Is there a way to get the parameters of a running JVM? Is there a command line tool like jstat which takes as input the pid of the JVM and returns its starting parameters? I am particularly interested in the -Xmx and -Xms values that were given when starting the JVM. Thank you.
Edit: To clarify my constraints. The JVM we would like to check is running on a production server. That's why, we prefer the minimum disruption. We are able to monitor the JVM using jstat, and so we hope there's a similar simple solution to access the parameters.
Edit: We also tried to get the parameters using jvisualvm. But in order to connect to a remote jvm, we need to run jstatd and modify the security settings of the JVM, which we found to be very disruptive and risky on a production server.
I am adding this new answer because as per JDK8 documentation jcmd is suggested approach now.
It is suggested to use the latest utility, jcmd instead of the previous jstack, jinfo, and jmap utilities for enhanced diagnostics and reduced performance overhead.
Below are commands to get your properties/flags you want.
jcmd pid VM.system_properties
jcmd pid VM.flags
We need pid, for this use jcmd -l, like below
username@users-Air:~/javacode$ jcmd -l
11441 Test
6294 Test
29197 jdk.jcmd/sun.tools.jcmd.JCmd -l
Now time to use these pids to get properties/flags you want
Command: jcmd 11441 VM.system_properties
11441:
#Tue Oct 17 12:44:50 IST 2017
gopherProxySet=false
awt.toolkit=sun.lwawt.macosx.LWCToolkit
file.encoding.pkg=sun.io
java.specification.version=9
sun.cpu.isalist=
sun.jnu.encoding=UTF-8
java.class.path=.
java.vm.vendor=Oracle Corporation
sun.arch.data.model=64
java.vendor.url=http\://java.oracle.com/
user.timezone=Asia/Kolkata
java.vm.specification.version=9
os.name=Mac OS X
sun.java.launcher=SUN_STANDARD
user.country=US
sun.boot.library.path=/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home/lib
sun.java.command=Test
http.nonProxyHosts=local|*.local|169.254/16|*.169.254/16
jdk.debug=release
sun.cpu.endian=little
user.home=/Users/XXXX
user.language=en
java.specification.vendor=Oracle Corporation
java.home=/Library/Java/JavaVirtualMachines/jdk-9.jdk/Contents/Home
file.separator=/
java.vm.compressedOopsMode=Zero based
line.separator=\n
java.specification.name=Java Platform API Specification
java.vm.specification.vendor=Oracle Corporation
java.awt.graphicsenv=sun.awt.CGraphicsEnvironment
sun.management.compiler=HotSpot 64-Bit Tiered Compilers
ftp.nonProxyHosts=local|*.local|169.254/16|*.169.254/16
java.runtime.version=9+181
user.name=XXXX
path.separator=\:
os.version=10.12.6
java.runtime.name=Java(TM) SE Runtime Environment
file.encoding=UTF-8
java.vm.name=Java HotSpot(TM) 64-Bit Server VM
java.vendor.url.bug=http\://bugreport.java.com/bugreport/
java.io.tmpdir=/var/folders/dm/gd6lc90d0hg220lzw_m7krr00000gn/T/
java.version=9
user.dir=/Users/XXXX/javacode
os.arch=x86_64
java.vm.specification.name=Java Virtual Machine Specification
java.awt.printerjob=sun.lwawt.macosx.CPrinterJob
sun.os.patch.level=unknown
MyParam=2
java.library.path=/Users/XXXX/Library/Java/Extensions\:/Library/Java/Extensions\:/Network/Library/Java/Extensions\:/System/Library/Java/Extensions\:/usr/lib/java\:.
java.vm.info=mixed mode
java.vendor=Oracle Corporation
java.vm.version=9+181
sun.io.unicode.encoding=UnicodeBig
java.class.version=53.0
socksNonProxyHosts=local|*.local|169.254/16|*.169.254/16
Command : jcmd 11441 VM.flags output:
11441:
-XX:CICompilerCount=3 -XX:ConcGCThreads=1 -XX:G1ConcRefinementThreads=4 -XX:G1HeapRegionSize=1048576 -XX:InitialHeapSize=67108864 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=1073741824 -XX:MaxNewSize=643825664 -XX:MinHeapDeltaBytes=1048576 -XX:NonNMethodCodeHeapSize=5830092 -XX:NonProfiledCodeHeapSize=122914074 -XX:ProfiledCodeHeapSize=122914074 -XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache -XX:-UseAOT -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseG1GC
For more instructions of usages of jcmd, see my blog post
If you are interested in getting the JVM parameters of a running java process, then just do kill -3 java-pid. You will get a core dump file in which you can find the jvm parameters used while launching the java application.
This technique applies for any java application running local or remote.
jvisualvm can be found in any JDK since JDK 6 Update 7. Video tutorial on jvisualvm is here.
_JAVA_OPTIONS is an env variable that can be expanded.
echo $_JAVA_OPTIONS
On Linux:
java -XX:+PrintFlagsFinal -version | grep -iE 'HeapSize|PermSize|ThreadStackSize'
On Mac OSX:
java -XX:+PrintFlagsFinal -version | grep -iE 'heapsize|permsize|threadstacksize'
On Windows:
C:\>java -XX:+PrintFlagsFinal -version | findstr /i "HeapSize PermSize ThreadStackSize"
Source: https://www.mkyong.com/java/find-out-your-java-heap-memory-size/
Alternatively, you can use jinfo
jinfo -flags <vmid>
jinfo -sysprops <vmid>
Windows 10 or Windows Server 2016 provide such information in their standard task manager. A rare case for production, but if the target JVM is running on Windows, the simplest way to see its parameters is to press Ctrl+Alt+Delete, choose the Processes tab and add the Command line column (by clicking the right mouse button on any existing column header).
On linux, you can run this command and see the result :
ps aux | grep "java"
If you can do this in java, try:
Example:
RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
List<String> jvmArgs = runtimeMXBean.getInputArguments();
for (String arg : jvmArgs) {
System.out.println(arg);
}
JConsole can do it. Also you can use a powerful jvisualVM tool, which also is included in JDK since 1.6.0.8.
You can use the JConsole command (or any other JMX client) to access that information.
Source: Stackoverflow.com