Crash on Linux produces no core or truncated core

Follow these directions in order, unless directed by IBM support.

NOTE: The settings below require a restart of your application server. If you also use a nodeagent to start your server(s), you will need to restart this as well. Changing ulimit settings additionally require the restart to occur on the same command line (or terminal) session.

1. Setting Ulimits
See Also: Guidelines for Setting Ulimits

To set ulimits on the core and file sizes to unlimited, run these two commands as the user who starts the nodeagent and/or application server

ulimit -c unlimited ulimit -f unlimited

You can run ulimit -a to verify current ulimit settings.

Ulimits can also be altered at a global level. See the FAQ for more information.



2. Verifying Hard Disk Space

Check your partitions where WebSphere Application Server resides and make sure there is enough space for the dump to be produced. Usually an error message will be seen in the native_stderr.log that indicates if the core was unable to be written.

To check all of your partitions, execute this command:

df -k

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Additional steps if still unable to capture a core file


3. Disable Signal Handlers

Sometimes a loaded library or external process can trap some signals, especially signal 3 and 11, which prevent any core file generation by the JVM.

a. Disable MQ Signal Traps

WebSphere MQ is known to trap a subset of signals that the JVM also uses. If you are using WebSphere MQ, or are not sure, simply add this environment variable to your configuration:




name:  MQS_NO_SYNC_SIGNAL_HANDLING value: true




b. Disable All Signal Handlers

To force the operating system to handle all signals sent to the JVM process, you can disable all JVM signal handlers.

For IBM SDK 5.0 and later, set this JVM argument:

-Xrs NOTE: On SDK 6.0, to prevent unintentional crashes due to SIGTRAP, clear the shared class cache by executing <WAS_HOME>/bin/clearClassCache.sh


For prior versions of the IBM SDK, set this environment variable:

name:  IBM_NOSIGHANDLER value: true

4. Disable Javacore Generation

On rare instances, disabling javacore generation will help produce a core file.
To disable, simply add the following environment variable:

name:  DISABLE_JAVADUMP value: true

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Frequently Asked Questions (FAQ)

What happens if I do not have write permission in the profile's root directory, or the directory I am redirecting javacores, heapdumps, and system core files to?

This will result in a failure when writing these files to the system. The error may be recorded in the native_stderr.log.



Even with all ulimit settings set to unlimited, core files are truncated at 2GB?

This is a limitation on 32-bit processes. You can avoid this issue if you enable large file support on the operating system, or use a 64-bit version of WebSphere Application Server.

Additionally, running out of free space can cause file truncation.



Can I test my configuration to see if a core can be generated?

Yes you can simulate a crash by sending a signal 6 to the JVM process. This will terminate the process.

kill -6 PID

An alternative is to use the gcore command. This will produce a core file and will allow the process to continue running.

gcore PID

Are ulimit settings permanent?

No, they are temporary and last as long as the session is alive. Ulimits are set on a per user basis, and the settings are applied per session, such as a command-line window. If a brand new session is started, and is not spawned from the current session, the ulimits will load the defaults.



Can I set ulimit settings globally?
By editing the /etc/security/limit.conf file, ulimit settings can be set globally.

However, if the application server is started by the init process at startup, these settings will not take effect. You will need to use the ulimt command line settings directly in the init.d script.



Where can core files be generated?

Normally found in the profile's root directory, but can be in a number of alternative locations. Try searching in these locations first:

• <WAS_HOME>/profiles/<PROFILE_NAME>
• <WAS_HOME>/bin/
• /tmp

If you cannot find a core file in any of these locations, search your entire machine for core* files.

On the IBM SDK, the environment variable IBM_COREDIR can be used to redirect core dumps to another location on the filesystem.