Develop Reference

tomcat not generating hprof file on outofmemory error

I have some memory leak issue in my web app which is deployed in tomcat. To find the root cause I enabled the HeapDumpOnOutOfMemory error by setting:
-XX:-HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/usr/local/tomcat/logs
and the memory settings in the tomcat is:
-Xms256m -Xmx768m -XX:PermSize=128m -XX:MaxPermSize=256m
When the out of memory issue happened, I see
java.lang.OutOfMemoryError: Java heap space
on the tomcat log file, but the .hprof file is not generated. Am I missing some settings here?

As #beny23 wrote you should use -XX:+HeapDumpOnOutOfMemoryError
and as is stated here:
The -XX:HeapDumpOnOutOfMemoryError Option This option tells the Java
HotSpot VM to generate a heap dump when an allocation from the Java
heap or the permanent generation cannot be satisfied. There is no
overhead in running with this option, so it can be useful for
production systems where the OutOfMemoryError exception takes a long
time to surface.
Check also your Java version since this option was introduced in 1.4.2 update 12, 5.0 update 7.

Increasing Java Heap Size

I'm trying to increase value of heap size of my jvm, but it doesn't work. Could anybody help me with this geek problem?
My configuration are follow: Windows 7 x64, 4 GB, i3 CPU
When I try something like -Xmx2000M I have nothing
Where are my errors?

I think you are expecting this.
$ java -Xmx2000M -Xms1000M -XshowSettings:all
VM settings:
Min. Heap Size: 1000.00M
Max. Heap Size: 1.95G
Ergonomics Machine Class: server
Using VM: Java HotSpot(TM) 64-Bit Server VM

Your command is half correct. You need to specify what you want to run with an increased heap size. Something like this
java -Xmx2000M -Xms1000M -jar <jar-file-name>.jar

you need to specify as well which class/jar you want to run. You cannot just increase the heap size per default for all java pplications. Instead you have to edit the command line of the program you are trying to run.

The error you have got in the last screen shot is about unavailability of the class file to run.
You should provide class file which includes main function while running java command.
java -Xmx2000M -Xms1000m MyClass
Considering you have MyClass.class in your classpath.

You need to provide something for JVM to run with these new settings.
The arguments you are using only configure the JVM, it still needs whatever jar or class file you want to run.
To permanently configure JVM profile on windows, follow these Instructions. The settings tool will let you edit runtime parameters:

may be I am late)
But I think you can use it. In IDEA choose Edit Configuration... on drop-down list(look on picture below). And then type in VM Options your parameters -Xmx2000M -Xms1000M.
How to find Edit Configuration on IDEA

Java 7 trigger heap dump without having JDK installed

How can I trigger a heap dump for a Java 7 VM running on Linux without having a JDK installed?
In earlier versions of Java it was possible to set the -XX:+HeapDumpOnCtrlBreak JVM option and then trigger a heap dump by using kill -QUIT <pid>. I have been unable to get this to work with Java 7. Is there an equivalent to this without needing the JDK installed to get JVisualVM or jmap.

VM option -XX:+HeapDumpOnCtrlBreak is no longer listed at http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html. So, I conclude that it's no longer supported.
From http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html:
Options that are specified with -XX are not stable and are subject to
change without notice.

You can generate a core dump with gcore, move it to another machine, and attach jmap to generate hprof file as described in Core dump taken with gcore, jmap conversion to hprof file format fails with Error message
See also accepted answer.

Could not create the Java virtual machine

facing some problem with java virtual machine initialization. when i am using root account i can properly work with java. but when i am a user account it returns following errors
user#host# $JAVA_HOME/bin/java -version
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.
It does not seems like a memory issue as the same command works with root account. Available memory (free -m) is more than 1200MB
Also i have tried increasing the JVM memory limits

Just be careful. You will get this message if you try to enter a command that doesn't exist, e.g.:
/usr/bin/java -v

I had this issue today, and for me the problem was that I had allocated too much memory:
-Xmx1024M -XX:MaxPermSize=1024m
Once I reduced the PermGen space, everything worked fine:
-Xmx1024M -XX:MaxPermSize=512m
I know that doesn't look like much of a difference, but my machine only has 4GB of RAM, and apparently that was the straw that broke the camel's back. The Java VM was failing immediately upon every action because it was failing to allocate the memory.

Set the JVM memory:
export _JAVA_OPTIONS=-Xmx512M

The problem got resolved when I edited the file /etc/bashrc with same contents as in /etc/profiles and in /etc/profiles.d/limits.sh and did a re-login.

Make sure the physical available memory is more then VM defined min/max memory.

classes loaded by jvm

I have a running jvm process and I want a tool to get classes loaded by that jvm, are there one?

You can use jmap -histo <PID>
It'll show histogram of loaded classes including classname, number of instances, size, etc

jinfo <pid>
will give you quite a bit information, including the classpath and the jars in the path.
see here
The jinfo command may be limited by the permissions granted to the principal running the command. The command will only list the JVMs for which the principle has access rights as determined by operating system specific access control mechanisms.
Note also that jinfo is not available on windows or linux itanium.

You can use the following in the command line
java -verbose:class ....
and the JVM will dump out what it's loading including all its locations

try visual VM. It is free but is not distributed with JRE/JDK but you can download it from official oracle website. Also you can make a heap dump and than you can view it by standard tools from JDK.

If the process has JMX enabled then you can use jvisualvm (bundled with the JDK) to examine such properties.