shafi@shafi-ahmad:$ ps -aef | grep firefox
shafi 23675 864 70 17:16 ? 00:00:05 /usr/lib/firefox/firefox
shafi 23750 2173 0 17:16 pts/1 00:00:00 grep --color=auto firefox

Above command shows firefox is running with pid 23675. I used this non java process id in the jmap command line.

shafi@shafi-ahmad:$ jmap -dump:live,format=b,file=heap_dump.hprof 23675
23675: Unable to open socket file: target process not responding or HotSpot VM not loaded
The -F option can be used when the target process is not responding

Error message "The -F option can be used when the target process is not responding" mislead the users.