Tomcat Log Management

Tomcat generates several types of logs. Understanding each log's role and configuring it properly is essential for incident diagnosis and performance analysis. This chapter covers catalina.out, the Access Log Valve, and Log4j2 integration.

Tomcat Log Types

Log File	Description	Default Location
`catalina.out`	Tomcat stdout/stderr (main log)	`$CATALINA_HOME/logs/`
`catalina.YYYY-MM-DD.log`	java.util.logging daily log	`$CATALINA_HOME/logs/`
`localhost.YYYY-MM-DD.log`	Virtual host log	`$CATALINA_HOME/logs/`
`localhost_access_log.txt`	HTTP access log (Access Log Valve)	`$CATALINA_HOME/logs/`
`manager.YYYY-MM-DD.log`	Manager app log	`$CATALINA_HOME/logs/`

catalina.out

catalina.out is the core log capturing Tomcat start/stop, app deploy/undeploy, errors, and more.

# Real-time monitoring
tail -f /opt/tomcat/latest/logs/catalina.out

# Filter errors only
grep -E "(ERROR|SEVERE|Exception)" /opt/tomcat/latest/logs/catalina.out

# Last 100 lines + real-time
tail -100f /opt/tomcat/latest/logs/catalina.out

Warning: catalina.out is not rotated by default. During long-term operation the file grows unbounded — logrotate configuration is essential.

logging.properties — Base Log Configuration

Configure Tomcat's internal logger (java.util.logging) via conf/logging.properties.

# $CATALINA_HOME/conf/logging.properties

handlers = 1catalina.org.apache.juli.AsyncFileHandler, \
           2localhost.org.apache.juli.AsyncFileHandler, \
           java.util.logging.ConsoleHandler

.handlers = 1catalina.org.apache.juli.AsyncFileHandler, java.util.logging.ConsoleHandler

1catalina.org.apache.juli.AsyncFileHandler.level = FINE
1catalina.org.apache.juli.AsyncFileHandler.directory = ${catalina.base}/logs
1catalina.org.apache.juli.AsyncFileHandler.prefix = catalina.
1catalina.org.apache.juli.AsyncFileHandler.suffix = .log
1catalina.org.apache.juli.AsyncFileHandler.encoding = UTF-8

2localhost.org.apache.juli.AsyncFileHandler.level = FINE
2localhost.org.apache.juli.AsyncFileHandler.directory = ${catalina.base}/logs
2localhost.org.apache.juli.AsyncFileHandler.prefix = localhost.
2localhost.org.apache.juli.AsyncFileHandler.suffix = .log

java.util.logging.ConsoleHandler.level = FINE
java.util.logging.ConsoleHandler.formatter = org.apache.juli.OneLineFormatter
java.util.logging.ConsoleHandler.encoding = UTF-8

# Suppress unnecessary logs
org.apache.coyote.http11.Http11Processor.level = WARNING

Log Levels (java.util.logging)

Level	Description
`SEVERE`	Critical errors
`WARNING`	Warnings
`INFO`	General information (default)
`FINE`	Detailed debug
`FINER`	More detailed
`FINEST`	Maximum detail

Access Log Valve — HTTP Access Log

Add AccessLogValve inside the Host element in server.xml.

Basic Configuration

<Host name="localhost" appBase="webapps" ...>
    <Valve className="org.apache.catalina.valves.AccessLogValve"
           directory="logs"
           prefix="localhost_access_log"
           suffix=".txt"
           pattern="combined"/>
</Host>

Custom Pattern with Response Time

<Valve className="org.apache.catalina.valves.AccessLogValve"
       directory="logs"
       prefix="access_log"
       suffix=".txt"
       rotatable="true"
       fileDateFormat="yyyy-MM-dd"
       pattern="%h %l %u %t &quot;%r&quot; %s %b %D &quot;%{Referer}i&quot; &quot;%{User-Agent}i&quot;"/>

Pattern Variable	Description
`%h`	Remote host (IP)
`%l`	Remote logical username
`%u`	Authenticated user
`%t`	Request time
`%r`	Request line (method + URI + protocol)
`%s`	HTTP status code
`%b`	Response bytes
`%D`	Processing time (milliseconds)
`%T`	Processing time (seconds)
`%{Header}i`	Request header value

JSON Format

<Valve className="org.apache.catalina.valves.AccessLogValve"
       directory="logs"
       prefix="access_log"
       suffix=".json"
       pattern="{&quot;time&quot;:&quot;%t&quot;,&quot;method&quot;:&quot;%m&quot;,&quot;uri&quot;:&quot;%U%q&quot;,&quot;status&quot;:%s,&quot;bytes&quot;:%b,&quot;duration_ms&quot;:%D,&quot;ip&quot;:&quot;%h&quot;}"/>

Log4j2 Integration (Recommended)

For more powerful logging in Java applications, use Log4j2.

