From a failed JPRT build:

Copying images/jdk/demo/applets/JumpingBox/JumpingBox$2.class
/usr/bin/cp -fP "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/support/demos/image/applets/JumpingBox/JumpingBox$2.class" "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox$2.class"
Images.gmk:340: recipe for target '/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox$2.class' failed
Copying images/jdk/demo/applets/JumpingBox/JumpingBox$3.class
/usr/bin/cp -fP "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/support/demos/image/applets/JumpingBox/JumpingBox$3.class" "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox$3.class"
Copying images/jdk/demo/applets/JumpingBox/JumpingBox.class
/usr/bin/cp -fP "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/support/demos/image/applets/JumpingBox/JumpingBox.class" "/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox.class"
make[3]: Leaving directory '/opt/jprt/T/P1/035741.iignatye/s/open/make'
make/Main.gmk:341: recipe for target 'jdk-image' failed
/usr/bin/cp: cannot create regular file '/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox.class': File exists
make[3]: *** [/opt/jprt/T/P1/035741.iignatye/s/build/linux-x64/images/jdk/demo/applets/JumpingBox/JumpingBox$2.class] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [jdk-image] Error 1
make[2]: *** Waiting for unfinished jobs....

The failing machine is a 16-way system so has a higher build parallelism level than normal.