jps 获取java进程pid
常用参数说明：
-m 输出传递给main方法的参数，如果是内嵌的JVM则输出为null。
-l 输出应用程序主类的完整包名，或者是应用程序JAR文件的完整路径。
-v 输出传给JVM的参数。
[root]# jps
25840 Bootstrap
14088 Bootstrap
21962 Jps
jstat 用来实时查看gc的状态，
jstat -gcutil 进程号 时间（毫秒）
jmap -heap 57836
Attaching to process ID 57836, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.80-b11
using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC //GC 方式
Heap Configuration: //堆内存初始化配置
MinHeapFreeRatio = 40 //对应jvm启动参数-XX:MinHeapFreeRatio设置JVM堆最小空闲比率(default 40)
MaxHeapFreeRatio = 70 //对应jvm启动参数-XX:MaxHeapFreeRatio设置JVM堆最大空闲比率(default 70)
MaxHeapSize = 3221225472 (3072.0MB) //对应jvm启动参数-XX:MaxHeapSize=设置JVM堆的最大大小
NewSize = 2147483648 (2048.0MB) //对应jvm启动参数-XX:NewSize=设置JVM堆的‘新生代’的默认大小
MaxNewSize = 2147483648 (2048.0MB) //对应jvm启动参数-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小
OldSize = 5439488 (5.1875MB) //对应jvm启动参数-XX:OldSize=<value>:设置JVM堆的‘老生代’的大小
NewRatio = 2 //对应jvm启动参数-XX:NewRatio=:‘新生代’和‘老生代’的大小比率
SurvivorRatio = 8 //对应jvm启动参数-XX:SurvivorRatio=设置年轻代中Eden区与Survivor区的大小比值
PermSize = 21757952 (20.75MB) //对应jvm启动参数-XX:PermSize=<value>:设置JVM堆的‘永生代’的初始大小
MaxPermSize = 268435456 (256.0MB) //对应jvm启动参数-XX:MaxPermSize=<value>:设置JVM堆的‘永生代’的最大大小
G1HeapRegionSize = 0 (0.0MB)
Heap Usage: //堆内存分步
New Generation (Eden + 1 Survivor Space): //新生代（伊甸区 + survior空间）
capacity = 1932787712 (1843.25MB)
used = 932694480 (889.4867706298828MB)
free = 1000093232 (953.7632293701172MB)
48.25643676277677% used //使用比例
Eden Space:
capacity = 1718091776 (1638.5MB)
used = 850139696 (810.7563934326172MB)
free = 867952080 (827.7436065673828MB)
49.4816230352528% used
From Space: //survior1区
capacity = 214695936 (204.75MB)
used = 82554784 (78.73037719726562MB)
free = 132141152 (126.01962280273438MB)
38.45195467509921% used
To Space: //survior2区
capacity = 214695936 (204.75MB)
used = 0 (0.0MB)
free = 214695936 (204.75MB)
0.0% used
concurrent mark-sweep generation: //老生代使用情况
capacity = 1073741824 (1024.0MB)
used = 19140736 (18.2540283203125MB)
free = 1054601088 (1005.7459716796875MB)
1.7826199531555176% used
Perm Generation: //perm区使用情况
capacity = 70467584 (67.203125MB)
used = 70145920 (66.8963623046875MB)
free = 321664 (0.3067626953125MB)
99.54352912113463% used
31913 interned Strings occupying 3591488 bytes.转载于:https://my.oschina.net/direnjie/blog/542216
来源：https://blog.csdn.net/chengyi76787/article/details/100787723