CentOS - Aug 2006 - connecting linux console using serial port

Quoting israel.garcia at cimex.com.cu:
> Hi, I have a serial modem connected to /dev/ttyS0 on my CentOS server, I
> want to set up this server to allow connections through this serial
> modem but only to the console.... (I want to log in)...
>
> PS: I don't want PPP, I just want to get my linux console through this
> serial modem...
>
> What do I have to configure on my linux?
Hmmm...  Do you want *console* (as in /dev/console) or just terminal  
access (as in /dev/ttySO)?

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>Quoting israel.garcia at cimex.com.cu:
>
>> Hi, I have a serial modem connected to /dev/ttyS0 on my CentOS server,
I
>> want to set up this server to allow connections through this serial
>> modem but only to the console.... (I want to log in)...
>>
>> PS: I don't want PPP, I just want to get my linux console through
this
>> serial modem...
>>
>> What do I have to configure on my linux?
>
>Hmmm...  Do you want *console* (as in /dev/console) or just terminal  
>access (as in /dev/ttySO)?
>
The easy way is to configure the modem so that it is in Auto-Answer mode all of
the time.  Once it is in auto-answer mode it will answer when you dial it and
then you will see what the is transmitted to it via the serial cable.  Then
follow the instructions for setting up Linux to use the serial port for
output/input.  If you don't have that information at your fingertips it is
as follows:

2.3	Configuring Headless Operation
By configuring ?headless? operating we will be able to manage the system via a
cable plugged into the serial port of the system.  This obviates the need to
plug a keyboard and monitor into it to perform changes.  Thus the term
?headless?.
2.3.1	Changes to /etc/inittab
The /etc/inittab file contains settings that get applied to the Operating
Systems at boot time.  There are some changes that need to be made to these
settings.  In order to edit the /etc/inittab file type:

vi /etc/inittab

Typing this command will open the /etc/inittab file for editing.

As stated earlier the 18th line down is the run level line. Add the following
line to the file:

S0:12345:respawn:/sbin/agetty 9600 linux

This line sets the Operating System to be able to send boot time information to
the serial port in addition to the console.

After you have made these changes to the /etc/inittab file press the colon (: )
key and then type wq to quit vi and save the changes.

2.3.2	Changes to /etc/securetty
The /etc/securetty sets the controls for which TTY devices that the root account
can log on via.  In order for us to be able to log onto the serial console as
root or to be able to su to root we must add a line to the file.  In order to
edit the /etc/secuertty file type:

vi /etc/securetty

Typing this command will open the /etc/secuertty file for editing.

Add the following line to the end of the file:

ttyS0

This line sets the Operating System to allow root to log on to the serial port
in addition to the console.

After you have made these changes to the /etc/securetty file press the colon (:
) key and then type wq to quit vi and save the changes.

2.3.3	Changes to the Boot Loader
In order for boot-time messages to be sent to the console, including the boot
loader information some changes must be made to the configuration file for it. 
The boot loader that CentOS uses is GRUB.  As such, the configuration file is
/etc/grub.conf.

The first change that we must make is to add some lines after the timeout line
in the GRUB configuration file.  In order to edit the /etc/grub.conf file type:

vi /etc/grub.conf

Typing this command will open the /etc/grub.conf file for editing.

Add the following two lines after the timeout line in the configuration file:

serial --unit=0 --speed=9600
terminal --timeout=5 serial console
Another change that we must make in the GRUB configuration file is to tell the
kernel to send out all kernel-level messages to the serial port in addition to
the console.  That is done by adding the following line to the end of the kernel
line:

console=tty1 console=ttyS0

After you have made these changes to the /etc/grub.conf file press the colon (:
) key and then type wq to quit vi and save the changes.

Once you have made these changes reboot the system by typing by typing:

reboot

The system will now reboot.

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Hi, I have a serial modem connected to /dev/ttyS0 on my CentOS server, I
want to set up this server to allow connections through this serial
modem but only to the console.... (I want to log in)...

PS: I don't want PPP, I just want to get my linux console through this
serial modem...

What do I have to configure on my linux?

Thanks for your time
Regards;
Israel

Quoting israel.garcia at cimex.com.cu:
> Just terminal access -> I want to login in my linux server connecting
> through the modem connected in /dev/ttyS0
Not sure if this is complete.

Install mgetty if not already present on your system.

Go to /etc/mgetty+sendfax directory.  If you have CallerID feature on  
your phone line (and you should get it if you don't have it yet), edit  
dialin.config file and add telephone numbers you will be dialing from.  
  At least this will prevent clueless script-kiddies from getting  
login prompt on your modem line.  I know that some of my modems get  
regullary probed from strange phone numbers (and those are dedicated  
modem lines -- no voice calls on them, not listed in white pages, too  
often on too many lines to be the simple case of wrong number).

While there, check login.config file.  If you don't want PPP on it,  
make sure /AutoPPP/ is commented (should be default).  Make sure "* -  
- /bin/login @" line is not commented (should be last line in the  
default config file).  That's the line that will give you login prompt.

Edit /etc/inittab and add something like this:
s0:2345:respawn:/sbin/mgetty -D -n 2 -s 115200 /dev/ttyS0

The "-n 2" tells mgetty to pick up the phone after second ring.  You  
need to wait till second ring because telephone company sends CallerID  
information between first and second ring.  If you configured mgetty  
to answer after first ring, it would never get CallerID information.

Execute "telinit q" as root (this tells init process to reread inittab
file).

Configure and connect modem and you should be set to go.  I do not  
recommend allowing root to login directly from modem line (could be  
configured by editing /etc/securetty and /etc/security/access.conf  
files if needed, but not wise idea).  Login as normal user, than su to  
root.

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uoting israel.garcia at cimex.com.cu:
> Hi, I have a serial modem connected to /dev/ttyS0 on my CentOS server,
I
> want to set up this server to allow connections through this serial
> modem but only to the console.... (I want to log in)...
>
> PS: I don't want PPP, I just want to get my linux console through this
> serial modem...
>
> What do I have to configure on my linux?
>Hmmm...  Do you want *console* (as in /dev/console) or just terminal  
>access (as in /dev/ttySO)?

Just terminal access -> I want to login in my linux server connecting
through the modem connected in /dev/ttyS0

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that by reading this message you agreed not to disturb frogs during
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