How to count the number of opened file descriptors of all running JVM's on a Linux host ?

for ((;;))
do
  declare sum=0
  for i in `pgrep -lf jdk | awk '{print $1}'`
  do
    ((sum += `sudo /usr/sbin/lsof -p $i | wc -l`))
  done
  echo "`date` java: $sum"
  sleep 5
done | tee fd-java.log

Or a faster alternative:

for ((;;))
do
  for i in `pgrep -lf jdk | awk '{print $1}'`
  do
    s="$s$i,"
  done
  echo "`date` java: `sudo /usr/sbin/lsof -p $s | wc -l`"
  sleep 5
done | tee fd-java.log

What if you need a break down per JVM ?

for ((;;))
do
  echo -n "`date` "
  for i in `pgrep -lf jdk | awk '{print $1}'`
  do
    echo -n "[$i]:"
    sudo /usr/sbin/lsof -p $i | wc -l | tr '\n' ','
    echo -n " "
  done
  echo ""
  sleep 5
done | tee fd-jvms.log