What is Print Command Line Flags: -XX:+PrintCommandLineFlags?

Usage:

• -XX:+PrintCommandLineFlags

Description:

The -XX:+PrintCommandLineFlags flag enables printing the values of the most
useful flags controlling the heap size and garbage collection, along with their
values. The values shown will either be the defaults provided by the JVM
installation, or the values as supplied by command line flags.

For example:

java -XX:+PrintCommandLineFlags -version

Prints (on an example device with 16 GB of RAM):

-XX:ConcGCThreads=2 -XX:G1ConcRefinementThreads=8 -XX:GCDrainStackTargetSize=64
-XX:InitialHeapSize=268435456 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=4294967296
-XX:MinHeapSize=6815736 -XX:+PrintCommandLineFlags
-XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache
-XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC

If the maximum heap size is set to 8 GB using the -Xmx option:

java -Xmx8g -XX:+PrintCommandLineFlags -version

then the output would reflect the value specified:

-XX:ConcGCThreads=2 -XX:G1ConcRefinementThreads=8 -XX:GCDrainStackTargetSize=64
-XX:InitialHeapSize=268435456 -XX:MarkStackSize=4194304 -XX:MaxHeapSize=8589934592
-XX:MinHeapSize=6815736 -XX:+PrintCommandLineFlags
-XX:ReservedCodeCacheSize=251658240 -XX:+SegmentedCodeCache
-XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseG1GC

The flags printed by -XX:+PrintCommandLineFlags are selected as the most
commonly used flags for tuning the performance of the JVM, however there are
many more flags not printed by this command. To see the complete set of flags
along with their values, use the -XX:+PrintFlagsFinal flag in combination with
-XX:+UnlockDiagnosticVMOptions and -XX:+UnlockExperimentalVMOptions.

Default Value:

-XX:+PrintCommandLineFlags is off by default, i.e. command line flags are not
printed.

Errors:

None

Arguments Related to -XX:+PrintCommandLineFlags:

TODO: link to -XX:+PrintFlagsFinal

Related Posts:

None

NOTE:

If you have additional comments, interesting experiences or even point of disagreement with this JVM argument description, please leave a comment. Your
insights will help the entire 10+ million java developer community to develop
one standard source of documentation for all the JVM arguments.