How to check heap usage of a running JVM from the

问题:

Can I check heap usage of a running JVM from the commandline, I mean the actual usage rather than the max amount allocated with Xmx.

I need it to be commandline because I don't have access to a windowing environment, and I want script based on the value , the application is running in Jetty Application server

回答1:

You can use jstat, like :

 jstat -gc pid

Full docs here : http://docs.oracle.com/javase/7/docs/technotes/tools/share/jstat.html

回答2:

For Java 8 you can use the following command line to get the heap space utilization in kB:

jstat -gc <PID> | tail -n 1 | awk '{split($0,a," "); sum=a[3]+a[4]+a[6]+a[8]; print sum}'

The command basically sums up:

• S0U: Survivor space 0 utilization (kB).
• S1U: Survivor space 1 utilization (kB).
• EU: Eden space utilization (kB).
• OU: Old space utilization (kB).

You may also want to include the metaspace and the compressed class space utilization. In this case you have to add a[10] and a[12] to the awk sum.

回答3:

If you start execution with gc logging turned on you get the info on file. Otherwise 'jmap -heap ' will give you what you want. See the jmap doc page for more.

Please note that jmap should not be used in a production environment unless absolutely needed as the tool halts the application to be able to determine actual heap usage. Usually this is not desired in a production environment.

回答4:

All procedure at once. Based on @Till Schäfer answer.

In KB...

jstat -gc $(ps axf | egrep -i "*/bin/java *" | egrep -v grep | awk '{print $1}') | tail -n 1 | awk '{split($0,a," "); sum=a[3]+a[4]+a[6]+a[8]+a[10]+a[12]; print sum}'

In MB...

jstat -gc $(ps axf | egrep -i "*/bin/java *" | egrep -v grep | awk '{print $1}') | tail -n 1 | awk '{split($0,a," "); sum=(a[3]+a[4]+a[6]+a[8]+a[10]+a[12])/1024; print sum" MB"}'

"Awk sum" reference:

 a[1] - S0C
 a[2] - S1C
 a[3] - S0U
 a[4] - S1U
 a[5] - EC
 a[6] - EU
 a[7] - OC
 a[8] - OU
 a[9] - PC
a[10] - PU
a[11] - YGC
a[12] - YGCT
a[13] - FGC
a[14] - FGCT
a[15] - GCT

Thanks!

NOTE: Works to OpenJDK!

FURTHER QUESTION: Wrong information?

If you check memory usage with the ps command, you will see that the java process consumes much more...

ps -eo size,pid,user,command --sort -size | awk '{ hr=$1/1024 ; printf("%13.2f Mb ",hr) } { for ( x=4 ; x<=NF ; x++ ) { printf("%s ",$x) } print "" }' |cut -d "" -f2 | cut -d "-" -f1