) Monitoring and Analyzing the Web Server Environment9

Web Server Log File Formats Most Web servers support at least two logging formats: Common Logfile Format (CLF) Extended Logfile Format (ELF) Most Web servers also allow the administrator to specify a custom format, along with the above formats A standard logfile format makes it easier for users to understand files from different servers Allows third-party logfile analysis tools to support many different Web servers Monitoring and Analyzing the Web Server Environment10

Common Logfile Format (CLF) The NCSA and CERN Web servers first used this file format Many Web servers now support this format (IIS, Apache, Netscape Enterprise, etc) Each line in the file represents a unique request Has a fixed format with seven fields to be logged: remotehost rfc1413 authuser [date] “request” status bytes Monitoring and Analyzing the Web Server Environment11

Common Logfile Format… remotehost – remote (client) hostname or IP number rfc1413 – remote username rfc1413 defines a protocol used to determine the identity of a client that requests a resource from the server Seldom used on Internet servers because it slows the server’s response A “-” is entered into the log if the server is unable to determine a userid authuser – when required, the username by which the user has authenticated is provided A “-” is used for normal unrestricted requests [date] – date and time of the request Enclosed in brackets for potential spaces “request” – HTTP request line exactly as it came from the client Enclosed in quotes for potential spaces status – HTTP status code returned to the client bytes – content length of document transferred Example: [24/Oct/2006:09:11: ] "GET /test.asp HTTP/1.1" Monitoring and Analyzing the Web Server Environment12

Extended Logfile Format (ELF) Used to log more information or omit certain fields Allows the administrator to specify exactly which fields to log and in what order Each represents a request like CLFs but the beginning of the file also contains some configuration directives Each directive line begins with a # Two directives are required and must precede all entries in the log file: Version – specifies the version of the ELF to use Fields – specifies what data to record in the logfile Monitoring and Analyzing the Web Server Environment13

Extended Logfile Format… Example: #Software: Microsoft Internet Information Services 5.1 #Version: 1.0 #Date: :04:57 #Fields: date time c-ip cs-method cs-uri-stem sc-status sc-bytes cs-version :04: GET /test.asp HTTP/1.1 The fields directive here specifies 8 out of several available fields: date – client request date time – client request time c-ip – client IP address cs-method – HTTP request method cs-uri-stem – file requested by client sc-status – HTTP status code returned to the client sc-bytes – number of bytes sent from server to client cs-version – version of HTTP used by client to connect to the server Monitoring and Analyzing the Web Server Environment14

Error Logs Contains informational messages and debugging information Useful for: Finding problems with the server Debugging server-side programs and new configurations Most server packages allow the administrator to control what types of messages are logged to the error log file The format is usually not configurable like ELFs but allows some flexibility in choosing the severity and type of messages to log E.g only critical messages may be logged if a server is running smoothly Monitoring and Analyzing the Web Server Environment15

Referrers Determines what Web page was used by the client to access a server May be the URL of a search engine or any Web site with a link to the Web server A “-” is used if there was no Referrer header sent The Referrer header is not sent in the following circumstances: The users enters the URL by hand The user clicked on a link to regular file and not a Web page on a public site The user loaded the URL from a bookmark file The Referrer URL is on a private (internal) Web site The user or browser has disabled sending the Referrer header Monitoring and Analyzing the Web Server Environment16

Monitoring IIS IIS has specific counters for use in the Performance Monitor The System event viewer provides specific information IIS has extensive logging capabilities There are default log formats used by various third-party applications that analyze logs Monitoring and Analyzing the Web Server Environment17

Monitoring Apache Error Logs By default, syslogd sends Apache messages to /var/log/boot.log Location of the error log ErrorLog logs/error_log Logs refers to /var/log/httpd You can create a different error log for each virtual host Monitoring and Analyzing the Web Server Environment18

Monitoring Apache Transfer Logs Transfer logs tell you about the use of your Web site The default log is based on a combined format Determined by the CustomLog directive in the configuration file (httpd.conf) There are a number of sample formats By default, logs are stored in /var/log/httpd/access_log Monitoring and Analyzing the Web Server Environment19

Monitoring DNS BIND uses a logging statement that you configure in named.conf BIND defines logging in two parts: Channel defines where logging is sent Category defines what will be sent If the channel is going to a file, use the versions option to define the number of backups Size option sets maximum size of the file print-time adds the date and time to the file Monitoring and Analyzing the Web Server Environment20

BIND Categories Monitoring and Analyzing the Web Server Environment21

Monitoring Exchange Server Exchange server uses the application portion of Event viewer You can enable four types of logs audit – access to mailboxes protocol – commands used for SMTP, etc message tracking – senders and receivers diagnostic – analyze detailed problems Monitoring and Analyzing the Web Server Environment22

Analysis Tools for the Web Server Analysis tools extract system data from logs and format the data For IIS, one of the popular tools is WebTrends Helps you determine the source of Web traffic Determines which pages are most popular Several different reports 123LogAnalyzer is available for both IIS and Apache Many reports are similar to WebTrends Monitoring and Analyzing the Web Server Environment23

Log File Analysis Simply looking at log files can provide a lot of information about activities or requests on a server Simply counting the number of lines in an access log file can help determine the number of hits Log files may be reviewed regularly to find the common errors logged Some of the common errors include: Dead links Requests for non-existing files CGI scripts not working properly Permissions problems Some of the open-source log analyzers are: Analog ( Webalizer ( Report Magic ( Monitoring and Analyzing the Web Server Environment24

Statistics With the help of several log analyzer programs, some of the statistical information that can be extracted include: Most requested pages Top entry pages (the first page clients enter a site through) Most used browsers Bandwidth utilization Most active domains Top referring sites and URLs Error counts Information about search engines (most common search engines, common queries, etc) Some of the widely used commercial log analyzer products include: WebTrends ( Wusage ( A database could also be used to store log information to increase efficiency of logging and report generation Not all Web servers support logging to a database Monitoring and Analyzing the Web Server Environment25