When I issue a kill -3 <pid> command to my Java program, it generates the thread dump on the console. How do I redirect this to a file?
Two options:
Run your Java application with stdout redirected
java com.example.MyApp > out.txt
Use jstack instead.
The jstack utility allows you to get a thread dump and send the output to the current console instead of the stdout of the Java application, allowing you to redirect it.
For example, if the PID of your Java application is 12345 (use the jps utility to find it quickly):
jstack 12345 > threads.txt
I usually use the NetBeans profiler, but jvisualvm is available from the command line.
If you want details of all threads and other JVM details, try jconsole.
Please append following JVM arguments to your application. Thread dump should be captured at dump.log.
-XX:+UnlockDiagnosticVMOptions -XX:+LogVMOutput -XX:LogFile=dump.log
Please note it does not redirect, but enables JVM diagnostic logging. So, there could be possible over head as well.
However, if you can have JDK in the environment, using jstack or jcmd (jcmd is preferred with JDK 1.8), you can capture thread dump and redirect to a file.
you can generate java thread dumps using 4 ways excluding the kill -QUIT way.
Related
Hadoop jvm process hangs without any error message,
I want to take a look into what JVM processes are doing (where they are stuck).
When I program in C++, I used GDB that can be attached to a running process and show the call stack of the threads.
How can I do the same thing for JVM?
You may use following command
kill -3 [PID]
This will print stack traces of all threads to the console of your java process. Another option is to use jstack utility which is bundled with jdk. Jstack does the same thing.
If it doesn't help then profilers should help. They can gather a lot more data than one thread dump.
I would like to automatically create a thread dump as part of a log collection script I have written.
I know that it is possible to generate a thread dump using jstack or kill -3 . The customer running the log collection script will only have a JRE installed so jstack is not an option.
If I use jstack and the pid of the JVM that the install4j launcher creates I get the thread dump...however invoking kill -3 with the same pid generates no output. I am currently directing both stderror and stdout to files using the install4j launcher configuration.
This is a linux launcher that is configured with the service option.
FWIW...I have tried not directing the output and also running my application as a console program instead of a service and none of these allow 'kill -3' to work.
I'm using install4j 6.0
Lastly, I do not want to use -XX:+UnlockDiagnosticVMOptions -XX:+LogVMOutput -XX:LogFile=dump.log because of the unknown overhead it might create.
Any help would be appreciated!
I would suggest to use the ThreadMXBean to get this information programmatically in the same process rather than use signal handlers from another process. The API documentation is at
http://docs.oracle.com/javase/8/docs/api/java/lang/management/ThreadMXBean.html
Here's a full example of how to use this MBean.
In that way you can write the information explicitly to wherever you want it to go.
any idea how do generate a java heapdump without JDK?
I'm able to obtain the processid but I don't have access to the machine directly and there's no JDK installed.
You can alternatively use the JVM parameter -XX:+HeapDumpOnCtrlBreak
and send a SIGQUIT signal (-3 kill for Unix and Ctrl-Break for
Windows) to the running Java process – the signal will also create a
heapdump without aborting the JVM
Is there an easier way? and how can I send a SIGQUIT to the process?
Thank you for your help
If you still have access via SSH/telnet you could use:
kill -QUIT <pid>
as you described in you quotation.
Other option in to access the application via JMX, i.e. jconsole or jvisialvm
To use JMX you need enabled JMX via the command line of the application
I want to get the thread dump of my web app that running on a jboss server.
I found two solutions for my problem :
Using the unix command : kill -3
Using the jstack tool that exists in the JDK.
Can anyone explain to me the difference between theses two methods?
Thanks in advance !
The jstack command can get a thread dump of a program running on a remote machine, and it also works on Windows.
kill -3 only works on local programs, and on Windows there is no kill.
From the oracle page of jstack:
The output from the jstack pid option is the same as that obtained by pressing Ctrl+\ at the application console (standard input) or by sending the process a QUIT signal.
Also remember that Ctrl+\ is equivalent to a SIGQUIT.
From what is kill -3 (unix.se):
kill -l shows us all signals. Following this hint 3 means SIGQUIT
So basically both of them do exactly the same thing, i.e asking for a coredump. Here are some pointers related to jstack:
Jstack performs deadlock detection by default.
Regarding official support, from the jstack man page:
Prints Java thread stack traces for a Java process, core file, or remote debug server. This command is experimental and unsupported.
This utility is unsupported and might not be available in future release of the JDK. In Windows Systems where the dbgeng.dll file is not present, Debugging Tools For Windows must be installed so these tools work.
Regarding the output difference, its basically the same thing. There is a one to one mapping between the outputs. See my output for the same application to demonstrate the mapping between the statuses of kill -3 and jstack. The mapping between the statuses are:
kill -3 | Jstack
------------------------------
RUNNABLE | IN_NATIVE
TIMED_WAITING | BLOCKED
WAITING | BLOCKED (PARK)
In Windows you have something called "taskkill /PID {yourpid} /F" for killin process. The process id can be obtained from netstat command or use viusal vm to know process id
I have a Java process. I am using log4j for logging purpose. I have specified in log4j.xml, location and name of log file. logging is working fine. I have problem with kill -3 logs here.
I trying to get process-dump using kill -QUIT <pid>/ killl -3 <pid>. I expected the dump generated by kill -3 to get updated in log file specified in log4j.xml.
But it is not happening that way. I need the dump to observer thread statuses. I do not know any other way to get process dump of a running process.
kill -3 should output to stdout, so it should be wherever your stdout goes. If not you could try playing with -XX:LogFile JVM option.
Alternative way is jstack as suggested by NPE.
Another alternative is to use jvisualvm - it will produce stackdump in its nice GUI and you can copy it from there.
I need the dump to observer thread statuses. I do not know any other way to get process dump of a running process.
You can use jstack for this.