Dependencies (Maven)

<!-- pom.xml -->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.23.1</version>
</dependency>
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.23.1</version>
</dependency>
<!-- JUL → Log4j2 bridge -->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-jul</artifactId>
    <version>2.23.1</version>
</dependency>

log4j2.xml Configuration

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="60">

    <Properties>
        <Property name="LOG_DIR">/opt/tomcat/latest/logs</Property>
        <Property name="APP_NAME">myapp</Property>
        <Property name="LOG_PATTERN">%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n</Property>
    </Properties>

    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout pattern="${LOG_PATTERN}"/>
        </Console>

        <RollingFile name="AppLog"
                     fileName="${LOG_DIR}/${APP_NAME}.log"
                     filePattern="${LOG_DIR}/${APP_NAME}.%d{yyyy-MM-dd}.%i.log.gz">
            <PatternLayout pattern="${LOG_PATTERN}"/>
            <Policies>
                <TimeBasedTriggeringPolicy interval="1" modulate="true"/>
                <SizeBasedTriggeringPolicy size="100 MB"/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingFile>

        <RollingFile name="ErrorLog"
                     fileName="${LOG_DIR}/${APP_NAME}-error.log"
                     filePattern="${LOG_DIR}/${APP_NAME}-error.%d{yyyy-MM-dd}.log.gz">
            <PatternLayout pattern="${LOG_PATTERN}"/>
            <ThresholdFilter level="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
            <Policies>
                <TimeBasedTriggeringPolicy interval="1" modulate="true"/>
            </Policies>
            <DefaultRolloverStrategy max="30"/>
        </RollingFile>
    </Appenders>

    <Loggers>
        <Root level="INFO">
            <AppenderRef ref="Console"/>
            <AppenderRef ref="AppLog"/>
            <AppenderRef ref="ErrorLog"/>
        </Root>

        <Logger name="com.example.myapp" level="DEBUG" additivity="false">
            <AppenderRef ref="AppLog"/>
        </Logger>

        <!-- Suppress noisy library logs -->
        <Logger name="org.springframework" level="WARN"/>
        <Logger name="org.hibernate" level="WARN"/>
    </Loggers>

</Configuration>

logrotate Configuration (catalina.out Rotation)

# /etc/logrotate.d/tomcat
/opt/tomcat/latest/logs/catalina.out {
    daily
    rotate 14
    compress
    delaycompress
    missingok
    notifempty
    copytruncate          # Rotate without restarting Tomcat (important!)
    dateext
    dateformat -%Y%m%d
}

/opt/tomcat/latest/logs/*.log
/opt/tomcat/latest/logs/*.txt {
    daily
    rotate 30
    compress
    delaycompress
    missingok
    notifempty
    copytruncate
    dateext
}

# Test logrotate configuration
sudo logrotate -d /etc/logrotate.d/tomcat

# Force immediate rotation
sudo logrotate -f /etc/logrotate.d/tomcat

Practical Log Analysis

# Analyze slow requests (processing time > 1000ms)
awk '{ if ($NF > 1000) print }' /opt/tomcat/latest/logs/localhost_access_log*.txt

# Count 500 error requests
awk '{print $9}' /opt/tomcat/latest/logs/localhost_access_log*.txt | \
  grep "^5" | sort | uniq -c | sort -rn

# Average response time for a specific URL
awk '/\/api\/users/ {sum+=$NF; cnt++} END {print "Avg:", sum/cnt "ms"}' \
  /opt/tomcat/latest/logs/localhost_access_log*.txt

# Check OutOfMemoryError occurrences
grep -c "OutOfMemoryError" /opt/tomcat/latest/logs/catalina.out

Summary

Log	Configuration Location	Key Role
catalina.out	Systemd service or bin/catalina.sh	Tomcat-wide events
java.util.logging	conf/logging.properties	Internal Tomcat components
Access Log	server.xml AccessLogValve	HTTP access records
Log4j2	WEB-INF or classpath	Structured app-level logging
logrotate	/etc/logrotate.d/tomcat	catalina.out file size control

Tomcat Log Types​

catalina.out​

logging.properties — Base Log Configuration​

Log Levels (java.util.logging)​

Access Log Valve — HTTP Access Log​

Basic Configuration​

Custom Pattern with Response Time​

JSON Format​

Log4j2 Integration (Recommended)​

Dependencies (Maven)​

log4j2.xml Configuration​

logrotate Configuration (catalina.out Rotation)​

Practical Log Analysis​

Summary​