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

Question

Is there a Command-line Tool  Linux  to check Heap Size  and Used Memory  of a Java Application   I have tried through jmap  But it gives info  about internal memory areas like Eden  PermGen etc   which is not useful to me    I am looking for something like    Max Memory  1GB Min Memory  256 MB Heap Memory  700 MB Used Memory  460 MB   That s all  I know that I can see this in JConsole etc   but I need a command-line tool  can t enable JMX etc    Do you know any such a tool  command

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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

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jstat -gccapacity javapid   ex  stat -gccapacity 28745  jstat -gccapacity javapid gaps frames  ex   stat -gccapacity 28745 550 10     Sample O P of above command  NGCMN    NGCMX     NGC     S0C   87040 0 1397760 0 1327616 0 107520 0   NGCMN   Minimum new generation capacity  KB   NGCMX   Maximum new generation capacity  KB   NGC Current new generation capacity  KB     Get more details about this at http   docs oracle com javase 1 5 0 docs tooldocs share jstat html

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This command shows the configured heap sizes in bytes   java -XX  PrintFlagsFinal -version   grep HeapSize   It works on Amazon AMI on EC2 as well

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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

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Using top command is the simplest way to check memory usage of the program  RES column shows the real physical memory that is occupied by a process   For my case  I had a 10g file read in java and each time I got outOfMemory exception  This happened when the value in the RES column reached to the value set in -Xmx option  Then by increasing the memory using -Xmx option everything went fine

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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

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Any approach should give you roughly same number  It is always a good idea to allocate the heap using -X  m -X  x for all generations  You can then guarantee and also do ps to see what parameters were passed and hence being used   For actual memory usages  you can roughly compare VIRT  allocated and shared  and RES  actual used  compare against the jstat values as well   For Java 8  see jstat for these values actually mean  Assuming you run a simple class with no mmap or file processing     jstat -gccapacity 32277  NGCMN    NGCMX     NGC     S0C   S1C       EC      OGCMN      OGCMX       OGC         OC       MCMN     MCMX      MC     CCSMN    CCSMX     CCSC    YGC    FGC 215040 0 3433472 0  73728 0  512 0  512 0  67072 0   430080 0  6867968 0   392704 0   392704 0      0 0 1083392 0  39680 0      0 0 1048576 0   4864 0   7225     2       jstat -gcutil 32277   S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT   6 25   0 00   7 96  18 21  98 01  95 29   7228   30 859     2    0 173   31 032   Max        NGCMX   S0C   S1C   EC      OGCMX     MCMX      CCSMX    3433472   512   512   67072   6867968   1083392   1048576   12 GB    roughly close and below to VIRT memory   Max Min  Used    215040   512   512   67072   430080    39680       4864      1GB    roughly close to RES memory    Don t quote me on this  but VIRT mem is roughly close to or more than Max memory allocated but as long as memory being used is free available in physical memory  JVM does not throw memory exception  In fact  max memory is not even checked against physical memory on JVM startup even with swap off on OS  A better explanation of what Virtual memory really used by a Java process is discussed here

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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

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There is no such tool till now to print the heap memory in the format as you requested The Only and only way to print is to write a java program with the help of Runtime Class   public class TestMemory    public static void main String    args         int MB   1024 1024         Getting the runtime reference from system     Runtime runtime   Runtime getRuntime           Print used memory     System out println  Used Memory               runtime totalMemory   - runtime freeMemory      MB          Print free memory     System out println  Free Memory              runtime freeMemory     mb          Print total available memory     System out println  Total Memory     runtime totalMemory     MB          Print Maximum available memory     System out println  Max Memory     runtime maxMemory     MB          reference https   viralpatel net blogs getting-jvm-heap-size-used-memory-total-memory-using-java-runtime

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In my case I needed to check the flags inside a docker container which didn t had most of the basic utilities  ps  pstree      Using jps I got the PID of the JVM running  in my case 1  and then with jcmd 1 VM flags I got the flags from the running JVM   It depends on what commands you have available  but this might help someone

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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

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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

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First get the process id  the first number from the process listed  from one of the following   or just use ps aux   grep java  if you prefer that   jps -lvm   Then use the process ID here   jmap -heap  MY PID 2 gt  dev null   sed -ne   Heap Configuration   p   jmap -permstat  MY PID

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Find the process id of your webapp java process from top  Use jmap heap  to get the heap allocation  I tested this on AWS-Ec2 for elastic beanstalk You can see in image below 3GB max heap for the application

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If using jrockit try the jrcmd command line tool  For example     jrcmd 5127 print memusage 5127  Total mapped                  1074596KB            reserved 3728KB  -              Java heap       786432KB            reserved 0KB  -              GC tables        26316KB           -          Thread stacks        13452KB             threads 34  -          Compiled code         9856KB            used 9761KB  -               Internal          840KB           -                     OS        15036KB           -                  Other       146632KB           -        Java class data        75008KB            malloced 74861KB  103221 in 18709 classes  - Native memory tracking         1024KB            malloced 102KB  8    For more commands  like heap diagnostics  use  jrcmd  help  to list them   https   blogs oracle com jrockit entry why is my jvm process larger t

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Late at party  but a very simple solution is to use the jpsstat sh script  It provides a simple live current memory  max memory and cpu use details    Goto GitHub project and download the jpsstat sh file Right click on jpsstat sh and goto permissions tab and make it executable                                        Now Run the script using following command   jpsstat sh   Here is the sample output of script -                                           PID    Name   CurHeap  MaxHeap    CPU                                        2777   Test3      1 26     1 26    5 8 2582   Test1      2 52     2 52    8 3 2562   Test2      2 52     2 52    6 4

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In terms of Java heap size  in Linux  you can use  ps aux   grep java   or  ps -ef   grep java   and look for -Xms  -Xmx to find out the initial and maximum heap size specified   However  if -Xms or -Xmx is absent for the Java process you are interested in  it means your Java process is using the default heap sizes  You can use the following command to find out the default sizes   java -XX  PrintFlagsFinal -version   grep HeapSize   or a particular jvm  for example    path to jdk1 8 0 102 bin java -XX  PrintFlagsFinal -version   grep HeapSize   and look for InitialHeapSize and MaxHeapSize  which is in bytes

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

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