Dialling in to a Serial modem

[slash50]

Hi There,

We have started to support a number of telephone exchanges running an embedded Linux server (SUSE sles 10)

The embedded server motherboard is very basic and only has 2 NIC's, 2 USB ports, video port and a serial port.

As these units are running on customer LAN's we have restricted remote access to their network. What we require is to set up a modem on the serial port which we can dial into and access at command level.

My familiarity with Linux is only beginning and I need some help in understanding what to do to enable this.

I have a US robotics serial modem set up.

Please help if you can, many thanks,
Chris

 

[RhythmAce]

Many linux distros come with a ppp server. This is what you'll need to setup and configure. After that you will be able to use a remote client to access the server.

 

[mrregan]

You will need something like this in your /etc/inittab file

S4:2345:respawn:/sbin/mgetty -D -x 3 -s 19200 /dev/ttyS4
S5:2345:respawn:/sbin/mgetty -D -x 5 -s 19200 /dev/ttyS5


the S4 and S5 are the two integrated serial ports on our system. The other parameters tell the mgetty service what speed and debug level to use for logs.

 

[slash50]

Thanks for your help.

It has to be dial up by modem as they provide an extra level of security (ie you must know the phone number and our modems are password protected).

 

[mrregan]

Another option you may want to consider is using one of their pcs (if they have access to the unix server and internet access). A free product like Logmein can be used to access the p.c., then telnet to the server. Logmein requires both the windows password and a logmein password.

 

[slash50]

We ar trying to obtain a solution where we do not use the data network though, it's often a common theme that customers will not give us access to their LAN. Plus, with all the different clients using different form of VPN client, we must make sure that all of our engineers have the correct software etc.

With a modem, all they need is the modem number and hyperterminal ;o)

 

[RhythmAce]

Perhaps I'm missing something but this article sounds a lot like what you are trying to do. Mind you that it is a little out of date but I just want to see if this is what you are talking about.

http://pcquest.ciol.com/content/linux/handson/199030105.asp

 

[elgrandeperro]

As a admin who has been on the other side, I would not like you to dial my box and start PPP. Essentially you now make your PC part of my operating network, (let alone if the client is routing, then you are connecting nets together.

I would prefer you login with plain serial dialup.

 

[slash50]

I don't think that is what we are trying to do. We purely want to have tty access through the serial port using a modem. We don't want it to be for any kind of "dial up networking" or using any part of the customers data network.

It's just so we can log into the Linux system at command level and enter our application specific command shell. We will not run any GUI or applications. Just command level alarm monitoring, log monitoring and config changes to the telephony system that runs on it.

Is this possible? I hope I have explained it well enough. Thanks for your help so far.

 

[elgrandeperro]

Yes, this mrregan comment about mgetty is the way to do it.
Here is a link, just ignore some of the PPP stuff. You just want a login shell.

http://linuxmafia.com/pub/linux/suse-linux-internals/chapter22.html

 

[mrregan]

The mgetty service I listed is for listening on the serial port that your modem is connected to. When the modem rings the port responds with a Login prompt and away you go. All you need to know is the /dev/tty name of your serial port.

 

[slash50]

Cool, how do I find out that?

 

[elgrandeperro]

dmesg | grep tty

It is probably ttyS0

 

[slash50]

Excellent, I'll give it a go!!!!

 

[mrregan]

Well, if you have two serial ports on the back of your machine, they are probably /dev/ttyS0 and /dev/ttyS1. You can verify their existence in the /dev directory. See if you have a /proc/tty/driver file. If so, look at it. The 1st column of numbers is the tty number. When you plug your modem into one of these ports, you should be able to talk to the modem with the cu command, something like
cu -l /dev/ttyS0 -s19200 -o for 19200 baud, odd parity. If the modem is conversing, (ie you have the right kind of cable and right port) you should be able to enter ATDT, then enter, and hear a dial tone. Use tilde period ~. to exit the cu command. By the way, if you modify /etc/inittab,
you will need to issue a 'telinit q' command to make the system re-examine the inittab file and start the mgetty.

 

[slash50]

Thanks ever so much for your help so far! I'm in London tomorrow but will test it when I get back to the office. Great help so far )

 

[slash50]

mgetty won't start. I rebooted my server after editing inittab and now it fails with a message saying mgetty failed to start... do I need to install the package?

 

[mrregan]

You would need to download an rpm or module for mgetty if you cant see it in your system. Doe the command:
'rpm -qa | grep mgetty' show any results. If so, you may
just have the wrong path in your inittab command.

 

[slash50]

hmmm, that command shows nothing ( just returns with the prompt

 

[mrregan]

Ok,
That sounds like you will need to download the mgetty for Suse. I am not familiar with Suse, but I presume you can google for it or look on a Suse download site.