Re: How to tell if someone is connected via vnc

Hi,

1. "How can I determine what the user responds, is there errorlevels or
anything like that?"

You can check for the exit status of the xmessage command

2. "What is the reason for doing ' > /dev/null 2>&1'"

It redirects any standard out and standard error to oblivion

Let's say you have a vnc session on port 5902. You want a script that checks
if there's a session and display a message to the user. And you want to know
if the user read the message. Here's what you could do. (you'll have to
adapt and add a loop in there if you have several vnc sessions)

Edit the linux user's ~/.vnc/xstartup and add an "xhost +" in it. Otherwise
you will not be able to display the message.

Use a script similar to this one: (of course, you will adapt and enhance)

#!/usr/bin/env bash

netstat -tape | grep ESTABLISHED | grep Xvnc | awk '{print $4}' | awk -F ":"
'{print $2}' > log-ports

for user in `cat log-ports`
do
case $user in
5902)
export DISPLAY=:2.0; xmessage -buttons "I
understand":10 -center -timeout 60 -file testmsg > /dev/null 2>&1
[ $? -eq 10 ] \
&& echo "$user acknowledged!" \
|| echo "No answer from $user!"
;;
esac

done

The user connected to 5902 will get a windowed message with a "I understand"
button. If he clicks on it, you'll know. If he doesn't, it'll time out after
60 seconds and return an exit status of 0 (zero): you'll know too .

Hope it helps,
Olivier


2008/1/31, Henning Larsen <hennlar@xxxxxxxx>:

Thanks for the good answer.

On Thu, 2008-01-31 at 15:05 +0100, Olivier Robert wrote:
Hi,

I would check for established VNC connections this way:

netstat -tape | grep ESTABLISHED | grep Xvnc

As for warning connected users. If you see there is an established vnc
session on port 5902, you could simply do:

export DISPLAY=:2.0; xmessage -center -timeout 60 -file shutdown.txt
/dev/null 2>&1

How can I determine what the user responds, is there errorlevels or
anything like that? Hundred years ago I was making a lot of advanced
BAT-files in msdos, but have not done much of those things in Linux yet.
I could or maybe should find out reading man-pages, but have already
asked. :)

What is the reason for doing ' > /dev/null 2>&1'

You could create a list of established connections, translate it to
active displays (5902 -> 2.0 | 5903 -> 3.0 ...) and send out a
message.

Hope it helps
Olivier

It helps a lot, Thanks

Henning Larsen



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