jstack-good

#!/bin/bash

PID=$1
if [ -z "$PID" ]; then
  echo usage: $0 pid
  exit 1
fi

determine_exe() {
  PID=$1

  # Try looking in proc for full path
  res=$(readlink -f /proc/$PID/exe)
  if [ "$?" -eq 0 ]; then
    echo $res
    return
  fi

  # Might not have permissions to do that, see if command
  # line is an absolute path
  argv0=$(cut -d "$(printf "\x00")" -f 1 /proc/$PID/cmdline)
  if [[ "$argv0" == /* ]]; then
    echo $argv0
    return
  fi
  return -1
}


EXE=$(determine_exe $PID)
if [ -z "$EXE" ] || [ ! -x "$EXE" ]; then
  echo Could not determine executable path for pid $PID
  exit 1
fi

EXE_BASE=$(basename "$EXE")
if [ "$EXE_BASE" != "java" ]; then
  echo Pid $PID does not appear to be a JVM.
  echo Executable $EXE is not java!
fi

case "$EXE" in
  */jre/bin/java)
    JAVA_HOME=${EXE%jre/bin/java}
    JSTACK="$JAVA_HOME/bin/jstack"
    ;;
  */bin/java)
    JSTACK="$(dirname $EXE)/jstack"
    ;;
  *)
    echo Executable $EXE does not appear to be in the normal
    echo Sun JRE directory layout. Expected .../jre/bin/java
    exit 1
    ;;
esac

if [ ! -x "$JSTACK" ]; then
  echo No jstack found at $JSTACK
  JSTACK=$(which jstack 2>/dev/null)
  if [ "$?" -eq 0 ]; then
    echo Will attempt to use the one on your path: $JSTACK
  else
    echo Also, none found on path!
    exit 1
  fi
fi

JAVA_UID=$(cat /proc/$PID/status  | grep Uid | awk '{print $2}')

sudo -u#$JAVA_UID $JSTACK $PID