# phpman > man > jhat(1)

> **TLDR:** Java heap analysis tool.
>
- Analyze a heap dump (from `jmap`), view via HTTP on port 7000:
  `jhat {{dump_file.bin}}`
- Analyze a heap dump, specifying an alternate port for the HTTP server:
  `jhat {{-p|-port}} {{port}} {{dump_file.bin}}`
- Analyze a dump letting `jhat` use up to 8 GB RAM (2-4x dump size recommended):
  `jhat -J-mx8G {{dump_file.bin}}`

*Source: tldr-pages*

---

[jhat(1)](https://www.chedong.com/phpMan.php/man/jhat/1/markdown)                                 Troubleshooting Tools                                [jhat(1)](https://www.chedong.com/phpMan.php/man/jhat/1/markdown)



## NAME
       jhat - Analyzes the Java heap. This command is experimental and unsupported.

## SYNOPSIS
       **jhat** [ _options_ ] _heap-dump-file_


       _options_
              The command-line options. See Options.

       _heap-dump-file_
              Java binary heap dump file to be browsed. For a dump file that contains multiple heap
              dumps, you can specify which dump in the file by appending **#<number>** to the file name,
              for example, **myfile.hprof#3**.

## DESCRIPTION
       The **jhat** command parses a Java heap dump file and starts a web server. The **jhat** command lets
       you to browse heap dumps with your favorite web browser. The **jhat** command supports
       predesigned queries such as show all instances of a known class **MyClass**, and Object Query
       Language (OQL). OQL is similar to SQL, except for querying heap dumps. Help on OQL is
       available from the OQL help page shown by the **jhat** command. With the default port, OQL help
       is available at <http://localhost:7000/oqlhelp/>

       There are several ways to generate a Java heap dump:

       • Use the **jmap** **-dump** option to obtain a heap dump at runtime. See [jmap(1)](https://www.chedong.com/phpMan.php/man/jmap/1/markdown).

       • Use the **jconsole** option to obtain a heap dump through **HotSpotDiagnosticMXBean** at runtime.
         See [jconsole(1)](https://www.chedong.com/phpMan.php/man/jconsole/1/markdown) and the **HotSpotDiagnosticMXBean** interface description at
         <http://docs.oracle.com/javase/8/docs/jre/api/management/extension/com/sun/management/HotSpotDiagnosticMXBean.html>

       • Heap dump is generated when an **OutOfMemoryError** is thrown by specifying the
         **-XX:+HeapDumpOnOutOfMemoryError** Java Virtual Machine (JVM) option.

       • Use the **hprof** command. See the HPROF: A Heap/CPU Profiling Tool at
         <http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html>

## OPTIONS
       -stack false|true
              Turns off tracking object allocation call stack. If allocation site information is not
              available in the heap dump, then you have to set this flag to **false**. The default is
              **true**.

       -refs false|true
              Turns off tracking of references to objects. Default is **true**. By default, back
              pointers, which are objects that point to a specified object such as referrers or
              incoming references, are calculated for all objects in the heap.

       -port _port-number_
              Sets the port for the **jhat** HTTP server. Default is 7000.

       -exclude _exclude-file_
              Specifies a file that lists data members that should be excluded from the reachable
              objects query. For example, if the file lists **java.lang.String.value**, then, then
              whenever the list of objects that are reachable from a specific object **o** are
              calculated, reference paths that involve **java.lang.String.value** field are not
              considered.

       -baseline _exclude-file_
              Specifies a baseline heap dump. Objects in both heap dumps with the same object ID are
              marked as not being new. Other objects are marked as new. This is useful for comparing
              two different heap dumps.

       -debug _int_
              Sets the debug level for this tool. A level of 0 means no debug output. Set higher
              values for more verbose modes.

### -version
              Reports the release number and exits

### -h
              Dsiplays a help message and exits.

### -help
              Displays a help message and exits.

### -J_flag_
              Passes **flag** to the Java Virtual Machine on which the **jhat** command is running. For
              example, **-J-Xmx512m** to use a maximum heap size of 512 MB.

## SEE ALSO
       • [jmap(1)](https://www.chedong.com/phpMan.php/man/jmap/1/markdown)

       • [jconsole(1)](https://www.chedong.com/phpMan.php/man/jconsole/1/markdown)

       • HPROF: A Heap/CPU Profiling Tool at
         <http://docs.oracle.com/javase/8/docs/technotes/samples/hprof.html>



JDK 8                                     21 November 2013                                   [jhat(1)](https://www.chedong.com/phpMan.php/man/jhat/1/markdown)