jvm
===

[`sysenv`在线教程](https://alibaba.github.io/arthas/arthas-tutorials?language=cn&id=command-sysenv)

> 查看当前JVM信息

### 使用参考

```
$ jvm
RUNTIME
--------------------------------------------------------------------------------------------------------------
 MACHINE-NAME                   37@ff267334bb65
 JVM-START-TIME                 2020-07-23 07:50:36
 MANAGEMENT-SPEC-VERSION        1.2
 SPEC-NAME                      Java Virtual Machine Specification
 SPEC-VENDOR                    Oracle Corporation
 SPEC-VERSION                   1.8
 VM-NAME                        Java HotSpot(TM) 64-Bit Server VM
 VM-VENDOR                      Oracle Corporation
 VM-VERSION                     25.201-b09
 INPUT-ARGUMENTS                []
 CLASS-PATH                     demo-arthas-spring-boot.jar
 BOOT-CLASS-PATH                /usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/j
                                re/lib/rt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/sunrsasign.jar:/usr/lib/jvm/
                                java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/us
                                r/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/l
                                ib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/classes
 LIBRARY-PATH                   /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib

--------------------------------------------------------------------------------------------------------------
 CLASS-LOADING
--------------------------------------------------------------------------------------------------------------
 LOADED-CLASS-COUNT             7529
 TOTAL-LOADED-CLASS-COUNT       7529
 UNLOADED-CLASS-COUNT           0
 IS-VERBOSE                     false

--------------------------------------------------------------------------------------------------------------
 COMPILATION
--------------------------------------------------------------------------------------------------------------
 NAME                           HotSpot 64-Bit Tiered Compilers
 TOTAL-COMPILE-TIME             14921(ms)

--------------------------------------------------------------------------------------------------------------
 GARBAGE-COLLECTORS
--------------------------------------------------------------------------------------------------------------
 PS Scavenge                            name : PS Scavenge                                                                             
 [count/time (ms)]                      collectionCount : 7                                                                            
                                        collectionTime : 68                                                                            
                                                                                                                                       
 PS MarkSweep                           name : PS MarkSweep                                                                            
 [count/time (ms)]                      collectionCount : 1                                                                            
                                        collectionTime : 47 

--------------------------------------------------------------------------------------------------------------
 MEMORY-MANAGERS
--------------------------------------------------------------------------------------------------------------
 CodeCacheManager               Code Cache

 Metaspace Manager              Metaspace
                                Compressed Class Space

 Copy                           Eden Space
                                Survivor Space

 MarkSweepCompact               Eden Space
                                Survivor Space
                                Tenured Gen


--------------------------------------------------------------------------------------------------------------
 MEMORY
--------------------------------------------------------------------------------------------------------------
 HEAP-MEMORY-USAGE                      init : 268435456(256.0 MiB)                                                                    
 [memory in bytes]                      used : 18039504(17.2 MiB)                                                                      
                                        committed : 181403648(173.0 MiB)                                                               
                                        max : 3817865216(3.6 GiB)                                                                      
                                                                                                                                       
 NO-HEAP-MEMORY-USAGE                   init : 2555904(2.4 MiB)                                                                        
 [memory in bytes]                      used : 33926216(32.4 MiB)                                                                      
                                        committed : 35176448(33.5 MiB)                                                                 
                                        max : -1(-1 B)  

--------------------------------------------------------------------------------------------------------------
 OPERATING-SYSTEM
--------------------------------------------------------------------------------------------------------------
 OS                             Linux
 ARCH                           amd64
 PROCESSORS-COUNT               3
 LOAD-AVERAGE                   29.53
 VERSION                        4.15.0-52-generic

--------------------------------------------------------------------------------------------------------------
 THREAD
--------------------------------------------------------------------------------------------------------------
 COUNT                          30
 DAEMON-COUNT                   24
 PEAK-COUNT                     31
 STARTED-COUNT                  36
 DEADLOCK-COUNT                 0

--------------------------------------------------------------------------------------------------------------
 FILE-DESCRIPTOR
--------------------------------------------------------------------------------------------------------------
 MAX-FILE-DESCRIPTOR-COUNT      1048576
 OPEN-FILE-DESCRIPTOR-COUNT     100
Affect(row-cnt:0) cost in 88 ms.
```

### THREAD相关

* COUNT: JVM当前活跃的线程数
* DAEMON-COUNT: JVM当前活跃的守护线程数
* PEAK-COUNT: 从JVM启动开始曾经活着的最大线程数
* STARTED-COUNT: 从JVM启动开始总共启动过的线程次数
* DEADLOCK-COUNT: JVM当前死锁的线程数

### 文件描述符相关

* MAX-FILE-DESCRIPTOR-COUNT：JVM进程最大可以打开的文件描述符数
* OPEN-FILE-DESCRIPTOR-COUNT：JVM当前打开的文件描述符数