Re: checking ssh tunnels: best practices?

[Marcel Gschwandl <tautau@gmx.ch>]

Hallo,

I use an ATI Mobility M7 and had nearly the same problem. After the
upgrade to XF4.2.1 I also had to disable the Option "UseFBDev" "true" in
the device section. After that everything worked fine.

Greetings
Marcel

On Thu, 2003-05-22 at 06:02, Tony Godshall wrote:
> Hi, all.
> 
> I've got a laptop (yes, I'm on this list, duh).  I take it
> to a jobsite with me, I take it home, I take it to the
> office.  Some places I can connect to the mailserver
> directly, but at other places I have to ssh through a leased
> line back to the office.
> 
> I've got ssh set up with tunnels for one smtp port,
> three POP ports, a VNC session, etc.  I set up exim 
> to send its mail through the tunnel smtp, and set up 
> fetchmail to fetch through the tunnel.
> 
> The problem is that sometimes these programs don't work
> right and hassle ensues if I start them up without starting
> up my ssh session first, or if the ssh session has dropped
> someplace along the way.  A lot of the time I'm working
> locally, so I might not notice that the tunnel went away,
> and exim will tell me that the message couldn't be
> delivered, etc.
> 
> The hack I've done is to make a little script,
> port_is_connected, so I can have my mutt-starter script
> abort with a line like this:
> 
>     port_is_connected $MAIL1SMTP localhost || exit 1
> 
> ...or less tersely...
> 
>     if ! port_is_connected $MAIL1SMTP localhost 
>     then
>       echo "check the ssh tunnel, dammit!"
>       exit 1
>     fi
> 
> Does this approach make sense, overall?
> 
> It took me a while to figure out how to do port_is_connected, but 
> eventually I located nmap.  This does the job pretty well
> and is pretty fast:
> 
>     nmap -p $MAIL1SMTP localhost | grep -q open
> 
> I had been using something like this...
> 
>     ps -ef | grep "ssh.*$MAIL1SMTP"
> 
> ... but I don't like that much for a variety of reasons.
> 
> So this is what I came up with for port_is_connected:
> 
>     #!/bin/sh
>     
>     port=""
>     host=""
>     err=""
>     
>     while [ -n "$1" ]
>     do
>     
>       case "$1" in
>     
>       -*) 
>         err="$err\nunexpected opt"
>         ;;
>     
>       *)
>         if [ -z "$port" ]
>         then
>           case "$1" in
>           [0-9]*)
>             port="$1"
>             ;;
>           *)
>             err="$err\nhuh? [$1]"
>             ;;
>           esac
>         elif [ -z "$host" ]
>         then
>           host="$1"
>         else
>           err="$err\ntoo many args [$1]"
>         fi
>         ;;
>     
>       esac
>     
>       shift
>     
>     done
>     
>     if [ -n "$err" ]; then printf "ERR$err\n"; exit 2; fi
>     
>     if [ -z "$port" ]; then err="$err\nno port specified"; fi
>     
>     if [ -n "$err" ]; then printf "ERR$err\n"; exit 2; fi
>     
>     if [ -z "$host" ]; then 
>       host=localhost
>       printf "no host given; assuming host[$host]\n" >&2
>     fi
>     
>     if nmap -p $port $host | grep -q open 
>     then
>       printf "port $host:$port is open: exit 0\n" >&2
>       exit 0
>     else
>       printf "port $host:$port is closed: exit 1\n" >&2
>       exit 1
>     fi
>     
> So, comments please.  Is this a good way to do it, or am I
> missing a better, obvious way?  Comments on style are also
> welcome.  
> 
> Tony 
>  
-- 
Marcel Gschwandl <tautau@gmx.ch>

The day Microsoft invents something that doesn't suck
is the day they start making vacuum cleaners. -- Ernst Jan Plugge