[lug] How to tell if an app is running/port is in use?

[D. Stimits]

Alan Robertson wrote:
> 
> Hi,
> 
> I'm writing an System V init script for an app which doesn't have one.
> 
> For the "status" case, I want to tell if the application is running.
> 
> This is a little hard since the application doesn't appear to make any lock
> files, and is all in Java, so the ps always shows "java" as the process name.
> 
> Another option would be to look and see if the app had it's ports open (it's
> a server which waits for clients to connect).

The following finds out what is using a particular port for either tcp
or udp:
  fuser -v -u -n tcp "somePortNumber" -n udp "somePortNumber"

You can modify that to just show tcp or udp. It might or might not give
all you need.

> 
> What's the best way to do that?
> 
>         Thanks!
> 
>         -- Alan Robertson
>            alanr at unix.sh
> 
> _______________________________________________
> Web Page:  http://lug.boulder.co.us
> Mailing List: http://lists.lug.boulder.co.us/mailman/listinfo/lug

I'm currently playing around with Redhat init scripts (I'm using 7.1),
here is a snippet to allow creation of such a script, but it is only an
excerpt, you'll maybe find some of it useful (it was originally from
other scripts I've hacked around with). It's purpose is for a network
game server, so it might have a lot in common. It works with lock files
even though the program itself does not have a concept of the lock
files. Adapt to your favorite distro. Forgive the line wrap, email is
notorious for that):

. /etc/init.d/functions
. /etc/sysconfig/network

[ ${NETWORKING} = "no" ] && exit 0

application="your_app"
the_path="/somewhere"
user="who_to_run_as"

lock_file="/var/lock/subsys/${application}

start()
{
  echo -n $"Starting $prog: "
  ulimit -S -c 0 >/dev/null 2>&1

  local proc_pid=$(pidof ${application})

  # case already started.
  if [ ! -z "${proc_pid}" ] ; then
    success $"(${application} already started, pid ${proc_pid}) startup"
    touch "${lock_file}"
    exit 0

  # case not started but lock file exists.
  elif [ -f "${lock_file}" ] ; then
    success "rm -f ${lock_file}" && passed "${lock_file} locked but not
alive, removing lock"
  fi

  # At this point, the server is neither locked nor started.
  daemon --user ${user_name} ${the_path}/${application} \
    && success $"${application} startup (pid $(pidof ${application}))"

  proc_pid=$(pidof ${binary_ex})

  # Case that startup attempt failed.
  if [ -z "${proc_pid}" ] ; then
    failure "${application} startup"
    rm -f "${lock_file}"
    echo -n '' > "${pid_file}"
    exit 1
	
  # Case of startup success.
  else
    touch "${lock_file}"
    echo "${proc_pid}" > "${pid_file}"
  fi

  exit 0
}

stop()
{
  local proc_pid=$(pidof ${application})
  if [ -n "${proc_pid}" ] ; then
    killproc ${application}
    echo -n '' > "${pid_file}"
    rm -f "${lock_file}"
  fi
}

restart()
{
  local proc_pid=$(pidof ${application})

  if [ -n "${proc_pid}" ] ; then
    killproc ${application} -HUP
    touch "${lock_file}"
    echo "${proc_pid}" > "${pid_file}"
  else
    start
  fi
}

case "$1" in
  start)
    start
    ;;
  stop)
    stop
    ;;
  restart)
    restart
    ;;
  status)
    status ${binary_ex}
    ;;
  describe)
    describe
    ;;
  *)
    echo "Usage:  ${binary_ex} <start|stop|status|restart|describe>"
esac