The command line of JDK is certainly one of the most familiar commands for general developers, such as java,javac,javap. However, there are many other command line tools under jdk/bin that are used to monitor the status of the JVM when it is running. Here's a detailed explanation of several commonly used tools and how to use them.

jstack

jstack(JVM Stack Trace) is used to generate a snapshot of the thread at the current time of the virtual machine.Thread snapshots are a collection of method stacks being executed by each thread in the current virtual machine. The main purpose of generating thread snapshots is to locate the causes of long thread pauses, such as thread deadlocks, deadlocks, long waiting times caused by requesting external resources, and so on, which are common causes of long thread pauses..When a thread pauses, look at the call stack of each thread through jstack to see what the unresponsive thread is doing behind the scenes or waiting for resources.

Command Format

jstack [option] LVMID

option parameter

• -F: Force output threads stack when normal output requests are not responded to
• -l: Display additional information about locks in addition to the stack
• -m: Displays the C/C++ stack if the local method is called

Example

$ jstack -l 45995
2019-08-14 17:34:36
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.45-b02 mixed mode):

"Attach Listener" #46 daemon prio=9 os_prio=31 tid=0x00007fc62527e800 nid=0x6b07 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-10" #44 daemon prio=5 os_prio=31 tid=0x00007fc61f359000 nid=0x8a03 waiting on condition [0x0000700002fa3000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-9" #43 daemon prio=5 os_prio=31 tid=0x00007fc620475000 nid=0x8803 waiting on condition [0x0000700002ea0000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-8" #42 daemon prio=5 os_prio=31 tid=0x00007fc61f002000 nid=0x8603 waiting on condition [0x0000700002d9d000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None
    ......