kill -3 to get java thread dump

Question

I am using kill -3 command to see the JVM s thread dump in unix  But where can I find the output of this kill command  I am lost

User · Answer

In the same location where the JVM s stdout is placed  If you have a Tomcat server  this will be the catalina  date  out file

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Steps that you should follow if you want the thread dump of your StandAlone Java Process  Step 1  Get the Process ID for the shell script calling the java program  linux  ps -aef   grep  runABCD   user1    8535    4369   0   Mar 25             0 00  bin csh  home user1 runABCD sh  user1 17796 17372   0 08 15 41 pts 49      0 00 grep runABCD   Step 2  Get the Process ID for the Child  which was Invoked by the runABCD  Use the above PID to get the childs   linux  ps -aef   grep   8535    user1    8536    8535   0   Mar 25           126 38  apps java jdk sun4 SunOS5 1 6 0 16 bin java -cp  home user1 XYZServer  user1  8535  4369   0   Mar 25             0 00  bin csh  home user1 runABCD sh  user1 17977 17372   0 08 15 49 pts 49      0 00 grep 8535   Step 3  Get the JSTACK for the particular process  Get the Process id of your XYSServer process  i e  8536  linux  jstack   8536    gt  threadDump log

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You could alternatively use jstack  Included with JDK  to take a thread dump and write the output wherever you want  Is that not available in a unix environment   jstack PID  gt  outfile

User · Answer

When using kill -3 one should see the thread dump in the standard output  Most of the application servers write the standard output to a separate file  You should find it there when using kill -3  There are multiple ways of getting thread dumps    kill -3  lt PID gt   Gives output to  standard output  If one has access to the console window where server is running  one can use Ctrl Break combination of keys to generate the stack trace on STDOUT  For hotspot VM s we can also use jstack command to generate a thread dump  It   s a part of the JDK  Syntax is as follows   Usage   jstack  -l   lt pid gt   to connect to running process  jstack -F  -m   -l   lt pid gt  to connect to a hung process    - For JRockit JVM we can use JRCMD command which comes with JDK Syntax      jrcmd  lt jrockit pid gt    lt command gt    lt arguments gt     -l   -f file   -p  -h

User · Answer

There is a way to redirect JVM thread dump output on break signal to separate file with LogVMOutput diagnostic option   -XX  UnlockDiagnosticVMOptions -XX  LogVMOutput -XX LogFile jvm log

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Find the process id  PS ID  Execute jcmd  PS ID  Thread print

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With Java 8 in picture  jcmd is the preferred approach    jcmd  lt PID gt  Thread print   Following is the snippet from Oracle documentation     The release of JDK 8 introduced Java Mission Control  Java Flight Recorder  and jcmd utility for diagnosing problems with JVM and Java applications  It is suggested to use the latest utility  jcmd instead of the previous jstack utility for enhanced diagnostics and reduced performance overhead   However  shipping this with the application may be licensing implications which I am not sure

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In Jboss you can perform the following   nohup  JBOSS HOME bin run sh -c  yourinstancename  JBOSS OPTS  gt  gt  console-  date   Y m d  out  2 gt  amp 1  lt   dev null  amp  kill -3  lt java pid gt    This will redirect your output threadump to the file console specified in the above command

User · Answer

The thread dump is written to the system out of the VM on which you executed the kill -3   If you are redirecting the console output of the JVM to a file  the thread dump will be in that file   If the JVM is running in an open console  then the thread dump will be displayed in its console

[java] kill -3 to get java thread dump

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