In the JDK bin directory, there are a variety of small tools to support debugging, monitoring, compile and run other functions.
root@root:/usr/lib/jvm/java-8-openjdk-amd64/bin# ls appletviewer hsdb jarsigner javadoc java-rmi.cgi jdb jinfo jps jstack keytool pack200 rmid serialver unpack200 xjc clhsdb idlj java javah jcmd jdeps jjs jrunscript jstat native2ascii policytool rmiregistry servertool wsgen extcheck jar javac javap jconsole jhat jmap jsadebugd jstatd orbd rmic schemagen tnameserv wsimport
1.jps: VM process status tool
You can list the virtual machines running processes and displays the virtual machine executes the main class (Main Class, main () function where the class) as well as the name of a local virtual machine these processes unique ID (LVMID.Local Virtual Machine Identifier)
root@root:~$ jps -help
usage: jps [-help]
jps [-q] [-mlvV] [<hostid>]
Definitions:
<hostid>: <hostname>[:<port>]
root@root:/home/dev# jps -l
1505 *.jar
1507 *.jar
jps option parameters:
-q: output only LVMID, omitted the name of the main class of
-m: passed to the main class main output virtual machine process starts () function parameters
-l: full name of the output of the master class, if the process is executed Jar package, JAR path output
JVM parameters output virtual machine process starts: -v
2.jmap: Java memory imaging tools
For raw heap dump snapshot.
The Usage:
the jmap [Option] <PID>
Option:
-dump: green heap dump snapshot -dump: [Live,] = the format B, File = <filename> <PID>
-heap: java heap show details
root@dev03:/home/dev# jmap -dump:format=b,file=heapDump 30138
Dumping heap to /home/wuh151/heapDump ...
Heap dump file created
root@root:/home/dev# jmap -heap 30138
Attaching to process ID 30138, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.242-b08
using thread-local object allocation.
Parallel GC with 8 thread(s)
Heap Configuration:
MinHeapFreeRatio = 0 ## corresponds jvm startup parameters -XX: MinHeapFreeRatio minimum idle setting JVM stack ratio (default 40)
MaxHeapFreeRatio ## = 100 corresponding to the start jvm parameters -XX: MaxHeapFreeRatio JVM stack disposed maximum idle ratio (default 70)
maxHeapSize = 1073741824 ( 1024.0MB) ## corresponding to the start jvm parameters -XX: maxHeapSize = set the maximum size of the JVM heap
NewSize = 178782208 (170.5MB) ## corresponding to the start jvm parameters -XX: NewSize = disposed JVM stack 'new generation' default size
MaxNewSize = 357564416 (341.0MB) ## corresponding to the start jvm parameters -XX: MaxNewSize = disposed JVM stack 'new generation' maximum size
OldSize = 358088704 (341.5MB) ## corresponding to the start jvm parameters -XX: OldSize = <value>: set JVM heap 'Older Generation' size
NewRatio = 2 ## corresponding to the start jvm parameters -XX: NewRatio =: 'new generation' and 'Older Generation' size ratio
SurvivorRatio = 8 ## corresponding to the start jvm parameters -XX: SurvivorRatio = Eden disposed in the young generation area size area ratio Survivor
MetaspaceSize = 1073741824 (1024.0MB)
CompressedClassSpaceSize = 268435456 (256.0MB)
MaxMetaspaceSize = 2147483648 (2048.0MB)
G1HeapRegionSize = 0 (0.0MB)
3.jstack: Java stack trace tool
Time for the current thread to generate a snapshot of the virtual machine. Thread is a snapshot of the current method of virtual machines each executing thread stack collection, generation thread snapshot aim is usually to locate the thread appears long pause.
Count the number of threads to use:
root @ dev03: / Home / dev # 2791 jstack the -l | grep 'java.lang.Thread.State' | WC the -l 48
Deadlock Detection:
Step one: View occupy high cpu process
top
Step two: Check occupy high cpu threading
top -H -p 17850
Step Three: Convert the thread ID
printf "the X-% \ the n-" 17880
45d8
Step Four: Locate the cpu usage thread
jstack 17850 | grep 45d8 -A 30
4.jstat: Virtual Machine Statistics Monitoring Tool
Various operating status monitor virtual machines.
Usage: jstat -help | -options
jstat - <the Option> [-t] [-h <Lines>] <vmid> [<interval The> [<COUNT>]]
Parameters interval count represents the number of times the query interval and, if the argument is omitted, Description only check once
the Option:
the -class monitor class loading, unloading quantity, total class load space and the time spent
-gc monitoring java heap status
-gcutil -gc with basically the same, the output of the main concerns has been used and what percentage of the total space
. ..
root@root:/home/dev# jstat -gcutil 25791
S0 S1 E O M CCS YGC YGCT FGC FGCT GCT
97.84 0.00 61.84 77.63 97.22 95.68 338 58.808 2 1.787 60.595
S0: 0 surviving area currently used ratio
S1: area currently used in a proportion surviving 1
E: Eden area using a proportional
O: the proportion of older years
M: using metadata area ratio
CCS: Use compression ratio
YGC: the number of the young generation garbage recycling
YGCT: the young generation garbage collection time
FGC: the number of years the old garbage collection
FGCT: old time's garbage collection
GCT: Total garbage collection time