Command-line Tool to find Java Heap Size and Memory Used (Linux)?

Question

Each Java process has a pid, which you first need to find with the jps command.

Once you have the pid, you can use jstat -gc [insert-pid-here] to find statistics of the behavior of the garbage collected heap.

• jstat -gccapacity [insert-pid-here] will present information about memory pool generation and space capabilities.

• jstat -gcutil [insert-pid-here] will present the utilization of each generation as a percentage of its capacity. Useful to get an at a glance view of usage.

See jstat docs on Oracle's site.

This command shows the configured heap sizes in bytes.

java -XX:+PrintFlagsFinal -version | grep HeapSize

It works on Amazon AMI on EC2 as well.

jvmtop is a command-line tool which provides a live-view at several metrics, including heap.

Example output of the VM overview mode:

 JvmTop 0.3 alpha (expect bugs)  amd64  8 cpus, Linux 2.6.32-27, load avg 0.12
 http://code.google.com/p/jvmtop

  PID MAIN-CLASS      HPCUR HPMAX NHCUR NHMAX    CPU     GC    VM USERNAME   #T DL
 3370 rapperSimpleApp  165m  455m  109m  176m  0.12%  0.00% S6U37 web        21
11272 ver.resin.Resin [ERROR: Could not attach to VM]
27338 WatchdogManager   11m   28m   23m  130m  0.00%  0.00% S6U37 web        31
19187 m.jvmtop.JvmTop   20m 3544m   13m  130m  0.93%  0.47% S6U37 web        20
16733 artup.Bootstrap  159m  455m  166m  304m  0.12%  0.00% S6U37 web        46

Try this it worked in Ubuntu and RedHat:

java -XX:+PrintFlagsFinal -version | grep -iE 'HeapSize|PermSize|ThreadStackSize'

For Windows:

java -XX:+PrintFlagsFinal -version | findstr /i "HeapSize PermSize ThreadStackSize"

For Mac

java -XX:+PrintFlagsFinal -version | grep -iE 'heapsize|permsize|threadstacksize'

The output of all this commands resembles the output below:

uintx InitialHeapSize                          := 20655360        {product}
uintx MaxHeapSize                              := 331350016       {product}
uintx PermSize                                  = 21757952        {pd product}
uintx MaxPermSize                               = 85983232        {pd product}
intx ThreadStackSize                           = 1024            {pd product}
java version "1.7.0_05"
Java(TM) SE Runtime Environment (build 1.7.0_05-b05)
Java HotSpot(TM) 64-Bit Server VM (build 23.1-b03, mixed mode)

To find the size in MB, divide the value with (1024*1024).

Without using JMX, which is what most tools use, all you can do is use

jps -lvm

and infer that the settings will be from the command line options.

You can't get dynamic information without JMX by default but you could write your own service to do this.

BTW: I prefer to use VisualVM rather than JConsole.

There is a command line tool with a visual aspect - jvm-mon. It is a JVM monitoring tool for the command line that disaplys:

• heap usage, size and max
• jvm processes
• cpu and GC usage
• top threads

The metrics and charts update while the tool is open.

Sample:

From Java8 and above, you may use below command:

jcmd JAVA_PROCESS_ID GC.heap_info

You may refer to sum of, total and used memory from the output.

Sample Command And Output: jcmd 9758 GC.heap_info

PSYoungGen  total 1579520K, used 487543K [0x0000000751d80000, 0x00000007c0000000, 0x00000007c0000000)
  eden space 1354240K, 36% used [0x0000000751d80000,0x000000076f99dc40,0x00000007a4800000)
  from space 225280K, 0% used [0x00000007b2400000,0x00000007b2400000,0x00000007c0000000)
  to   space 225280K, 0% used [0x00000007a4800000,0x00000007a4800000,0x00000007b2400000)
ParOldGen       total 3610112K, used 0K [0x0000000675800000, 0x0000000751d80000, 0x0000000751d80000)
  object space 3610112K, 0% used [0x0000000675800000,0x0000000675800000,0x0000000751d80000)
Metaspace       used 16292K, capacity 16582K, committed 16896K, reserved 1064960K
  class space    used 1823K, capacity 1936K, committed 2048K, reserved 1048576K

For more details on jcmd command, visit link here