Symptoms

JIRA fails to start due to a NoClassDefFoundError for org/apache/log4j/Appender.

The following appears in the atlassian-jira.log:

java.lang.NoClassDefFoundError: org/apache/log4j/Appender
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:58)

Cause

This typically happens because some classes are missing from the $JIRA_INSTALL/lib/ directory, in this case the log4j class. These classes are jar files which can be checked through file system.

Resolution

1. Verify if the JAR exists within the $JIRA_INSTALL/lib directory.
2. If not, download the JIRA version from our downloads archive (this will either be a tarball or a ZIP, depending on the OS. Do not download the installer version).
3. Extract it into a temporary directory and add in the missing JAR file from the downloaded archive into the $JIRA_INSTALL/lib directory.
4. Start Jira.